Synthesis and reactions of a cyclopentadienyl-amidinate titanium tert- Butoxyimido compound

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Synthesis and Reactions of a Cyclopentadienyl-Amidinate Titanium

tert-Butoxyimido Compound

Laura R. Groom,^†Andrew D. Schwarz,^†Ainara Nova,^‡,§Eric Clot,*^,‡and Philip Mountford*^,†

^†Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansﬁeld Road, Oxford OX1 3TA, U.K.

^‡Institut Charles Gerhardt, Universite

France

́ ̀

Montpellier 2, CNRS 5253, cc 1501, Place Eugene Bataillon, 34095 Montpellier Cedex 5,

S

* Supporting Information

ABSTRACT: We report the ﬁrst detailed reactivity study of a

group 4 alkoxyimido complex, namely Cp*Ti{PhC(NⁱPr)₂}-

(NO^tBu) (19), with heterocumulenes, aldehydes, ketones,

F₅

organic nitriles, Ar CCH, and B(Ar )₃(Ar^F= C₆F₅).

5

Compound 19 was synthesized via imide/alkoxyamine

t

exchange from Cp*Ti{PhC(NⁱPr)₂}(N^tBu) and BuONH₂.

Reaction of 19 with CS₂and Ar′NCO (Ar′ = 2,6-C₆H₃Pr₂) gave the [2 + 2] cycloaddition products Cp*Ti{PhC(NⁱPr)₂}-

{SC(S)N(O^tBu)} and Cp*Ti{PhC(NⁱPr)₂}{N(O^tBu)C(NAr′)O}, respectively, whereas reaction with 2 equiv of TolNCO

aﬀorded Cp*Ti{PhC(NⁱPr)₂}{OC(NTol)N(Tol)C(NO^tBu)O} following a sequence of cycloaddition−extrusion and cyclo-

i

t

addition−insertion steps. Net NO^tBu group transfer was observed with both BuNCO and PhC(O)R, yielding the oxo-bridged

dimer [Cp*Ti{PhC(NⁱPr)₂}(μ-O)]₂and either the alkoxycarbodiimide ^tBuNCNO^tBu or the oxime ethers PhC(NO^tBu)R (R =

H (25a), Me (25b), Ph (25c)). DFT studies showed that in the reaction with PhC(O)R (R = H, Me) the product distribution

between the syn and anti isomers of PhC(NO^tBu)R was under kinetic control. Reaction of 19 with ArCN gave the TiN_α

insertion products Cp*Ti{PhC(NⁱPr)₂}{NC(Ar)NO^tBu} (Ar = Ph (28), 2,6-C₆H₃F₂(27), Ar^F(26)) containing tert-

5

butoxybenzimidamide ligands. Reaction of 19 or 26 with an excess of Ar^F⁵CN gave Cp*Ti{PhC(NⁱPr)₂}{NC(Ar^F⁵)NC(Ar^F⁵)-

N(C{Ar^F⁵}NO^tBu)} (29) following net head-to-tail coupling of 2 equiv of Ar^F⁵CN across the TiN_αbond of 26. Reductive

N_α−O_βbond cleavage was observed with Ar^F⁵CCH, forming Cp*Ti(O^tBu){NC(Ar^F⁵)C(H)N(ⁱPr)C(Ph)N(ⁱPr)} (30). Addition

of 2 equiv of [Et₃NH][BPh₄] to 19 in THF-d₈resulted in protonolysis of the amidinate ligand, forming [PhC(NHⁱPr)₂][BPh₄]

and the cationic alkoxyimido complex [Cp*Ti(NO^tBu)(THF-d₈)₂]⁺. In contrast, reaction with B(Ar^F⁵)₃resulted in elimination of

isobutene and formation of Cp*Ti{PhC(NⁱPr)₂}{η²-ON(H)B(Ar^F⁵)₃}.

diaryl- and alkylidenehydrazido complexes have accompanied

the synthetic, structural, and reactivity studies.^{8e,g,k,s,9b,11}Like

their imido analogues, group 4 hydrazido complexes undergo a

range of reactions at the MN_αbond, undergoing cyclo-

addition, cycloaddition−insertion, cycloaddition−elimination,

and NNR₂group transfer with unsaturated substrate-

s,^{8a,f,h,l−n,p−r,u,v,9f,h}and also 1,2-addition of Si−H or Si−Cl

bonds.^8t,wIn addition, both N_α−N_βbond reductive cleavage

and insertion reactions with oxidizable substrates such as CO,⁷

isonitriles,^8r,9aand alkynes^8h,p,9m,12are also becoming estab-

lished for these complexes (in contrast to the situation for their

group 5 or 6 analogues, which show no such reactivity with

unsaturated substrates¹³).

Prompted by this unusual and interesting chemistry, we have

very recently started to develop synthetic methodologies for the

hitherto unknown titanium alkoxyimido complexes (L)Ti

NOR,¹⁴with the hope of accessing both new TiN_αmultiple-

bond chemistry as well as N_α−O_βbond reactivity. For example,

the mechanism^8p,9i,mof alkyne insertion into the N_α−N_βbond

of certain titanium and zirconium hydrazides is related to that

INTRODUCTION

■

Group 4 alkyl- and arylimido complexes (L)MNR (M =

group 4 metal, R = alkyl, aryl) have been studied in

considerable depth over the past 20 years.¹Much of this

work has centered on the wide range of stoichiometric

reactions that the polar MN multiple bond (formally a

σ²π⁴triple bond in most instances^1e,2,3) undergoes with both

saturated and unsaturated substrates. Catalytic applications of

these complexes usually involve the imido group as the reactive

site, most notably in alkene, allene, and alkyne hydro-

amination.⁴In some instances it acts as a supporting or

spectator ligand, in particular in the context of oleﬁn

polymerization for the group 4 metals.⁵Alongside this

chemistry, and building on initial reports by Wiberg⁶and

Bergman,⁷the related terminal dialkyl- or diarylhydrazido(2−)

complexes (L)MN−NR₂(R = alkyl, aryl) have increasingly

been studied in terms of synthesis and reactivity for M = Ti,⁸

Zr⁹in particular. Terminal alkylidene hydrazido complexes of

titanium, (L)TiNNCRR′ (R, R′ = hydrocarbyl, H)which

can alternatively be viewed as highly reduced diazoalkane

specieshave also been reported and studied for their

reactions with H₂, silanes, and unsaturated polar and nonpolar

substrates.¹⁰Investigations of the bonding in group 4 dialkyl-,

Received: October 14, 2013

Published: November 26, 2013

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Figure 1. Selected examples of previous transition-metal alkoxyimido complexes.^14,16

for (reductive) cleavage of the peroxide ligand O_α−O_βbond in

Cp*₂Hf(R)(OO^tBu) to form Cp*₂Hf(OR)(O^tBu) (R = H,

alkyl).¹⁵However, although transition-metal imido and

hydrazido compounds have been extensively studied across

the transition-metal series, the corresponding alkoxyimides

remain poorly explored, in terms of both synthesis and bonding

and also with respect to the reactivity of such complexes.

The ﬁrst alkoxyimido complex was reported in the early

1980s, namely the trimetallic ruthenium structure

Ru₃(CO)₁₀(NOMe) (1; Figure 1),^16afollowed a few years

later by the monomeric Ta(NOMe)Cl₃(bipy) (2)^16band half-

sandwich group 5 (e.g., 3) and 6 complexes.^16b,c,17We recently

reported the syntheses and electronic structures of the ﬁrst

group 4 alkoxyimido complexes (e.g., 4−6) along with a

preliminary example of their reactivity with alkynes (vide

infra).¹⁴Rational synthetic routes to terminal alkoxyimido

complexes have so far included methylation of metal nitroso

compounds_,^16a,18dehydrohalogenation of metal chloride

compounds,^16b,cand protonolysis of metal amide com-

pounds.¹⁴Crystallographic studies and DFT calculations

suggest that, like hydrazides and imides, the alkoxyimido ligand

is a four-electron donor with a formal charge of 2−, capable of

bonding to transition metals through one σ- and two π-bonds.¹⁴

To date, the reactivity of alkoxyimido complexes is very

limited. Reactions of 1 with certain alkynes formed

Ru₃(CO)₉(μ₃-NOMe)(μ₃-η²-RCCPh) (R = H, Ph),¹⁹while

heating at 90 °C in toluene resulted in N−O bond cleavage to

give the corresponding nitrene Ru₃(CO)₉(OMe)(N).²⁰Hydro-

genation of 1 in the presence of Ru₃(CO)₁₂generated a

mixture of species, including Ru₅(μ-H)₃(CO)₁₃(μ₄-NH)(μ₃-

OMe), also following reductive N−O bond cleavage.²⁰

Furthermore, transmetalation of 1 using CpMo(CO)₃H led

to the mixed Ru/Mo trimetallic structures Ru₂Mo(μ-H)-

(CO)₈(Cp)(μ₃-NOMe) and Ru₂Mo(μ-H)(CO)₈(Cp)(μ₃-

NH).^17c

one reaction involving a titanium alkoxyimide ligand has been

reported, namely the reaction of PhCCMe and 6 resulting in 7

(Figure 2) via reductive cleavage of the N_α−O_βbond and

Figure 2. Reaction products following reaction of Ti(N₂N^Me)(NX)-

(py) (X = O^tBu (6), NPh₂(8)) with PhCCMe.^8h,p,14aThe fragments

derived from the TiNX and alkyne moieties are shown in red and

blue, respectively.

formation of two new N−C bonds.^14aThe mechanism

proceeds via initial cycloaddition of the alkyne to TiN_α

followed by N_α−O_βbond cleavage and net insertion into one of

the N−SiMe₃bonds of the N₂N^Meligand. In contrast, the

corresponding reaction of PhCCMe with the hydrazide

analogue Ti(N₂N^Me)(NNPh₂)(py) (8) also gives initial

TiN cycloaddition but ultimately yields the vinylimido

product Ti(N₂N^Me){NC(Ph)C(Me)NPh₂}(py) (9; Figure

2).^8h,p

To develop further the chemistry of titanium alkoxyimido

systems, we turned to the cyclopentadienyl-amidinate support-

ing ligand set which, together with related ligands,^8m,n,x,21has

proved a robust and ﬂexible platform for studying and

comparing the reactivity of imido and also dimethyl-, diphenyl-,

and alkylidenehydrazido compounds of the type Cp*Ti{MeC-

(NⁱPr)₂}(N^tBu) (10), Cp*Ti{MeC(NⁱPr)₂}(NAr) (Ar = Tol

(11a), Xyl (11b, Xyl = 2,6-C₆H₃Me₂)),²²Cp*Ti{MeC-

(NⁱPr)₂}(NNR₂) (R = Ph (12), Me (13)),^8h,q,t,u,wand

Cp*Ti{MeC(NⁱPr)₂}(NNCPh₂) (14).^10fIn this contribution

we report the ﬁrst imide/alkoxyamine exchange strategy for the

synthesis of a terminal alkoxyimido complex and report on its

reactivity with unsaturated molecules, including CS₂, isocya-

nates, aldehydes, ketones, nitriles, Ar^F⁵CCH, and B(Ar^F⁵)₃.

Reaction of Ti(NO^tBu)Cl₂(NHMe₂)₂or Ti(NO^tBu)-

Cl₂(py)₃(4; Figure 1) with neutral tridentate or lithiated

anionic nitrogen based ligand sets yielded a range of group 4

alkoxyimido complexes: for instance, Ti(NO^tBu)(Me₃[9]-

aneN₃)Cl₂(5, Me₃[9]aneN₃= trimethyl-1,4,7-triazacyclono-

nane; Figure 1) and Ti(N₂N^Me)(NO^tBu)(py) (6, N₂N^Me

=

MeN(CH₂CH₂NSiMe₃)₂; Figure 1).¹⁴However, as yet only

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synthesis utilizing an alkylimide/alkoxyamine ligand exchange

methodology.

The molecular structure of 19, determined by X-ray

crystallography, is shown in Figure 3 and selected bond lengths

RESULTS AND DISCUSSION

■

Synthesis and Bonding Analysis of Cyclopentadienyl-

Amidinate Alkoxyimido Compounds. In our previous

report we found that stable monomeric titanium alkoxyimido

compounds were only accessible using the bulky tert-butoxy

group. Therefore, in this present study, we have focused

exclusively on this substituent.^14bWe have previously shown

that all of the complexes Cp*Ti{MeC(NⁱPr)₂}(NAr) (11),^22d

Cp*Ti{MeC(NⁱPr)₂}(NNR₂) (R = Ph (12), Me (13))^8uand

Cp*Ti{MeC(NⁱPr)₂}(NNCPh₂) (14)^10fcan be synthesized

from the readily prepared^22dCp*Ti{MeC(NⁱPr)₂}(N^tBu) (10)

via tert-butylimide-arylamine/hydrazine exchange reactions.

Consequently, this strategy was also employed to make the

corresponding alkoxyimido complex Cp*Ti{MeC(NⁱPr)₂}-

t

(NO^tBu) (15) from 10 and BuONH₂, itself conveniently

prepared in multigram quantitites.²³Compound 15 was

isolated as a dark green viscous oil in eﬀectively quantitative

yield (eq 1).

Figure 3. Displacement ellipsoid plot (20% probability) of Cp*Ti-

{PhC(NⁱPr)₂}(NO^tBu) (19). H atoms are omitted for clarity.

and angles are given in Table 1. Compound 19 possesses a

three-legged piano-stool geometry around titanium with η⁵-

C₅Me₅, κ²N,N′-PhC(NⁱPr)₂, and η¹-NO^tBu ligands. The bond

lengths and angles associated with the Cp*Ti{PhC(NⁱPr)₂}

fragment are similar to those found for the xylylimido and

hydrazido homologues 11b,^22d12, 13,^8uand 14^10fand for

cyclopentadienyl and amidinate complexes of titanium(4+) in

general.²⁷The metric parameters associated with the Ti

NO^tBu group are similar to those for the previously reported

titanium tert-butoxyimides.¹⁴The short average Ti(1)−N(1)

distance of 1.713(2) Å lies within the expected range for

titanium tert-butoxyimides (range 1.686(2)−1.734(2) Å) and,

together with the near-linear TiN−O average angle of

162.9(2)°, indicates substantial TiN_αmultiple-bond charac-

ter as expected. The Ti(1)−N(1) bond distance is comparable

within error to that of the dimethylhydrazide 13 (1.723(2) Å)

but signiﬁcantly shorter than for the xylylimido and diphenyl-

and alkylidenehydrazido compounds 11b, 12, and 14

(1.738(2), 1.734(2), and 1.751(2) Å, respectively). The average

N(1)−O(1) bond distance (1.379(3) Å) is indicative of a single

bond,²⁸and the average N(1)−O(1)−C(1) angle of 112.8(2)°

is consistent with the bent geometry found for (L)MN−OR

linkages in general.²⁷In our previous studies¹⁴of tert-

butoxyimido compounds we found that the TiN_αdistances

were generally intermediate between those in the homologous

alkylimido and phenylimido analogues and shorter than in the

diphenylhydrazido counterparts. Although a crystallographically

characterized alkylimido analogue is not available for

Although 15 could be obtained in analytically pure form,

diﬃculty in handling prompted us to develop a more crystalline

derivative. Alternative amidinate ligand precursors, Li[PhC-

(NⁱPr)₂] (16),²⁴Li[MeC(NTol)₂],²⁵and Li[^tBuC(NⁱPr)₂],²⁵

were prepared by nucleophilic addition to the corresponding

carbodiimide and subsequently reacted with Cp*Ti(N^tBu)Cl-

(py) (17)²⁶by analogy with the synthesis of 10^22dand certain

analogues.^22c,dThe reactions with Li[MeC(NTol)₂] and

Li[^tBuC(NⁱPr)₂] proved unsuccessful, the latter being con-

sistent with previous results regarding the synthesis of

aluminum amidinate complexes, where steric constraints

prevented ligand complexation.²⁵However, in the case of 16,

heating at 60 °C for 18 h in benzene aﬀorded Cp*Ti{PhC-

(NⁱPr)₂}(N^tBu) (18; Scheme 1) as a dark red oil in near-

quantitative yield. Subsequent tert-butylimide/tert-butoxyamine

t

exchange between 18 and BuONH₂yielded Cp*Ti{PhC-

(NⁱPr)₂}(NO^tBu) (19; Scheme 1), again in quantitative yield

when followed by ¹H NMR spectroscopy. Larger scale reactions

aﬀorded 19 as a ﬁne green powder in multigram quantities and

70% isolated yield. This is the ﬁrst example of an alkoxyimide

Scheme 1. Synthesis of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19) Starting from Li[PhC(NⁱPr)₂] (16) and Cp*Ti(N^tBu)Cl(py) (17)

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a

Table 1. Selected Bond Lengths (Å) and Angles (deg) for Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19)

Ti(1)−Cp_cent

Ti(1)−N(1)

Ti(1)−N(2)

Cp_cent−Ti(1)−N(1)

Cp_cent−Ti(1)−N(2)

Cp_cent−Ti(1)−N(3)

2.054 [2.048]

Ti(1)−N(3)

N(1)−O(1)

O(1)−C(1)

N(2)−Ti(1)−N(3)

Ti(1)−N(1)−O(2)

N(1)−O(1)−C(1)

2.121(3) [2.119(3)]

1.381(4) [1.377(4)]

1.460(5) [1.456(5)]

1.709(3) [1.716(3)]

2.114(3) [2.131(3)]

122.02 [120.97]

122.46 [122.26]

120.85 [120.95]

64.02(12) [63.99(12)]

163.8(3) [161.9(3)]

113.1(3) [112.4(3)]

a

Cp_centis the computed centroid for the Cp* ring carbons. Values in brackets are for the other crystallographically independent molecule.

comparison, the experimental data for 19 in comparison with

11b, 12, 13, and 14 appear consistent with these trends.

A number of computational studies into the bonding of

group 4 imido and hydrazido complexes have previously been

carried out, and the electronic structure of the MNR and

MNNR₂(R = alkyl, aryl) moieties is well under-

stood.^{2,8e,g,k,s,9b,11}So far, however, there has been only one

computational study of any alkoxyimido complex. This focused

on the model compound Ti(NOMe)Cl₂(NHMe₂)₂(an

analogue of the real compound possessing a TiNO^tBu

group), in comparison with the imido and hydrazido systems

Ti(NR)Cl₂(NHMe₂)₂(R = Me, Ph, NMe₂).^14bTo gain further

understanding into the bonding of alkoxyimido complexes,

DFT calculations were carried out on the model system

CpTi{MeC(NMe)₂}(NOMe) (1Q_OMe) using the B3PW91

functional. The geometry, key orbital representations, and

associated energies are shown in Figure 4. Comparative DFT

the orientation of the −Ph,−NMe₂, and −NPh₂substituents

(vide infra), the energy of π_his relatively insensitive to the N_α

substituents and varies nonsystematically between the com-

plexes. However, the energy of π_vis very dependent on the N_α

substituent. As described previously,^8uin the case of the −NR₂

groups (1Q_NMe₂and 1Q_NPh₂) the N_βlone pair (LP)

destabilizes π_vthrough an antibonding interaction (the energy

of π_vin these complexes is −4.30 and −4.24 eV, respectively; cf.

−5.47 eV in the benchmark model 1Q_Me). Likewise, in

1Q_Ph, interaction of one of the ﬁlled −Ph ring π-MOs with π_v

is also destabilizing (energy of π_v−4.98 eV). As can be seen in

Figure 4, the −OMe substituent of 1Q_OMe possesses an

approximately pure 2p lone pair due to the formal sp²

hybridization at O. This LP is oriented (dihedral angle

Cp_cent−Ti···O−R = 130.0° in 1Q_OMe; cf. 125.2° in the real

compound 19) such that it can interact, in an antibonding way,

with both π_hand π_v, which results in a π_venergy of −4.92 eV.

