Complexes of [(dadi)Ti(L/X)]m That Reveal Redox Non-Innocence and a Stepwise Carbene Insertion into a Carbon-Carbon Bond

Article abstract of DOI:10.1021/acs.organomet.8b00188

The addition of donors to (dadi)Ti(THF) (1-THF, dadi = [{-CH=N(1,2-C₆H₄)N(2,6-ⁱPr₂-C₆H₃)}₂]ⁿ) afforded the adducts [(dadi)Ti(L/X)]^m (1-L, m = 0, N₂CPh₂; m = -1, X = Cl^-, N₃^-, OⁱPr^-, CH₃^-, ^neoPe^-, CH=CH₂^-, CCPh^-, CCTMS^-, H(D)^-). In all adducts, the chelate was in the (dadi)^4- redox state. For certain anions, evidence for intimate binding of the Li⁺ counterion was explored spectroscopically. Treatment of 1-THF with PhHCN₂, yielded {PhC₃H₃(-NC₆H₄-2-NAr)₂}Ti(THF) (3, Ar = 2,6-ⁱPr₂-C₆H₃), which contains a cyclopropanated dadi ligand. The mechanism was explored by calculations, and the addition of Ph₂CN₂ to 3 produced a nacnac derivative, {PhC(CHNC₆H₄-2-NAr)₂}Ti(??²-HNNCPh₂) (4, Ar = 2,6-ⁱPr₂-C₆H₃), generated via hydrogen transfer from the cyclopropane.

Full text of DOI:10.1021/acs.organomet.8b00188

Article
Cite This: Organometallics XXXX, XXX, XXX−XXX
m
Complexes of [(dadi)Ti(L/X)] That Reveal Redox Non-Innocence and
a Stepwise Carbene Insertion into a Carbon−Carbon Bond
†
†
‡
†
Spencer P. Heins, Wesley D. Morris, Thomas R. Cundari, Samantha N. MacMillan,
†
†
,†
Emil B. Lobkovsky, Nicholas M. Livezey, and Peter T. Wolczanski*
†
Department of Chemistry & Chemical Biology, Baker Laboratory, Cornell University, Ithaca, New York 14853, United States
Department of Chemistry, CASCaM, University of North Texas, Denton, Texas 76201, United States
‡
*
S Supporting Information
ABSTRACT: The addition of donors to (dadi)Ti(THF) (1-
i
n
THF, dadi = [{−CHN(1,2-C H )N(2,6- Pr −C H )} ] )
6
4
2
6
3
2
m
afforded the adducts [(dadi)Ti(L/X)] (1-L, m = 0, N CPh ;
2
2
−
−
i
−
−
neo
−
−
m = −1, X = Cl , N , O Pr , CH , Pe , CHCH ,
3
3
2
−
−
−
CCPh , CCTMS , H(D) ). In all adducts, the chelate was in
4−
the (dadi) redox state. For certain anions, evidence for
intimate binding of the Li counterion was explored
+
spectroscopically. Treatment of 1-THF with PhHCN , yielded
2
i
{
PhC H (-NC H -2-NAr) }Ti(THF) (3, Ar = 2,6- Pr −
3
3
6
4
2
2
C H ), which contains a cyclopropanated dadi ligand. The
6
3
mechanism was explored by calculations, and the addition of
2
i
Ph CN to 3 produced a nacnac derivative, {PhC(CHNC H -2-NAr) }Ti(η -HNNCPh ) (4, Ar = 2,6- Pr −C H ), generated
2
2
6
4
2
2
2
6
3
via hydrogen transfer from the cyclopropane.
n
1
. INTRODUCTION
system, the electronic features of (dadi) are more readily seen,
as (dadi)TiL (1-L; x = 1, L = THF, PMe Ph; x = 2, L =
CNMe) complexes are stabilized as Ti(IV) chelated by
x
2
In two recent communications, a diamide−diimine chelate,
i
n
n
[
{−CHN(1,2-C H )N(2,6- Pr −C H )} ] = (dadi) (n = 0
6
4
2
6
3
2
4−
(
dadi) , whereas the metric parameters of (dadi)TiX
to −4)), was introduced as a designed redox noninnocent
(
2−
1
,2
(2X; X = O, NAd) are consistent with (dadi) . Although
adduct-free (dadi)Ti (1) has not been isolated or
spectroscopically observed, its calculated ground state (GS)
RNI) ligand. As illustrated in Scheme 1, complexes of iron
and chromium, i.e., (dadi)M (M = Fe, Cr(THF)), reacted with
organoazides
from aziridination followed by ring-opening, according to
calculations. Other products were generated from apparent
nitrene insertion into C−H bonds when an electron deficient
azide was the substrate. In both reaction sequences, products
possessing higher formal oxidation states were not found to be
particularly stable, according to calculations, and more oxidized
redox states of the dadi ligand were not feasible. In fact, the
reactivity could be rationalized by recognizing that iron did not
vary from +2, and chromium was stable at a charge state
3
−6
to afford nitrene-insertion products derived
3
−
↓
↑
is best ascribed as {(dadi) } Ti , lending credence to
descriptions of the effective charge on titanium as between
1
7
+
3 and +4.
Herein further studies of [(dadi)Ti(L/X)]m adducts and
dadi)Ti = X species are given in an attempt to further assay
RNI character by spectroscopy and crystallography. In
addition, attempts at generating alkylidene species analogous
(
8
to (dadi)TiNAd (2NAd) have led to cyclopropanation
9
chemistry, and calculations suggest that carbene transfer from
10
2
7
PhHCN
is more convoluted than the analogous nitrene
between +2 and +3.
transfer chemistry.
According to calculations, electronic structures of the
complexes, particularly (dadi)Cr(THF), proved to be intrinsi-
cally interesting. Metric parameters of (dadi)Fe were
consistent with (dadi) chelating high spin (S = 2) Fe(II),
i.e., {(dadi) }Fe , whereas the ground state of the
chromium THF adduct was best described as an admixture
2
. RESULTS
2
−
m
2
.1. Adducts of (dadi)Ti (1). 2.1.1. [(dadi)Ti(L/X)] (L =
ClLi(THF) , 1-Cl·Li; THF, 1-THF). Initial attempts at the
synthesis of (dadi)Ti (1) were conducted via metathesis as
Scheme 2 describes. After generating green (dadi)Li in situ,
the addition of (tmeda) TiCl afforded a dark green solution
2
−
↑↑↑↑
4
3−
of a (dadi) radical antiferromagnetically coupled to Cr(III)
2
2
−
11
(
ST = 1), and an S = 1 excited state of (dadi)
2
2
antiferromagnetically coupled to high spin Cr(II), i.e.,
2−
↓↓ ↑↑↑↑
3−
↓
↑↑↑
α{(dadi) }* Cr
In the case of titanium, (dadi)Ti(THF) (1-THF) served as a
source of (dadi)Ti (1) in the catalytic carbonylation of
+ (1 − α){(dadi) } Cr with α > 0.5.
Special Issue: In Honor of the Career of Ernesto Carmona
Received: April 5, 2018
2
adamantyl azide to adamanyl isocyanate, AdNCO. In this
©
XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Scheme 1. Previous Studies Revealed Nitrene Insertions, Likely via Aziridine Transients, and the Catalytic Carbonylation of
n
AdN by (dadi)Ti (1), a Process That Utilizes the Redox Non-Innocence (RNI) of (dadi)
3
Scheme 2. Metatheses of (tmeda) TiCl with (dadi)M Afford Different Adducts Depending on M
2
2
2
1
2,13
2−
2
from which the chloride adduct, [(dadi)TiCl][Li(THF) ] (1-
NMR spectra.
In the case of (dadi) , the sp backbone
4
−
4−
Cl·Li) was isolated in ∼90% yield. Attempts to displace Cl
from 1-Cl·Li proved difficult, hence it was reasoned that the
significantly less soluble NaCl should be targeted as a
imine protons are of interest, but in the reduced (dadi) form
of the ligand, the same protons are also sp by virtue of being
attached to the olefin. Experimentally, there is no significant
difference between the shifts of the dianion and the formal
tetraanion, hence distinguishing between ligand redox states
necessitates structural information.
2
biproduct. The switch to (dadi)Na , which was isolated as a
2
2
blue solid in 94% yield, afforded the olive-green THF adduct,
dadi)Ti(THF) (1-THF), in 40−50%. Fortunately, 1-THF
was found to be a much more labile starting material and was
2
(
The addition of sodium azide to form [(dadi)TiN ][Na(15-
3
used almost exclusively in the remaining synthetic studies.
c-5) (1-N ·Na) was conducted in the hope of generating
3
m
2−
IV
−
2.1.2. General Synthesis of [(dadi)Ti(L/X)] . Preparation of
[{(dadi) }Ti N] , but a variety of thermal and photo-
chemical attempts were unsuccessful at cleanly forming the
the THF complex, (dadi)Ti(THF) (1-THF), afforded a ready
means of preparing a variety of adducts via simple substitution.
Scheme 3 portrays the adducts, which were synthesized in
THF in roughly 40−90% yields as given. Each adduct was
determined to be five-coordinate, by virtue of observing four
1
4−23
nitride anion.
The IR spectrum of 1-N ·Na manifested a
3
−
1
ν(N ) at 2077 cm , consistent with a simple azide complex.
3
Similarly, treatment of (dadi)Ti(THF) (1-THF) with Ph C
2
NN failed to elicit the generation of N and the
2
1
24−33
independent isopropyl Me groups in H NMR spectra. As
diphenylalkylidene complex.
Instead, a simple green
i
34
previously noted, the 2,6- Pr −C H aryl groups are aligned
adduct, (dadi)Ti(NNCPh ) (1-NNCPh ), was ob-
2
6
3
2
2
2
roughly face-to-face in the dadi ligand, and rotation about the
ipso-carbon−nitrogen bonds are severely hampered by sterics
upon chelation to a metal. Consequently, the isopropyl Me
groups are diastereotopic and are observed as two doublets if
two mirror planes are present, and four doublets if one mirror
plane is present, as in the case of the 5-coordinate adducts,
although they are often overlapping. In related ligand systems,
it is often possible to distinguish between the two redox forms
served, and calculations (vide infra) suggest it is η -N CPh .
2 2
The bronze-colored isopropoxide derivative, [(dadi)Ti-
i
i
(O Pr)][Li(THF) ] (1-O Pr·Li), is tentatively formulated as
4
an ion pair due to the observation of THF molecules that
persist in benzene-d solution.
