New sandwich and half-sandwich titanium hydrazido compounds

Article abstract of DOI:10.1021/om200068k

New mono- and bis-cyclopentadienyl terminal titanium hydrazido(2-) compounds were prepared by tert-butyl imide/N,N-disubstituted hydrazine exchange reactions. Reaction of Cp*Ti(N^tBu)Cl(py) (1) with Ph ₂NNH₂ gave the terminal hydrazide Cp*Ti(NNPh ₂)Cl(py) (4), whereas the corresponding reaction of CpTi(N ^tBu)Cl(py) gave the dimer Cp₂Ti₂(μ- η¹:η¹-NNPh₂)(μ-η²: η¹-NNPh₂)Cl₂. Reaction of 1 with Me ₂NNH₂ (1 equiv) also gave a dimer, Cp* ₂Ti₂(μ-η¹:η¹-NNMe ₂)(μ-η²:η¹-NNMe₂)Cl ₂ (8), while the reaction with 2 equiv of Me₂NNH ₂ gave Cp*Ti(η²-NHNMe₂)₂Cl (7) containing two η²-bound hydrazide(1-) ligands. Formation of 7 and 8 proceeds via a common intermediate, Cp*Ti(NH^tBu) (η²-NHNMe₂)Cl, observed by NMR spectroscopy. Reaction of 4 with LiNHNPh₂ gave the mixed hydrazide(2-)/hydrazide(1-) derivative Cp*Ti(NNPh₂)(NHNPh₂)(py) (10). The corresponding reaction of 1 formed Cp*Ti(N^tBu)(NHNPh ₂)(py), which rearranged to Cp*Ti(NH^tBu)(NNPh ₂)(py). The titanocene derivative Cp₂Ti(NNPh ₂)(py) (14) was prepared by reaction of Cp₂Ti(N ^tBu)(py) (13) with Ph₂NNH₂, whereas the corresponding reaction with Me₂NNH₂ gave mixtures including CpTi(NH^tBu)(μ-η¹:η¹- NNMe₂)(μ-η²:η¹-NNMe ₂)TiCp(η¹-Cp). The electronic structure of 14 was investigated by DFT and compared to that of the imido complex 13. Whereas the HOMO of the formally 20 valence electron compound 13 is a ligand-centered orbital based both on the Cp rings and on the imido N, in 14 this is the HOMO-1 and one of the Ti=N_α π-bonding MOs is the HOMO, destabilized by an N_α-N_β antibonding interaction.

Full text of DOI:10.1021/om200068k

ARTICLE
pubs.acs.org/Organometallics
New Sandwich and Half-Sandwich Titanium Hydrazido Compounds
Jonathan D. Selby,† Marta Feliz,‡ Andrew D. Schwarz,† Eric Clot,*,‡ and Philip Mountford*,†
†Chemistry Research Laboratory, Department of Chemistry, University of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.