The destabilizing eﬀect is thus comparable to that found in

1Q_Ph but less than that in the hydrazido analogues 1Q_NR₂.

This trend is analogous to that found in the model compounds

Ti(NR)Cl₂(NHMe₂)₂(R = OMe, Me, Ph, NMe₂).^14b

The trends in experimental and computed TiNR bond

distances can also be accounted for by the nature of the R

substituent. As noted previously,^8ua second-order NBO

(natural bond orbital) perturbation analysis²⁹of 1Q_NR₂(R

= Me (pyramidal N_β), Ph (planar N_β)) found signiﬁcant

donation (19.2 and 26.1 kcal mol⁻¹, respectively) from the

−NR₂LP into the TiN_απ*_vNBO, thus lengthening the

TiN_αbond. In the case of 1Q_Ph a smaller interaction

between a ﬁlled ring π orbital and π*_v(12.1 kcal mol⁻¹) was

accompanied by competition from a Ph ring π* acceptor orbital

for the −NPh 2p AO (as indicated by a stabilization energy of

26.2 kcal mol⁻¹between π_vand a Ph ring π* NBO). This

combination of “push-pull” eﬀects accounts for the longer

MNR bonds found in general for arylimido compounds in

comparison to their alkylimido counterparts.^27,30In 1Q_OMe

the NBO analysis found donation from the oxygen LP into

both π*_vand π*_h(interaction energy 8.7 and 9.7 kcal mol⁻¹,

respectively) as a consequence of the orientation of the −OMe

group. The net interaction energy of 18.4 kcal mol⁻¹is

comparable to that for 1Q_NMe₂for the TiN_απ* orbital

alone and consistent with the experimental and computational

similarity of the (L)TiNOR and (L)TiNNMe₂bond

distances and the lengthening of the (L)TiNOR bond in

Figure 4. (top) DFT model compound CpTi{MeC(NMe)₂}(NOMe)

(1Q_OMe) and associated isosurfaces and energies of the HOMO

(π_v) and HOMO-2 (π_h). (bottom) DFT computed isodesmic reaction

between 1Q_Me and MeONH₂(electronic energy).

calculations have previously been carried out on the imido and

hydrazido homologues CpTi{MeC(NMe)₂}(NR) (R = Me

(1Q_Me), Ph (1Q_Ph), NMe₂(1Q_NMe₂, pyramidal N_β),

NPh₂(1Q_NPh₂, planar N_β)).^8uAdditional details for these

model complexes can be found in the Supporting Information

(Figure S1a,b). The DFT calculations predict TiNR bond

lengths in the order TiNMe (1.688 Å) < TiNOMe (1.698

Å) < TiNNMe₂(1.705 Å) < TiNPh (1.709 Å) < Ti

NNPh₂(1.713 Å), consistent with the experimental and

previous computational results described above.^14b

All of the complexes have formal TiN_αtriple bonds

containing two orthogonal 3d_π−2p_πinteractions (denoted π_v

and π_h) with a predominantly ligand-based, out-of-phase 2p AO

combination from the nitrogen atoms of the amidinate ligand

being either the HOMO-1 or HOMO (for 1Q_Me). This latter

MO can mix with π_hunder the approximate C_ssymmetry of

CpTi{MeC(NMe)₂}(NR). Because of this mixing eﬀect and

t

comparison to (L)TiNR (R = Bu or Me) in both cases.

Figure 4 also shows the DFT computed reaction of 1Q_Me

and MeONH₂, forming 1Q_OMe and MeNH₂. The ΔE value

of −3.9 kcal mol⁻¹is comparable to those for the

corresponding processes for PhNH₂, Ph₂NNH₂, and

Me₂NNH₂(ΔE = −2.5, −5.1, −4.0 kcal mol⁻¹, respectively),^8u

consistent with experiment where the tert-butylimido/amine or

hydrazine exchange reactions of Cp*Ti{RC(NⁱPr)₂}(N^tBu) (R

= Me (10), Ph (18)) are all quantitative.

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Reactions with Heterocumulenes. As mentioned, the

reaction chemistry of alkoxyimido compounds in general is

virtually unexplored and so we have started to develop their

reactions with a range of unsaturated substrates. Group 4 imido

and hydrazido complexes typically undergo [2 + 2] cyclo-

addition reactions with heterocumulenes such as CO₂,

isocyanates, and their heavier congeners. Further reactions

such as retrocyclization, extrusion of a new organic species, and

insertion of a second molecule of substrate into the ﬁrst-formed

metallacycles have all been observed.^{1a−f,8a,f,h,l−n,p−r,u,v,9f,h}The

most relevant systems for comparison with 19 are clearly the

homologous cyclopentadienyl-amidinate systems Cp*Ti{MeC-

products Cp*Ti{MeC(NⁱPr)₂}{N(R)C(S)S} (R = NMe₂,

NPh₂, NNCPh₂; ca. δ 150−160 ppm).^8u,10fCompound 20

was isolated in 65% yield and characterized by elemental

analysis and ¹H and ¹³C NMR and IR spectroscopy. No further

reaction with CS₂was observed at room temperature. Like the

hydrazide-derived products, 20 is stable in solution for days,

although heating at 70 °C for up to 1 week generated unknown

mixtures. This is in contrast to the arylimido counterparts

Cp*Ti{MeC(NⁱPr)₂}{N(Ar)C(S)S} (Ar = Xyl, Tol) which

extrude the corresponding isothiocyanate, ArNCS, forming the

sulﬁdo-bridged dimer [Cp*Ti{MeC(NⁱPr)₂}(μ-S)]₂.^22d

The reactions of 19 with the representative isocyanates

t

(NⁱPr)₂}(NR) (R = Bu (10), aryl (11), NPh₂(12), NMe₂

t

i

Ar′NCO, TolNCO, and BuNCO (Ar′ = 2,6-C₆H₃Pr₂) are

summarized in Scheme 2 and discussed below. No reaction was

observed between 19 and the isothiocyanate Ar′NCS at room

temperature, while heating at 60 °C gave complex mixtures.

Reaction with TolNCS (1 or 2 equiv) also resulted in unknown

mixtures, and so reactions with isothiocyanates were not

pursued further.

(13), NCPh₂(14)) which have been studied in considerable

detail previously.^{8h,q,t,u,w,10f,22}

When the reaction of 19 with CO₂(ca. 1.1 atm pressure) was

followed by ¹H NMR spectroscopy in C₆D₆at room

temperature, mixtures from which no single products could

be identiﬁed were observed. In contrast, addition of 1 equiv or

more of CS₂to a benzene solution of 19 resulted in the single

Reaction with the bulkier Ar′NCO formed the cycloaddition

product Cp*Ti{PhC(NⁱPr)₂}{OC(NAr′)N(O^tBu)} (21) with-

in 90 min at room temperature. The compound was isolated in

40% yield, and no further reaction was observed. Although 21

could not be structurally authenticated, the ¹H NMR spectrum

of 21 in toluene-d₈at −30 °C is indicative of C₁symmetry and

a ROESY NMR experiment was consistent with the κ²N,O-

coordination mode shown in Scheme 2. The IR spectrum

shows a ν(CN) band at 1631 cm⁻¹, which compares well

with a number of imido- and hydrazido-derived analogues of

the type Cp*Ti{MeC(NⁱPr)₂}{N(R)C(NAr′)O} (R = aryl,

NPh₂, NCPh₂) (ν(CN) in the range 1609−1622

cm⁻¹).^8u,10f,22dLike these previous arylimido and hydrazido

products, 21 was stable to carbodiimide (Ar′NCNO^tBu)

elimination, although unknown decomposition species were

1

apparently C_s-symmetric product 20 according to H NMR

spectroscopy at room temperature. However, on cooling a

sample to −60 °C in toluene-d₈the PhC(NⁱPr)₂ligand

isopropyl resonances decoalesced into four doublets (diaster-

eotopic CHMe₂) and two septets (CHMe₂), consistent with the

C₁-symmetric thiocarbamate-type [2 + 2] cycloaddition

product Cp*Ti{PhC(NⁱPr)₂}{SC(S)N(O^tBu)} (20; eq 2).

1

observed by H NMR spectroscopy over 2 days in C₆D₆.

When it was followed on the NMR tube scale, the reaction

between 19 and 1 equiv of TolNCO gave unknown mixtures.

However, upon reaction with 2 equiv of TolNCO, one major

The ¹³C NMR spectrum at −50 °C revealed an SCS resonance

at δ 148.1 ppm, analogous to the hydrazido cycloaddition

a

Scheme 2. Reactions of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19) with Isocyanates

a

i

Ar′ = 2,6-C₆H₃Pr₂.

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product (22) was formed within 30 min, which was isolated in

60% yield on scale-up. Compound 22 was identiﬁed by NMR

spectroscopy and X-ray crystallography as the “double-

insertion” compound Cp*Ti{PhC(NⁱPr)₂}{OC(NTol)N(Tol)-

C(NO^tBu)O}. The solid-state structure is shown in Figure 5,

previously reported Cp*Ti{MeC(NⁱPr)₂}{OC(NR)N(Tol)C-

(NTol)O} (R = NMe₂, NCPh₂), formed by reaction of 13 or

14 with 2 equiv of TolNCO,^8u,10falthough in 22 the six-

membered ring has a signiﬁcantly more nonplanar arrangement.

The IR spectrum of 22 shows two ν(CN) bands at 1623 and

1587 cm⁻¹which are comparable to those seen in the previous

cases (1623, 1604 and 1619, 1599 cm⁻¹for 13 and 14,

respectively). Although the unsymmetrical structure found for

22 has the aforementioned precedents in the hydrazide

literature, this type of “double insertion” product is relatively

unusual, with C_s-symmetric products of the type Cp*Ti{MeC-

(NⁱPr)₂}{OC(E)N(R)C(E)O} (R = Tol, NPh₂; E = O, NTol)

usually being formed in the case of reactions of CO₂or

TolNCO with Cp*Ti{MeC(NⁱPr)₂}(NR) (R = Tol (11a),

NPh₂(12, for CO₂only)), and these reactions have been

studied in detail both experimentally and computational-

ly.^8u,22a,d,e

Scheme 3 shows the proposed mechanism for formation of

22, which is analogous to that determined by DFT calculations

for 13 and consistent with the reactions of 19 with Ar′NCO

8u

t

and BuNCO (vide infra). Thus, [2 + 2] cycloaddition of

TolNCO to 19 forms the intermediate 22_int1, which is the

analogue of the fully characterized 21. The species 22_int1 is

not observed and undergoes extrusion (retrocyclization) of the

t

Figure 5. Displacement ellipsoid plot (20% probability) of Cp*Ti-

{PhC(NⁱPr)₂}{OC(NTol)N(Tol)C(NO^tBu)O} (22). H atoms are

omitted for clarity.

tert-butoxy carbodiimide BuONCNTol, forming the transient

titanium oxo species Cp*Ti{PhC(NⁱPr)₂}(O). Although such

species can easily dimerize, they are also able to undergo

cycloaddition reactions with carbodiimides or other unsaturated

species.^8a,31In this case, cycloaddition of the extruded

^tBuONCNTol to the transient oxo species is rapid in

comparison with dimerization, either re-forming 22_int1 or

the isomeric 22_int2 containing a Ti−N(Tol) single bond. As

we have shown previously^22dsuch ureato species are able to

insert isocyanates, in this case forming 22. Interestingly,

although Scheme 3 proposes 22_int1 as a likely intermediate,

this compound apparently does not undergo insertion of

TolNCO into the Ti−N(O^tBu) bond in preference to

rearrangement to 22_int2. We attribute this to the electron-

withdrawing nature of the −O^tBu group decreasing the

nucleophilicity of the Ti−N(O^tBu) nitrogen in comparison to

Ti−N(Tol) or/and the steric bulk of the tert-butyl substituent.

Table 2. Selected Bond Lengths (Å) and Angles (deg) for

a

Cp*Ti{PhC(NⁱPr)₂}{OC(NTol)N(Tol)C(NO^tBu)O} (22)

Ti−Cp_cent

Ti(1)−N(2)

Ti(1)−N(3)

Ti(1)−O(2)

Ti(1)−O(3)

N(1)−C(5)

N(1)−O(1)

Cp_cent−Ti(1)−N(2)

Cp_cent−Ti(1)−N(3)

Cp_cent−Ti(1)−O(2)

Cp_cent−Ti(1)−O(3)

N(2)−Ti(1)−N(3)

Ti(1)−O(2)−C(5)

Ti(1)−O(3)−C(6)

2.049

N(4)−C(5)

N(4)−C(6)

N(4)−C(7)

N(5)−C(6)

O(1)−C(1)

1.4141(16)

1.4024(15)

1.4267(16)

1.2822(17)

1.4539(15)

1.3337(15)

1.3184(15)

84.63(4)

2.0726(10)

2.0979(10)

1.9197(9)

1.9527(9)

1.2851(17)

1.4242(14)

114.88

O(2)−C(5)

O(3)−C(6)

O(2)−Ti(1)−O(3)

O(2)−C(5)−N(4)

C(5)−N(1)−O(1)

N(1)−O(1)−C(1)

C(5)−N(4)−C(6)

N(4)−C(6)−O(3)

N(4)−C(6)−N(5)

116.67

115.65(10)

109.93(10)

110.71(9)

117.85(10)

113.47(10)

119.30(11)

t

110.36

As shown in Scheme 2, reaction of 19 with BuNCO over a

113.45

period of 16 h resulted in a gradual color change from green to

yellow along with formation of a yellow precipitate, identiﬁed as

the oxo-bridged dimer [Cp*Ti{PhC(NⁱPr)₂}(μ-O)]₂(23). A

number of analogues of 23 have been reported previously from

reactions of this type.^22a,c,dThe molecular structure and

selected bond lengths and angles for 23, which lie within the

expected ranges,²⁷are presented in Figure S2 and Table S1 of

the Supporting Information. Careful evaporation of the ﬁltrate

gave the alkoxycarbodiimide byproduct ^tBuNCNO^tBu (24) as a

colorless oil, which was characterized by NMR and IR

spectroscopy and high-resolution FI mass spectrometry. The

IR spectrum showed ν(CN) bands at 2257 and 2065 cm⁻¹in

the expected range.³²Unfortunately, due to its relatively high

volatility, 24 could only be isolated as a pure sample in ca. 10%

yield (suﬃcient to enable full characterization). However, since

63.73(4)

113.21(7)

131.78(8)

a

Cp_centis the computed centroid for the Cp* ring carbons.

and selected bond length and angles are given in Table 2. The

solution ¹H and ¹³C NMR spectra are consistent with the solid-

state structure, in particular conﬁrming the C₁symmetry of the

compound and the presence of two inequivalent tolyl groups

derived from the TolNCO.

The molecular structure shows a ﬁve-coordinate titanium

center in a four-legged piano-stool geometry. In addition to the

η⁵-C₅Me₅and κ²N,N′-PhC(NⁱPr)₂supporting ligands, two new

Ti−O bonds make up part of the newly formed six-membered

ring derived from the two TolNCO moieties and the original

NO^tBu fragment of 19. The N(4)−C(5), N(4)−C(6), and

N(4)−C(7) bonds are consistent with C−N single bonds,

whereas the N(1)−C(5) and N(5)−C(6) bonds are signiﬁ-

cantly shorter, consistent with the double-bond representation

shown in Scheme 2. The structure is reminiscent of the

t

the reaction of 19 with BuNCO is quantitative (as judged by

¹H NMR monitoring in C₆D₆(no intermediates analogous to

21 were observed)), 24 could be isolated as diethyl ether

solutions in high yield. No examples of alkoxycarbodiimides

have previously been reported, although amino-carbodiimides

have been reported previously by others³³and also by our

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Scheme 3. Proposed Mechanism for the Reaction of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19) with TolNCO Leading to

Cp*Ti{PhC(NⁱPr)₂}{OC(NTol)N(Tol)C(NO^tBu)O} (22)

Scheme 4. Reaction of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19) with PhC(O)H, PhC(O)Me, and PhC(O)Ph

group via a cycloaddition−elimination protocol similar to that

forming 24.^8u,10fThe cycloaddition−extrusion reaction leading

to 23 and 24 is analogous to that found previously for reactions

formed as one of two isomers, syn or anti, where anti is deﬁned

as a Z arrangement of the nitrogen-bound and highest

molecular weight carbon-bound substituents.^36bAs discussed

above, reaction of 19 with ^tBuNCO demonstrated the potential

t

of Cp*Ti{MeC(NⁱPr)₂}(NR) (R = Bu (10), Ar (11)) and

t

Cp*Ti{MeC(NⁱPr)₂}(NNMe₂) (13) with BuNCO. With 11

for NO^tBu transfer to another fragment (in that case BuNC,

t

unstable cycloaddition intermediates could be observed, but

ultimately in all cases carbodiimides were formed along with the

corresponding oxo-bridged dimer.

forming BuNCNO^tBu (24)). To explore the scope of the

NO^tBu group transfer processes further, reactions with selected

aldehydes and ketones were carried out. Scheme 4 summarizes

the reactions of 19 with PhC(O)H, PhC(O)Me, and

PhC(O)Ph, along with the proposed likely intermediates.

Reaction of 19 with PhC(O)H in C₆D₆at room temperature

gave quantitative formation of the oxo-bridged dimer [Cp*Ti-

{PhC(NⁱPr)₂}(μ-O)]₂(23) and oxime ether PhC(NO^tBu)H,

(25a) in a ca. 4:1 ratio of geometric isomers. Scale-up and

distillation (80−110 °C, 8 × 10⁻²mbar) gave 25a as a colorless

Reactions with Aldehydes and Ketones. The metathesis

reactions between transition-metal imido compounds and

organic carbonyls to form ketimines or aldimines via cyclo-

addition−elimination reactions is well-established.^{1b,c,e,13b,34}In

particular, both Cp*Ti{MeC(NⁱPr)₂}(N^tBu) (10) and Cp*Ti-

{MeC(NⁱPr)₂}(NTol) (11a) undergo ketone and aldehyde

CO/TiNR bond metathesis reactions with MeC(O)Me,

PhC(O)Ph, PhC(O)H, and PhCOMe, and in some instances

[2 + 2] cycloaddition intermediates were observed.^22dBy

analogy, we reasoned that reactions of 19 with aldehydes or

ketones should give access to oxime ethers (i.e., compounds of

the general type RC(NOR′)R″).³⁵

1

oil in 70% yield. On the basis of the H and ¹³C NMR spectra

(vide infra), the two isomers are assigned as anti (major) and

syn (minor), denoted 25a_anti and 25a_syn in Scheme 4.

Following their formation, no signiﬁcant interconversion

between the two isomers was observed in solution or upon

sublimation. This is consistent with previous studies which

found that, unlike the case for imines, it is only under harsh

thermal or photochemical conditions that syn−anti isomer-

ization of oxime ethers is observed.³⁷

The main synthetic routes to oxime ethers are reaction of an

oxime with carbon electrophiles, such as alkyl halides, epoxides,

and activated oleﬁns, and reaction of an aldehyde or ketone

with the HCl salt of the alkoxyamine.^23,35,36Oxime ethers are

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Figure 6. Gibbs free energy diagram (kcal mol⁻¹) at 298 K for the cycloaddition−extrusion reactions of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19) with

PhC(O)H (left) and Ph(CO)Me (right). Values in parentheses are the Gibbs free energies at 253 K. The Cp*Ti{PhC(NⁱPr)₂}(O) side product is

not shown.