6
2.1.3. Selected NMR Spectroscopic Features of [(dadi)Ti(L/
m
X)] . As the X-ray crystal structures (vide infra) and some
NMR spectra indicate, structural ambiguities persist in whether
the main group counterion is an integral part of the complex
1
of the ligand through routine chemical shift changes in H
B
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
a
Scheme 3. Various Adducts Prepared from (dadi)Ti(THF) (1-THF) and Suitable Reagents in THF
a
Precipitation or crystallization was from pentane in most cases.
7
1
Figure 1. NMR spectra of the hydride anion, [(dadi)TiH][Li(THF) ] (1-H·Li) in C D : (a) Li NMR spectrum showing J . (b) H NMR
3
6
6
HLi
spectrum showing JHLi, the diamide methine, the four methyl doublets that indicate 5-coordination, and the remaining resonances attributable to
aryl and Me CH groups.
2
−
2−
via binding to X or through complexation to the C N part
Hz, Jgem = −4.20 Hz; C HH at δ 5.9995, J = 14.65 Hz, J
=
2
2
β
cis
gem
4
−
7
of the dadi backbone. Hydrocarbyl adducts manifest shifted
H and C{ H} resonances upon complexation in addition to
−4.20 Hz. While lithium−carbon coupling ( Li (I = 3/2,
1
13
1
35
2
92.5−96%)) does not appear in this sp -hydrocarbyl
13 1
color changes from the green hue of (dadi)Ti(THF) (1-THF)
to a typical red/red-brown coloration of the adducts. The Ti−
CH unit of (dadi)Ti(CH )·Li(THF) (1-CH ·Li) was
derivative, the C{ H} NMR spectrum of [(dadi)TiCCPh]-
[Li(THF) ] (1-CCPh·Li) exhibited a quartet at δ 138.72 with
2
a JCLi of 6.8 Hz, suggestive of a significant C −Li interaction in
3
3
2
3
α
1
observed as singlets at δ 0.79 in the H NMR spectrum, and
benzene-d solution. No coupling was observed for C (δ
6
β
1
3
1
1
δ 36.07 in the C{ H} NMR spectrum. Curiously, the H
142.69), nor was any lithium−carbon coupling observed in the
corresponding trimethylsilylacetylide derivative, [(dadi)-
TiCCSiMe ][Li(THF) ] (1-CCTMS·Li), whose C -shift at δ
neo
neo
NMR spectral shifts for the Pe group in (dadi)Ti( Pe)·
neo
Li(THF)2.4 (1- Pe·Li) appear in a “normal” range at δ 1.21
3
2
α
1
3
(
CH ) and δ 0.89 (Me ), but the corresponding
C
162.27 was at considerably lower field than the phenylacetylide
derivative. The remaining resonances in both alkynyl anions
are quite similar.
2
3
resonances are shifted considerably: TiCH , δ 86.83; C , δ
9.94; (CH ) , δ 34.8.
2
β
3
3 3
The vinyl derivative, (dadi)Ti(CHCH )·Li(THF) (1-
2.1.4. Spectroscopic and Dynamic Features of (dadi)TiHLi
2
3−4
CHCH ·Li) manifests a non-first-order ABX pattern in its
(1-H·Li). The hydride anion, [(dadi)TiH][Li(THF) ] (1-H·
2
2
1
35
1
H NMR spectrum, necessitating a simulation: δ 8.2265, C H,
Li), features a quartet at δ 10.22 (JHLi = 11.3 Hz) in its H
α
Jtrans = 20.90 Hz; J = 14.65 Hz; δ 6.0046, C HH, J = 20.90
NMR spectrum in C D , as Figure 1 illustrates. To distinguish
cis
β
trans
6
6
C
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
7
Table 1. Diffusion Coefficients for Individual dadi, THF, and Lithium Resonances as Determined by H and Li DOSY
,
a b
Experiments
1
2
6
1H (δ) THF-d8
2
6
7Li (δ)
2
6
H (δ) C D6
D (cm /s) (× 10 )
D (cm /s) (× 10 )
D (cm /s) (× 10 )
6
0
1
1
1
1
.9
4.13(3)
4.04(3)
4.11(3)
4.10(3)
0.84
3.21
5.18
6.05
6.18
6.24
6.44
6.89
10.46
5.00(3)
5.2(1)
4.9(2)
5.0(2)
4.9(2)
4.9(2)
4.9(2)
4.85(4)
4.9(3)
−0.27 (C D )
−0.49 (THF-d8)
5.2(1)
5.5(4)
6
6
.01
.09
.14
.32
c
c
8.9(9) 67%
4
.6(9) 33%
3
3
.08
.45
4.0(1)
8.7(6) 73%
4
.5(9) 27%
3
5
6
6
6
1
.61
.68
.31
.5
.63
0.22
4.5(1)
4.1(1)
4.10(6)
4.1(1)
4.10(3)
4.1(2)
d
avg
4.1(2)
5.0(5)
a
Diffusion coefficients were measured using double pulsed gradient stimulated spin−echo (DPGSE) experiments with convection compensation
7
1
using the DgscsteSL_cc or Dbppste_cc pulse sequence as provided in VnmrJ 3.2 at 295 K. The Li signal in C D was H-decoupled. The following
6
6
1
7
parameter values were used: H nucleus, δ = 0.0018 s, Δ = 0.1244 s; Li nucleus, δ = 0.004 s, Δ = 0.0987 s. Gradient strength was varied from 2.1 to
b
2
2
2
5
8.6 G/cm in 24 linear increments. D was determined from plots of ln(I/I ), the integrated intensities, vs δ γ (Δ−δ/3)G , where the constants
0
have their usual definitions; see the Supporting Information for the relevant equations and details. Igor Pro was used for the fits and the reported
c
d
errors. Deviation from linear behavior was observed, indicating free and bound THF in C D prompting biexponential decay fits. THF
6
6
(
biexponentially determined D’s) not included.
4−
2−
a
Table 2. Comparative Distances (Å) of {(dadi) }TiL (1-L ) and {(dadi) }TiX (2X)
x
x
1
C C2
1
2
compd
-Cl·Li
TiNim
TiNam
C C
C N
C N
C N
im
TiL/X
im im
im im
am
1
2
2
2
2
2
2
2
2
2
.999(4)
.044(4)
.021(2)
.060(2)
.016(2)
.056(2)
.019(2)
.033(2)
.033(2)
.035(2)
2.008(4)
2.018(4)
2.002(2)
2.020(2)
2.014(2)
2.016(2)
2.003(2)
2.009(2)
2.064(2)
2.068(2)
2.022(24)
2.122(5)
2.084(5)
2.074(5)
2.121(5)
2.054(2)
2.064(2)
2.087(29)
1.343(7)
1.348(2)
1.349(2)
1.338(3)
1.350(3)
1.371(6)
1.382(6)
1.383(2)
1.393(2)
1.385(2)
1.392(2)
1.379(3)
1.381(3)
1.373(2)
1.371(2)
1.381(8)
1.297(8)
1.293(7)
1.303(8)
1.300(8)
1.297(2)
1.301(2)
1.299(4)
1.402(6)
1.422(5)
1.414(2)
1.407(2)
1.407(2)
1.404(2)
1.411(3)
1.406(3)
1.396(2)
1.395(2)
1.406(8)
1.373(7)
1.384(8)
1.374(7)
1.375(7)
1.377(2)
1.375(2)
1.376(4)
1.411(6)
1.413(6)
1.398(2)
1.416(2)
1.415(2)
1.419(2)
1.413(3)
1.408(3)
1.418(3)
1.423(2)
1.413(7)
1.413(8)
1.425(8)
1.420(8)
1.418(8)
1.419(2)
1.418(2)
1.391(6)
1.392(6)
1.397(2)
1.400(2)
1.394(2)
1.403(2)
1.396(3)
1.396(3)
1.403(2)
1.401(2)
1.397(4)
1.389(8)
1.402(7)
1.386(8)
1.376(8)
1.395(2)
1.388(2)
1.389(9)
2.310(2)
1
1
1
2.133(2)
2.131(2)
2.605(2)
b
-CH ·Li
3
c
-PMe Ph
2
2.236(2)
2.248(2)
c
1-(CNMe)2
d
1
-L (avg)
2.032(19)
1.346(5)
1.436(8)
x
2
2
2
2
2
2
.172(5)
.193(5)
.166(5)
.200(5)
.160(2)
.194(2)
1.702(5)
1.702(5)
1.636(2)
b
2NAd
1.428(9)
1.433(2)
1.432(4)
c
2O
e
2X (avg)
2.181(17)
1.419(4)
a
b
c
d
4−
All distances given to the thousandth place for ready comparison. Two molecules per asymmetric unit. Ref 2. Average of all {(dadi) }TiL (1-
x
e
2−
L ) distances. Average of all {(dadi) }TiX (2X) distances.
x
1
7
between 1-H·Li and a potential η -AlH complex, the Li NMR
methine resonances, and typical aromatic signals. In THF-d8,
the hydride collapses to a broad singlet (Δν ∼ 4 Hz), which
4
spectrum was taken, revealing a clear doublet at δ −0.27 with
the requisite 11.3 Hz coupling. The H NMR spectrum of 1-H·
Li also reveals typical aspects of the (dadi)Ti framework,
including the aforementioned four Me doublets, differing
1
/2
1
1
was absent in the H NMR spectrum of the corresponding
deuteride (1-D·Li). An absorption at 1800 cm− (ν(TiH)) is
observed in the IR spectrum of 1-H·Li, and while it was absent
1
D
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
in the corresponding 1-D·Li IR spectrum, no clear ν(TiD) is
evident, although subtle changes in the fingerprint region are
−
1
seen around 1270 cm , consistent with the deuteride. The
hydride stretch of 1800 cm− is of high energy for an early
metal but consistent with an anionic hydride that carries
1
7
substantial charge.