‡Institut Charles Gerhardt, Universitꢀe Montpellier 2, CNRS 5253, cc 1501, Place Eugꢁene Bataillon, 34095 Montpellier Cedex 5, France
S Supporting Information
b
ABSTRACT:
New mono- and bis-cyclopentadienyl terminal titanium hydrazido(2ꢀ) compounds were prepared by tert-butyl imide/N,N-
disubstituted hydrazine exchange reactions. Reaction of Cp*Ti(NtBu)Cl(py) (1) with Ph2NNH2 gave the terminal hydrazide
Cp*Ti(NNPh2)Cl(py) (4), whereas the corresponding reaction of CpTi(NtBu)Cl(py) gave the dimer Cp2Ti2(μ-η1:η1-NNPh2)-
(μ-η2:η1-NNPh2)Cl2. Reaction of 1 with Me2NNH2 (1 equiv) also gave a dimer, Cp*2Ti2(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)Cl2
(8), while the reaction with 2 equiv of Me2NNH2 gave Cp*Ti(η2-NHNMe2)2Cl (7) containing two η2-bound hydrazide(1ꢀ)
ligands. Formation of 7 and 8 proceeds via a common intermediate, Cp*Ti(NHtBu)(η2-NHNMe2)Cl, observed by NMR
spectroscopy. Reaction of 4 with LiNHNPh2 gave the mixed hydrazide(2ꢀ)/hydrazide(1ꢀ) derivative Cp*Ti(NNPh2)-
(NHNPh2)(py) (10). The corresponding reaction of 1 formed Cp*Ti(NtBu)(NHNPh2)(py), which rearranged to Cp*Ti-
(NHtBu)(NNPh2)(py). The titanocene derivative Cp2Ti(NNPh2)(py) (14) was prepared by reaction of Cp2Ti(NtBu)(py) (13)
with Ph2NNH2, whereas the corresponding reaction with Me2NNH2 gave mixtures including CpTi(NHtBu)(μ-η1:η1-NNMe2)
(μ-η2:η1-NNMe2)TiCp(η1-Cp). The electronic structure of 14 was investigated by DFT and compared to that of the imido
complex 13. Whereas the HOMO of the formally 20 valence electron compound 13 is a ligand-centered orbital based both on the
Cp rings and on the imido N, in 14 this is the HOMOꢀ1 and one of the TidNR π-bonding MOs is the HOMO, destabilized by an
NRꢀNβ antibonding interaction.
’ INTRODUCTION
bond but also insertion into the TidNR and NRꢀNβ bonds and/or
NRꢀNβ bond cleavage.3f,g,5,9 Apart from Wiberg’s initial report of
Cp2Ti{NN(SiMe3)2}, no titanocene hydrazide has been reported,
although a structurally characterized zirconium example is known.7a
Two reports of half-sandwich terminal group 4 hydrazides have
appeared containing additional chelating N,N0-donor groups.9a,l
Here we report our recent results in the area of titanium hydrazido
chemistry, targeting new sandwich and half-sandwich complexes.
We hope that the new compounds reported herein will provide
a platform for further future reactivity studies as well as aiding
in understanding the differences between hydrazido and imido
compounds.
A wide range of titanium imido compounds (L)TidNR (R =
alkyl or aryl) have now been synthesized and studied in detail with
regard to their structures, bonding, and reactivity, as summarized in a
series of reviews and articles.1,2 In contrast, the apparently related
hydrazido complexes (L)TidNNR2 were hardly developed at all
until relatively recently, although they have, for example, been
postulated as intermediates in hydrohydrazination catalysis.3 The
first report of a terminal titanium hydrazide was by Wiberg4 for the
synthesis of Cp2Ti{NN(SiMe3)2} from Cp2TiCl2 and Me3SiNN-
SiMe3, a reagent that decomposes above ꢀ35 °C. Subsequently we
found that Ti(NtBu)(Me4taa) reacted with Ph2NNH2 to give
Ti(NNPh2)(Me4taa) (H2Me4taa = tetramethyl dibenzotetraaza-
[14]annulene).5 However, the first structurally characterized exam-
ples only appeared in 2004 and 2005,3c,6 and to date relatively few
classes of titanium hydrazido compound are known. Nonetheless,
compounds containing the terminal TidNNR2 group (and their
zirconium counterparts7) show a range of exciting reactivity8
involving both saturated and unsaturated substrates. This involves
not only addition to the polar and unsaturated TidNR multiple
’ RESULTS AND DISCUSSION
Half-Sandwich Compounds. We have previously shown that
the half-sandwich tert-butyl imido complexes CpRTi(NtBu)-
Received: January 25, 2011
Published: March 31, 2011
r
2011 American Chemical Society
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Scheme 1. Reactions of CpRTi(NtBu)Cl(py) (CpR = Cp* (1)
or Cp (2)) with Ph2NNH2
Figure 1. Displacement ellipsoid plot (25% probability) of Cp*Ti-
(NNPh2)Cl(py) (4). H atoms are omitted.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Cp*Ti(NNPh2)Cl(py) (4)a
Cl(py) (CpR = Cp* (1) or Cp (2)) can be readily prepared from
Ti(NtBu)Cl2(py)n (n = 2 or 3) and either LiCp* or NaCp.10
Unfortunately, the corresponding reactions of the known9c Ti-
(NNPh2)Cl2(py)3 (3) with these metalated reagents gave un-
known mixtures. As an alternative approach we used the imido
compounds 1 and 2 themselves and Ph2NNH2 in an imide/
hydrazine exchange protocol,5,9a,9c,9g as shown in Scheme 1.