Comparison with literature data established the minor isomer

as 25a_syn, which gives a diagnostic H NMR singlet for syn-

the corresponding imines PhC(NTol)R and the μ-oxo dimer

[Cp*Ti{MeC(NⁱPr)₂}(μ-O)]₂.^22dThe metallacycles 25_in-

t_R_up/downdiﬀer in the orientation of the substrate-derived R

and Ph substituents, each diastereomer leading speciﬁcally to

one isomer of PhC(NO^tBu)R as illustrated.

1

PhC(NO^tBu)H at δ 8.03 ppm.^36dLiterature data for 25a_anti

are more limited, but the presence of the anti-PhC(NO^tBu)H

singlet at δ 7.27 ppm is consistent with other NMR studies on

the geometric isomerism of oxime ethers.^36c,38The o-C₆H₅

hydrogens for 25a_anti are found at δ 7.85 ppm, consistent

with the aryl ring being cis to the O^tBu group.^36bThe

assignments were conﬁrmed by comparison of the experimental

¹³C NMR data with the corresponding ¹³C isotropic magnetic

shielding tensors calculated by DFT (Figure S3 of the

Supporting Information). Interestingly, the DFT calculations

showed that the minor isomer 25a_syn is 1.9 kcal mol⁻¹more

thermodynamically stable than 25a_anti at 298 K. This

suggests that the overall reaction is governed by kinetic/

mechanistic constraints, given that 25a_syn and 25a_anti do

not interconvert once formed.

Although no intermediates were observed at room temper-

ature in the reactions of 19, when PhC(O)H was added to a

precooled toluene-d₈solution of 19 at −50 °C two products

1

were observed in the H NMR spectrum within 5 min. The

spectra were consistent with formation of the cycloaddition

intermediates Cp*Ti{PhC(NⁱPr)₂}{N(O^tBu)C(Ph)(H)O}

(25a_int), present as major and minor isomers in a ca. 7:3

ratio. Warming to −10 °C gave complete consumption of the

minor isomer to form 23 and 25a_syn. The major isomer

extruded 25a_anti only slowly at this temperature, but on

warming to 0 °C the reaction reached completion within 30

min. The major and minor isomers are tentatively assigned as

the metallacycles 25a_int_H_upand 25a_int_H_down,respec-

tively, but due to the numerous overlapping resonances in the

¹H NMR spectrum it was not possible to assign the data

completely. In a similar way, when the reaction of 19 with

PhC(O)Me was carried out under analogous conditions, no

reaction was observed until −30 °C, and at this point one major

cycloaddition intermediate, tentatively assigned as the cyclo-

addition product 25b_int_Me_up, was observed. This started to

undergo extrusion at −10 °C, and upon warming to 0 °C the

reaction reached completion within 25 min. Note that although

only one cycloaddition intermediate was unambiguously

identiﬁed at low temperature (because of the low proportion

of 19 converting to the other diastereomer), two isomers of the

oxime ether (25b_syn and 25b_anti, 9:1 ratio) were formed on

warming, as in the room-temperature experiment.

Reaction of 19 with PhC(O)Me at room temperature

aﬀorded PhC(NO^tBu)Me^36e(25b; Scheme 4), which again was

readily separated from 23 by distillation in very good yield

(75%). The known compound PhC(NO^tBu)Me also exists as a

mixture of syn and anti isomers, 25b_syn and 25b_anti, and the

assignments were conﬁrmed by comparison with literature

NMR values^36eand DFT calculated isotropic ¹³C magnetic

shielding tensors. However, in this case it is now the syn isomer

which is the major species, formed in a ca. 9:1 ratio with respect

to the anti counterpart. As was also the case for 25a, DFT

calculations found that 25b_syn is more thermodynamically

stable than 25b_anti by 5.6 kcal mol⁻¹at 298 K.

On the basis of DFT studies discussed below, Scheme 4

shows the two likely metallacyclic intermediates, denoted

25_int_R_downand 25_int_R_up(R = H, Me), formed en route

to the anti and syn isomers of 25a and 25b, respectively.

Metallacycles of this type have been explicitly observed by us

previously in the reactions of Cp*Ti{MeC(NⁱPr)₂}(NTol)

(11a) with PhC(O)R (R = H, Me, Ph), which ultimately give

In an additional attempted crossover-type experiment,

PhC(O)H was added to a solution of 19 in toluene-d₈at

−50 °C, at which temperature the cycloaddition products

25a_int_H_upand 25a_int_H_downwere both formed as above

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and were stable to extrusion. Subsequently, 1 equiv of

TolC(O)H was added and, following a further 10 min at

−50 °C, the solution was warmed to room temperature, at

which point extrusion took place eﬀectively immediately. The

¹H NMR spectrum showed no detectable consumption of the

TolC(O)H, showing that extrusion of PhC(NO^tBu)H from

25a_int_H_upand 25a_int_H_downis much faster than loss of

PhC(O)H to re-form 19 (which could then react with either

PhC(O)H or TolC(O)H). For comparison, when the reaction

of 19 with TolC(O)H was carried out in a separate NMR tube

scale reaction, TolC(NO^tBu)H (25d) was formed immediately

as a mixture of anti and syn isomers in a 7:3 ratio, respectively.

19.7 kcal mol⁻¹), loss of the product PhC(NO^tBu)R is more

kinetically favorable (via TS2, ΔG^⧧= 8.6−14.5 kcal mol⁻¹).

Second, elimination of PhC(NO^tBu)R from 25_int_R_down

gives exclusively the anti isomer, while elimination from

25_int_R_upgives exclusively the syn isomer.

The relative energies of TS1, TS2, and 25_int_R_up/down

account qualitatively for the experimental observations and

product isomer selectivity for R = H, Me. In the case of

PhC(O)H, formation of 25a_int_H_down(path 1) via TS1 is

kinetically favored by ΔΔG^⧧= 2.2 kcal mol⁻¹. Once formed,

extrusion of the thermodynamically less stable product

25a_anti via TS2 is predicted to be slower than extrusion of

25a_syn from the minor isomer 25a_int_H_up. In the case of

PhC(O)Me, however, the relative energies of TS1 for paths 1

and 2 (and the relative energies of 25b_int_Me_up/downand

25a_int_H_up/down) swap over due to the inﬂuence of the

substrate −Me group. There is, therefore, a higher kinetic

preference for the 25b_int_Me_upmetallacycle and, in turn, the

more stable product 25b_syn, in accord with experiment.

Reactions with Nitriles. Although the reactions of nitriles

with transition-metal nitrides,³⁹alkylidenes,⁴⁰and alkylidynes⁴¹

are very well established, the corresponding reactions with

transition-metal imides are almost unknown. The ﬁrst example

was for Ti(N₂N^py)(N^tBu)(py) (N₂N^py= (2-NC₅H₄)CMe-

(CH₂NSiMe₃)₂) with MeCN and gave rise to the dimeric

complex Ti₂(N₂N^py)₂{μ-NC(Me)(N^tBu)}₂.⁴²More recently,

reactions of ﬂuorinated benzonitriles Ar^F^xCN (Ar^F^x= Ar^F²(2,6-

1

These were characterized by H and ¹³C NMR spectroscopy

and high-resolution mass spectroscopy. In a further NMR tube

scale experiment, the reaction of a 1:1 mixture of PhC(O)H

and TolC(O)H with 1 equiv of 19 formed a 1:1 mixture of 25a

and 25d, conﬁrming that the two aldehydes can compete

eﬀectively when both are available prior to metallacycle

formation.

Finally, as mentioned, the tolylimide 11a reacts with

PhC(O)Ph to give the ketimine PhC(NTol)Ph, although this

reaction took 9 days to reach completion at room

temperature.^22dThe synthesis of the corresponding oxime

ether PhC(NO^tBu)Ph (25c) has been previously attempted by

Rad and Khalaﬁ-Nezhad et al. during their studies of the use of

alcohols and oximes, in the presence of DBU, PPh₃, CCl₄,and

^tBu₄NI, to prepare such species.³⁵We found that addition of

PhC(O)Ph to 19 in C₆D₆quantitatively formed 25c (Scheme

4), albeit at a much slower rate (2 days at room temperature)

than for PhC(O)R (R = H, Me). At 70 °C, the reaction was ca.

90% complete within 2 h and reached quantitative conversion

within 17 h. On scale-up, 25c was isolated by sublimation as a

cream-colored solid in 93% yield. The structure was conﬁrmed

by X-ray crystallography (Figure S4 and Table S2 of the

Supporting Information).

Figure 6 shows the DFT computed reaction proﬁle for the

reaction of 19 with PhC(O)R (R = H, Me). The actual

experimental molecules have been considered in the calcu-

lations. Gibbs free energy values are given at 298 and 253 K,

and the calculations include D3 corrections for dispersion (see

Computational Details). Two pathways were found, shown in

blue (path 1) and red (path 2), leading to anti- and syn-

PhC(NO^tBu)R, respectively (R = H, Me). In both cases (R =

H, Me) the reaction proceeds via an entropically disfavored [2

+ 2] cycloaddition of the substrate CO group to TiNO^tBu

via TS1, forming the intermediate metallacycle 25_int_R_down

(path 1) or 25_int_R_up(path 2). These species diﬀer in the

orientation of the R group with respect to the Cp* ligand and

are predicted to be observable at low temperature in each case

(less unfavorable TΔS contribution to the ΔG value for 19 +

PhC(O)R → 25_int_R_up/down; see the ΔG values at 253 K in

Figure 6). For R = Me, steric interactions destabilize both

metallacycles in comparison with those formed from PhC(O)-

H, but 25b_int_Me_downis destabilized more (with respect to

25a_int_H_down) than 25b_int_Me_up.All of the 25_in-

t_R_up/downspecies are unstable with respect to extrusion of

the oxime ether and Cp*Ti{PhC(NⁱPr)₂}(O) (the dimerization

energy for this to form 23 was not calculated but is known

experimentally to be exergonic).

C₆H₃F₂), Ar^F(C₆F₅)) with diamido-amine- or diamido-ether-

5

supported hydrazides (L)Ti(NNPh₂)(py)_n(L = N₂N^Me, N₂N^py,

O(CH₂CH₂NSiMe₃)₂; n = 1, 2) gave net TiN_αinsertion

products of the type (L)Ti{NC(Ar^F^x)NNPh₂}(py)_ncontaining

a new class of hydrazonamide ligand.^8p,r,12These reactions are

reminiscent of the ZrP insertion reaction of Cp₂Zr(PMes*)-

(PMe₃) (Mes* = 2,4,6-C₆H₂Bu₃) with PhCN.⁴³Very recently,

t

we found that the alkylidene hydrazide Cp*Ti{MeC(NⁱPr)₂}-

(NNCPh₂) (14) undergoes head-to-tail coupling of two

molecules of ArCN (Ar = Ph, Ar^F⁵) across the TiN_αbond

to form Cp*Ti{MeC(NⁱPr)₂}{N(NCPh₂)C(Ar)NC(Ar)N},

containing a six-membered metallacycle.^10fAlthough hydrazo-

namide-type intermediates were proposed, none were observed

experimentally. In contrast, none of the imido analogues of 14,

namely 10 and 11, showed any reactivity toward nitriles. The

double nitrile addition reactions of 14 were the ﬁrst of their

kind for any hydrazido or related complex, although multiple

coupling of two alkynes⁴⁴or of an alkyne and a nitrile^8racross

(L)TiNR (R = hydrocarbyl, NPh₂) bonds are known. The

only related example of a similar double addition of nitriles was

reported for the transient oxo and sulﬁdo complexes Cp*₂Zr-

(E) (E = O, S).⁴⁵

Scheme 5 shows the reactions of 19 with various

benzonitriles ArCN (Ar = Ph, Ar^F², Ar^F⁵), varying the extent

of ﬂuorination of the phenyl ring. When it was monitored on an

NMR tube scale in C₆D₆, the reaction with Ar^F⁵CN was

complete within 5 min to give Cp*Ti{PhC(NⁱPr)₂}{NC(Ar^F⁵)-

NO^tBu} (26), as established by X-ray diﬀraction (vide infra).

The corresponding reaction with Ar^F²CN was slightly slower

(80% and 100% conversion to 27 after 5 min and 1 h,

respectively), whereas with PhCN the reaction only reached

completion, forming 28, after 19 h (70% after 1 h). The NMR

spectra for 26−28 were very similar, consistent with the

formation of the new tert-butoxybenzimidamide complex

Cp*Ti{PhC(NⁱPr)₂}{NC(Ar)NO^tBu} in each case. Com-

pounds 27 and 26 were isolated on a preparative scale as a

Two important points should be noted regarding possible

extrusion processes from 25_int_R_up/down. First, although

elimination from 25_int_R_up/downof the starting PhC(O)R is

predicted to be feasible via transition state TS1 (ΔG^⧧= 17.1−

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NO^tBu (Ar = Ar^F⁵, Ar^F²). However, upon addition of ^tBuONH₂

Scheme 5. Reaction of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19)

a

1

complicated mixtures were observed in the H and ¹⁹F NMR

with Benzonitriles

spectra from which no products could be identiﬁed.

Diﬀraction-quality crystals of 26 were grown from a saturated

hexane solution at −80 °C. The molecular structure is shown in

Figure 7, and selected bond lengths and angles are given in

a

Figure 7. Displacement ellipsoid plot (20% probability) of Cp*Ti-

{PhC(NⁱPr)₂}{NC(Ar^F⁵)NO^tBu} (26). H atoms are omitted for

clarity.

The inset gives the likely metallacycle intermediate (not observed).

green oil or solid in 97% and 33% yields, respectively, and

characterized by ¹H, ¹³C, and ¹⁹F NMR, mass, and IR

spectroscopy and elemental analysis. The low yield for 26 is

attributed to its high solubility. Attempted scale-up of the

reaction with PhCN was unsuccessful, producing unknown

mixtures. Similarly disappointing results were obtained using

MeCN.

Table 3. Selected Bond Lengths (Å) and Angles (deg) for

a

Cp*Ti{PhC(NⁱPr)₂}{NC(Ar^F⁵)NO^tBu} (26)

Ti−Cp_cent

Ti(1)−N(1)

Ti(1)−N(3)

Ti(1)−N(4)

2.046

N(2)−C(1)

N(2)−O(1)

O(1)−C(8)

C(1)−C(2)

1.285(6)

1.429(5)

1.448(5)

1.497(6)

The slower rates of reaction with Ar^F²CN and PhCN in

comparison with Ar^F⁵CN are consistent with our previous

studies of benzonitriles with Ti(N₂N^Me)(NNPh₂)(py). DFT

calculations showed that increased ﬂuorination of the nitrile

substrate both lowered the activation barrier to the

intermediate metallacycles Ti(N₂N^py){N(NPh₂)C(Ar)N} and

increased the thermodynamic stability of the ﬁnal products

Ti(N₂N^py){NC(Ar^F^x)NNPh₂}(py) by stabilizing the electron-

rich TiNC(Ar)NPh₂group.^8rAn analogous intermediate

(see inset to Scheme 5) is likely in the reactions reported here

(although not observed), and our inability to isolate 28 is

attributed to its likely lower stability. To further test these

hypotheses, competition experiments were carried out.

Reaction of 27 with Ar^F⁵CN (1 equiv) resulted in immediate

formation of 26 and free Ar^F²CN, consistent with the more

electron deﬁcient nitrile yielding the more thermodynamically

stable insertion product. This reaction also highlighted the

reversibility of these insertion reactions, which previously had

not been observed. Likewise, addition of Ar^F⁵CN to in situ

generated 28 also led to immediate formation of 26 and free

PhCN.

1.747(4)

2.080(4)

2.074(4)

1.362(5)

121.78

N(1)−C(1)

Cp_cent−Ti(1)−N(1)

Cp_cent−Ti(1)−N(3)

Cp_cent−Ti(1)−N(4)

N(3)−Ti(1)−N(4)

Ti(1)−N(1)−C(1)

N(1)−C(1)−N(2)

C(1)−N(2)−O(1)

N(2)−O(1)−C(8)

167.0(3)

121.7(4)

109.5(3)

110.6(3)

120.38

121.87

64.97(15)

a

Cp_centis the computed centroid for the Cp* ring carbons.

Table 3. Compound 26 is a four-coordinate titanium complex

with a three-legged piano-stool geometry around the metal and

η⁵-C₅Me₅, κ²N,N′ amidinate, and η¹-tert-butoxypentaﬂuoroben-

zimidamide ligands. The Ti(1)−N(1) and N(2)−C(1) bond

lengths (1.747(4) and 1.285(6) Å, respectively) indicate a

multiple TiN bond and CN double bond, whereas the

N(1)−C(1) and N(2)−O(1) bond lengths (1.362(5) and

1.429(5) Å, respectively) are more consistent with single

bonds, indicating limited delocalization across the Ti

NC(Ar^F⁵)NO^tBu fragment. In comparison to 19 the Ti(1)−

N(1) bond is signiﬁcantly longer (1.747(4) vs 1.713(2)

(average) Å) but is still consistent with a TiN_αtriple

bond. Related molecular structures of hydrazonamides (L)Ti-

{NC(Ar^F^x)NNPh₂}(py)_n(n = 1, 2) also show longer TiN_α

bond lengths in comparison to the parent hydrazido

compounds (L)Ti(NNPh₂)(py)_n, which is explained by the

ﬂuorinated aryl ring withdrawing electron density away from

N_α.^8r,12

Analogues of tert-butoxypentaﬂuorobenzimidamide, H₂NC-

(Ar^F⁵)NO^tBu, such as O-alkylbenzamidoximes, H₂NC-

(C₆H₄Br)NOR, have been shown to be useful in the synthesis

of O-alkoxyamidine compounds which show antimicrobial

activity.⁴⁶Synthesis of the O-alkylbenzamidoxime compounds

is nontrivial, requiring multiple steps and toxic stannyl

reagents.⁴⁶With this in mind, BuONH₂was added to both

t

26 and 27, with the hope of eﬀecting benzimidamide/

alkoxyamine exchange and generating 19 and H₂NC(Ar)-

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Addition of 2 equiv of Ar^F⁵CN to 19 in C₆D₆aﬀorded an

approximately statistical mixture of 26 and a new product,

identiﬁed by NMR spectroscopy and X-ray crystallography as

Cp*Ti{PhC(NⁱPr)₂}{NC(Ar^F⁵)NC(Ar^F⁵)N(C{Ar^F⁵}NO^tBu)}

(29; Scheme 5), after 5 h at room temperature. The

compounds 26 (and Ar^F⁵CN) and 29 are in equilibrium, and

warming the NMR tube solution to 60 °C favored 26, as

expected on the basis of entropic considerations. Addition of 5

equiv of Ar^F⁵CN to 19 led to the sole formation of 29 within 45

min. On scale-up using 5 equiv of Ar^F⁵CN, 29 was isolated as an

orange solid in 49% yield. When pure 29 is dissolved in C₆D₆,

an equilibrium mixture of it and 26 and Ar^F⁵CN is formed

(26:29 ratio ca. 50:50; K_eq= 1.4 × 10⁻⁴M²after 23 h at room

Table 4. Selected Bond Lengths (Å) and Angles (deg) for

Cp*Ti{PhC(NⁱPr)₂}{NC(Ar^F⁵)NC(Ar^F⁵)N(C{Ar^F⁵}NO^tBu)}

a

(29)

Ti(1)−Cp_cent

Ti(1)−N(1)

Ti(1)−N(3)

Ti(1)−N(5)

Ti(1)−N(6)

N(1)−C(1)

N(2)−C(1)

N(2)−C(8)

Cp_cent−Ti(1)−N(1)

Cp_cent−Ti(1)−N(3)

Cp_cent−Ti(1)−N(5)

Cp_cent−Ti(1)−N(6)

N(5)−Ti(1)−N(6)

N(1)−Ti(1)−N(3)

2.089

N(3)−C(8)

N(3)−C(15)

N(4)−C(15)

N(4)−O(1)

O(1)−C(22)

C(1)−C(2)

C(8)−C(9)

1.3634(18)

1.4280(17)

1.2808(18)

1.4058(15)

1.4700(16)

1.5085(18)

1.5118(18)

1.8756(12)

2.1820(11)

2.2267(11)

2.0829(12)

1.2673(18)

1.3850(17)

1.3139(18)

107.87

Ti(1)−N(1)−C(1)

C(1)−N(2)−C(8)

N(3)−C(15)−N(4)

C(15)−N(4)−O(1)

N(4)−O(1)−C(22)

140.68(10)

117.07(11)

118.49(12)

111.19(11)

111.07(10)

118.69

1

temperature). The H NMR spectrum of 29 in toluene-d₈at

110.92

−10 °C showed the formation of a C₁-symmetric product with

characteristic inequivalent isopropyl groups on the PhC(NⁱPr)₂

ligand. Restricted rotation on the NMR time scale for two of

the ﬂuorinated rings resulted in ﬁve separate ¹⁹F resonances per

ring in the ¹⁹F NMR spectrum, together with three further

resonances for the third ring. On the basis of the solid-state

structure, the two constrained rings are assigned to those

containing C(9) and C(16).