The coupling observed between the lithium and hydride
nuclei in C D suggests the lithium-hydride bond in [(dadi)-
6
6
TiH][Li(THF) ] (1-H·Li) has significant covalency. When
3
dissolved in THF-d , the coupling is disrupted, prompting
8
several explanations: (1) The rate of intermolecular lithium
exchange is fast on the NMR spectroscopic time scale,
effectively decoupling the hydride and lithium. (2) The
lithium is solvated by THF but exists as a tight ion-pair. (3)
THF completely solvates the lithium, separating it from the
Figure 2. Molecular view of the anion pertaining to [(dadi)TiCl]-
[Li(THF) ] (1-Cl·Li). Table 2 contains selected distances, while its
4
core angles (deg) are Cl−Ti−N1, 106.85(11); Cl−Ti−N2,
105.73(11); Cl−Ti−N3, 96.01(12); Cl−Ti−N4, 104.79(12); N1−
Ti−N2, 76.02(15); N1−Ti−N3, 145.88(16); N1−Ti−N4,
117.33(14); N2−Ti−N3, 73.55(15); N2−Ti−N4, 140.75(15);
N3−Ti−N4, 79.27(15).
−
7
[
(dadi)TiH] anion. (4) 36Li quadrupolar relaxation is
unusually solvent-dependent.
n
The many resonances attributable to (dadi) permit
significant redundancy in the measurement of diffusion
3
7,38
coefficients by the gradient method,
and these are listed
7
successful X-ray structure determination of [(dadi)TiCH ]-
3
along with average diffusion coefficients in Table 1. The Li
diffusion coefficients of 5.2(1) × 10−6 and 5.5(4) × 10 cm /
−6
2
[Li(THF) ] (1-CH ·Li). One of two independent molecules of
2 3
the methyl adduct is pictured in Figure 3, selected refinement
details are given in the Supporting Information, and
comparative metric parameters are listed in Table 2.
sec in C D and THF-d , respectively, do not differ
6
6
8
significantly, suggesting the lithium is associated with the
dadi complex in either solvent. Furthermore, the average
−
6
diffusion coefficients for the dadi ligand of 4.1(2) × 10 and
−
6
2
5
.0(5) × 10 cm /sec in C D and THF-d , respectively, are
6 6 8
on the same order of magnitude as those observed for the
lithium, providing further evidence that it is associated with the
dadi complex in THF solution. These observations are
+
inconsistent with a fully solvated and separated Li (THF)n
cation but are consistent with a tight ion pair or integral HLi
bonding in THF but with fast exchange. If exchange is
occurring in C D solution, then it must be significantly slower
6
6
in order for the JHLi to be retained. Since 1-H·Li exhibits a
clean JLiH, it is unlikely that quadrupolar relaxation is significant
enough to be a factor in THF-d8.
2
.1.5. Structure of [(dadi)TiCl][Li(THF) ] (1-Cl·Li). Dark
4
green crystals were harvested from the metathesis procedure in
Scheme 2, and a single crystal X-ray structure characterization
(
(
Table 2) revealed the chloride adduct, [(dadi)TiCl][Li-
THF) ] (1-Cl·Li). The Li cation was coordinated by four
4
THF molecules, and the [(dadi)TiCl] anion is roughly square
pyramidal, as Figure 2 illustrates. Metric parameters for the
chloride adduct are listed in Table 2 along with some
comparative distances from related complexes. The N2−Ti−
N3 “bite angle” is 73.55(15)°, while the imine-amide angles are
Figure 3. View of one of the two molecules of [(dadi)TiCH ][Li-
3
(
THF) ] (1-CH ·Li) in the asymmetric unit. Table 2 contains
2 3
selected average distances, while its average core angles (deg) are C−
Ti−N(11,21), 97.03(5), 96.58(5); C−Ti−N(14,24), 103.33(5),
1
02.31(5); C−Ti−N(12,22), 94.73(5), 94.81(5); C−Ti−N(13,23),
7
6.02(15) and 79.27(15)°, whose subtle variation reflects the
110.03(5), 105.88(5); N(11,21)−Ti−N(12,22), 79.10(4), 78.74(4);
i
skewed face-to-face orientation of the 2,6- Pr −C H groups.
N(11,21)−Ti−N(13,23), 141.73(4), 144.67(4); N(11,21)−Ti−N-
2
6
3
(
7
14,24), 123.94(4), 125.41(4); N(12,22)−Ti−N(13,23), 72.35(4),
The Ti is out of the imine-amide plane by ∼0.487 Å (∠N2−
Ti−N4 = 140.75(15)°, ∠N1−Ti−N3 = 145.88(16)°), while
the diamides are opened up relative to the other core angles at
2.60(4); N(12,22)−Ti−N(14,24), 147.70(4), 147.60(4); N-
(13,23)−Ti−N(14,24), 76.35(4), 76.33(4).
1
17.33(14)°. The d(Ti−Cl) was 2.3104 Å, and the “imine”
nitrogen−titanium bond lengths (d(TiN) = 1.999(4),
.044(4) Å) were essentially identical to those of the amides
d(TiN) = 2.008(4), 2.018(4) Å), significant evidence that
dadi) is the redox state of the chelate. In corroboration, the
CN(imine) distances are 1.371(6) and 1.382(6) Å, more
1-CH ·Li is a pseudosquare pyramidal species that has
3
2
(
(
additional coordination to a Li(THF) “cation” bound to the
2
4−
ene-diamide backbone of the dadi ligand. The titanium is out
4
−
of the N -plane by 0.384 (0.342) Å, and the resulting C−Ti−N
4
angles are all >90°, with the methyl canted slightly toward the
ene-diamide (95.8(12)° (avg)) backbone versus the aryla-
mides (105.4(34)° (avg)). The bite angle of the ene-diamide
averages 72.48(18)°, while the opposing angle between the
arylamides averages 127.7(32)°. The remaining ene-amide/
arylamide bite angles average 78.9(3) and 76.34(2)°.
appropriate for C−N single bonds, and d(C7−C8) = 1.343(7),
3
9
a bond length closer to a carbon−carbon double bond.
2
.1.6. Structure of [(dadi)TiCH ][Li(THF) ] (1-CH ·Li).
3 2 3
Hydrocarbyl adducts of (dadi)Ti (1) crystallized as thin plates
or were susceptible to solvent loss, but repeated efforts led to a
E
DOI: 10.1021/acs.organomet.8b00188
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Article
Scheme 4. Imide Formation from RN and Cyclopropanation of the dadi Backbone with PhHCN2
3
The titanium−carbon bond distance of 2.1318(16) Å (avg)
40
is roughly equivalent to the sum of covalent radii (2.08 Å)
and the arylamide-titanium (2.012(8) Å (avg)), and ene-
diamide-titanium bond lengths (2.019(4), 2.058(3) Å (avg))
4−
are clearly both consistent with a tetraanionic (dadi) ligand.
The average CN(imine) distance is 1.388(5) Å, consistent
with C−N single bonds, and the average backbone CC bond
length of 1.3487(6) Å is essentially a normal double bond
3
9
distance. The distinct molecules of 1-CH ·Li possess
3
different d(C−Li) values (2.625(3), 2.421(3) Å), but both
distances are substantially greater than the sum of covalent
radii (2.00 Å), yet well within the sum of the van der Waals
radii (∼3.5 Å). The lithium appears to be loosely bound to the
ene-diamide nitrogens and carbons at 2.417(36) (avg) and
2
.387(36) (avg) Å, respectively, along with typical lithium−
oxygen interactions from the THF at 1.934(17) Å (avg).
.2. RN , RCHN and (dadi)Ti(THF) (1-THF). 2.2.1. Syn-
Figure 4. View of one of two (dadi)TiNAd (2NAd) molecules
in the asymmetric unit. Table 2 contains selected average distances,
while its average core angles (deg) are NTi−N(11,21), 108.4(2),
108.1(2); NTi−N(14,24), 108.8(2), 108.7(2); NTi−N(12,22),
99.2(2), 91.7(2); NTi−N(13,23), 91.1(2), 100.0(3); N(11,21)−
Ti−N(12,22), 75.52(18), 74.75(18); N(11,21)−Ti−N(13,23),
2
3
2
thesis of (dadi)TiNAd (2NAd). Unlike the treatment of
3
−6
(
dadi)M (M = Fe, Cr(THF)) with organoazides,
which
1
resulted in the nitrene insertions described in Scheme 1,
exposure of (dadi)Ti(THF) (1-THF) to stoichiometric
1
43.51(19), 136.08(19); N(11,21)−Ti−N(14,24), 123.73(19),
amounts of AdN permitted isolation of maroon-red (dadi)-
3
2
123.76(19); N(12,22)−Ti−N(13,23), 71.01(18), 71.37(19); N-
TiNAd (2NAd), as previously reported (Scheme 4). The
(12,22)−Ti−N(14,24), 135.79(19), 143.18(19); N(13,23)−Ti−N-
(14,24), 74.85(19), 74.99(19).
reaction of 1-THF was essentially immediate in benzene, and
2
NAd was reproducibly prepared in yields >70%. An NMR
tube experiment with TMSN cleanly produced a material
3
(
>90%) consistent with the imide (dadi)TiNTMS (2
importantly, the d(CN) distances are appropriate for double
bonds at 1.300(6) Å (avg), while the d(CC) of the dadi
backbone is clearly a single bond distance (1.437(3) Å
i
NTMS), but the addition of 2,6- Pr −C H N to 1-THF
produced a complicated product containing multiple isopropyl
groups, indicative of a complex lacking any mirror symmetry.
2
6
3
3
39
(
avg)).