Similar approaches have been used to prepare half-sandwich
titanium aryl imido complexes.11
Ti(1)ꢀN(1)
1.734(2)
2.3532(9)
1.368(3)
1.411(4)
121.1
Ti(1)ꢀN(3)
Ti(1)ꢀCpcent
N(2)ꢀC(1)
2.179(2)
2.043
Ti(1)ꢀCl(1)
N(1)ꢀN(2)
N(2)ꢀC(7)
CpcentꢀTi(1)ꢀN(1)
CpcentꢀTi(1)ꢀCl(1)
N(1)ꢀN(2)ꢀC(1)
C(1)ꢀN(2)ꢀC(7)
1.443(4)
CpcentꢀTi(1)ꢀN(3)
Ti(1)ꢀN(1)ꢀN(2)
N(1)ꢀN(2)ꢀC(7)
111.5
116.6
163.5(2)
119.7(2)
115.8(2)
122.0(2)
a Cpcent is the computed Cp* ring carbon centroid.
Reaction of 1 with Ph2NNH2 in benzene at room temperature
gave the monomeric half-sandwich compound Cp*Ti(NNPh2)-
1
Cl(py) (4) in 83% isolated yield. When followed by H NMR
aryl imido and diphenyl hydrazido homologues have been noted
previously.6
spectroscopy in C6D6, the conversion was quantitative and the
expected tBuNH2 side-product was observed. No intermediates
(e.g., an amido-hydrazido(1ꢀ) species of the type Cp*Ti-
The reaction between CpTi(NtBu)Cl(py) (2) and Ph2NNH2
was assessed on the NMR tube scale in C6D6 (Scheme 1).
Immediate conversion to the known15 hydrazide-bridged com-
pound Cp2Ti2(μ-η1:η1-NNPh2)(μ-η2:η1-NNPh2)Cl2 (5) and
free pyridine was observed. Compound 5 was previously pre-
pared by reaction of CpTiCl3 with Ph2NNH2 and BuLi. Addition
of an excess of pyridine to solutions of 5 failed to convert it to a
monomeric analogue of 4, in contrast to our previous observa-
tions for Cp2Ti2(μ-NtBu)2Cl2, which can be converted to 2 in
this way.10 That 2 reacts with Ph2NNH2 to form dimeric 5
whereas Cp*Ti(NtBu)Cl(py) (1) forms monomeric 4 is readily
attributed to greater steric protection afforded by the C5Me5
ligand.
(NHtBu)(NHNPh2)) were observed. The H and 13C NMR
1
spectra of 4 show the expected resonances for Cp*, diphenyl
hydrazido, and pyridine ligands. Diffraction-quality crystals were
grown from a saturated pentane solution. The solid-state struc-
ture is shown in Figure 1, and selected bond distances and angles
are listed in Table 1.
Figure 1 confirms 4 as a pseudotetrahedral terminal hydrazido-
(2ꢀ) compound. The geometry is very similar to that of 1 itself,
and a number of aryl imido analogues Cp*Ti(NAr)Cl(py) (Ar =
i
t
i
2,6-C6H3Br2, 2,6-C6H3 Pr2, 2-C6H4 Bu, 2-C6H4 Pr).11b The
TiꢀCp* centroid, TiꢀCl, and TiꢀNpy distances are comparable
to those of Cp*Ti(NAr)Cl(py) but slightly shorter than in 1 due
to the higher labilizing ability of the tert-butyl imido ligand.1e,13
The main point of interest is the terminal TidNꢀNPh2 ligand,
10 examples of which have now been structurally characterized
according the current Cambridge Structural Database.14 The
TidNR and NRꢀNβ distances of 1.734(2) and 1.368(3) Å,
respectively, are equivalent within error to the known mean
values for this linkage and, by analogy with recent DFT calcula-
tions, indicative of a σ2π4 triple bond and formally dianionic
[NNPh2]2ꢀ ligands.6,9c,9e The TidNR distance in 4 is within the
range of TidNAr distances in Cp*Ti(NAr)Cl(py) (1.730(2)ꢀ
1.753(2) Å), but considerably longer than the TidNtBu bond in
1 (av 1.697(3) Å). Similar trends in TidN distances for alkyl and
The reactions of 1 with Me2NNH2 are summarized in Scheme 2.