120.15

61.60(4)

79.92(5)

a

Cp_centis the computed centroid for the Cp* ring carbons.

with the NMR data. Of particular interest is the approximately

planar, six-membered metallacycle. The N(1)−C(1) and

N(2)−C(1) bond lengths are signiﬁcantly diﬀerent

(1.2673(18) vs 1.3850(17) Å, Δ_N−C= 0.118(3) Å) and are

consistent with NC and N−C double and single bonds,

respectively.²⁸Although their N(3)−C(8) and N(2)−C(8)

counterparts are also diﬀerent (1.3634(18) vs 1.3139(18) Å)

and are consistent with single- and double-bond character, the

diﬀerence (Δ_N−C= 0.050(3) Å) is somewhat smaller. These

data, together with the rather diﬀerent Ti(1)−N(1) and

Ti(1)−N(3) distances (Δ_Ti−N= 0.306(2) Å) suggest (cf. Figure

9) contributions from both A′ and A″ resonance forms to the

In contrast to the reaction with Ar^F⁵CN, addition of an excess

of Ar^F²CN to 19 gave only the insertion product 27. This

diﬀerence between Ar^F²CN and Ar^F⁵CN is reminiscent of the

reactions of 14 with PhCN and Ar^F⁵CN to form Cp*Ti{MeC-

(NⁱPr)₂}{N(NCPh₂)C(Ar)NC(Ar)N}. While the product with

Ar = Ar^F⁵was stable in solution at room temperature, that with

Ar = Ph was much more labile and on treatment with 2 equiv of

Ar^F⁵CN underwent exchange of one PhCN unit to give a

mixed-nitrile metallacycle.^10f

Addition of pentane to an Et₂O solution of 29 and Ar^F⁵CN

followed by slow cooling to 4 °C resulted in diﬀraction-quality

orange crystals. The molecular structure is shown in Figure 8,

Figure 9. Resonance contributions to the bonding in Cp*Ti{PhC-

(NⁱPr)₂}{N(C(Ar^F⁵)NO^tBu)C(Ar^F⁵)NC(Ar^F⁵)N} (29). [Ti] = Cp*Ti-

{PhC(NⁱPr)₂}.

bonding in 29, leading to the net description A. Likewise, the

bond distances to the amidinate ligand, Ti(1)−N(5) and

Ti(1)−N(6), are also unequal (2.2267(11) and 2.0829(12) Å,

respectively), with the longer Ti(1)−N(5) bond being trans to

the shorter Ti(1)−N(1) bond. With speciﬁc reference to the

NC(Ar^F⁵)NO^tBu fragment that remains intact during the

reaction, the N(3)−C(15) bond distance is signiﬁcantly longer

than that found in 26 (1.4280(17) vs 1.362(5) Å, respectively),

which is attributed to the change in nitrogen hybridization from

sp in 26 to sp²in 29 and a loss of conjugation between N(3)

and C(15). Otherwise, the other geometric parameters are

similar to those seen in 26. The structural parameters for the

six-membered metallacycle in 29 are similar to those in the

corresponding fragment of Cp*Ti{MeC(NⁱPr)₂}{N(NCPh₂)-

C(Ar^F⁵)NC(Ar^F⁵)N}, except in that case the contribution from

the resonance form corresponding to A″ in Figure 9 seemed to

be slightly larger (Δ_N−C= 0.080(7) and 0.014(7) Å in

comparison with the values mentioned above) while the

Figure 8. Displacement ellipsoid plot (20% probability) of Cp*Ti-

{PhC(NⁱPr)₂}{NC(Ar^F⁵)NC(Ar^F⁵)N(C{Ar^F⁵}NO^tBu)} (29). H atoms

are omitted for clarity.

and selected bond lengths and angles are given in Table 4. Like

Cp*Ti{PhC(NⁱPr)₂}{OC(NTol)N(Tol)C(NO^tBu)O} (22),

compound 29 is a half-sandwich titanium complex with a

four-legged piano-stool geometry around the metal and η⁵-

C₅Me₅and κ²N,N′ amidinate ligands. The solid-state structure

conﬁrms coupling of a further two molecules of Ar^F⁵CN across

the TiN_αbond of 26 in a head-to-tail manner, consistent

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a

Scheme 6. Potential Pathways for the Formation of Cp*Ti{PhC(NⁱPr)₂}{N(C(Ar^F⁵)NO^tBu)C(Ar^F⁵)NC(Ar^F⁵)N} (29)

a

[Ti] = CpTi{PhC(NⁱPr)₂}; Ar^F= C₆F₅.

5

Scheme 7. Reaction of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19)

with Ar^F⁵CCH and Proposed Mechanism of Formation for

Cp*Ti(O^tBu){NC(Ar^F⁵)C(H)N(ⁱPr)C(Ph)N(ⁱPr)} (30)

diﬀerence in Ti−N_metallacycledistances (1.868(4) and 2.147(3)

Å) was comparable with that for 29.

Scheme 6 illustrates two alternative routes for the formation

of 29 from 26. Both begin by the [2 + 2] cycloaddition of

Ar^F⁵CN to TiN_αof 26 to form the azametallacyclobutene

intermediate 29_int1, as found in both titanium imido and

hydrazido chemistry.^8r,42Insertion of another 1 equiv of

Ar^F⁵CN into the new Ti−N(CAr^F⁵) bond would lead directly to

29. On the other hand, ring opening via 29_int2 and [2 + 2]

cycloaddition (to form 29_int3), followed by isomerization,

would also aﬀord 29. An analogous mechanism was proposed

for the formation of Cp*Ti{MeC(NⁱPr)₂}{N(NCPh₂)C(Ar^F⁵)-

NC(Ar^F⁵)N} from 14. However, when the reaction was

1

followed by H NMR spectroscopy, no intermediates were

seen prior to 29 and therefore which of the two pathways is

operative cannot be identiﬁed.

Reactions with Alkynes. As mentioned in the Introduc-

tion, reactions of group 4 imides and hydrazides with alkynes

has been a topic of continuing interest for over 20 years,

producing a range of new C−N bond forming reactions, some

of which are catalytic.^{1a−f,4,7,8c,d,f,h,i,l,n,p,v,9i,m,o,34k,40e,47}In the

case of terminal alkynes, there is also the possibility of

competitive 1,2-C−H bond activation across the MNR

bond.^{10d,21,47d,48}Of particular relevance are the N_α−N_βbond

reductive cleavage reactions^8h,p,9m,12available for hydrazides. As

mentioned above, the only previously reported reaction of a

group 4 alkoxyimido complex with alkynes is that of

Ti(N₂N^Me)(NO^tBu)(py) (6) with PhCCMe, forming 7 (Figure

2) via N−O bond cleavage.^14a

1

singlet at δ 6.86 ppm of relative intensity 1 H in the H NMR

spectrum assigned to the incorporated alkyne moiety. At ﬁrst

sight the NMR data appear to indicate formation of the [2 + 2]

cycloaddition product 30_int1 (or its isomer with CAr^F⁵bound

to Ti) depicted in Scheme 7, analogous to the case for

Cp*Ti{PhC(NⁱPr)₂}{SC(S)N(O^tBu)} (20) and Cp*Ti{PhC-

(NⁱPr)₂}{OC(NAr′)N(O^tBu)} (21) and the metallacyclobu-

tene species formed between Ar^F⁵CCH and 14, Cp*Ti{MeC-

(NⁱPr)₂}{N(NCPh₂)C(Ar^F⁵)C(H)} (31).^10fHowever, the shift

of δ 6.86 ppm for the alkyne-derived CCH is at much higher

ﬁeld than is usually found for such [2 + 2] cycloaddition

products (for example δ 9.19 ppm in the case of

31).^{8p,r,21,44a,47e,49}In addition, the ¹³C resonances for the

HCCAr^F⁵residue (δ 138.9 and 108.8 ppm, respectively) are also

inconsistent with the formation of a cycloaddition product (δ

167.8 and 140.3 ppm for 31 by way of example). Most

Disappointingly, no reactions were observed between

Cp*Ti{MeC(NⁱPr)₂}(NO^tBu) (15) and alkynes such as

CF₃

PhCCMe and Ar^CFCCMe (Ar = 4-C₆H₄CF₃). NMR tube

3

scale reactions of Ar^CFCCH and 19 gave complicated mixtures.

3

In contrast, the reaction of Ar^F⁵CCH with 19 in C₆D₆resulted

in a purple solution and a single product, Cp*Ti(O^tBu){NC-

(Ar^F⁵)C(H)N(ⁱPr)C(Ph)N(ⁱPr)} (30), after 16 h at room

temperature (Scheme 7). Compound 30 was isolated in 80%

yield upon scale-up.

The H, ¹³C, and ¹⁹F NMR spectra for 30 revealed a C₁-

1

symmetric species with two inequivalent ⁱPr groups, resonances

attributable to Ph, Cp*, and C₆F₅groups (with ﬁve inequivalent

F environments at 223 K due to restricted rotation), and a

importantly, a H−¹³C HMBC experiment (Figure S5 in the

1

Supporting Information) revealed coupling of the HCCAr^F⁵-

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derived hydrogen with one of the isopropyl group NC(H)-

MeMe carbons and also between NC(H)MeMe and HCCAr^F⁵.

crystal X-ray diﬀraction showed these to be [PhC(NⁱPrH)₂]-

[BPh₄] (33-BPh₄; eq 3).

1

A H ROESY NMR experiment also showed through-space

interactions between one NC(H)MeMe and HCCAr^F⁵.

Considering these NMR data, the product is assigned as

Cp*Ti(O^tBu){NC(Ar^F⁵)C(H)N(ⁱPr)C(Ph)N(ⁱPr)} (30;

Scheme 7).

The mechanism of formation of 30 is probably similar to that

previously described for the formation of 7 and 9 (Figure 2)

and recent hydrazide reactions involving azirinyl intermedia-

tes.^{8p,9i,m,12,14a}Thus, initial cycloaddition (30_int1) precedes

N_α−O_βbond cleavage and formation of an azirinyl

intermediate (30_int2). This in turn undergoes nucleophilic

attack by one of the amidinate nitrogens. Noninnocent

behavior of an amidinate ligand in these types of complexes

is not unprecedented, having previously been observed in the

reaction of Cp*Ti{MeC(NⁱPr)₂}(N^tBu) (10) with CS₂, which

involves insertion of CS₂into a Ti−N_amidinatebond to generate

the crystallographically authenticated [Cp*Ti{N(ⁱPr)C(Me)N-

(ⁱPr)C(S)S}(μ-S)]₂(32).^22d

The molecular structure and selected bond lengths and

angles are given in Figure S6 and Table S3 of the Supporting

Information, and the metric data are within the expected

ranges. Compound 33-BPh₄was independently synthesized via

anion exchange between [PhC(NⁱPrH)₂]Cl and Na[BPh₄] and

isolated in 63% yield. [Cp*Ti(NO^tBu)(THF)₂][BPh₄] (34-

BPh₄; eq 3) is formed alongside 33-BPh₄. Attempts to isolate

34-BPh₄on scale-up as either the THF or bipy adduct (to form

a less labile species) were unsuccessful. However, direct

evidence for 34⁺was found using positive ion electrospray

mass spectrometry for a solution of 33 and 34 generated in situ

in THF-d₈. Complexes with both one and two coordinated

THF molecules were identiﬁed in the mass spectrum with the

correct isotope distribution (m/z 343 and 415, respectively).

Group 4 hydrazides M(N₂N^py)(NNPh₂)(py) are known to

R

Unfortunately, while the reaction of 19 shows that reductive

cleavage of the alkoxyimido N_α−O_βbond is possible with the

appropriate alkyne, treatment with CO or the isonitriles XylNC

readily form zwitterionic N_αadducts of the type M(N₂N^py)-

R

{η²-N(NPh₂)B(Ar^F⁵)₃} (35; N₂N^py= (2-NC₅H₄)CMe-

R

t

(CH₂NR)₂; M = Ti, R = SiMe₃(a); M = Zr (b), Hf (c), R

or BuNC (reagents that are known to induce N_α−N_βbond

8r,9b

= SiMe₂Bu)) with B(Ar^F⁵)₃.

On the other hand, although

t

cleavage in a number of hydrazido compounds^7,8r,9a) led to the

formation of complex and unknown mixtures and these

reactions were not investigated further.

13 showed no apparent reactivity toward B(Ar^F⁵)₃,^8wit was

hoped that the corresponding reaction of 19 with B(Ar^F⁵)₃

might nevertheless provide additional insight into the chemistry

of the alkoxyimido functional group.

Alkylation, Protonation, and Related Reactions. Since

the discovery that group 6 hydrazide compounds were found to

be possible intermediates in the reduction of dinitrogen to

ammonia,⁵⁰reactions of these complexes with proton sources

and alkylating agents have been intensely explored.^13c,d,51

Reactions with alkyl halides resulted in alkylation at N_β,

whereas protonation reactions resulted in reaction at either N_α

or N_β. Although analogous reactions with group 4 hydrazides

are much more limited,^8c,ja recent detailed study from our

group showed that reaction of Cp*Ti{MeC(NⁱPr)₂}(NNMe₂)

(13) with alkyl halides (MeI, EtI, and PhCH₂Br) resulted

exclusively in alkylation at N_β, whereas protonation with

[Et₃NH][BPh₄] gave exclusively protonation of N_α.^8t,wSo as to

understand better the nature of the group 4 MNO^tBu group,

reactions of 19 with a number of potential Brønsted and Lewis

acids were carried out.

Reactions of 19 with the alkylating agents MeI, [Me₃O]-

[BF₄], and Me₂SO₄were disappointing, ultimately resulting in

unknown mixtures. Reaction with [HNEt₃][BPh₄] in THF-d₈

required 2 equiv to reach completion, yielding a new set of

resonances in the ¹H NMR spectrum consistent with NEt₃and

apparently a new titanium complex. Removal of the THF-d₈

and NEt₃byproducts and redissolving the remaining solid in

C₆D₅Br resulted in diﬀraction-quality colorless crystals. Single-

Compound 19 reacted very slowly with 1 equiv of B(Ar^F⁵)₃

in C₆D₆at room temperature, giving less than 10% conversion

to a new compound, Cp*Ti{PhC(NⁱPr)₂}{η²-ON(H)B(Ar^F⁵)₃}

(36), after 24 h. Heating for 5 days at 70 °C drove the reaction

to ca. 70% completion, and use of an excess of borane also

eﬀected complete conversion at room temperature after 2 days

(after which time the excess borane remained unreacted).

1

When the reaction was monitored by H NMR, isobutene was

also formed (either at room temperature or at 70 °C) alongside

36, as judged by multiplet and triplet (⁴J = 1.2 Hz) resonances

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at δ 4.74 (2 H) and 1.58 (6 H) ppm.⁵²The reaction was scaled

up in benzene at 70 °C for 16 h to give 36 as an orange

crystalline solid whose identity was conﬁrmed by single-crystal

X-ray diﬀraction. The molecular structure is shown in Figure

10, and selected bond lengths and angles are given in Table 5.

N-bound) coordination, and over 20 with N-substituted η²-

ON(H)R ligands (average N−O distance 1.396 Å, range

1.371−1.498 Å) have been reported, all for transition metals in

groups 5−9.²⁷With respect to titanium, seven Ti(+4)

complexes with η²-ON(R)R′ ligands (R, R′ = alkyl) have

been structurally authenticated (average distances (range): N−

O = 1.429 (1.402−1.446), Ti−O = 1.912 (1.872−1.980), Ti−

N = 2.128 (2.095−2.230) Å):²⁷for example, Ti(η²-ONMe₂)₄

and Cp*TiMe₂{η²-ON(^tBu)Me}.⁵⁴The Ti(1)−O(1), Ti(1)−

N(1), and N(1)−O(1) distances for 36 lie near to or within

these ranges. The N(1)−B(1) bond length of 1.5850(18) Å in

36 is comparable to those in M(N₂N^py){η²-N(NPh₂)B(Ar^F⁵)₃}

R

(35; 1.562(3)−1.598(3) Å)^8r,9band also, for example, [B-

(Ar^F⁵)₃(N₃)]⁻(1.583(2) Å),⁵⁵Ti(NEt₂)₃{NH₂B(Ar^F⁵)₃}

(1.595(3) Å), and CpTi(NMe₂)₂{NH₂B(Ar^F⁵)₃} (1.598(2)

Å).⁵⁶The Ti(1)···F(1) interaction in 36 (2.2903(8) Å, which

is less than the sum of the van der Waals radii of 3.92 Å⁵⁷) is

electrostatic in nature and presumably augmented by the formal

positive charge on titanium. A similar Ti···F interaction was

found in Ti(N₂^SiMe3N^py){η²-N(NPh₂)B(Ar^F⁵)₃} (35a),^8ralbeit

with a slightly longer distance of 2.4840(15) Å. Also, as found

in 35a, there is a small but signiﬁcant lengthening of the

C(25)−F(1) bond (1.3814(16) Å) in comparison to the other

aryl C−F bond lengths (range 1.3361(17)−1.3565(16) Å).

Taken together, these structural parameters are consistent with

the zwitterionic representation of 36 shown in Scheme 8.

Furthermore, 36 is therefore the ﬁrst fully authenticated

nitroxyl complex of a group 4 metal, stabilized by borane

coordination.

Figure 10. Displacement ellipsoid plot (20% probability) of

Cp*Ti{PhC(NⁱPr)₂}{η²-ON(H)B(Ar^F⁵)₃} (36). C-bound H atoms

are omitted for clarity.