.2.3. Cyclopropanation of dadi . The generation of
2.2.2. Structure of (dadi)TiNAd (2NAd). A single
4−
2
crystal X-ray structural determination of (dadi)TiNAd (2
NAd) was conducted, and even though the data set was
twinned, it was refined to the extent that the imide structure
consistent with previous NMR spectroscopic characterization
was confirmed. A molecular view, showing the Ti roughly 0.53
(
dadi)TiNAd (2NAd) suggested that titanium alkyli-
42−55
24−33
denes
can be similarly formed via diazoalkanes. After
5
6
attempts at protonation
of (dadi)Ti(CHCH )·Li-
2
(
THF)3−4 (1-CHCH ·Li) and hydride abstraction from
2
(dadi)Ti(CH )·Li(THF) (1-CH ·Li) failed to elicit the
3
2
3
Å above the N plane, is given in Figure 4. The d(TiN) was
desired (dadi)TiCHR (R = Me, H), a conventional route
4
5
,6,41
1
.702(5) Å (avg), a typical value for Ti(IV) imides,
and
via diazoalkanes was attempted. As previously stated, Ph CN
2
2
34
the diimine titanium−nitrogen distances of 2.183(17) Å (avg)
simply produced the aforementioned adduct, (dadi)Ti(N
are somewhat longer than the amide Ti−N bond lengths of
NCPh ) (1-NNCPh ), but use of PhHCN generated a red
2
2
2
2−
9,10
2
.100(25) (avg). This disparity is in line with the (dadi)
complex with a cyclopropanated
(NC H -2-NAr) }Ti(THF) (3, Ar = 2,6- Pr −C H ), in 70%
yield (Scheme 4).
backbone, {PhC H -
3
3
i
formalism and stands in contrast to the nearly equal values
6
4
2
2
6
3
attributable to d(TiN) in (dadi)4 (Table 2). Most
−
F
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Article
The observation of a mirror plane and resonances consistent
with 5-coordination in the H NMR spectrum of 3 were
2.2.5. Nacnac Formation. The formation of a cyclo-
1
n
propanated backbone of (dadi) suggested that reversible C−C
puzzling in view of its assimilation of PhHCN and retention of
bond formation could be a means of storing and releasing
2
12,57−67
THF. It appeared that the carbene fragment, PhHC:, had been
incorporated into the dadi ligand and was not simply attached
to titanium. An attempt was made to detect a plausible
electrons in a redox noninnocent (RNI) fashion.
A
possible hindrance to RNI is the transfer of a cyclopropane
hydrogen subsequent to ring-opening, which would generate a
nacnac fragment in place of the original diimine. The reactivity
of {PhC H (-NC H -2-NAr) }Ti(THF) (3) was probed via
PhHCN adduct, or other intermediate, by variable temper-
2
1
ature H NMR spectroscopy, but broad, unchanging
3
3
6
4
2
resonances observed between −100 and −80 °C in THF-d
various potential oxidants and proton acceptors, and while
most generated mixtures, the addition of Ph CN yielded a
8
were not decipherable. Upon warming to −65 °C, broad
resonances were still observed, and about 60% conversion to
product {PhC H -(NC H -2-NAr) }Ti(THF) (3) was appa-
2
2
1
single product (>90%) that was dissymmetric. H NMR
spectroscopic resonances that revealed the loss of a cyclo-
3
3
6
4
2
−
1
rent, consistent with a barrier to cyclopropanation of ∼15 kcal/
mol. Further warming to −55 °C revealed total conversion,
and one dominant isomer was produced (>95%) according to
propane hydrogen, and a ν(NH) at 3303 cm in its IR
spectrum, were consistent with the generation of a nacnac
1
3,62
2
tetradentate chelate,
{PhC(CHNC H -2-NAr) }Ti(η -
6 4 2
1
i
H NMR spectroscopy. Direct cyclopropanation of the
HNNCPh ) (4, Ar = 2,6- Pr −C H ). Despite the exo-
2
2
6
3
4
−
(
dadi) ligand, without PhHCN binding to the metal, was
regiochemistry of the cyclopropane β-hydrogen, transfer to
the α-nitrogen of coordinated Ph CN occurs, perhaps
subsequent to ring opening, to generate the trianionic
2
calculated to have a barrier incommensurate with the observed
rate.
2
2
3−
2
.2.4. Structure of {PhC H -2,3-NC H -2-Ar)}Ti(THF) (3).
{PhC(CHNC
H
6
4
-2-NAr)
2
}
ligand. The chemistry provides
3
3
6 4
Figure 5 illustrates a molecular view of 5-coordinate
a blueprint to how reversible C−C bond formation can be
utilized in a redox noninnocent fashion, but it is likely that the
β-carbon of the cyclopropane unit will need to have two non-
63
hydrogen substituents.
.2.6. Structure of {PhC(CHNC H -2-NAr) }Ti(η -HNNCPh )
2
2
6
4
2
2
(4). Pictured in Figure 6 is a molecular view of {PhC-
Figure 5. Molecular view of {PhC H (-NC H -2-Ar) }Ti(THF) (3,
3
3
6
4
2
i
Ar = 2,6- Pr ). Selected interatomic distances (Å) and angles (deg):
2
Ti−O, 2.0796(9); Ti−N1, 2.0228(10); Ti−N2, 1.9892(11); Ti−N3,
1
1
1
9
.9915(10); Ti−N4, 2.0089(10); N3−C19, 1.4364(17); N2−C20,
.4292(17); C19−C20, 1.495(2); C19−C39, 1.518(2); C20−C39,
.518(2); O−Ti−N1, 104.94(4); O−Ti−N2, 93.64(4); O−Ti−N3,
6.83(4); O−Ti−N4, 100.32(4); N1−Ti−N2, 78.85(4); N1−Ti−
N3, 147.35(5); N1−Ti−N4, 120.63(4); N2−Ti−N3, 75.72(4); N2−
Ti−N4, 151.29(4); N3−Ti−N4, 77.78(4).
2
Figure 6. Molecular view of {PhC(CHNC H -2-NAr) }Ti(η -
6
4
2
i
HNNCPh ) (4, Ar = 2,6- Pr −C H , Scheme 4). Selected interatomic
2
2
6
3
distances (Å) and angles (deg): Ti−N1, 2.0023(12); Ti−N2,
2
.1316(12); Ti−N3, 2.1389(12); Ti−N4, 2.0115(12); Ti−N5,
i
{
PhC H (-NC H -2-NAr) }Ti(THF) (3, Ar = 2,6- Pr −
1.9243(13); Ti−N6, 2.1899(13); N2−C19, 1.3288(18); C19−C20,
3
3
6
4
2
2
4
−
C H ), showing that the (CH) N backbone of the (dadi)
1.389(2); C20−C21, 1.393(2); N3−C21, 1.3322(18); N1−Ti−N2,
6
3
2
2
7
8.00(5); N1−Ti−N3, 129.24(5); N1−Ti−N4, 111.13(5); N1−Ti−
ligand was cyclopropanated, yielding a product with the phenyl
group oriented toward the titanium core, and the proton of the
N5, 92.67(5); N1−Ti−N6, 126.72(5); N2−Ti−N3, 79.83(4); N2−
Ti−N4, 156.03(5); N2−Ti−N5, 92.95(5); N2−Ti−N6, 85.43(5);
N3−Ti−N4, 77.42(4); N3−Ti−N5, 133.64(5); N3−Ti−N6,
“
carbene” directed away. The titanium−nitrogen distances
average 2.003(16) Å and can be all be assigned as amide
9
5.96(5); N4−Ti−N5, 108.23(5); N4−Ti−N6, 104.32(5); N5−
linkages. The titanium is slightly out of the N -amide plane
4
Ti−N6, 37.68(5).
(
0.3 Å), as the O−Ti−N angles are >90°, and the THF is
oriented away from the aryl amides (O−Ti−N1/N4 =
04.94(4)/100.32(4)), presumably due to sterics. All distances
2
i
1
(CHNC H -2-NAr) }Ti(η -HNNCPh ) (4, Ar = 2,6- Pr ) that
6 4 2 2 2
and angles are appropriate for the cyclopropane unit, and the
reveals the asymmetry in the compound evident by NMR
spectroscopy. The nacnac portion of the ligand is characterized
by d(Ti−N) of 2.1316(12) and 2.1389(12) Å, while the
remainder of the tetradentate chelate is similar to that of
n
(
dadi) . Aryldiamide bite angles of 78.85(4) and 77.78(4)° are
accompanied by the backbone diimine bite angle of 75.72(4)°,
titanium-amide nitrogen distances are normal (Ti−N1,
2
leaving the usual open arylamide−titanium−arylamide angle of
2.0023(12); Ti−N4, 2.0115(12)). The η -HNNCPh linkage
2
1
20.63(4)°.
is angled across the face of the nacnac-diarylamide titanium
G
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↑
3− III ↓
Figure 7. Progressively more oxidizing X, O > NAd > CHPh, and the dadi redox consequences compared to that of calculated {(dadi)· } Ti
4
−
IV
n
(
1) and adducts [{(dadi) }Ti -L] (1-L).
Figure 8. Geometries of unrestricted singlet (0.0 kcal/mol; a) and unrestricted triplet (3.4 kcal/mol; b) DFT (ONIOM(M06/6-311+G(d):UFF)
calculations of (dadi)TiC(H)Ph (2-C·HPh). The restricted singlet (0.5 kcal/mol) is not shown but similar to panel a.
core such that the mirror symmetry is broken. Its amide
d(TiN) is 1.9243(13) Å, and its titanium−β-N distance is
considerably longer at 2.1899(13) Å, although clearly within
reason for a simple donor interaction. The remaining distances
and angles, a selected group of which are indicated in the
caption of Figure 6, are as expected for this low symmetry
complex.
Attempts to generate (dadi)TiCRR′ have failed, and
according to calculations, the generation of a stable alkylidene
may not be possible since the RR′C: fragment is not oxidizing
4−
enough to pull electrons from (dadi) . As indicated in Figure
7., calculations on a benzylidene portray it as a diradical
6
6,67
↑ 3− IV
↓
species
best considered (dadi· ) Ti (C· (H)Ph) (2-C·
HPh). Figure 8 illustrates the calculated geometries of 2-C·
HPh which show the d(CN ) to be 1.33 Å, and d(CC) = 1.39
im
3
. DISCUSSION
.1. Redox Parameters of [(dadi) Ti(=X/L)] . The metric
Å, values that are between those found for dianionic (n = −2)
n
n
n
and tetraanionic (n = −4) forms of (dadi) . The d(TiC) of
3
2.02 Å in the singlet geometries is consistent with a double
parameters in Table 2 unquestionably show two discrete states
n
bond, but the ligand metrics force one to conclude that
of (dadi) are n = −2 for (dadi)Ti = X (2X) species and n =
3−
2
−
unpaired spin density on (dadi·) is likely antiferromagnet-
−
4 for adducts (dadi)TiL (1-L). In order to generate (dadi) ,
−
ically coupled to a radical benzylidene anion (:C·PhH) . The
the ligand(s) X or L need to be oxidizing enough to pull 2
electrons out of (dadi) . As previously discussed, even a
3−
4
−
triplet version, having the (dadi·) ferromagnetically coupled
−
to the (:C·PhH) , is only 3.4 kcal/mol above the singlet.
ligand with significant backbonding capability, such as CO or
2
n
Previous calculations on (dadi)Ti (1), a species that has not
been isolated or observed with confidence, have shown it to be
CNR, does not convert the (dadi) from n = −4 to n = −2. In
the case of azide RN , a nitrene precursor, the RN generated
3
2−
3−
↓
III ↑
via N loss is a potent enough oxidant to generate RN by
best construed as {(dadi) } Ti , where the electron on
titanium is antiferromagnetically coupled to an odd electron on
2
4−
oxidizing the dadi . It is interesting that the titanium does not
change its formal oxidation state, as the ligands are far more
7
3−
the dadi ligand. The donation of any L to 1, even a weak
redox active and incur all the redox changes. Nitrene insertions
into the dadi backbone of the Fe and Cr species illustrated in
Scheme 1 occur because RN does not have the oxidizing power
in these systems to fully convert the metal to M(IV). As a
consequence, nitrene or imidyl (M(III)) chemistry rather than
imide chemistry is observed.
ligand such as THF, increases the electron density at the metal
4−
and causes the transfer of another electron to (dadi) ; hence,
4−
IV
all (dadi)TiL (1-L) are {(dadi) }Ti -L.