The stoichiometric (1:1) reaction following mixing of the imide
and hydrazine in toluene or benzene at room temperature
proceeded over two to three days to form the hydrazide-bridged
dimer Cp*2Ti2(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)Cl2 (8). For-
mation of 8 was accompanied by several side-products including
the mono(hydrazido(1ꢀ)) species Cp*Ti(η2-NHNMe2)Cl2 (9)
and the bis(hydrazido(1ꢀ)) Cp*Ti(η2-NHNMe2)2Cl (7), in-
dicative of redistribution reactions. Compound 9 was indepen-
dently prepared from Cp*TiCl3 and LiNHNMe2 and structurally
characterized (see the SI for details). The homologue CpTi-
(η2-NHNMe2)Cl2 has been reported previously.16 Compound 7
is discussed further below. Preliminary NMR tube scale reactions
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ARTICLE
Scheme 2. Reactions of Cp*Ti(NtBu)Cl(py) (1) with Me2NNH2
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Cp*2Ti2(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)Cl2 (8)a
Ti(1)ꢀN(1)
Ti(1)ꢀN(3)
Ti(1)ꢀCl(1)
Ti(1)ꢀCpcent(1)
N(1)ꢀN(2)
N(3)ꢀN(4)
Cpcent(1)ꢀTi(1)ꢀN(1) 126.1
Cpcent(1)ꢀTi(1)ꢀN(3) 120.2
Cpcent(1)ꢀTi(1)ꢀCl(1) 111.6
1.903(2)
1.829(2)
Ti(2)ꢀN(1)
Ti(2)ꢀN(3)
2.003(2)
2.010(2)
2.217(2)
2.3271(5)
2.077
2.3600(5) Ti(2)ꢀN(4)
2.077
Ti(2)ꢀCl(2)
Ti(2)ꢀCpcent(2)
1.393(2)
1.384(2)
Cpcent(2)ꢀTi(2)ꢀN(1) 114.8
Cpcent(2)ꢀTi(2)ꢀN(3) 132.7
Cpcent(2)ꢀTi(2)ꢀN(4) 115.8
Cpcent(2)ꢀTi(2)ꢀCl(2) 111.8
N(1)ꢀN(2)ꢀC(1)
N(1)ꢀN(2)ꢀC(2)
N(3)ꢀN(4)ꢀC(4)
112.8(2)
113.8(2)
N(3)ꢀN(4)ꢀC(3)
115.7(2)
127.65(12)
a Cpcent(1) and Cpcent(2) are the computed Cp* ring centroids for Ti(1)
and Ti(2), respectively.
Figure 2. Displacement ellipsoid plot (30% probability) of Cp*2Ti2(μ-
η1:η1-NNMe2)(μ-η2:η1-NNMe2)Cl2 (8). H atoms are omitted.
process most likely involves a “windscreen wiper” type mechanism17
and an approximately C2h symmetric transition state where both
hydrazide ligands are bound in a μ-η1:η1-manner.
between Me2NNH2 and 2 in C6D6 showed the formation of a
pyridine-free product assumed to be analogous to 5 and 8. This
compound was not pursued on the preparative scale.