Table 5. Selected Bond Lengths (Å) and Angles (deg) for

a

Cp*Ti{PhC(NⁱPr)₂}{η²-ON(H)B(Ar^F⁵)₃} (36)

The spectroscopic data for 36 are consistent with the solid-

Ti(1)−Cp_cent

Ti(1)−N(1)

Ti(1)−N(2)

Ti(1)−N(3)

2.063

Ti(1)−F(1)

N(1)−B(1)

N(1)−O(1)

C(25)−F(1)

2.2903(8)

1.5850(18)

1.4392(14)

1.3814(16)

1

state structure. The H and ¹³C data are indicative of a C₁-

2.1242(12)

2.1620(11

2.0576(11)

1.8549(10)

147.04

symmetric complex containing Cp* and PhC(NⁱPr)₂ligands,

but no tert-butyl group, this being the source of the eliminated

isobutene. A signal at δ 6.05 ppm is assigned to the N-bound

hydrogen, and the IR spectrum shows a ν(N−H) band at 3296

cm⁻¹. The ¹¹B NMR spectrum shows as resonance at δ −8

ppm, consistent with a tetracoordinate boron.⁵⁸Note that at

room temperature no exchange between free and coordinated

B(Ar^F⁵)₃is observed on the NMR time scale. The ¹⁹F NMR

spectrum of pure 36 is broad at room temperature, but cooling

to −20 °C shows 13 separate ﬂuorine environments.

Examination of the relative intensities and changes in

appearance on warming to room temperature establishes that,

at −20 °C, two of the C₆F₅rings display restricted rotation on

the NMR time scale whereas one is able to rotate relatively

freely. From the appropriate coalescence points the activation

free energies for exchange within and between the rings were

found to be comparable within error (ΔG^⧧= 13.1(1) and

12.7(1) kcal mol⁻¹at 291 and 268 K, respectively), indicating a

geared process as illustrated in Scheme 8.⁵⁹

T(1)-O(1)

Cp_cent−Ti(1)−N(1)

Cp_cent−Ti(1)−N(2)

Cp_cent−Ti(1)−N(3)

Cp_cent−Ti(1)−O(1)

Cp_cent−Ti(1)−F(1)

N(2)−Ti(1)−N(3)

N(1)−Ti(1)−O(1)

Ti(1)−N(1)−O(1)

Ti(1)−O(1)−N(1)

Ti(1)−N(1)−B(1)

63.23(4)

41.72(4)

59.07(6)

79.21(6)

139.51(9)

116.16

110.77

106.97

101.30

a

Cp_centis the computed centroid for the Cp* ring carbons.

Compound 36 is a half-sandwich titanium complex with η⁵-

C₅Me₅, κ²N,N′ amidinate, and η²-ON(H)B(Ar^F⁵)₃ligands as

well as a Ti···F interaction between the metal and an o-C₆F₅

ﬂuorine atom. The distances and angles associated with the

Cp*Ti{PhC(NⁱPr)₂} fragment are unexceptional, and so we

focus on the ON(H)B(Ar^F⁵)₃moiety, which formally comprises

a HNO (nitroxyl) ligand⁵³additionally N-bound to B(Ar^F⁵)₃.

Four structurally characterized complexes containing HNO as a

ligand, with either η²(one example) or η¹(three examples, all

i

2

F₅

Scheme 8. Mechanism for Ar^FRing Exchange in Cp*Ti{PhC(N Pr)₂}{η -ON(H)B(Ar )₃} (36)

5

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Scheme 9. Reaction of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19) with B(Ar^F⁵)₃and Proposed Mechanism for formation of

Cp*Ti{PhC(NⁱPr)₂}{η²-ON(H)B(Ar^F⁵)₃} (36)

A proposed mechanism for the formation of 36 is given in

Scheme 9. Since 19 itself is thermally stable at 70 °C for several

days in solution, we propose that isobutene elimination is

preceded by borane coordination to the alkoxyimido nitrogen

{NC(Ar^F⁵)NC(Ar^F⁵)N(C{Ar^F⁵}NO^tBu)} (29) was formed.

Reactions with both Ar^F⁵CCH and [HNEt₃][BPh₄] led to

reactions involving the amidinate supporting ligand, with the

reaction using Ar^F⁵CCH inducing N_α−O_βbond cleavage and

that with [HNEt₃][BPh₄] giving protonation of the amidinate

ligand. Finally reaction with B(Ar^F⁵)₃resulted in loss of

isobutene to give Cp*Ti{PhC(NⁱPr)₂}{η²-ON(H)B(Ar^F⁵)₃}

(36), the ﬁrst example of a HNO (nitroxyl) adduct for a

group 4 metal (with B(Ar^F⁵)₃stabilization).

R

in a manner analogous to that in M(N₂N^py){η²-N(NPh₂)B-

(Ar^F⁵)₃} (35). This generates a formally zwitterionic species,

potentially with coordination of the O-tert-butyl group to the

formally cationic metal center, depicted as 36_int. Indeed,

isobutene elimination is not uncommon from cationic group 4

complexes containing either tert-butoxy ligands⁶⁰or ligands

with −O^tBu substituents such as Carpentier’s cationic tert-butyl

enolate systems.^52a,61Subsequent intramolecular hydrogen

transfer to nitrogen leads to alkene elimination and formation

of the new borane-stabilized nitroxyl ligand. Finally we note

that, whereas AlMe₃readily coordinates to the oxygen atom of

Cp*TiMe₂(η²-ONEt₂) to form Cp*TiMe₂{η²-O(AlMe₃)-

NEt₂},⁶²excess B(Ar^F⁵)₃does not coordinate to the nitroxyl

oxygen of 36.

EXPERIMENTAL SECTION

Representative syntheses are given below. Further information is given

in the Supporting Information.

■

Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19). To a solution of Cp*Ti{PhC-

(NⁱPr)₂}(N^tBu) (18; 7.67 g, 16.8 mmol) in Et₂O (15 mL), cooled to

−78 °C, was added ^tBuONH₂in toluene (1.8 M, 13.0 mL, 23.5 mmol)

and the solution was slowly warmed to room temperature. A color

change from red to dark green-black was observed. After 3.5 h the

volatiles were removed under reduced pressure to aﬀord 19 as a dark

green oil, which was triturated in hexane (25 mL) and ﬁltered. The

resultant green solid was then washed with cold hexane (3 × 15 mL),

cooled to −78 °C, ﬁltered, and dried in vacuo. Yield: 5.56 g (70%).

Diﬀraction-quality crystals were grown from a saturated hexane

CONCLUSIONS

■

We have reported the ﬁrst use of imide/alkoxyamine exchange

to synthesize new alkoxyimido complexes, namely Cp*Ti-

{MeC(NⁱPr)₂}(NO^tBu) (15) and Cp*Ti{PhC(NⁱPr)₂}-

(NO^tBu) (19). Following this, the ﬁrst thorough investigation

into the reactions of alkoxyimido complexes with small

unsaturated molecules was undertaken. The reaction outcomes

are reminiscent of those seen with imido and diphenyl-,

dimethyl-, and alkylidenehydrazido compounds. Although

reaction with CO₂produced complicated mixtures, addition

of CS₂gave the stable cycloaddition product Cp*Ti{PhC-

(NⁱPr)₂}{SC(S)N(O^tBu)} (20). The reactions of 19 with

isocyanates were dependent on the steric bulk of the isocyanate

substituent. Thus, with Ar′NCO the cycloaddition product

Cp*Ti{PhC(NⁱPr)₂}{N(O^tBu)C(NAr′)O} (21) was isolated,

with TolNCO 2 equiv was needed to synthesis the “rearranged-

double insertion” product Cp*Ti{PhC(NⁱPr)₂}{OC(NTol)N-

(Tol)C(NO^tBu)O} (22), and ﬁnally with ^tBuNCO the

carbodiimide derivative ^tBuONCN^tBu (24) was formed

following extrusion from the unstable cycloaddition inter-

mediate. Cycloaddition−extrusion reaction pathways were also

seen with aldehydes and ketones, generating the oxo dimer 23

and corresponding oxime ethers PhC(NO^tBu)H (25a) and

PhC(NO^tBu)Me (25b) as a mixture of geometric isomers.

DFT calculations showed that the product distribution was

attributed to the energy barrier to cycloaddition formation. The

reaction also yielded the new oxime ether PhC(NO^tBu)Ph

(25c) in high yield, which was inaccessible following alternative

routes. Reactions of 19 with Ar^F⁵CN and Ar^F²CN led to the net

TiN_αinsertion products Cp*Ti{PhC(NⁱPr)₂}{NC(Ar^F^x)-

1

solution slowly cooled to −80 °C. H NMR (C₆D₆, 299.9 MHz, 293

K): δ 7.51 (1 H, d, ³J = 8.1 Hz, o_a-C₆H₅), 7.23−7.07 (4 H, m,

3

overlapping o_b-C₆H₅, m-C₆H₅and p-C₆H₅), 3.66 (2 H, sept, J = 6.3

Hz, NCHMeMe), 2.21 (15 H, s, C₅Me₅), 1.15 (9 H, s, NOCMe₃),

3

1.02 (6 H, d, J = 6.3 Hz, NCHMeMe), 0.91 (6 H, d, J = 6.3 Hz,

NCHMeMe) ppm. ¹³C{¹H} NMR (C₆D₆, 75.4 MHz, 293 K): δ 164.8

(PhCN₂), 135.1 (i-C₆H₅), 128.9, 128.6, 128.3 (p-C₆H_5,m-C₆H₅, o_b-

C₆H₅), 127.7 (o_a-C₆H₅), 119.5 (C₅Me₅), 80.4 (NOCMe₃), 49.9

(NCHMeMe), 27.0 (NOCMe₃), 26.8 (NCHMeMe), 25.6

(NCHMeMe), 12.1 (C₅Me₅) ppm. IR (NaCl plates, Nujol mull,

cm⁻¹): 1642 (w), 1357 (s), 1336 (s), 1260 (m), 1222 (m), 1168 (m),

1142 (s), 1076 (w), 1017 (m), 845 (m), 783 (w), 750 (m), 737 (m),

707 (s). EI-MS: m/z 473 [M]⁺(2%). Anal. Found (calcd for

C₂₇H₄₃N₃OTi): C, 68.61 (68.49); H, 9.17 (9.15); N, 8.58 (8.87).

Cp*Ti{PhC(NⁱPr)₂}(SC(S)N(O^tBu)) (20). To a solution of Cp*Ti-

{PhC(NⁱPr)₂}(NO^tBu) (19; 0.250 g, 0.528 mmol) in benzene (5 mL)

was added CS₂(38.1 μL, 0.634 mmol), all at room temperature. A

color change from green to dark brown was observed. After 6 h the

volatiles were removed under reduced pressure to aﬀord 20 as a dark

brown oily solid, which was then triturated with pentane (5 mL) and

ﬁltered; the resultant brown powder was dried in vacuo. Yield: 0.190 g

1

(65%). H NMR (toluene-d₈, 499.9 MHz, 223 K): δ 6.97 (2 H, m, o-

C₆H₅), 6.91 (1 H, m, p-C₆H₅), 6.72 (2 H, m, m-C₆H₅), 3.36 (2 H, m,

overlapping NCH_aMeMe and NCH_bMeMe), 2.02 (15 H, s, C₅Me₅),

1.54 (9 H, s, NOCMe₃), 0.98 (3 H, d, ³J = 6.5 Hz, NCH_aMeMe), 0.95

(3 H, d, ³J = 6.5 Hz, NCH_aMeMe), 0.89 (3 H, d, ³J = 6.5 Hz,

NCH_bMeMe), 0.85 (3 H, d, ³J = 6.5 Hz, NCH_bMeMe) ppm. ¹³C{¹H}

NMR (toluene-d₈, 125.7 MHz, 223 K): δ 167.3 (PhCN₂), 148.1

(SC(S)N), 132.6 (i-C₆H₅), 131.2 (C₅Me₅), 129.6 (o_a-C₆H₅), 129.0 (p-

C₆H₅), 128.7 (o_b-C₆H₅), 128.5 (m_a-C₆H₅), 128.1 (m_b-C₆H₅), 78.6

(NOCMe₃), 51.7 (NCH_bMeMe), 51.6 (NCH_aMeMe), 28.7

(NOCMe₃), 25.7 (NCH_bMeMe), 25.6 (NCH_bMeMe), 25.16, 25.17

NO^tBu} (Ar^F= Ar^F(26), Ar^F(27)). With an excess of

Ar^F⁵CN, the unusual insertion compound Cp*Ti{PhC(NⁱPr)₂}-

x

5

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(overlapping NCH_aMeMe and NCH_aMeMe), 14.5 (C₅Me₅) ppm. IR

(NaCl plates, Nujol mull, cm⁻¹): 1639 (w), 1359 (s), 1330 (s), 1217

(m), 1197 (s), 1170 (m), 1142 (m), 1120 (m), 1103 (m), 1075 (w),

1040 (w), 1019 (m), 987 (w), 928 (s), 910 (s), 860 (w), 781 (s), 711

(m). Anal. Found (calcd for C₂₈H₄₃N₃OS₂Ti): C, 61.37 (61.18); H,

7.74 (7.89); N, 7.82 (7.64).

1422 (m), 1356 (s) 1337 (s), 1279 (w), 1250 (m), 1217 (m), 1195

(m), 1142 (m), 1112 (m), 1103 (w), 1088 (m), 1043 (w), 1021 (m),

1001 (m), 955 (m), 932 (w), 916 (w), 869 (w), 826 (w), 814 (m),

807 (m), 788 (w), 780 (m), 734 (m), 726 (m), 713 (w), 707 (m), 678

(w), 646 (w), 619 (m). EI-MS: m/z 353 [OC(NO^tBu)N(Tol)C-

(NTol)O]⁺(60%). Anal. Found (calcd for C₄₃H₅₇N₅O₃Ti): C, 70.09

(69.81); H, 7.59 (7.77); N, 9.42 (9.47).

Cp*Ti{PhC(NⁱPr)₂}{OC(NAr′)N(O^tBu)} (21). To a solution of

Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19; 0.320 g, 0.676 mmol) in Et₂O (5

mL) was added Ar′NCO (144 μL, 0.676 mmol), all at room

temperature. An immediate color change from green to red-brown was

observed. After 3.5 h, the volatiles were removed under reduced

pressure to aﬀord 21 as a dark brown solid, which was then triturated

with hexane (5 mL) at −30 °C and ﬁltered; the resultant brown

Reaction of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) with ^tBuNCO: Syn-

t

thesis of [Cp*Ti{PhC(NⁱPr)₂}(μ-O)]₂(23) and BuNCNO^tBu (24).

To a solution of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19; 0.500 g, 1.06

mmol) in Et₂O (5 mL) was added ^tBuNCO (121 μL, 1.06 mmol), all

at room temperature. A color change from green to yellow was

observed. After 16 h the solution was ﬁltered, giving 23 as a yellow

solid which was dried in vacuo. Yield: 0.289 g (68%). Removal of the

volatiles from the ﬁltrate gave 24 as a colorless liquid. Yield: ca. 10%,

due to the volatility of 24 itself. Diﬀraction-quality crystals of 23 were

grown from a saturated hexane solution at 4 °C.

1

powder was dried in vacuo. Yield: 0.184 g (40%). H NMR (toluene-

d₈, 499.9 MHz, 243 K): δ 7.59 (1 H, d, ³J = 7.5 Hz, o_a-C₆H₅), 7.31 (1

3

H, d, J = 7.5 Hz, o_b-C₆H₅), 7.22−7.00 (5 H, m, m-C₆H₅, m-2,6-

i

C₆H₃Pr₂, p-2,6-C₆H₃Pr₂), 6.88 (1 H, m, p-C₆H₅), 3.73 (1 H, sept, ³J =

1

Data for [Cp*Ti{PhC(NⁱPr)₂}(μ-O)]₂(23). H NMR (C₆D₆, 299.9

6.5 Hz, NCH_aMeMe), 3.64 (1 H, br sept, 2,6-C₆H₃(CH_aMeMe)₂),

3

MHz, 293 K): δ 7.35 (2 H, m, o-C₆H₅), 7.15 (3 H, m, overlapping m-

3.18 (1 H, br sept, 2,6-C₆H₃(CH_bMeMe)₂), 3.06 (1 H, sept, J = 6.5

3

C₆H₅and p-C₆H₅), 3.69 (2 H, sept, J = 6.3 Hz, NCHMeMe), 2.28

Hz, NCH_bMeMe), 2.08 (15 H, s, C₅Me₅), 1.75 (3 H, br d, 2,6-

C₆H₃(CH_aMeMe)₂), 1.64 (3 H, br d, 2,6-C₆H₃(CH_bMeMe)₂), 1.50 (9

H, s, NOCMe₃), 1.42 (3 H, br d, 2,6-C₆H₃(CH_aMeMe)₂), 1.27 (3 H,

d, ³J = 6.5 Hz, NCH_aMeMe), 1.21 (3 H, br d, 2,6-C₆H₃(CH_bMeMe)₂),

(15 H, s, C₅Me₅), 1.28 (6 H, d, ³J = 6.6 Hz, NCHMeMe), 1.09 (6 H,

3

d, J = 6.3 Hz, NCHMeMe) ppm. ¹³C{¹H} NMR (C₆D₆, 75.4 MHz,

293 K): δ 172.0 (PhCN₂), 137.0 (i-C₆H₅), 128.3, 128.2, 127.9

(overlapping with solvent p-C₆H₅, m-C₆H₅, o-C₆H₅), 122.7 (C₅Me₅),

48.4 (NCHMeMe), 26.2 (NCHMeMe), 25.6 (NCHMeMe), 13.7

(C₅Me₅) ppm. IR (NaCl plates, Nujol mull, cm⁻¹): 1419 (m), 1359

(m), 1323 (s), 1261 (w), 1210 (m), 1165 (m), 1141 (m), 1108 (w),

1014 (m), 938 (w), 799 (w), 780 (m), 738 (w), 707 (m), 637 (s), 597

(m). EI-MS: m/z 669 [M − Cp*]⁺(2%), 402 [Cp*Ti{PhC(NⁱPr)₂}-

(O)]⁺(90%). Anal. Found (calcd for C₄₆H₆₈N₄O₂Ti₂): C, 68.78

(68.65); H, 8.87 (8.52); N, 6.81 (6.96).

3

0.93 (3 H, d, J = 6.5 Hz, NCH_aMeMe), 0.63 (6 H, d, J = 6.5 Hz,

NCH_bMeMe) ppm. ¹³C{¹H} NMR (toluene-d₈, 125.7 MHz, 243 K): δ

170.7 (PhCN₂), 154.4 (OCN), 145.7 (i-2,6-C₆H₃Pr₂), 140.0 (o_a-2,6-

C₆H₃Pr₂), 139.5 (o_b-2,6-C₆H₃Pr₂), 132.9 (i-C₆H₅), 129.1, 128.2,

128.5, (p-2,6-C₆H₃Pr₂, m_a-C₆H₅and m_b-C₆H₅), 128.8 (o_a-C₆H₅

i

overlapping with solvent), 128.6 (C₅Me₅overlapping with solvent),

i

127.5 (p-C₆H₅), 122.6 (o_b-C₆H₅), 121.6 (m_b-2,6-C₆H₃Pr₂), 121.3 (m_a-

i

2,6-C₆H₃Pr₂), 80.8 (NOCMe₃), 50.5 (NCH_aMeMe), 50.3

t

1

Data for BuNCNO^tBu (24). H NMR (C₆D₆, 299.9 MHz, 293 K):

δ 1.25 (9 H, s, NOCMe₃), 1.05 (9 H, s, NCMe₃) ppm. ¹³C{¹H} NMR

(C₆D₆, 75.4 MHz, 293 K): δ 154.7 (NCN), 79.2 (NOCMe₃), 57.8

(NCMe₃), 30.4 (NCMe₃), 27.1 (NOCMe₃) ppm. Solution IR (NaCl

plates, Et₂O, cm⁻¹): 2257 (m), 2065 (s). FI-HRMS found (calcd for

C₉H₁₈N₂O): m/z 170.1421 (170.1419).