Figure 9 illustrates a truncated molecular orbital diagram of
(dadi)Ti(THF) (1-THF), showing a 2.85 eV gap between the
HOMO, an orbital with backbone carbon−carbon double
H
DOI: 10.1021/acs.organomet.8b00188
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Article
Figure 9. Truncated molecular orbital diagram of (dadi)Ti(THF) (1-THF), showing empty d-orbitals (M06/6-311+G(d) orbital energies at the
4−
ONIOM(M06/6-311+G(d):UFF) optimized minimum of singlet 1-THF), and the four, highest occupied (dadi) molecular orbitals.
bond and diamide character, and the LUMO, a d-orbital of
roughly xy-character. It is also clear that the empty d-orbitals,
which span only 0.87 eV, reflect the low symmetry of the
system and are difficult to assign. The HOMO is 0.83 eV above
the HOMO−1, an orbital that has most of its spin density on
the aryl rings. In general, the MO diagram is quite similar to
addition to lithium-hydride coupling support the contention
that Li may be directly bound in [(dadi)TiH][Li(THF)3−5
(1-H·Li). Figure 10 illustrates potential structures of these
]
2
that of (dadi)Ti(PMe Ph) (1-PMe Ph), which has a HOMO/
2
2
LUMO gap of 2.96 eV, and a 0.85 eV gap between its HOMO
and HOMO−1. Both MO diagrams are consistent with a
4
−
(
dadi) redox state of the chelate, and both show the HOMO
to be the same NCCNπ orbital that clearly indicated CC
double bond character.
Evidence of intimate lithium bonding in the case of
[
(dadi)TiCCPh][Li(THF) ] (1-CCPh·Li) stems from the
Figure 10. Plausible structures of complexes exhibiting JLiH based on
the crystal structure of [(dadi)TiCH ][Li(THF) ] (1-CH ·Li).
2
observation of JCLi, while gradient diffusion experiments in
3
2
3
I
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Figure 11. Computed intermediates (ΔG° (ΔH°)) relative to (dadi)Ti(THF) (1) in three cyclopropanation mechanisms. A “direct carbene
1
transfer” to the dadi backbone possesses a lower barrier than one involving the intermediacy of (dadi)TiCHPh, and it is likely to occur via an η -
NNCPhH. The product with opposite cyclopropane stereochemistry has a lower free energy of −40.7 kcal/mol (ΔH° = −44.0 kcal/mol).
Calculations at the M06/6-311+G(d)/ONIOM(M06/6-311+G(d):UFF level.
species based on the X-ray crystal structure of [(dadi)TiCH ]-
formation of a titanaaziridine ensues via attack at an imine
nitrogen, and it is considerably stable at ΔG° = −30.0 kcal/
mol. The barrier to cyclopropanation via the titanaaziridine
(via TiCHPh), which is a two-step process, is quite substantial
3
[
[
Li(THF) ] (1-CH ·Li, Figure 3). While the alkyl complexes
2 3
neo
(dadi)TiR][Li(THF) ] (1-R·Li, R = Me,
Pe) do not
2
3
manifest lithium−hydrogen coupling, it may be that the sp
and sp (e.g., [(dadi)TiCHCH ][Li(THF) ] (1-CHCH ·
2
⧧
⧧
at ΔG = 40.4 kcal/mol (ΔH = 38.1 kcal/mol). It appears
2
2
2
Li)) constituents lack the appropriate orbital overlap for
likely that sterics impact the ability of PhHCN to transfer
2
significant interaction. The crystal structure in Figure 2
PhHC: to the titanium; otherwise, the titanaaziridene might be
a free energy sink in the system, as the benzylidene radical (2-
C·(H)Ph) is not likely to be a stable species. In contrast, the
supports a modest CH ···Li contact, and the s- and sp-
3
interactions of the hydride 1-H·Li and acetylide 1-CCPh·Li
complexes, respectively, are likely to permit enough orbital
overlap for JLi(C/H) to be observed.
1
simple η -NNCHPh adduct is ideally positioned above the
dadi backbone for carbene transfer, and it is the clear path of
choice. Note that this cyclopropanation contrasts with the
nitrene mediated aziridination of the dadi ligand illustrated in
Scheme 1.
3
.2. Mechanism of the Cyclopropanation of (dadi)Ti-
(
THF) (1-THF). The mechanism of the dadi cyclopropanation
revealed in Scheme 4 was assumed to occur via the generation
of (dadi)TiCHPh, but calculations invoke a different process.
First, exogenous cyclopropanation of the dadi ligand by
The generally accepted mechanism for transition-metal-
catalyzed cyclopropanations derived from diazoalkanes as-
sumes the transfer of the carbene fragment to the metal prior
PhHCN does not appear feasible, as the 1,3-dipolar addition
2
32
6
8
⧧
to its transfer to substrate. Little mechanistic work has been
mechanism was calculated to have a barrier of ΔG = 50.4
⧧
done on the process, likely due to the lack of observable
intermediates, aside from the elegant spectroscopic study by
Berry and Lancaster pertaining to dirhodium-catalyzed cyclo-
kcal/mol (ΔH = 53.7 kcal/mol). Figure 11 illustrates three
plausible mechanisms initiated by binding of PhHCN to
2
1
titanium, which is slightly unfavorable for both the η - (3.0
kcal/mol, red) and η -NNCHPh (2.7 kcal/mol, green) species
and significantly unfavorable for the carbon-bound η −C-
N CPhH adduct (20.6 kcal/mol). Two paths refer to direct
6
9
2
propanations. While the chemistry described herein is
intramolecular, it does suggest that concluding alkylidenes
must be intermediates in cyclopropanation may not be wise,
especially in instances where potent Lewis acidic centers are
involved. Note that Mindiola has recently shown that
alkylidene formation from Ph PCH is productive in
1
2
cyclopropanation (direct carbene transfer) from the diazo-
alkane adducts to the dadi ligand, and the third involves the
intermediacy of the titanium alkylidene (via TiCHPh, blue).
3
2
promoting alkane dehydrogenation via methylene transfer to
Ti(II), so titanium alkylidenes can form via a standard
1
The calculations support direct cyclopropanation from the η -
⧧
⧧
N CHPh adduct, as its ΔG of 18.2 kcal/mol (ΔH = 18.1
70
2
oxidation path. In the (dadi)Ti system, titanium alkylidenes
kcal/mol) is reasonably close to the crude experimental barrier
do not have similar stabilities.
of ∼15 kcal/mol.
While the transfer of PhHC: to titanium is more favorable
⧧
4. CONCLUSIONS
(
=
ΔG° = −14.1 kcal/mol), a considerable barrier is found (ΔG
1
m
31.0 kcal/mol) for dinitrogen loss via the unfavorable η -C−
N CPhH adduct at 20. 6 kcal/mol to form
dadi· ) Ti (C· (H)Ph) (2-C·(H)Ph). More importantly,
The formation of adducts [(dadi)Ti(L/X)] (1-L, m = 0,
−
−
i
−
−
neo
−
N CPh ; m = −1, X = Cl , N , O Pr , CH , Pe , CH
CH , CCPh , CCTMS , H(D) ) were prepared via L or X
2
2
2
2
3
3
↑
3− IV
↓
−
−
−
−
−
(
J
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
addition to (dadi)Ti(THF) (1-THF). No donor has proven to
be “oxidizing” enough to extract electron density from the
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
4−
dadi ligand. Previous work established that PR and CNR led
3
2
to Ti(IV) species, and all of the donors utilized herein
generate [{(dadi) }Ti (L/X)] , although structural evidence
AUTHOR INFORMATION
4
−
IV
n
■
Corresponding Author
was obtained for only 1-Cl·Li and 1-CH . Even when potential
3
−
*Tel.: 607-255-7220. E-mail: ptw2@cornell.edu.
2
e oxidants are added, redox changes at the ligand are difficult
to realize. Organoazides AdN3 and Me SiN3 led to the
ORCID
3
formation of imide species (dadi)TiNR (2NR, R = Ad,
Thomas R. Cundari: 0000-0003-1822-6473
Peter T. Wolczanski: 0000-0003-4801-0614
Notes
SiMe ), and the structure of 2NAd clearly shows oxidation
3
2−
of the ligand to (dadi) . In contrast, attempts to prepare
alkylidenes in a related fashion from Ph CN and PhHCN
2
2
2
The authors declare no competing financial interest.
failed to yield the desired (dadi)TiCHRR′ species.
In the case of PhHCN , its addition to (dadi)Ti(THF) (1-
2
ACKNOWLEDGMENTS
THF) afforded {PhC H (-NC H -2-NAr) }Ti(THF) (3), a
3
3
6
4
2
■
1
4−
complex in which the CC bond in the backbone of (dadi)
Support from the National Science Foundation (CHE-
402149; CHE-1664580) and Cornell University is gratefully
was cyclopropanated. Initially, this reaction appeared to be
analogous to previous nitrene insertions, but calculations
suggested the contrary. The reaction that would form an
alkylidene upon dinitrogen extrusion was calculated to yield
acknowledged, as is the U.S. Department of Energy, Office of
Basic Energy Sciences for partial support of this research
(
TRC, DE-FG02-03ER15387). NSF support for the CCB
↑
3− IV
↓
(
dadi ) Ti (C· (H)Ph) (2-C·(H)Ph), a complex in which
NMR facility (NSF-MRI CHE-1531632) is appreciated, as is
technical aid from Ivan Keresztes. We thank Bufan Zhang for
analytical support. This paper is dedicated to Ernesto Carmona
formation of a full titanium−carbon double bond is
incomplete. The alkylidene is not a potent enough oxidant,
and the chelate is in the (dadi)3 state, rendering 2-C·(H)Ph
highly reactive. It would be expected to immediately attack the
−
(
University of Seville), whose research in organometallic
chemistry, especially metal−carbon double bonds, serves as
inspiration for parts of this work.