Formation of 8 presumably proceeds via transiently formed
Cp*Ti(NNMe2)Cl, which then dimerizes rather than being
trapped by pyridine as in the case of 4 above. Addition of extra
pyridine or DMAP (4-dimethylaminopyridine) to the reaction
mixture did not lead to a base-stabilized monomer. Likewise, 8
could not be cleaved by the addition of pyridine or DMAP.
Terminal TidNNMe2 groups are still relatively uncommon for
the group 4 metals because of the more nucleophilic nature of the
β-nitrogen when stabilizing phenyl substituents are absent. Non-
etheless, a number of terminal dimethyl hydrazido compounds
have now been structurally characterized for titanium where
polydentate chelating ligands have been employed.3c,g,9a,b,g The
most relevant example in this context is Cp*Ti{MeC(NiPr)2}-
(NNMe2), prepared from the corresponding tert-butyl imido
compound and Me2NNH2,9a in which the amidinate ligand pre-
vents dimerization.
Carrying out the initial addition of Me2NNH2 to 1 at ꢀ78 °C
in toluene followed by workup after three days and recrystalliza-
tion from benzene gave pure 8 in 50% isolated yield. The solid-
state structure is shown in Figure 2, and selected bond lengths
and angles are listed in Table 2. Figure 2 confirms the pyridine-
free, dimeric nature of 8. There are two types of bridging hydrazide
ligands: one is bound in a μ-η1:η1-manner, bridging only through
NR (i.e., N(1)); the other has μ-η2:η1-coordination with both NR
and Nβ (i.e., N(3) and N(4)) bonded to the second titanium. This
overall coordination mode is analogous to that in 5 and also
Bergman’s Cp4Zr2(μ-η1:η1-NNPh2)(μ-η2:η1-NNPh2).7a The
second common arrangement is for both bridging ligands to adopt
a μ-η2:η1-NNR2 coordination mode.3c,6 At room temperature the
1H and 13C NMR spectra show a time-averaged spectrum with
equivalent Cp* and β-NMe2 groups. On cooling to ꢀ30 °C in
toluene-d8, two separate sets of signals for these groups were
observed, consistent with the solid-state structure. The fluxional
Monitoring the reaction between 1 and Me2NNH2 in C6D6
showed the intermediate formation of Cp*Ti(NHtBu)(η2-
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Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Cp*Ti(η2-NHNMe2)2Cl (7)a
Ti(1)ꢀN(1)
1.882(2)
2.005(2)
2.4437(8)
1.411(3)
0.86(4)
105.5
Ti(1)ꢀN(2)
2.304(2)
2.157(2)
2.094
Ti(1)ꢀN(3)
Ti(1)ꢀN(4)
Ti(1)ꢀCl(1)
Ti(1)ꢀCp*cent
N(1)ꢀN(2)
N(3)ꢀN(4)
1.420(3)
0.86(4)
143.1
N(1)ꢀH(1)
N(3)ꢀH(2)
CpcentꢀTi(1)ꢀN(1)
CpcentꢀTi(1)ꢀN(3)
CpcentꢀTi(1)ꢀCl(1)
Ti(1)ꢀN(1)ꢀN(2)
Ti(1)ꢀN(3)ꢀH(2)
N(4)ꢀN(3)ꢀH(2)
CpcentꢀTi(1)ꢀN(2)
CpcentꢀTi(1)ꢀN(4)
Ti(1)ꢀN(1)ꢀH(1)
N(2)ꢀN(1)ꢀH(1)
Ti(1)ꢀN(3)ꢀN(4)
110.4
124.4
108.8
150(2)
116(2)
75.94(14)
87.57(15)
126(2)
110(3)
a Cpcent is the computed Cp* ring carbon centroid.
Figure 3. Displacement ellipsoid plot (25% probability) of Cp*Ti-
(η2-NHNMe2)2Cl (7). Carbon-bound H atoms are omitted. Nitrogen-
bound H atoms are drawn as spheres of arbitrary radius.
Ti(1)ꢀN(4) (2.157(2) Å). Five-legged piano stool complexes
are relatively unusual. It appears that the compact and chelating
nature of NHNMe2 permits the higher coordination number.