(NCH_bMeMe), 29.5 (2,6-C₆H₃(CH_aMeMe)₂), 28.5 (overlapping

NOCMe₃and 2,6-C₆H₃(CH_bMeMe)₂), 27.5 (NCH_bMeMe), 26.5

(NCH_aMeMe), 26.2 (NCH_aMeMe), 25.1 (2,6-C₆H₃(CH_aMeMe)₂),

23.8 (2,6-C₆H₃(CH_aMeMe)₂), 23.6 (2,6-C₆H₃(CH_bMeMe)₂), 23.2

(NCH_bMeMe), 21.5 (2,6-C₆H₃(CH_bMeMe)₂), 12.9 (C₅Me₅) ppm. IR

(NaCl plates, Nujol mull, cm⁻¹): 1631 (s), 1583 (s), 1510 (m), 1394

(s), 1359 (s), 1335 (s), 1220 (m), 1188 (m), 1148 (m), 1119 (m),

1102 (w), 1066 (m), 1045 (m), 1022 (m), 973 (m), 936 (w), 858 (w),

832 (w), 790 (m), 782 (m), 753 (w), 730 (s), 705 (m), 681 (w), 555

(w). Anal. Found (calcd for C₄₀H₆₀N₄O₂Ti): C, 71.04 (70.99); H, 8.73

(8.94); N, 8.06 (8.28).

PhC(NO^tBu)H (25a). To a solution of Cp*Ti{PhC(NⁱPr)₂}-

(NO^tBu) (19; 0.250 g, 0.528 mmol) in C₆H₆(5 mL) was added

PhC(O)H (53.7 μL, 0.528 mmol), all at room temperature. An

immediate color change to yellow was observed. After 30 min the

volatiles were removed under reduced pressure and the resulting solid

sublimed (80−110 °C, 8 × 10⁻²mbar, 2 h) onto a dry ice/acetone

cold ﬁnger, yielding 25a as a colorless oil at room temperature. Yield:

Cp*Ti{PhC(NⁱPr)₂}{OC(NTol)N(Tol)C(NO^tBu)O} (22). To a sol-

ution of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19; 0.250 g, 0.528 mmol) in

benzene (10 mL) was added TolNCO (140 μL, 1.11 mmol), all at

room temperature. An immediate color change from green to brown-

red was observed. After 2.5 h, the volatiles were removed under

reduced pressure to aﬀord 22 as a light brown crystalline solid.

Pentane (10 mL) was added and the solution concentrated by half

before cooling to −80 °C. The resulting solid was then isolated by

ﬁltration and the red-brown powder dried in vacuo. Yield: 0.235 g

(60%). Diﬀraction-quality crystals were grown from a saturated Et₂O

solution at 4 °C. ¹H NMR (C₆D₆, 299.9 MHz, 293 K): δ 7.72 (2 H, d,

³J = 8.1 Hz, o_a−C₆H₄Me), 7.39 (2 H, d, ³J = 7.5 Hz, o−C₆H₅), 7.16 (2

H, m, o_b−C₆H₄Me), 7.06−7.00 (7 H, m, overlapping m−C₆H₅, p-

C₆H₅, m_a−C₆H₄Me, m_b−C₆H₄Me), 3.67 (2 H, overlapping sept,

NCH_aMeMe and NCH_bMeMe), 2.20 (3 H, s, p_b-C₆H₄Me), 2.12 (3 H,

1

0.066 g (70%). The H NMR spectrum indicated an approximately

20:80 mixture of the syn and anti isomers.

1

Major Isomer (anti). H NMR (C₆D₆, 299.9 MHz, 293 K): δ 7.85

(2 H, d, o-C₆H₅), 7.27 (1 H, s, PhC(H)), 7.15−7.00 (3 H, m,

overlapping m-C₆H₅and p-C₆H₅), 1.39 (9 H, s, CMe₃) ppm. ¹³C{¹H}

NMR (C₆D₆, 75.4 MHz, 293 K): δ 144.7 (PhC(H)), 132.0 (i-C₆H₅),

131.2 (o-C₆H₅), 129.6 (p-C₆H₅), 128.5 (m-C₆H₅), 79.4 (CMe₃), 27.6

(CMe₃) ppm.

1

Minor Isomer (syn). The H NMR spectrum was consistent with

the literature values.^36b¹H NMR (C₆D₆, 299.9 MHz, 293 K): δ 8.03 (1

H, s, PhC(H)), 7.45 (2 H, d, o-C₆H₅), 7.15−7.00 (3 H, m, overlapping

m-C₆H₅and p-C₆H₅), 1.38 (9 H, s, CMe₃) ppm. ¹³C{¹H} NMR

(C₆D₆, 75.4 MHz, 293 K): δ 147.4 (PhC(H)), 133.8 (i-C₆H₅), 129.4

(p-C₆H₅), 128.8 (m-C₆H₅), 127.1 (o-C₆H₅), 79.0 (CMe₃), 27.8

(CMe₃) ppm.

3

s, p_a-C₆H₄Me), 1.99 (15 H, s, C₅Me₅), 1.49 (3 H, d, J = 6.6 Hz,

3

NCH_aMeMe), 1.10 (9 H, s, NOCMe₃), 1.05 (3 H, d, J = 6.9 Hz,

Common Data. IR (thin ﬁlm, cm⁻¹): 3095 (w), 3058 (w), 3026

(w), 2975 (br, s), 2929 (br, m), 2868 (w), 1636 (m), 1491 (m), 1472

(w), 1448 (m), 1387 (m), 1364 (s), 1318 (w), 1297 (w), 1262 (m),

1190 (m), 1183 (m), 1101 (w), 1078 (w), 1031 (w), 950 (s), 933 (m),

915 (m), 882 (w), 839 (w), 819 (w), 806 (w), 757 (m), 692 (s), 629

(m). FI-HRMS found (calcd for C₁₁H₁₅NO): m/z 177.1152

(177.1154).

NCH_bMeMe), 0.96 (3 H, d, ³J = 6.6 Hz, NCH_aMeMe), 0.91 (3 H, d, ³J

= 6.9 Hz, NCH_bMeMe) ppm. ¹³C{¹H} NMR (C₆D₆, 75.4 MHz, 293

K): δ 170.4 (PhCN₂), 156.4 (OC_aN), 153.9 (OC_bN), 148.5 (i_b-

C₆H₄Me), 141.3 (i_a-C₆H₄Me), 134.4 (m_a-C₆H₄Me), 133.8 (i-C₆H₅),

130.3 (C₅Me₅), 129.6, 129.0, 128.3 (p-C₆H_5,m_b-C₅H₄Me, m-C₆H₅),

129.2 (p_b-C₆H₄Me), 129.2 (o-C₆H₅), 128.6 (p_a-C₆H₄Me), 128.5 (o_a-

C₆H₄Me), 124.5 (o_b-C₆H₄Me),76.7 (NOCMe₃), 51.2 (NCH_bMeMe),

50.9 (NCH_aMeMe), 27.6 (NOCMe₃), 26.6 (NCH_aMeMe) 25.4

(NCH_bMeMe), 24.8 (NCH_bMeMe), 24.0 (NCH_aMeMe), 21.1 (p_a-

C₆H₄Me), 21.1 (p_b-C₆H₄Me), 12.8 (C₅Me₅) ppm. IR (NaCl plates,

Nujol mull, cm⁻¹): 1623 (s), 1587 (s), 1575 (s), 1512 (m), 1506 (m),

PhC(NO^tBu)Me (25b). To a solution of Cp*Ti{PhC(NⁱPr)₂}-

(NO^tBu) (19; 0.200 g, 0.423 mmol) in C₆H₆(5 mL) was added

PhC(O)Me (49.3 μL, 0.423 mmol), all at room temperature. A color

change from green to yellow was observed. After 30 min the volatiles

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were removed under reduced pressure and the resulting solid was

sublimed (80−110 °C, 8 × 10⁻²mbar, 2 h) onto a dry ice/acetone

cold ﬁnger, giving 25b as a yellow liquid at room temperature. Yield:

0.061 g (75%). The ¹H NMR spectrum indicated an approximately 9:1

mixture of the syn and anti isomers and was consistent with the

literature values.^36e

127.2 (C₅Me₅), 116.0 (1 C, m, i-C₆F₅), 114.2 (1 C, m, i-C₆F₅), 110.9

(1 C, m, i-C₆F₅), 280.2 (OCMe₃), 51.5 (NCH_bMeMe), 46.2

(NCH_aMeMe), 27.3 (OCMe₃), 27.1 (NCH_aMeMe), 25.5

(CH_aMeMe), 24.5 (NCH_bMeMe) 13.0 (C₅Me₅) ppm. ¹³C{¹⁹F}

NMR (toluene-d₈, 75.4 MHz, 263 K): 145.4 (o_2b-C₆F₅), 144.6

(overlapping o₃-C₆F₅and o_1b-C₆F₅), 144.3 (overlapping o_1a-C₆F₅and

o_2a-C₆F₅) 142.1 (p₁-C₆F₅), 141.8 (p₂-C₆F₅), 141.1 (p₃-C₆F₅), 138.4

(m_1b-C₆F₅), 137.8 (m₃-C₆F₅), 137.7 (m_2a-C₆F₅), 137.6 (m_2b-C₆F₅),

137.1 (m_1a-C₆F₅), ¹⁹F{¹H} NMR (toluene-d₈, 470.4 MHz, 263 K):

−126.7 (1 F, d, ³J = 23.0 Hz, o_1a-C₆F₅), −134.16 (1 F, d, ³J = 22.1 Hz,

o_1b-C₆F₅), −137.0 (1F, d, ³J = 23.5 Hz, o_2a-C₆F₅), - 140.6 (1 F, app d,

³J = 14.6 Hz, o_2b-C₆F₅), −141.9 (2 F, m, o₃-C₆F₅), −150.9 (1 F, t, ³J =

20.7 Hz, p₁-C₆F₅), −154.0 (1 F, t, ³J = 21.2 Hz, p₂-C₆F₅), 155.5 (1 F, t,

³J = 21.6, p₃-C₆F₅), −162.9 (2 F, m, m₃-C₆F₅), −163.2 (2 F, t, ³J = 22.1

Hz, m_1b-C₆F₅), −163.9 (2 F, t, m, m_2a-C₆F₅), −164.1 (2 F, m, m_2b-

C₆F₅), 165.0 (2 F, m, m_1a-C₆F₅) ppm. IR (NaCl plates, Nujol mull,

cm⁻¹): 1651 (w), 1595 (s), 1522 (s), 1491 (s), 1408 (s), 1366 (m),

1341 (w), 1316 (m), 1226 (w), 1215 (m), 1195 (m), 1147 (w), 1130

(m), 1117 (m), 1104 (w), 1078 (w), 1020 (w), 997 (s), 936 (m), 901

(w), 880 (w), 822 (m), 787 (w), 776 (w), 727 (w), 711 (w), 696 (w),

603 (w), 577 (w). Anal. Found (calcd for C₄₈H₄₃F₁₅N₆OTi): C, 54.88

(54.76); H, 4.17 (4.12); N, 7.82 (7.98).

Major Isomer (syn). ¹H NMR (CDCl₃, 499.9 MHz, 293 K): δ 7.69

(2 H, d, ³J = 8.0 Hz, o-C₆H₅), 7.38−7.33 (3 H, m, overlapping m-C₆H₅

and p-C₆H₅), 2.22 (Me), 1.37 (9 H, s, CMe₃) ppm. ¹³C{¹H} NMR

(CDCl₃, 125.7 MHz, 298 K): δ 152.5 (PhC(Me)), 137.7 (i-C₆H₅),

128.7 (p-C₆H₅), 128.4 (m-C₆H₅), 126.0 (o-C₆H₅), 78.8 (CMe₃), 27.9

(CMe₃), 12.4 (Me) ppm.

1

Minor Isomer (anti). H NMR (C₆D₆, 299.9 MHz, 293 K): δ 7.59

(2 H, m, o-C₆H₅), 7.39−7.31 (3 H, m, overlapping m-C₆H₅and p-

C₆H₅), 2.21 (Me), 1.30 (9 H, s, CMe₃) ppm. ¹³C{¹H} NMR (CDCl₃,

125.7 MHz, 293 K): δ 151.2 (PhC(Me)), 135.0 (i-C₆H₅), 128.6 (p-

C₆H₅), 128.5 (o-C₆H₅), 127.9 (m-C₆H₅), 78.2 (CMe₃), 27.6 (CMe₃),

21.9 (Me) ppm.

Cp*Ti{PhC(NⁱPr)₂}{NC(Ar^F⁵)NO^tBu} (26). To a solution of Cp*Ti-

{PhC(NⁱPr)₂}(NO^tBu) (19; 0.230 g, 0.486 mmol) in benzene (10

mL) was added Ar^F⁵CN (61.2 μL, 0.486 mmol), all at room

temperature. An immediate color change from green to lime green

was observed. After 1 h, the volatiles were removed under reduced

pressure to aﬀord 26 as a green oily solid. Et₂O (5 mL) was added and

the solution cooled to −80 °C. The resulting green crystalline solid

was isolated by ﬁltration and dried in vacuo. Yield: 0.118 g (33%).

Diﬀraction-quality crystals were grown from a saturated hexane

solution at −80 °C. ¹H NMR (C₆D₆, 499.9 MHz, 293 K): δ 7.35 (1 H,

d, ³J = 8.0 Hz, o_a-C₆H₅), 7.12−7.06 (2 H, m, m-C₆H₅), 7.00 (1 H, t, ³J

= 7.5 Hz, p-C₆H₅), 6.93 (1 H, d, ³J = 7.5 Hz, o_b-C₆H₅), 3.40 (2 H, sept,

³J = 6.5 Hz, NCHMeMe), 2.21 (15 H, s, C₅Me₅), 1.40 (9 H, s,

NOCMe₃), 0.81 (6 H, d, ³J = 6.0 Hz, NCHMeMe), 0.77 (6 H, d, ³J =

6.5 Hz, NCHMeMe) ppm. ¹³C{¹H} NMR (C₆D₆, 125.7 MHz, 293 K):

Cp*Ti(O^tBu){NC(Ar^F⁵)C(H)N(ⁱPr)C(Ph)N(ⁱPr)} (30). To a stirred

solution of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19; 0.298 g, 0.629 mmol)

in Et₂O (5 mL) was added a solution of Ar^F⁵CCH (0.121 g, 0.629

mmol) in Et₂O (5 mL), all at room temperature. A color change from

green to purple was observed. After 16 h, the volatiles were removed

under reduced pressure and the resultant purple oily solid was

extracted into cold pentane (2 × 5 mL) and cooled to −78 °C. The

volatiles were removed under reduced pressure to aﬀord 30 as a purple

1

powder, which was dried in vacuo. Yield: 0.290 g (69%). H NMR

(C₆D₆, 499.9 MHz, 293 K): δ 6.86 (3 H, m, overlapping o-C₆H₅and

3

NC(Ar^F⁵)C(H)N), 6.70 (2 H, t, J = 7.0 Hz, m-C₆H₅), 6.64 (1 H, m,

1

δ 166.9 (PhCN₂), 150.1 (NC(C₆F₅)N), 143.2 (2 C, d, J_C−F= 244.9

3

p-C₆H₅), 3.91 (1 H, sept, J = 6.5 Hz, N(CH_aMeMe)C(H)), 3.61 (1

1

Hz, o-C₆F₅), 140.4 (1 C, d, J_C−F= 249.9 Hz, p-C₆F₅), 137.8 (2 C, d,

H, sept, ³J = 6.5 Hz, NCH_bMeMe), 2.09 (15 H, s, C₅Me₅), 1.37 (9 H,

s, OCMe₃), 1.32 (3 H, d, ³J = 6.5 Hz, NCH_aMeMe), 1.29 (3 H, d, ³J =

6.5 Hz, NCH_aMeMe), 1.27 (3 H, d, ³J = 6.5 Hz, NCH_bMeMe), 0.77 (3

¹J_C−F= 249.1 Hz, m-C₆F₅), 133.1 (i-C₆H₅), 129.0 (p-C₆H₅), 128.9 (m-

C₆H₅), 127.4 (o_a-C₆H₅), 127.2 (o_b-C₆H₅), 123.6 (C₅Me₅), 113.2 (1 C,

2

t, J_C−F= 22.4 Hz, i-C₆F₅) 78.0 (NOCMe₃), 50.9 (NCHMeMe), 27.9

3

H, d, J = 6.5 Hz, NCH_bMeMe) ppm. ¹³C{¹H} NMR (C₆D₆, 125.7

(NOCMe₃), 26.4 (NCHMeMe), 24.2 (NCHMeMe), 12.4 (C₅Me₅)

MHz, 293 K): δ 161.6 (PhCN₂), 138.9 (NC(Ar^F⁵)C(H)N), 136.0 (i-

C₆H₅), 128.5 (p-C₆H₅), 127.5 (m-C₆H₅), 127.4 (o-C₆H₅), 122.8

ppm. ¹⁹F{¹H} NMR (C₆D₆, 282.1 MHz, 293 K): δ −140.6 (2 F, m, o-

3

C₆F₅), −157.7 (1 F, t, J = 20.6 Hz, p-C₆F₅), −163.9 (2 F, app t, m-

2

3

(C₅Me₅), 114.6 (1 C, t of d, J_C−F= 15.1 Hz, J_C−F= 3.5 Hz, i-C₆F₅),

108.8 (NC(Ar^F⁵)C(H)N), 82.2 (OCMe₃), 53.8 (NCH_aMeMe), 50.2

(NCH_bMeMe), 33.1 (OCMe₃), 27.0 (NCH_bMeMe), 26.7

(NCH_aMeMe), 24.9 (NCH_bMeMe), 24.6 (NCH_aMeMe), 12.3

(C₅Me₅) ppm. Note: ¹⁹F{¹H} NMR is broad at 293 K, and therefore

¹³C{¹⁹F} and ¹⁹F{¹H} NMR spectra were recorded at 223 K. ¹³C{¹⁹F}

NMR (toluene-d₈, 75.4 MHz, 223 K): 142.2 (o_a-C₆F₅), 141.2 (o_b-

C₆F₅), 137.3 (m_b-C₆F₅), 137.0 (m_a-C₆F₅), 135.5 (p-C₆F₅) ¹⁹F{¹H}

C₆F₅) ppm. IR (NaCl plates, Nujol mull, cm⁻¹): 1651 (w), 1528 (m),

1512 (s), 1492 (s), 1364 (s), 1340 (s), 1294 (m), 1259 (m), 1221

(m), 1194 (m), 1169 (m), 1140 (m), 1108 (m), 1033 (m), 1019 (m),

989 (s), 943 (s), 892 (M), 817 (w), 793 (m), 780 (m), 740 (m), 725

(m), 707 (m), 669 (m), 612 (m), 577 (m). EI-MS: m/z 666 [M]⁺

(7%). Anal. Found (calcd for C₃₄H₄₃N₄OF₅Ti): C, 61.38 (61.26); H,

6.59 (6.50); N, 8.30 (8.40).

Cp*Ti{PhC(NⁱPr)₂}{N(C(Ar^F⁵)NO^tBu)C(Ar^F⁵)NC(Ar^F⁵)N} (29). To a

solution of Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19; 0.250 g, 0.528 mmol)

in benzene (5 mL) was added Ar^F⁵CN (0.333 mL, 2.64 mmol), all at

room temperature. A color change from dark green to lime green (26)

to red was observed. After 6 h at room temperature, the volatiles were

removed under reduced pressure, leaving behind an orange oil.