“imine” nitrogen to generate a metallaaziridene, from which
further reactivity has large activation energies. It is likely that
N loss only occurs after or during cyclopropanation, which is
2
REFERENCES
1
■
calculated to occur from an η -N CHPh adduct.
2
(
1) Heins, S. P.; Morris, W. D.; Wolczanski, P. T.; Lobkovsky, E. B.;
It was immediately recognized that reversible C−C bond
Cundari, T. R. Nitrene Insertion into CC and CH Bonds of Diamide-
diimine Ligated Chromium and Iron Complexes. Angew. Chem., Int.
Ed. 2015, 54, 14407−14411.
formation from {PhC H (-NC H -2-NAr) }Ti(THF) (3)
3
3
6
4
2
could be a means of electron storage, a different construct of
redox noninnocence (RNI). In this case, the β-hydrogen on
the cyclopropane ring of 3 has proven to be a hindrance, as
indicated by treatment of the compound with Ph CN , which
(
2) Heins, S. P.; Wolczanski, P. T.; Cundari, T. R.; MacMillan, S. N.
Redox non-innocence permits catalytic nitrene carbonylation by
(dadi)TiNAd (Ad = adamantyl). Chem. Sci. 2017, 8, 3410−3418.
(3) Katsuki, T. Azide compounds: Nitrogen sources for atom-
efficient and ecologically benign nitrogen-atom-transfer reactions.
Chem. Lett. 2005, 34, 1304−1309.
4) Huang, X. Y.; Bergsten, T. M.; Groves, J. T. Manganese-
Catalyzed Late-Stage Aliphatic C-H Azidation. J. Am. Chem. Soc.
015, 137, 5300−5303.
5) Wigley, D. E.; Karlin, K. D. Organoimido Complexes of the
2
2
2
yielded a nacnac derivative, {PhC(CHNC H -2-NAr) }Ti(η -
6
4
2
HNNCPh ) (4), upon hydrogen transfer. Construction of
2
ligand systems capable of RNI via reversible C−C bond
formation is now being sought through application of related
chelates with two constituents in the β-position.
(
2
(
5
. EXPERIMENTAL SECTION
Transition-metals. Prog. Inorg. Chem. 1994, 42, 239−482.
(6) Nugent, W. A.; Mayer, J. M. Metal−Ligand Multiple Bonds;
Wiley-Interscience: New York, 1988.
Full experimental details are given in the Supporting Information,
including gradient diffusion plots, X-ray crystal structure information,
computational procedures, synthetic procedures, and spectra.
Qualitative descriptions of the synthetic experiments and crystallo-
graphic data collection and refinements are given in the schemes,
figures, and tables.
(7) Wolczanski, P. T. Flipping the Oxidation State Formalism:
Charge Distribution in Organometallic Complexes as Reported by
Carbon Monoxide. Organometallics 2017, 36, 622−631.
(8) (a) Peloso, R.; Carmona, E. Non-heteroatom-substituted
alkylidene complexes of groups 10 and 11. Coord. Chem. Rev. 2018,
355, 116−132. (b) Schrock, R. R. High Oxidation State Multiple
Metal-carbon Bonds. Chem. Rev. 2002, 102, 145−179. (c) Vougiou-
kalakis, G. C.; Grubbs, R. H. Ruthenium-based Heterocyclic Carbene-
coordinated Olefin Metathesis Catalysts. Chem. Rev. 2010, 110,
746−1787. (d) Esteruelas, M. A.; Lopez, A. M.; Olivan, M. Osmium-
carbon double bonds: Formation and reactions. Coord. Chem. Rev.
007, 251, 795−840.
9) (a) Bruckner, R. Organic Mechanisms; Harmata, M., Ed.;
Springer: Berlin, 2010. (b) Candeias, N. R.; Afonso, C. A. M.
Developments in the Photochemistry of Diazo Compounds. Curr.
Org. Chem. 2009, 13, 763−787. (c) Engel, P. S. Mechanism of the
Thermal and Photochemical Decomposition of Azoalkanes. Chem.
Rev. 1980, 80, 99−150. (d) Crawford, R. J.; Mishra, A. Mechanism of
Thermal Decomposition of 1-Pyrazolines and Its Relationship to
Cyclopropane Isomerizations. J. Am. Chem. Soc. 1966, 88, 3963−
3969.
ASSOCIATED CONTENT
Supporting Information
■
*
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.organo-
met.8b00188.
1
2
(
Gradient diffusion plots, X-ray crystal structure
information, computational procedures, synthetic pro-
cedures, and spectra (PDF)
Accession Codes
CCDC 1836208−1836212 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
K
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(
10) (a) Levesque, E.; Goudreau, S. R.; Charette, A. B. Improved
ligand: iron-carbon double bond stabilized by tetramethyldibenzote-
traazaannulene. Chem. Commun. 1997, 2297−2298.
Zinc-Catalyzed Simmons-Smith Reaction: Access to Various 1,2,3-
Trisubstituted Cyclopropanes. Org. Lett. 2014, 16, 1490−1493.
b) Creary, X. Tosylhydrazome Salt Pyrolyses: Phenyldiazomethanes.
(26) Esposito, V.; Solari, E.; Floriani, C.; Re, N.; Rizzoli, C.; Chiesi-
Villa, A. Binding and redox properties of iron(II) bonded to an oxo
surface modeled by calix[4]arene. Inorg. Chem. 2000, 39, 2604−2613.
(27) Li, Y.; Huang, J.-S.; Zhou, Z.-Y.; Che, C.-M.; You, X.-Z.
Remarkably stable iron porphyrins bearing nonheteroatom-stabilized
carbene or (Alkoxycarbonyl) carbenes: Isolation, X-ray crystal
structures, and carbon atom transfer reactions with hydrocarbons. J.
Am. Chem. Soc. 2002, 124, 13185−13193.
(
Org. Synth. 1986, 64, 207−216.
11) Edema, J. J. H.; Duchateau, R.; Gambarotta, S.; Hynes, R.;
Gabe, E. Novel Titanium(II) Amine Complexes L TiCl [L = 1/2
(
4
2
N,N,N′,N′-Tetramethylethylenediamine (TMEDA), 1,2 N,N,N′-
Trimethylethylenediamine, Pyridine, 1/2 2,2′-Bipyridine]: Synthesis
and Crystal Structure of Monomeric trans-(TMEDA) TiCl . Inorg.
Chem. 1991, 30, 154−156.
(
Lobkovsky, E. B.; Pierpont, A. W.; Cundari, T. R. Synthetic
Approaches to (smif) Ti (smif = 1,3-di-(2-pyridyl)-2-azaallyl) Reveal
Redox Non-Innocence and C-C Bond-Formation. Inorg. Chem. 2012,
2
2
(28) (a) Russell, S. K.; Hoyt, J. M.; Bart, S. C.; Milsmann, C.;
Stieber, S. C. E.; Semproni, S. P.; DeBeer, S.; Chirik, P. J. Synthesis,
electronic structure and reactivity of bis(imino)pyridine iron carbene
complexes: evidence for a carbene radical. Chem. Sci. 2014, 5, 1168−
1174. (b) Russell, S. K.; Lobkovsky, E.; Chirik, P. J. N-N Bond
Cleavage in Diazoalkanes by a Bis(imino)pyridine Iron Complex. J.
Am. Chem. Soc. 2009, 131, 36−37.
(29) Iluc, V. M.; Hillhouse, G. L. Three-Coordinate Nickel Carbene
Complexes and Their One-Electron Oxidation Products. J. Am. Chem.
Soc. 2014, 136, 6479−6488.
(30) Hanna, T. E.; Keresztes, I.; Lobkovsky, E.; Bernskoetter, W. H.;
Chirik, P. J. Synthesis of a base-free titanium imido and a transient
alkylidene from a titanocene dinitrogen complex. Studies on TiNR
hydrogenation, nitrene group transfer, and comparison of 1,2-addition
rates. Organometallics 2004, 23, 3448−3458.
(31) Polse, J. L.; Kaplan, A. W.; Andersen, R. A.; Bergman, R. G.
Synthesis of an eta(2)-N-2-titanium diazoalkane complex with both
imido- and metal carbene-like reactivity patterns. J. Am. Chem. Soc.
1998, 120, 6316−6328.
(32) (a) Davies, H. M. L.; Antoulinakis, E. G. Intermolecular Metal-
Catalyzed Carbenoid Cyclopropanations. In Organic Reactions;
Overman, L. E., Ed.; John Wiley & Sons: New York, 2001. (b) Davies,
H. M. L.; Beckwith, R. E. J. Catalytic enantioselective C-H activation
by means of metal-carbenoid-induced C-H insertion. Chem. Rev.
2003, 103, 2861−2903.
(33) Beckhaus, R.; Santamaria, C. Carbene complexes of titanium
group metals - formation and reactivity. J. Organomet. Chem. 2001,
617−618, 81−97.
(34) Dartiguenave, M.; Menu, M. J.; Deydier, E.; Dartiguenave, Y.;
Siebald, H. Crystal and molecular structures of transition metal
complexes with N- and C-bonded diazoalkane ligands. Coord. Chem.
Rev. 1998, 178-180, 623−663.
(35) Reich, H. J.; Borst, J. P.; Dykstra, R. R.; Green, D. P. A Nuclear
Magnetic Resonance Spectroscopic Technique for the Character-
ization of Lithium Ion-pair Structures in THF and THF/HMPA
Solution. J. Am. Chem. Soc. 1993, 115, 8728−8741.
(36) Fraenkel, G.; Subramanian, S.; Chow, A. The Carbon-lithium
Bond in Monomeric Aryllithiums - Dynamics of Exchange,
Relaxation, and Rotation. J. Am. Chem. Soc. 1995, 117, 6300−6307.
(37) Wu, D.; Chen, A.; Johnson, C. An Improved Diffusion-ordered
Spectroscopy Experiment Incorporating Bipolar-Gradient Pulses. J.