Compound 7 is the second example of a structurally authenti-
cated bis(η2-hydrazido(1ꢀ)) species.3c It is not clear why it
and the related 6 do not preferentially exist as the hydrazido
(2ꢀ)-amino isomeric alternatives Cp*Ti(NNMe2)(H2NR)Cl
(R = NMe2 or tBu, respectively), which would be the analogues
of 4. In this context we note Winter’s group 5 dialkyl hydrazido-
(2ꢀ)/dialkyl hydrazine complexes [M(NNR2)Cl2(η2-H2NNR2)
(TMEDA)]þ (M = Nb or Ta, NR2 = NMe2 or NC5H10).19
A number of imido-amino complexes of the type (L)Ti(NtBu)-
(H2NtBu) have been structurally characterized.14,20
To gain a better understanding of the structural relationships
between group 4 hydrazido(2ꢀ) and hydrazido(1ꢀ) ligands, the
compound Cp*Ti(NNPh2)(NHNPh2)(py) (10) was prepared
by the reaction of Cp*Ti(NNPh2)Cl(py) (4) with LiNHNPh2
(eq 1). For comparison, the mixed hydrazido(2ꢀ)/tert-butyl
amido derivative Cp*Ti(NNPh2)(NHtBu)(py) (11) was synthe-
sized by the same route.
NHNMe2)Cl (6) and free pyridine after one hour (Scheme 2).
Over two to three days the signals for 6 were replaced by those
t
for 8 and BuNH2. Attempts to isolate 6 on a preparative scale
were unsuccessful and led to mixtures, among which 8 was the
major product. The structural assignment of 6 as a mixed amide-
hydrazide(1ꢀ) compound is based on one- and two-dimensional
1H and 13C NMR spectra. For example, the CMe3 quaternary
carbon appears at δ13C = 58.9 ppm, consistent18 with an amido
rather than an imido group (for TidNtBu these invariably appear
in the range 70 ( 2ꢀ3 ppm1b,e) and which correlates with just
one of the two NH resonances at δ1H = 5.40 and 5.10 ppm. The
η2 coordination of the NHNMe2 ligand is proposed by analogy
with the structurally authenticated related compounds CpRTi-
(η2-NHNMe2)Cl2 (CpR = Cp or Cp* (9))16 and Cp*Ti-
(η2-NHNMe2)2Cl (7).
As mentioned, compound 7 was observed in minor amounts
in the 1:1 stoichiometric reaction of Cp*Ti(NtBu)Cl(py) (1)
with Me2NNH2. Changing the stoichiometry to 1:2 afforded
1
7 as a pale yellow solid in 62% isolated yield. The H NMR
resonances for the NH and NMe2 moieties of 7 are close to
those for the η2-NHNMe2 group in 6. When the reaction
was performed in C6D6 on the NMR tube scale, 7 was the
sole organometallic product, and the expected free pyridine
t
and BuNH2 side products were also observed. Compound
7 is stable in solution at room temperature for at least
several days. However, heating an NMR sample in C6D6 at
70 °C for 16 h gave irreversible conversion to dimeric 8 and free
Me2NNH2.
Both compounds have been structurally characterized, and the
molecular structures are presented in Figure 4. Selected distances
and angles are given in Tables 4 and 5, respectively. The solution
NMR data are consistent with the solid-state structures. For 11
the NHCMe3 hydrogen correlates with the CMe3 quaternary
Diffraction-quality crystals of 7 were grown by slowly cooling a
saturated hexane solution. The molecular structure is shown in
Figure 3, and selected distances and angles are listed in Table 3.