Pentane (5 mL) was added and then removed under reduced pressure

to aﬀord 29 as an orange powder, which was dried in vacuo. Yield:

0.400 g (88%). An analytically pure sample was obtained by washing

with pentane (5 mL) at room temperature, and the resultant orange

powder was dried in vacuo. Yield: 0.222 g (49%). Diﬀraction-quality

crystals were grown in the presence of Ar^F⁵CN from an Et₂O/pentane

mixture at 4 °C. ¹H NMR (toluene-d₈, 499.9 MHz, 263 K): δ 7.45 (1

H, d, ³J = 8.0 Hz, o_a-C₆H₅), 7.20 (1 H, d, ³J = 7.5, o_b-C₆H₅), 7.12 (2 H,

m, m-C₆H₅), 7.06 (1 H, m, p-C₆H₅), 3.83 (1 H, app sept, ³J = 6.5 Hz,

3

NMR (toluene-d₈, 282.1 MHz, 223 K): δ −142.6 (1 H, d, J = 21.7

Hz, o_a-C₆F₅), −144.5 (1 H, d, ³J = 24.8 Hz, o_b-C₆F₅), −165.7 (1 H, t,

³J = 23.7 Hz, m_a-C₆F₅), −166.2 (1 H, t, ³J = 20.9 Hz, m_b-C₆F₅), −167.6

3

(1 H, t, J = 21.7 Hz, p-C₆F₅) ppm. IR (NaCl plates, Nujol mull,

cm⁻¹): 1641 (w), 1603 (w), 1562 (w), 1544 (w), 1514 (s), 1484 (s),

1453 (s), 1342 (m), 1319 (w), 1260 (m), 1246 (m), 1211 (m), 1181

(m), 1092 (m), 1018 (m), 1002 (s), 980 (m), 910 (w), 803 (w), 748

(w), 715 (w), 702 (w). EI-MS: m/z 665 [M]⁺(65%). Anal. Found

(calcd for C₃₅H₄₄F₅N₃OTi): C, 63.27 (63.16); H, 6.72 (6.66); N, 6.24

(6.31).

Cp*Ti{PhC(NⁱPr)₂}{η²-ON(H)B(Ar^F⁵)₃} (36). To a solution of

Cp*Ti{PhC(NⁱPr)₂}(NO^tBu) (19; 0.127 g, 0.269 mmol) in benzene

(5 mL) was added a solution of B(Ar^F⁵)₃(0.159 g, 0.538 mmol) in

benzene (5 mL), and the mixture was heated to 70 °C. A color change

from green to orange was observed. After 16 h the volatiles were

removed under reduced pressure and the resulting orange solid

washed with pentane (1 × 5 mL) at room temperature to aﬀord 36 as

an orange powder. Yield: 0.150 g (60%). An analytically pure sample

was obtained from subsequent washing with benzene (2 × 5 mL) at

room temperature and the orange powder dried in vacuo. Yield:

0.0671 mg (27%). Diﬀraction-quality crystals were grown from the

3

NCH_aMeMe), 3.40 (1 H, app sept, J = 6.5 Hz, NCH_bMeMe), 2.27

3

(15 H, s, C₅Me₅), 1.22 (9 H, s, OCMe₃), 1.06 (3 H, d, J = 7.0 Hz,

NCH_aMeMe), 1.01 (3 H, d, ³J = 6.5 Hz, NCH_bMeMe), 0.80 (3 H, d, ³J

= 6.0 Hz, NCH_bMeMe), 0.73 (3 H, d, ³J = 6.5 Hz, NCH_aMeMe) ppm.

¹³C{¹H} NMR (toluene-d₈, 125.7 MHz, 263 K): δ 174.7 (PhCN₂),

155.7 (NCN), 148.2 (NCN), 146.9 (NCN), 129.4 (o_b-C₆H₅), 129.1

(p-C₆H₅), 128.8 (o_a-C₆H₅overlapping with solvent), 127.6 (m-C₆H₅),

7536

dx.doi.org/10.1021/om401008a | Organometallics 2013, 32, 7520−7539

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slow cooling of a saturated benzene solution. ¹H NMR (CD₂Cl₂, 499.9

MHz, 293 K): δ 7.51−7.41 (3 H, m, overlapping m-C₆H₅and p-

C₆H₅), 7.34 (1 H, m, o_a-C₆H₅), 7.19 (1 H, m, o_b-C₆H₅), 6.05 (1 H, s,

NH), 3.61 (1 H, sept, ³J = 6.5 Hz, NCH_aMeMe), 3.22 (1 H, sept, ³J =

Present Address

^§Centre for Theoretical and Computational Chemistry,

Department of Chemistry, University of Oslo, P.O. Box 1033,

Blindern, 0315 Oslo, Norway.

3

6.5 Hz, NCH_bMeMe), 2.10 (15 H, s, C₅Me₅), 1.11 (3 H, d, J = 6.5

Notes

Hz, NCH_aMeMe), 0.87 (3 H, d, ³J = 6.5 Hz, NCH_aMeMe), 0.74 (3 H,

d, ³J = 6.5 Hz, NCH_bMeMe), 0.60 (3 H, d, ³J = 6.5 Hz, NCH_bMeMe)

ppm. ¹³C{¹H} NMR (CD₂Cl₂, 125.7 MHz, 293 K): δ 170.3 (PhCN₂),

The authors declare no competing ﬁnancial interest.

148.7 (6 C, br d, ¹J_C−F= 237.1 Hz, o-C₆F₅), 139.8 (3 C, br d, ¹J_C−F

=

ACKNOWLEDGMENTS

■

249.4 Hz, p-C₆F₅), 137.5 (6 C, br d, ¹J_C−F= 249.7 Hz, m-C₆F₅), 133.1

(i-C₆H₅), 130.0 (C₅Me₅), 129.7, 129.1, 129.0, 128.8 (o_a-C₆H_5,m-C₆H₅

and p-C₆H₅), 127.9 (o_b-C₆H₅), 121.1 (3 C, br s, i-C₆F₅), 51.1

(NCH_aMeMe), 50.3 (NCH_bMeMe), 26.8 (NCH_aMeMe), 26.2

(NCH_bMeMe), 24.0 (NCH_bMeMe), 23.6 (NCH_aMeMe), 12.5

(C₅Me₅) ppm. ¹¹B{¹H} NMR (CD₂Cl₂, 96.2 MHz, 298 K): δ −8

(B(C₆F₅)₃) ppm. Note: ¹⁹F{¹H} NMR is broad at 298 K and therefore

was recorded at 253 K. ¹⁹F{¹H} NMR (CD₂Cl₂, 282.1 MHz, 253 K): δ

−129.0 (1 F, br d., o_1a-C₆F₅), −130.5 (1 F, br d., o_1b-C₆F₅), −136.1 (2

F, br d., o₂-C₆F₅), −145.5 (v br s, 2 F, o₃-C₆F₅), −158.4 (1 F, br t, p₃-

C₆F₅), −158.7 (1 F, br t, p₁-C₆F₅), −160.2 (1 F, br t, p₂-C₆F₅), −161.6

(2 F, br t, m₃-C₆F₅), −164.2 (1 F, br t, m_1b-C₆F₅), −165.2 (1 F, br t,

m_1a-C₆F₅), −166.3 (2 F, br t, m₂-C₆F₅) ppm. IR (NaCl plates, Nujol

mull, cm⁻¹): 3296 (w), 1644 (m), 1517 (s), 1338 (m), 1281 (m),

1220 (w), 1147 (w), 1092 (s), 1043 (w), 1021 (m), 980 (m), 958 (m),

811 (w), 782 (w), 732 (w), 723 (w), 708 (m), 695 (m), 676 (m). EI-

MS: m/z 417 [M-B(C₆F₅)₃]⁺, 512 [B(C₆F₅)₃]⁺. Anal. Found (calcd for

C₄₁H₃₅BF₁₅N₃OTi): C, 52.83 (52.99); H, 3.82 (3.80); N, 4.57 (4.52).

Computational Details. All the calculations have been performed

with the Gaussian09 package at the B3PW91 level of hybrid density

functional theory.⁶³For the optimization of geometry, the titanium

atom was represented by the relativistic eﬀective core potential

(RECP) from the Stuttgart group and the associated basis sets,

augmented by an f polarization function.⁶⁴The remaining atoms (C,

H, N, O) were represented by a 6-31G(d,p) basis set. The solvent

(toluene) inﬂuence was taken into consideration through single-point

calculations on the gas-phase optimized geometry with the SMD

model of PCM calculations.⁶⁵For the PCM calculations the basis set

on Ti was kept as in the gas-phase optimizations, but the remaining

atoms were treated with a 6-311+G(d,p) basis set. All energies

reported in Figure 6 are Gibbs free energies obtained by summing the

PCM electronic energy, the gas-phase Gibbs contribution (T = 298,

253 K), and D3(bj) dispersion corrections.⁶⁶The MO energies and

the reaction energy in Figure 4 are from the gas-phase optimized

geometry. NMR (GIAO) calculations of the magnetic shielding

tensors of the oxime ethers (Figure S3 in the Supporting Information)

were performed using an IGLOO-II basis set for the atoms.⁶⁷

We thank Wolfson College, Oxford, for a Junior Research

Fellowship to A.D.S., the Department of Chemistry, Oxford, for

a scholarship to L.R.G., the Spanish MINECO for a

postdoctoral fellowship to A.N., and the research council of

Norway for a Centre of Excellence Grant (Grant No. 179568/

V30).

REFERENCES

■

(1) (a) Wigley, D. E. Prog. Inorg. Chem. 1994, 42, 239. (b) Duncan,

A. P.; Bergman, R. G. Chem. Rec. 2002, 2, 431. (c) Mountford, P.

Chem. Commun. 1997, 2127. (d) Gade, L. H.; Mountford, P. Coord.

Chem. Rev. 2001, 216−217, 65. (e) Hazari, N.; Mountford, P. Acc.

Chem. Res. 2005, 38, 839. (f) Fout, A. R.; Kilgore, U. J.; Mindiola, D. J.

Chem. Eur. J. 2007, 13, 9428. (g) Kozak, C. M.; Mountford, P. Angew.

Chem., Int. Ed. 2004, 43, 1186.

(2) (a) Cundari, T. R. J. Am. Chem. Soc. 1992, 114, 7879. (b) Lin, Z.;

Hall, M. B. Coord. Chem. Rev. 1993, 123, 149. (c) Mountford, P.;

Swallow, D. J. Chem. Soc., Chem. Commun. 1995, 2357. (d) Kaltsoyan-

nis, N.; Mountford, P. J. Chem. Soc., Dalton Trans. 1999, 781.

(e) Cundari, T. R. Chem. Rev. 2000, 100, 807. (f) Schwarz, A. D.;

Nielson, A. J.; Kaltsoyannis, N.; Mountford, P. Chem. Sci. 2012, 3, 819.

(g) Dunn, S. C.; Hazari, N.; Jones, N. M.; Moody, A. G.; Blake, A. J.;

Cowley, A. R.; Green, J. C.; Mountford, P. Chem. Eur. J. 2005, 11,

2111. (h) Nikonov, G. I.; Blake, A. J.; Mountford, P. Inorg. Chem.

1997, 36, 1107.

(3) For ease of representation the Ti−NX (X = R, NR₂, OR)

moieties are all drawn as “TiN”, although in most cases the Ti−N

linkage is best considered to be a triple bond.

(4) (a) Bytschkov, I.; Doye, S. Eur. J. Org. Chem. 2003, 935.

(b) Doye, S. Synlett 2004, 1653. (c) Schafer, L. L.; Lee, A. V. Eur. J.

Inorg. Chem. 2007, 2243. (d) Muller, T. E.; Hultzsch, K. C.; Yus, M.;

Foubelo, F.; Tada, M. Chem. Rev. 2008, 108, 3795.

(5) (a) Adams, N.; Arts, H. J.; Bolton, P. D.; Cowell, D.; Dubberley,

S. R.; Friederichs, N.; Grant, C.; Kranenburg, M.; Sealey, A. J.; Wang,

B.; Wilson, P. J.; Cowley, A. R.; Mountford, P.; Schroder, M. Chem.

Commun. 2004, 434. (b) Bolton, P. D.; Mountford, P. Adv. Synth.

Catal. 2005, 347, 355. (c) Bigmore, H. R.; Dubberley, S. R.;

Kranenburg, M.; Lawrence, S. C.; Sealey, A. J.; Selby, J. D.; Zuideveld,

M.; Cowley, A. R.; Mountford, P. Chem.Commun. 2006, 436.

(d) Bigmore, H. R.; Zuideveld, M.; Kowalczyk, R. M.; Cowley, A.

R.; Kranenbrug, M.; McInnes, E. J. L.; Mountford, P. Inorg. Chem.

2006, 45, 6411. (e) Wilson, P. J.; Blake, A. J.; Mountford, P.; Schroder,

M. Chem. Commun. 1998, 1007.

(6) Wiberg, N.; Haring, H.-W.; Huttner, G.; Friedrich, P. Chem. Ber.

1978, 111, 2708.

(7) Walsh, P. J.; Carney, M. J.; Bergman, R. G. J. Am. Chem. Soc.

1991, 113, 6343.

(8) (a) Blake, A. J.; McInnes, J. M.; Mountford, P.; Nikonov, G. I.;

Swallow, D.; Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999, 379.

(b) Thorman, J. L.; Woo, L. K. Inorg. Chem. 2000, 39, 1301. (c) Li, Y.;

Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2004, 126, 1794. (d) Banerjee,

S.; Shi, Y.; Cao, C.; Odom, A. L. J. Organomet. Chem. 2005, 690, 5066.

(e) Parsons, T. B.; Hazari, N.; Cowley, A. R.; Green, J. C.; Mountford,

P. Inorg. Chem. 2005, 44, 8442. (f) Banerjee, S.; Odom, A. L.

Organometallics 2006, 25, 3099. (g) Patel, S.; Li, Y.; Odom, A. L. Inorg.

Chem. 2007, 46, 6373. (h) Selby, J. D.; Manley, C. D.; Feliz, M.;

Schwarz, A. D.; Clot, E.; Mountford, P. Chem. Commun. 2007, 4937.

(i) Banerjee, S.; Barnea, E.; Odom, A. L. Organometallics 2008, 27,

1005. (j) Clulow, A. J.; Selby, J. D.; Cushion, M. G.; Schwarz, A. D.;

̈

ASSOCIATED CONTENT

■

S

* Supporting Information

̈

Text, ﬁgures, tables, and CIF ﬁles giving general experimental

procedures and details of starting materials, remaining details of

the synthesis and characterization data for new compounds, X-

ray data collection and processing parameters and X-ray

crystallographic data for the structure determinations, and

further details of the DFT calculations (Cartesian coordinates,

pcm energy, NMR (GIAO) calculations of the magnetic

shielding tensors of the oxime ethers 25a and 25b, Gibbs and

dispersion corrections for the species in Figure 6). This material

is available free of charge via the Internet at http://pubs.acs.org.

AUTHOR INFORMATION

■

Corresponding Authors

*E-mail for E.C.: eric.clot@univ-montp2.fr.

*E-mail for P.M.: philip.mountford@chem.ox.ac.uk.

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Article

Mountford, P. Inorg. Chem. 2008, 47, 12049. (k) Selby, J. D.; Manley,

C. D.; Schwarz, A. D.; Clot, E.; Mountford, P. Organometallics 2008,

27, 6479. (l) Selby, J. D.; Schulten, C.; Schwarz, A. D.; Stasch, A.; Clot,

E.; Jones, C.; Mountford, P. Chem. Commun. 2008, 5101.

(m) Weitershaus, K.; Fillol, J. L.; Wadepohl, H.; Gade, L. H.

Organometallics 2009, 28, 4747. (n) Weitershaus, K.; Wadepohl, H.;

Gade, L. H. Organometallics 2009, 28, 3381. (o) Janssen, T.; Severin,

R.; Diekmann, M.; Friedemann, M.; Haase, D.; Saak, W.; Doye, S.;

Beckhaus, R. Organometallics 2010, 29, 1806. (p) Schofield, A. D.;

Nova, A.; Selby, J. D.; Manley, C. D.; Schwarz, A. D.; Clot, E.;

Mountford, P. J. Am. Chem. Soc. 2010, 132, 10484. (q) Tiong, P. J.;

Schofield, A. D.; Selby, J. D.; Nova, A.; Clot, E.; Mountford, P. Chem.

Commun. 2010, 46, 85. (r) Schofield, A. D.; Nova, A.; Selby, J. D.;

Schwarz, A. D.; Clot, E.; Mountford, P. Chem. Eur. J. 2011, 17, 265.

(s) Selby, J. D.; Feliz, M.; Schwarz, A. D.; Clot, E.; Mountford, P.

Organometallics 2011, 30, 2295. (t) Tiong, P. J.; Nova, A.; Clot, E.;

Mountford, P. Chem. Commun. 2011, 47, 3147. (u) Tiong, P. J.; Nova,

A.; Groom, L. R.; Schwarz, A. D.; Selby, J. D.; Schofield, A. D.; Clot,

E.; Mountford, P. Organometallics 2011, 30, 1182. (v) Schwarz, A. D.;

Onn, C. S.; Mountford, P. Angew. Chem., Int. Ed. 2012, 51, 12298.

(w) Tiong, P. J.; Nova, A.; Schwarz, A. D.; Selby, J. D.; Clot, E.;

Mountford, P. Dalton Trans. 2012, 41, 2277. (x) Schweitzer, P. D.;

Wadepohl, H.; Gade, L. H. Organometallics 2013, 32, 3697−3709.

(9) (a) Herrmann, H.; Fillol, J. L.; Wadepohl, H.; Gade, L. H. Angew.

Chem., Int. Ed. 2007, 46, 8426. (b) Herrmann, H.; Fillol, J. L.;

Gehrmann, T.; Enders, M.; Wadepohl, H.; Gade, L. H. Chem. Eur. J.

2008, 14, 8131. (c) Herrmann, H.; Fillol, J. L.; Wadepohl, H.; Gade, L.

H. Organometallics 2008, 27, 172. (d) Herrmann, H.; Gehrmann, T.;

Wadepohl, H.; Gade, L. H. Dalton Trans. 2008, 6231. (e) Herrmann,

H.; Wadepohl, H.; Gade, L. H. Dalton Trans. 2008, 2111.

(f) Gehrmann, T.; Fillol, J. L.; Wadepohl, H.; Gade, L. H. Angew.

Chem., Int. Ed. 2009, 48, 2152. (g) Munha, R. F.; Veiros, L. F.; Duarte,

M. T.; Fryzuk, M. D.; Martins, A. M. Dalton Trans. 2009, 7494.

(h) Gehrmann, T.; Fillol, J. L.; Wadepohl, H.; Gade, L. H.

Organometallics 2010, 29, 28. (i) Gehrmann, T.; Fillol, J. L.; Scholl,

S. A.; Wadepohl, H.; Gade, L. H. Angew. Chem., Int. Ed. 2011, 50,

5757. (j) Gehrmann, T.; Fillol, J. L.; Wadepohl, H.; Gade, L. H.

Organometallics 2012, 31, 4504. (k) Gehrmann, T.; Kruck, M.;

Wadepohl, H.; Gade, L. H. Chem. Commun. 2012, 48, 2397.

(l) Gehrmann, T.; Plundrich, G. T.; Wadepohl, H.; Gade, L. H.

Organometallics 2012, 31, 3346−3354. (m) Gehrmann, T.; Scholl, S.