Magn. Reson., Ser. A 1995, 115, 260−264.
(38) Jerschow, A.; Muller, N. Suppression of convection artifacts in
stimulated-echo diffusion experiments. Double-stimulated-echo ex-
periments. J. Magn. Reson. 1997, 125, 372−375.
(39) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. Tables of Bond Lengths Determined by X-ray and
Neutron Diffraction. 1. Bond Lengths in Organic Compounds. J.
Chem. Soc., Perkin Trans. 2 1987, S1−S19.
(40) Pauling, L. Atomic Radii and Interatomic Distances in Metals. J.
Am. Chem. Soc. 1947, 69, 542−553.
(41) (a) Hazari, N.; Mountford, P. Reactions and applications of
titanium imido complexes. Acc. Chem. Res. 2005, 38, 839−849.
(b) Schwarz, A. D.; Nielson, A. J.; Kaltsoyannis, N.; Mountford, P.
The first group 4 metal bis(imido) and tris(imido) complexes. Chem.
Sci. 2012, 3, 819−824.
(42) (a) McDade, C.; Green, J. C.; Bercaw, J. E. A Kinetic and
M e c h a n i s t i c S t u d y o f t h e T h e r m o l y s i s o f B i s -
(pentamethylcyclopentadienyl)dimethyltitanium(IV). Organometallics
12) Frazier, B. A.; Wolczanski, P. T.; Keresztes, I.; DeBeer, S.;
2
5
(
1, 8177−8186.
13) Williams, V. A.; Wolczanski, P. T.; Sutter, J.; Meyer, K.;
Lobkovsky, E. B.; Cundari, T. R. Iron Complexes Derived from
−
n
{
nacnac-(CH py) } and {nacnac-(CH py)(CHpy)} Ligands: Stabi-
2 2 2
lization of Fe(II) via Redox Non-innocence. Inorg. Chem. 2014, 53,
459−4474.
14) Vogel, C.; Heinemann, F. W.; Sutter, J.; Anthon, C.; Meyer, K.
An iron nitride complex. Angew. Chem., Int. Ed. 2008, 47, 2681−2684.
15) Sabenya, G.; Lazaro, L.; Gamba, I.; Martin-Diaconescu, V.;
4
(
(
Andris, E.; Weyhermuller, T.; Neese, F.; Roithova, J.; Bill, E.; Lloret-
Fillol, J.; Costas, M. Generation, Spectroscopic, and Chemical
Characterization of an Octahedral Iron(V)-Nitrido Species with a
Neutral Ligand Platform. J. Am. Chem. Soc. 2017, 139, 9168−9177.
(
16) Walstrom, A.; Pink, M.; Yang, X.; Tomaszewski, J.; Baik, M.-H.;
Caulton, K. G. A facile approach to a d(4) RuN: Moiety. J. Am.
Chem. Soc. 2005, 127, 5330−5331.
(
17) Maity, A. K.; Murillo, J.; Metta-Magana, A. J.; Pinter, B.;
Fortier, S. A Terminal Iron(IV) Nitride Supported by a Super Bulky
Guanidinate Ligand and Examination of Its Electronic Structure and
Reactivity. J. Am. Chem. Soc. 2017, 139, 15691−15700.
(
18) Schendzielorz, F. S.; Finger, M.; Volkmann, C.; Wu
̈
rtele, C.;
Schneider, S. A Terminal Osmium(IV) Nitride: Ammonia Formation
and Ambiphilic Reactivity. Angew. Chem., Int. Ed. 2016, 55, 11417−
1
1420.
(
19) (a) Scheibel, M. G.; Askevold, B.; Heinemann, F. W.; Reijerse,
E. J.; de Bruin, B.; Schneider, S. Closed-shell and open-shell square-
planar iridium nitrido complexes. Nat. Chem. 2012, 4, 552−555.
b) Scheibel, M. G.; Wu, Y. L.; Stuckl, A. C.; Krause, L.; Carl, E.;
Stalke, D.; de Bruin, B.; Schneider, S. Synthesis and Reactivity of a
Transient, Terminal Nitrido Complex of Rhodium. J. Am. Chem. Soc.
(
2
(
013, 135, 17719−17722.
20) Tran, B. L.; Krzystek, J.; Ozarowski, A.; Chen, C. H.; Pink, M.;
Karty, J. A.; Telser, J.; Meyer, K.; Mindiola, D. J. Formation and
Reactivity of the Terminal Vanadium Nitride Functionality. Eur. J.
Inorg. Chem. 2013, 2013, 3916−3929.
(
21) Atienza, C. C. H.; Bowman, A. C.; Lobkovsky, E.; Chirik, P. J.
Photolysis and Thermolysis of Bis(imino)pyridine Cobalt Azides: C-
H Activation from Putative Cobalt Nitrido Complexes. J. Am. Chem.
Soc. 2010, 132, 16343−16345.
(
22) Schoffel, J.; Rogachev, A. Y.; DeBeer George, S.; Burger, P.
̈
Isolation and Hydrogenation of a Complex with a Terminal Iridium-
Nitrido Bond. Angew. Chem., Int. Ed. 2009, 48, 4734−4738.
(
Neese, F.; Wiedhardt, K. An octahedral coordination complex of
iron(VI). Science 2006, 312, 1937−1941.
(
23) Berry, J. F.; Bill, E.; Bothe, E.; DeBeer George, S.; Mienert, B.;
24) (a) Schwab, P.; Grubbs, R. H.; Ziller, J. W. Synthesis and
applications of RuCl (CHR′)(PR ) : The influence of the
2
3 2
alkylidene moiety on metathesis activity. J. Am. Chem. Soc. 1996,
1
18, 100−110. (b) Schwab, P.; France, M. B.; Ziller, J. W.; Grubbs, R.
H. A Series of Well-defined Metathesis Catalysts - Synthesis of
RuCl (CHR′)(PR ) and Its Reactions. Angew. Chem., Int. Ed. Engl.
2
3 2
1
(
995, 34, 2039−2041.
25) Klose, A.; Solari, E.; Floriani, C.; Re, N.; Chiesi-Villa, A.;
Rizzoli, C. Iron-carbene functionalities supported by a macrocyclic
L
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
1
982, 1, 1629−1634. (b) Bulls, A. R.; Schaefer, W. P.; Serfas, M.;
Temperature Dehydrogenation of Ethane, Propane, Linear Alkanes
C4-C8, and Some Cyclic Alkanes by Titanium-Carbon Multiple
Bonds. J. Am. Chem. Soc. 2013, 135, 14754−14767. (b) Cavaliere, V.
N.; Crestani, M. G.; Pinter, B.; Pink, M.; Chen, C.-H.; Baik, M.-H.;
Mindiola, D. J. Room Temperature Dehydrogenation of Ethane to
Ethylene. J. Am. Chem. Soc. 2011, 133, 10700−10703.
(54) Flores, J. A.; Cavaliere, V. N.; Buck, D.; Pinter, B.; Chen, G.;
Crestani, M. G.; Baik, M.-H.; Mindiola, D. J. Methane activation and
exchange by titanium-carbon multiple bonds. Chem. Sci. 2011, 2,
1457−1462.
Bercaw, J. E. Intramolecular C-H Bond Activation of Benzyl Ligands
by Metalated Cyclopentadienyl Derivatives of Permethylhafnocene -
Molecular Structure of (η -C Me )(η ,η -C Me CH )HfCH C H
and the Mechanism of Rearrangement to its Hafnabenzocyclobutene
Tautomer (η -C Me ) HfCH -o-C H . Organometallics 1987, 6,
5
5
1
5
5
5
4
2
2
6
5
5
5
5
2
2
6
4
1
(
219−1226.
43) (a) van Doorn, J. A.; van der Heijden, H.; Orpen, A. G.
Tantalum and Titanium Alkylidene Complexes Bearing Phosphi-
noalkoxide Ligands - Reversible Ortho-metalation of a Titanium
Alkylidene. Organometallics 1994, 13, 4271−4277. (b) van Doorn, J.
A.; van der Heijden, H.; Orpen, A. G. Titanium Alkylidenes via
Dineopentyl Complexes. Organometallics 1995, 14, 1278−1283.
(55) (a) Fan, H.; Fout, A. R.; Bailey, B. C.; Pink, M.; Baik, M.-H.;
Mindiola, D. J. Understanding intermolecular C-F bond activation by
a transient titanium neopentylidyne: experimental and theoretical
studies on the competition between 1,2-CF bond addition and [2 +
(
44) (a) Chamberlain, L. R.; Rothwell, I. P.; Huffman, J. C.
Intramolecular Activation of Aliphatic Carbon Hydrogen Bonds at
Tantalum(V) Metal Centers - A Comparison of Activation by Methyl
and Methylidene Functional Groups. J. Am. Chem. Soc. 1986, 108,
2
4
]-cycloaddition/beta-fluoride elimination. Dalton Trans. 2013, 42,
163−4174. (b) Kurogi, T.; Carroll, P. J.; Mindiola, D. J. A radical
coupled pathway to a stable and terminally bound titanium
1
502−1509. (b) Vilardo, J. S.; Lockwood, M. A.; Hanson, L. G.;
methylidene. Chem. Commun. 2017, 53, 3412−3414.
Clark, J. R.; Parkin, B. C.; Fanwick, P. E.; Rothwell, I. P.
Intramolecular activation of aromatic C-H bonds at tantalum(v)
metal centers: evaluating cyclometallation ’resistant’ and ’immune’
aryloxide ligation. J. Chem. Soc., Dalton Trans. 1997, 3353−3362.
(56) Lindley, B. M.; Swidan, A.; Lobkovsky, E. B.; Wolczanski, P. T.;
Adelhardt, M.; Sutter, J.; Meyer, K. Fe(IV) alkylidenes via protonation
of Fe(II) vinyl chelates and a comparative Mossbauer spectroscopic
study. Chem. Sci. 2015, 6, 4730−4736.
57) (a) Franceschi, F.; Solari, E.; Scopelliti, R.; Floriani, C. Metal-
̈
(
45) Plundrich, G. T.; Wadepohl, H.; Gade, L. H. Synthesis and
(
Reactivity of Group 4 Metal Benzyl Complexes Supported by
mediated transfer of electrons between two different C-C single bonds
that function as electron-donor and electron-acceptor units. Angew.