1
The solid-state structure of 7 is fully consistent with H NMR
carbon which appears at δ = 56.3 ppm, consistent with an
13C
data assuming fast exchange of the β-NMe2 groups. The TiꢀCp*
centroid and TiꢀCl distances are somewhat longer than their
counterparts in either 4 or 9, reflecting the higher coordination
number of 7. The two η2-hydrazido(1ꢀ) ligands are arranged in
an approximate “paddlewheel” geometry, with the [Ti(1), N(3),
N(4)] plane lying approximately perpendicular to the [Cp*
centroid, Ti(1), N(1), N(2)] plane. This differing orientation
has an influence on the TiꢀNR and TiꢀNβ distances. Thus
Ti(1)ꢀN(1) (1.882(2) Å) is shorter than Ti(1)ꢀN(3)
(2.005(2) Å), whereas Ti(1)ꢀN(2) (2.304(2) Å) is longer than
amido group being preserved in solution (see below for the
independently prepared hydrazido(1ꢀ)/tert-butyl imido isomer
Cp*Ti(NtBu)(NHNPh2)(py) (12)). There are only three struc-
turally authenticated η1-hydrazido(1ꢀ) compounds for group
47c,21 and none for titanium. Of these, one is for a η1-NHNPh2
ligand, namely, Zr(N2*Npy)(NHNPh2)Cl (NRꢀNβ = 1.427(8) Å;
ples of a mixed η1-hydrazido(2ꢀ)/η1-hydrazido(1ꢀ) complex
have been reported, namely, Mo(NNPh2)(NHNPh2)(acac)-
Cl2 and [Mo(NNPh2)(NHNPh2)Cl4]ꢀ.22,23 The ModNR and
t
N2*Npy = (2-NC5H4)CMe(CH2NSiMe2 Bu)2).7c Two exam-
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Figure 4. Displacement ellipsoid plot (20% probability) of Cp*Ti(NNPh2)(NHNPh2)(py) (10, left) and Cp*Ti(NNPh2)(NHtBu)(py) (11, right).
Carbon-bound H atoms are omitted. H(1) is drawn as a sphere of arbitrary radius.
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
Cp*Ti(NNPh2)(NHNPh2)(py) (10)a
Table 5. Selected Bond Lengths (Å) and Angles (deg) for
Cp*Ti(NNPh2)(NHtBu)(py) (11)a
Ti(1)ꢀN(1)
1.742(2)
1.976(2)
2.201(2)
2.080
N(2)ꢀC(7)
N(3)ꢀN(4)
N(3)ꢀH(1)
N(4)ꢀC(13)
N(4)ꢀC(19)
1.388(4)
1.415(3)
0.94(4)
Ti(1)ꢀN(1)
1.741(3)
1.950(3)
2.202(3)
2.075
N(1)ꢀN(2)
1.379(4)
1.433(4)
1.380(5)
0.79(5)
Ti(1)ꢀN(3)
Ti(1)ꢀN(3)
N(2)ꢀC(1)
Ti(1)ꢀN(5)
Ti(1)ꢀN(4)
Ti(1)ꢀCpcent
N(2)ꢀC(7)
N(3)ꢀH(1)
Ti(1)ꢀN(3)ꢀC(13)
N(1)ꢀN(2)ꢀC(1)
N(1)ꢀN(2)ꢀC(7)
C(1)ꢀN(2)ꢀC(7)
Ti(1)ꢀCpcent
1.419(4)
1.388(3)
N(1)ꢀN(2)
1.369(3)
1.435(4)
122.6
CpcentꢀTi(1)ꢀN(1)
CpcentꢀTi(1)ꢀN(3)
CpcentꢀTi(1)ꢀN(4)
Ti(1)ꢀN(1)ꢀN(2)
Ti(1)ꢀN(3)ꢀH(1)
121.9
138.2(3)
115.9(3)
120.8(3)
122.6(3)
N(2)ꢀC(1)
114.9
CpcentꢀTi(1)ꢀN(1)
CpcentꢀTi(1)ꢀN(3)
CpcentꢀTi(1)ꢀN(5)
Ti(1)ꢀN(1)ꢀN(2)
N(1)ꢀN(2)ꢀC(1)
N(1)ꢀN(2)ꢀC(7)
C(1)ꢀN(2)ꢀC(7)
Ti(1)ꢀN(3)ꢀN(4)
Ti(1)ꢀN(3)ꢀH(1)
N(4)ꢀN(3)ꢀH(1)
N(3)ꢀN(4)ꢀC(13)
N(3)ꢀN(4)ꢀC(19)
C(13)ꢀN(4)ꢀC(19)
128.23(19)
120.(2)
112.3
114.1
165.5(2)
112.6
112.(2)
115(3)
163.4(2)
115.6(2)
121.5(2)
121.5(2)
116.2(2)
119.4(2)
124.2(2)
a Cpcent is the computed Cp* ring carbon centroid.