A.; Fillol, J. L.; Wadepohl, H.; Gade, L. H. Chem. Eur. J. 2012, 18,

3925. (n) Scholl, S. A.; Plundrich, G. T.; Wadepohl, H.; Gade, L. H.

Inorg. Chem. 2013, 52, 10158−10166. (o) Scholl, S. A.; Wadepohl, H.;

Gade, L. H. Organometallics 2013, 32, 937−940.

(15) van Asselt, A.; Santarsiero, B. D.; Bercaw, J. E. J. Am. Chem. Soc.

1986, 108, 8291.

(16) (a) Stevens, R. E.; Gladfelter, W. L. J. Am. Chem. Soc. 1982, 104,

6454. (b) Haug, K.; Hiller, W.; Strahle, J. Z. Anorg. Allg. Chem. 1986,

̈

533, 49. (c) Green, M. L. H.; James, J. T.; Sanders, J. F. Chem.

Commun. 1996, 1343.

(17) (a) Sharp, W. B.; Daff, P. J.; McNeil, W. S.; Legzdins, P. J. Am.

Chem. Soc. 2001, 123, 6272. (b) Arashiba, K.; Matsukawa, S.; Kuwata,

S.; Tanabe, Y.; Iwasaki, M.; Ishii, Y. Organometallics 2006, 25, 560.

(c) Lee, K. K.-H.; Wong, W. T. J. Organomet. Chem. 1999, 577, 323.

(18) Barr, M. E.; Bjarnason, A.; Dahl, L. F. Organometallics 1994, 13,

1981.

(19) Ho, E. N.-M.; Wong, W.-T. J. Chem. Soc., Dalton Trans. 1998,

4215.

(20) Lee, K. K.-H.; Wong, W.-T. J. Chem. Soc., Dalton Trans. 1996,

1707.

(21) Weitershaus, K.; Ward, B. D.; Kubiak, R.; Muller, C.; Wadepohl,

H.; Doye, S.; Gade, L. H. Dalton Trans. 2009, 4586.

(22) (a) Guiducci, A. E.; Cowley, A. R.; Skinner, M. E. G.;

Mountford, P. Dalton Trans. 2001, 1392. (b) Boyd, C. L.; Guiducci, A.

E.; Dubberley, S. R.; Tyrrell, B. R.; Mountford, P. Dalton Trans. 2002,

4175. (c) Boyd, C. L.; Clot, E.; Guiducci, A. E.; Mountford, P.

Organometallics 2005, 24, 2347. (d) Guiducci, A. E.; Boyd, C. L.;

Mountford, P. Organometallics 2006, 25, 1167. (e) Guiducci, A. E.;

Boyd, C. L.; Clot, E.; Mountford, P. Dalton Trans. 2009, 5960.

(23) Davies, S. G.; Goodwin, C. J.; Hepworth, D.; Roberts, P. M.;

Thomson, J. E. J. Org. Chem. 2010, 75, 1214.

(24) Richter, J.; Feiling, J.; Schmidt, H.-G.; Noltemeyer, M.; Brueser,

W.; Edelmann, F. T. Z. Anorg. Allg. Chem. 2004, 630, 1269.

(25) Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G.

Organometallics 1997, 16, 5183.

(26) Dunn, S. C.; Mountford, P.; Robson, D. A. J. Chem. Soc., Dalton

Trans. 1997, 293.

(27) Fletcher, D. A.; McMeeking, R. F.; Parkin, D. J. Chem. Inf.

Comput. Sci. 1996, 36, 746 (the UK Chemical Database Service: CSD

version 5.34 updated May 2013)..

(28) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,

A. G.; Taylor, R. J. Chem. Soc., Perkin Trans. 2 1987, S1.

(29) Weinhold, F.; Landis, C. R., Valency and Bonding: A Natural

Bond Orbital Donor-Acceptor Perspective; Cambridge University Press:

Cambridge, U.K., 2005.

(30) Blake, A. J.; Collier, P. E.; Dunn, S. C.; Li, W.-S.; Mountford, P.;

Shishkin, O. V. J. Chem. Soc., Dalton Trans. 1997, 1549.

(31) (a) Housemekerides, C. E.; Ramage, D. L.; Kretz, C. M.; Shontz,

J. T.; Pilato, R. S.; Geoffroy, G. L.; Rheingold, A. L.; Haggerty, B. S.

Inorg. Chem. 1992, 31, 4453. (b) Polse, J. L.; Andersen, R. A.;

Bergman, R. G. J. Am. Chem. Soc. 1995, 117, 5393.

(32) (a) Williams, D. H.; Fleming, I. Spectroscopic Methods in Organic

Chemistry, 5th ed.; McGraw-Hill: New York, 1995. (b) Sakai, S.;

Fujinami, T.; Otani, N.; Aizawa, T. Chem. Lett. 1976, 811. (c) Kiyoi,

T.; Seko, N.; Yoshino, K.; Ito, Y. J. Org. Chem. 1993, 58, 5118.

(d) Tang, J.; Mohan, T.; Verkade, J. G. J. Org. Chem. 1994, 59, 4931.

(33) (a) Cooley, J. H.; Evain, E. J.; Willett, R. D.; Blanchette, J. T. J.

Org. Chem. 1989, 54, 1048. (b) Sarker, S.; Cooley, J. H.; Willett, R. D.;

Rheingold, A. L. J. Org. Chem. 1995, 60, 476.

(10) (a) Kool, L. B.; Rausch, M. D.; Alt, H. G.; Herberhold, M.; Hill,

A. F.; Thewalt, U.; Wolf, B. J. Chem. Soc., Chem. Commun. 1986, 408.

(b) Arvanitis, G. M.; Smegal, J.; Meier, I.; Wong, A. C. C.; Schwartz, J.;

Van Engen, D. Organometallics 1989, 8, 2717. (c) Kaplan, A. W.; Polse,

J. L.; Ball, G. E.; Andersen, R. A.; Bergman, R. G. J. Am. Chem. Soc.

1998, 120, 11649. (d) Polse, J. L.; Kaplan, A. W.; Andersen, R. A.;

Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 6316. (e) Hanna, T. E.;

Keresztes, I.; Lobkovsky, E.; Bernskoetter, W. H.; Chirik, P. J.

Organometallics 2004, 23, 3448. (f) Tiong, P. J.; Groom, L. R.; Clot, E.;

Mountford, P. Chem. Eur. J. 2013, 19, 4198.

(34) (a) Thorman, J. L.; Woo, L. K. Inorg. Chem. 2000, 39, 1301.

(b) Lee, S. Y.; Bergman, R. G. J. Am. Chem. Soc. 1996, 118, 6396.

(c) Nugent, W. A.; McKinney, R. J.; Kasowski, V.; Van-Catledge, F. A.

Inorg. Chim. Acta 1982, 65, L91. (d) Doxsee, K. M.; Farahi, J. B. Chem.

Commun. 1990, 1452. (e) Rocklage, S. M.; Schrock, R. R. J. Am. Chem.

Soc. 1980, 102, 7809. (f) Moubaraki, B.; Murray, K. S.; Nichols, P. J.;

Thompson, S.; West, B. O. Polyhedron 1993, 13, 485. (g) Royo, P.;

Sanchez-Nieves, J. J. Organomet. Chem. 2000, 597, 61. (h) Walsh, P. J.;

Hollander, F. J.; Bergman, R. G. Organometallics 1993, 12, 3705.

(i) Duncan, A. P.; Bergman, R. G. Chem. Rec. 2002, 2, 431. (j) Hanna,

T. E.; Keresztes, I.; Lobkovsky, E.; Bernskoetter, W. H.; Chirik, P. J.

Organometallics 2004, 23, 3448. (k) Wang, H.; Chan, H.; Xie, Z.

Organometallics 2005, 24, 3772.

(11) Kahlal, S.; Saillard, J.-Y.; Hamon, J.-R.; Manzur, C.; Carrillo, D.

J. Chem. Soc., Dalton Trans. 1998, 1229.

(12) Unruangsri, J.; Morgan, H.; Schwartz, A. D.; Schofield, A. D.;

Mountford, P. Organometallics 2013, 32, 3091−3107.

(13) (a) Johnson, B. F. G.; Haymore, B. L.; Dilworth, J. D. In

Comprehensive Coordination Chemistry; Wilkinson, G., Gillard, R. D.,

McCleverty, J. A., Eds.; Pergamon Press: Oxford, U.K., 1987; Vol. 2, p

100. (b) Nugent, W. A.; Mayer, J. M. Metal-Ligand Multiple Bonds.;

Wiley-Interscience: New York, 1988. (c) Schrock, R. R. Acc. Chem. Res.

2005, 38, 955. (d) Hidai, M. Coord. Chem. Rev. 1999, 185−186, 99.

(14) (a) Schwarz, A. D.; Nova, A.; Clot, E.; Mountford, P. Chem.

Commun. 2011, 47, 4926. (b) Schwarz, A. D.; Nova, A.; Clot, E.;

Mountford, P. Inorg. Chem. 2011, 50, 12155.

7538

dx.doi.org/10.1021/om401008a | Organometallics 2013, 32, 7520−7539

Organometallics

Article

(35) Rad, M. N. S.; Khalafi-Nezhad, A.; Karimitabar, F.; Behrouz, S.

Synthesis 2010, 1724.

(52) (a) Lian, B.; Toupet, L.; Carpentier, J.-F. Chem. Eur. J. 2004, 10,

4301. (b) Bolton, P. D.; Adams, N.; Clot, E.; Cowley, A. R.; Wilson, P.

J.; Schroder, M.; Mountford, P. Organometallics 2006, 25, 5549.

(36) (a) Buchanan, G. W.; Dawson, B. A. Can. J. Chem. 1978, 56,

2200. (b) Buehler, E. J. Org. Chem. 1967, 32, 261. (c) McCarroll, A. J.;

Walton, J. C. Perkin 2 2000, 1868. (d) De, L. H. J. P.; Rangel, N. A.;

Tetalman, M. A.; Tsai, C.-K. J. Org. Chem. 2007, 72, 4126. (e) De, L.

H. J. P.; Tsai, C.-K. J. Org. Chem. 2004, 69, 3057.

(37) (a) Padwa, A.; Albrecht, F. J. Am. Chem. Soc. 1972, 94, 1000.

(b) Grubbs, E. J.; Villarreal, J. A. Tetrahedron Lett. 1969, 1841.

(c) Curtin, D. Y.; Grubbs, E. J.; McCarty, C. G. J. Am. Chem. Soc.

1966, 88, 2775.

(38) Pejkovic-Tadic, I.; Hranisavljevic-Jakovljevic, M.; Nesic, S.;

Pascual, C.; Simon, W. Helv. Chim. Acta 1965, 48, 1157.

(39) (a) Chisholm, M. H.; Delbridge, E. E.; Kidwell, A. R.; Quinlan,

K. B. Chem. Commun. 2003, 126. (b) Gdula, R. L.; Johnson, M. J. A.;

Ockwig, N. W. Inorg. Chem. 2005, 44, 9140.

(40) (a) Wood, C. D.; McLain, S. J.; Schrock, R. R. J. Am. Chem. Soc.

1979, 101, 3210. (b) Schrock, R. R.; Fellmann, J. D. J. Am. Chem. Soc.

1978, 100, 3359. (c) Doxsee, K. M.; Farahi, J. B.; Hope, H. J. Am.

Chem. Soc. 1991, 113, 8889. (d) Hessen, B.; Buijink, J.-K. F.; Meetsma,

A.; Teuben, J.; Helgesson, G.; Hakansson, M.; Jagner, S.; Spek, A. L.

Organometallics 1993, 12, 2268. (e) Basuli, F.; Aneetha, H.; Huffman,

J. C.; Mindiola, D. J. J. Am. Chem. Soc. 2005, 127, 17992.

(41) (a) Listemann, M. L.; Schrock, R. R. Organometallics 1985, 4,

74. (b) Freudenberger, J. H.; Schrock, R. R. Organometallics 1986, 5,

398. (c) Chisholm, M. H.; Folting, K.; Lynn, M. L.; Tiedtke, D. B.;

Lemoigno, F.; Eisenstein, O. Chem. Eur. J. 1999, 5, 2318. (d) Geyer, A.

M.; Gdula, R. L.; Wiedner, E. S.; Johnson, M. J. A. J. Am. Chem. Soc.

2007, 129, 3800. (e) Bailey, B. C.; Fout, A. R.; Fan, H.; Tomaszewski,

J.; Huffman, J. C.; Gary, J. B.; Johnson, M. J. A.; Mindiola, D. J. J. Am.

Chem. Soc. 2007, 129, 2234. (f) Geyer, A. M.; Wiedner, E. S.; Gary, J.

B.; Gdula, R. L.; Kuhlmann, N. C.; Johnson, M. J. A.; Dunietz, B. D.;

Kampf, J. W. J. Am. Chem. Soc. 2008, 130, 8984.

̈

(53) Greenwood, N. N.; Earnshaw, A. Chemistry of the Elements, 2nd

ed.; Butterworth-Heinemann: Oxford, U.K., 1997.

(54) (a) Mitzel, N. W.; Parsons, S.; Blake, A. J.; Rankin, D. W. H. J.

Chem. Soc., Dalton Trans. 1996, 2089. (b) Dove, A. P.; Xie, X.;

Waymouth, R. M. Chem. Commun. 2005, 2152.

(55) Fraenk, W.; Klapotke, T. M.; Krumm, B.; Noth, H.; Suter, M.;

̈

Vogt, M.; Warchhold, M. Can. J. Chem. 2002, 80, 1444.

(56) Mountford, A. J.; Clegg, W.; Coles, S. J.; Harrington, R. W.;

Horton, P. N.; Humphrey, S. M.; Hursthouse, M. B.; Wright, J. A.;

Lancaster, S. J. Chem. Eur. J. 2007, 13, 4535.

(57) Alvarez, S. Dalton Trans. 2013, 42, 8617.

(58) Hermanek, S. Chem. Rev. 1992, 92, 325.

(59) Jordan, R. B. Reaction Mechanisms of Inorganic and Organo-

metallic Systems; Oxford University Press: Oxford, U.K., 1998.

(60) Stoebenau, E. J.; Jordan, R. F. J. Am. Chem. Soc. 2003, 128, 8162.

(61) Lian, B.; Lehmann, C. W.; Navarro, C.; Carpentier, J.-F.

Organometallics 2005, 24, 2466.

(62) Dove, A. P.; Kiesewetter, E. T.; Ottenwaelder, X.; Waymouth, R.

M. Organometallics 2009, 28, 405.

(63) (a) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;

Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,

B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.

P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;

Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,

T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A.;

Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,

K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;

Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,

N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;

Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;

Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;

Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;

(42) Pugh, S. M.; Trosch, D. J. M.; Wilson, D. J.; Bashall, A.; Cloke,

̈

F. G. N.; Gade, L. H.; Hitchcock, P. B.; McPartlin, M.; Nixon, J. F.;

Mountford, P. Inorg. Chem. 2000, 19, 3205.

Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.;

Foresman, J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09,

Revision A.2; Gaussian, Inc., Wallingford, CT, 2009. (b) Becke, A. D. J.

Chem. Phys. 1993, 98, 5648. (c) Perdew, J. P.; Wang, Y. Phys. Rev. B

1992, 45, 13244.

(64) (a) Andrae, D.; Haussermann, U.; Dolg, M.; Stoll, H.; Preuss, H.

Theor. Chim. Acta 1990, 77, 123. (b) Ehlers, A. W.; Bohme, M.;

Dapprich, S.; Gobbi, A.; Hollwarth, A.; Jonas, V.; Kohler, K. F.;

Stegmann, R.; Veldkamp, A.; Frenking, G. Chem. Phys. Lett. 1993, 208,

111.

(65) (a) Tomasi, J.; Mennucci, B.; Cammi, R. Chem. Rev. 2005, 105,

2999. (b) Marenich, A. V.; Cramer, C. J.; Truhlar, D. G. J. Phys. Chem.

B 2009, 113, 6378.

(66) (a) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. 2010, 132,

154104; (b) Grimme, S.; Ehrlich, S.; Goerigk, L. J. Comput. Chem.

2011, 32, 1456.

(43) Breen, T. L.; Stephan, D. W. J. Am. Chem. Soc. 1995, 117, 11914.

(44) (a) Vujkovic, N.; Ward, B. D.; Maisse-Francois, A.; Wadepohl,

H.; Mountford, P.; Gade, L. H. Organometallics 2007, 26, 5522.

(b) Lokare, K. S.; Ciszewski, J. T.; Odom, A. L. Organometallics 2004,

23, 5386.

(45) Carney, M. J.; Walsh, P. J.; Hollander, F. J.; Bergman, R. G.

Organometallics 1992, 11, 761.

(46) Ansede, J. H.; Anbazhagan, M.; Brun, R.; Easterbrook, J. D.;

Hall, J. E.; Boykin, D. W. J. Med. Chem. 2004, 47, 4335.

(47) (a) McGrane, P. L.; Jensen, M.; Livinghouse, T. J. Am. Chem.

Soc. 1992, 114, 5459. (b) McGrane, P. L.; Livinghouse, T. J. Am. Chem.

Soc. 1993, 115, 11485. (c) Bennett, J. L.; Wolczanski, P. T. J. Am.

Chem. Soc. 1997, 119, 10696. (d) Polse, J. L.; Andersen, R. A.;

Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 13405. (e) Ward, B. D.;

Maisse-Francois, A.; Mountford, P.; Gade, L. H. Chem. Commun. 2004,

704. (f) Zhao, G.; Basuli, F.; Kilgore, U. J.; Fan, H.; Aneetha, H.;

Huffman, J. C.; Wu, G.; Mindiola, D. J. J. Am. Chem. Soc. 2006, 128,

13575. (g) Cao, C.; Shi, Y.; Odom, A. L. Org. Lett. 2002, 4, 2853.

(h) Ackermann, L.; Born, R. Tetrahedron Lett. 2004, 45, 9541.

(i) Khedkar, V.; Tillack, A.; Michalik, M.; Beller, M. Tetrahedron Lett.

2004, 45, 3123. (j) Tillack, A.; Jiao, H.; Garcia Castro, I.; Hartung, C.

G.; Beller, M. Chem. Eur. J. 2004, 10, 2409. (k) Odom, A. L. Dalton

Trans. 2005, 225. (l) Dissanayake, A. A.; Odom, A. L. Chem. Commun.

2012, 48, 440. (m) Manley, C. D. Synthesis and reactivity of titanium

hydrazido compounds; University of Oxford, Oxford, U.K., 2007; Part II

Thesis (Honour School of Natural Science).

(67) Kutzelnigg, W.; Fleischer, U.; Schindler, M. The IGLO-Method:

Ab Initio Calculation and Interpretation of NMR Chemical Shifts and

Magnetic Susceptibilities; Springer-Verlag: Heidelberg, Berlin, Germany,

1990; NMR Basic Principles and Progress Vol. 23, p 165.

(48) Blake, R. E.; Antonelli, D. M.; Henling, L. M.; Schaefer, W. P.;

Hardcastle, K. I.; Bercaw, J. E. Organometallics 1998, 17, 718.

(49) Bolton, P. D.; Feliz, M.; Cowley, A. H.; Clot, E.; Mountford, P.

Organometallics 2008, 27, 6096.

(50) Chatt, J.; Pearman, A. J.; Richards, R. L. Nature 1975, 253, 39.

(51) Fryzuk, M. D. Chem. Rec. 2003, 3, 2.

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Synthesis and reactions of a cyclopentadienyl-amidinate titanium tert- Butoxyimido compound

DOI: 10.1021/om401008a

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