Chem., Int. Ed. 2000, 39, 1685−1687. (b) Crescenzi, R.; Solari, E.;
Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. One- and two-electron
oxidative pathways leading to cyclopropane-containing oxidized
porphyrinogens and C-C-coupled porphyrinogens from alkali cation
and transition metal meso-octaethylporphyrinogen complexes. J. Am.
Chem. Soc. 1999, 121, 1695−1706. (c) Gallo, E.; Solari, E.; Re, N.;
Floriani, C.; Chiesi-Villa, A.; Rizzoli, C. Carbon-carbon bonds
functioning as electron shuttles: The generation of electron-rich
manganese(II) Schiff base complexes and their redox chemistry. J.
Am. Chem. Soc. 1997, 119, 5144−5154. (d) Gambarotta, S.; Floriani,
C.; Chiesi-Villa, A.; Guastini, C. Carbon-carbon Bond Formation and
Cleavage Resulting from a Long-range Metal-promoted Redox
Process in the Reactions of Nickel(II) Complexes of N,N′-ortho-
Phenylenebid(salicylideneamine). J. Chem. Soc., Chem. Commun.
Carbazolide-Based PNP Pincer Ligands. Inorg. Chem. 2016, 55, 353−
3
65.
(
46) (a) van der Heijden, H.; Hessen, B. Intermolecular C-H
Activation by Reactive Titanocene Alkylidene Intermediates. J. Chem.
Soc., Chem. Commun. 1995, 145−146. (b) van der Heijden, H.;
Hessen, B. ’Tucked-in’ titanocene alkyls and alkylidenes. Inorg. Chim.
Acta 2003, 345, 27−36. (c) Deckers, P. J. W.; Hessen, B. C-H bond
activation processes in cationic and neutral titanium benzyl
compounds with cyclopentadienyl-arene ligands. Organometallics
2
(
002, 21, 5564−5575.
47) Zhang, S.; Tamm, M.; Nomura, K. 1,2-C-H Activation of
Benzene Promoted by (Arylimido)vanadium(V)-Alkylidene Com-
plexes: Isolation of the Alkylidene, Benzyne Complexes. Organo-
metallics 2011, 30, 2712−2720.
(
48) Andino, J. G.; Kilgore, U. J.; Pink, M.; Ozarowski, A.; Krzystek,
J.; Telser, J.; Baik, M.-H.; Mindiola, D. J. Intermolecular C-H bond
activation of benzene and pyridines by a vanadium(III) alkylidene
including a stepwise conversion of benzene to a vanadium-benzyne
complex. Chem. Sci. 2010, 1, 351−356.
1982, 0, 756−758. (e) Gambarotta, S.; Mazzanti, M.; Floriani, C.;
Zehnder, M. A Tetranuclear Polyfunctional Sodium-vanadium(III)
Complex Containing a Vanadium(III)-vanadium(III) Double-bond. J.
Chem. Soc., Chem. Commun. 1984, 0, 1116−1118. (f) Gambarotta, S.;
Urso, F.; Floriani, C.; Chiesivilla, A.; Guastini, C. Carbon-carbon
Bond Forming and Breaking by a Metal-assisted Redo Process in a
Nickel(II) Schiff-base Complex. Inorg. Chem. 1983, 22, 3966−3972.
(
49) (a) Wada, K.; Pamplin, C. B.; Legzdins, P.; Patrick, B. O.;
Tsyba, I.; Bau, R. Intermolecular activation of hydrocarbon C-H
bonds under ambient conditions by 16-electron neopentylidene and
benzyne complexes of molybdenum. J. Am. Chem. Soc. 2003, 125,
(58) Hulley, E. B.; Wolczanski, P. T.; Lobkovsky, E. B. Carbon-
7
035−7048. (b) Adams, C. S.; Legzdins, P.; Tran, E. C-H activation
carbon Bond Formation from Azaallyl and Imine Couplings About
of substituted arenes by tungsten alkylidene complexes: Products,
Metal-metal Bonds. J. Am. Chem. Soc. 2011, 133, 18058−18061.
selectivity, and mechanism. Organometallics 2002, 21, 1474−1486.
(59) Frazier, B. A.; Williams, V. A.; Wolczanski, P. T.; Bart, S.;
(
c) Pamplin, C. B.; Legzdins, P. Thermal activation of hydrocarbon
Meyer, K.; Cundari, T. R.; Lobkovsky, E. B. C-C Bond Formation and
Related Reactions at the CNC Backbone in (smif)FeX (smif = 1,3-di-
C-H bonds by Cp*M(NO) complexes of molybdenum and tungsten.
Acc. Chem. Res. 2003, 36, 223−233.
(
2-pyridyl)-2-azaallyl): Dimerizations, 3 + 2 Cyclization, and
(
50) Cheon, J.; Rogers, D. M.; Girolami, G. S. Mechanistic studies of
Nucleophilic Attack; Transfer Hydrogenations and Alkyne Trimeriza-
the thermolysis of tetraneopentyltitanium(IV) 0.1. Solution evidence
that titanium alkylidenes activate saturated hydrocarbons. J. Am.
Chem. Soc. 1997, 119, 6804−6813.
tion (X = N(TMS) , dpma (di-(2-pyridyl-methyl)-amide)). Inorg.
2
Chem. 2013, 52, 3295−3312.
(60) Williams, V. A.; Hulley, E. B.; Wolczanski, P. T.; Lancaster, K.
(
51) Cavaliere, V. N.; Mindiola, D. J. Methane: a new frontier in
organometallic chemistry. Chem. Sci. 2012, 3, 3356−3365.
M.; Lobkovsky, E. B. Pushing the limits of redox non-innocence:
4
n
(
52) (a) Bailey, B. C.; Fan, H.; Huffman, J. C.; Baik, M.-H.;
pseudo square planar [{κ -Me
2
C(CH
2
NCHpy)
2
}Ni] (n = 2+, 1+,
Mindiola, D. J. Intermolecular C-H bond activation reactions
promoted by transient titanium alkylidynes. Synthesis, reactivity,
kinetic, and theoretical studies of the Ti C linkage. J. Am. Chem. Soc.
0, −1, −2) favor Ni(II). Chem. Sci. 2013, 4, 3636−3648.
(61) Williams, V. A.; Wolczanski, P. T.; Sutter, J.; Meyer, K.;
Cundari, T. R.; Lobkovsky, E. B. Iron Complexes Derived from
−
n
2
007, 129, 8781−8793. (b) Bailey, B. C.; Fan, H.; Baum, E. W.;
{nacnac-(CH py) } and {nacnac-(CH py)(CHpy)} Ligands: Stabi-
2 2 2
Huffman, J. C.; Baik, M.-H.; Mindiola, D. J. Intermolecular C-H bond
lization of Fe(II) via Redox Non-innocence. Inorg. Chem. 2014, 53,
4459−4474.
(62) Morris, W. D.; Wolczanski, P. T.; Sutter, J.; Meyer, K.; Cundari,
T. R.; Lobkovsky, E. B. Iron and Chromium Complexes Containing
Tridentate Chelates Based on Nacnac and Imino- and Methyl-
activation promoted by a titanium alkylidyne. J. Am. Chem. Soc. 2005,
1
27, 16016−16017.
53) (a) Crestani, M. G.; Hickey, A. K.; Gao, X. F.; PInter, B.;
Cavaliere, V. N.; Ito, J.-I.; Chen, C. H.; Mindiola, D. J. Room
(
M
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Pyridine Components: Triggering C-C(X) Bond Formation. Inorg.
Chem. 2014, 53, 7467−7484.
(
63) Hulley, E. B.; Williams, V. A.; Morris, W. D.; Wolczanski, P. T.;
Hernandez-Burgos, K.; Lobkovsky, E. B.; Cundari, T. R. Disparate
́
Reactivity from Isomeric {Me C(CH NCHpy) } and {Me C-
2
2
2
2
(
2
CHNCH py) } Chelates in Iron Complexation. Polyhedron
2
2
014, 84, 182−191.
(
64) Lindley, B. M.; Wolczanski, P. T.; Cundari, T. R.; Lobkovsky,
E. B. 1st Row Transition Metal and Lithium Pyridine-ene-amide
Complexes Exhibiting N- and C-Isomers and Ligand-based Activation
of Benzylic C-H Bonds. Organometallics 2015, 34, 4656−4688.
(
65) Jacobs, B. P.; Wolczanski, P. T.; Lobkovsky, E. B. Oxidatively
Triggered Carbon-carbon Bond Formation in Ene-amide Complexes.
Inorg. Chem. 2016, 55, 4223−4232.
(
66) (a) Dzik, W. I.; Xu, X.; Zhang, X. P.; Reek, J. N. H.; de Bruin,
B. ’Carbene Radicals’ in Co-II(por)-Catalyzed Olefin Cyclopropana-
tion. J. Am. Chem. Soc. 2010, 132, 10891−10902. (b) Dzik, W. I.;
Zhang, X. P.; de Bruin, B. Redox Noninnocence of Carbene Ligands:
Carbene Radicals in (Catalytic) C-C Bond Formation. Inorg. Chem.
2
(
011, 50, 9896−9903.
67) Dzik, W. I.; de Bruin, B. Open-shell organometallics: reactivity
at the ligand. Organometallic Chemistry 2011, 37, 46.
68) Branchadell, V.; Muray, E.; Oliva, A.; Ortun
(
̃
o, R. M.;
Rodríguez-García, C. Theoretical study of the mechanism of the
addition of diazomethane to ethylene and formaldehyde. Comparison
of conventional ab initio and density functional methods. J. Phys.
Chem. A 1998, 102, 10106−10112.
(
69) Kornecki, K. P.; Briones, J. F.; Boyarskikh, V.; Fullilove, F.;
Autschbach, J.; Schrote, K. E.; Lancaster, K. M.; Davies, H. M. L.;
Berry, J. F. Direct Spectroscopic Characterization of a Transitory
Dirhodium Donor-Acceptor Carbene Complex. Science 2013, 342,
3
(
51−354.
70) Solowey, D. P.; Mane, M. V.; Kurogi, T.; Carroll, P. J.; Manor,
B. C.; Baik, M.-H.; Mindiola, D. J. A new and selective cycle for
dehydrogenation of linear and cyclic alkanes under mild conditions
using a base metal. Nat. Chem. 2017, 9, 1126−1132.
N
DOI: 10.1021/acs.organomet.8b00188
Organometallics XXXX, XXX, XXX−XXX