and TiꢀNHNPh2 (0.234(3) Å) and NRꢀNβ (0.046(4) Å)
bond lengths in 10 are comparable to the corresponding
differences for Mo(NNPh2)(NHNPh2)(acac)Cl2 and [Mo-
(NNPh2)(NHNPh2)Cl4]ꢀ.22,23 However, the absolute values
of the NRꢀNβ distances in the ModNNPh2 (av 1.309 Å) and
ModNHNPh2 (av 1.358 Å) functional groups are signifi-
cantly smaller than in 10, consistent with the diminished
reducing ability of the later metal, as it approaches its highest
formal oxidation state.24
a Cpcent is the computed Cp* ring carbon centroid.
MoꢀNR distances differ by ca. 0.20 Å, and the NRꢀNβ distances
by ca. 0.050 Å, with those for the ModNNPh2 ligand being the
shorter in each case.
The metric parameters associated with the TidNNPh2 moi-
eties in 10 and 11 are equivalent to those of Cp*Ti(NNPh2)Cl-
(py) (4) within error, although there is an apparent trend toward
longer TidNR and NRꢀNβ distances, as would be expected
since the NHNPh2 and NHtBu ligands are better σ and π
donors than Cl. The TiꢀNHNPh2 and TiꢀNHtBu distances
are comparable and longer than the TidNR counterparts and
lie within the expected ranges for titanium amide-type
complexes.14 The TiꢀNHR bond in 11 is a little shorter than
in 10, consistent with the better donor ability of NHtBu. The
hydrazido(1ꢀ) ligand NRꢀNβ distance of 1.415(3) Å in 10 is
significantly longer than that for the hydrazido(2ꢀ) ligands in
4, 10, or 11 (or for previously characterized TidNNPh2
compounds in general (av 1.360(7) Å)14) and is the same
within error as that in Zr(N2*Npy)(NHNPh2)Cl (NRꢀNβ =
1.427(8) Å) and also in Ph2NNH2 itself (1.418(2) Å).9b We
have discussed the nature of the residual NRꢀNβ multiple
bond in TidNNR2 systems elsewhere.9c,l These trends in
TidN, TiꢀN, and NRꢀNβ distances are consistent with the
NNPh2 and NHNPh2 ligands being highly reduced 2ꢀ and
1ꢀ ligands as expected. The difference between the TidNNPh2
As mentioned, Cp*Ti(NNPh2)(NHtBu)(py) (11) is stable in
solution as the hydrazido(2ꢀ)/tert-butyl amido isomer, suggest-
ing that the hydrazido(1ꢀ)/tert-butyl imido alternative is ther-
modynamically unfavored. To probe this further, we prepared
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Figure 6. Displacement ellipsoid plot (25% probability) of one of the
four crystallographically independent molecules of Cp2Ti(NNPh2)(py)
(14). H atoms are omitted.
Figure 5. Optimized geometry of TS-12-11.
the alternative isomer Cp*Ti(NtBu)(NHNPh2)(py) (12) from
LiNHNPh2 and Cp*Ti(NtBu)Cl(py) (1) in C6D6 according to
eq 2. The quaternary TidNCMe3 resonance of 12 appears at
Scheme 3. Reactions of Cp2Ti(NtBu)(py) (13) and
Cp*CpTi(NtBu)(py) (16) with Ph2NNH2 and Me2NNH2
δ13C = 67.1 ppm, consistent with an imido group. Upon forma-
tion, compound 12 starts to isomerize to 11, and after several
days the conversion is complete (this process can be accelerated
by heating to 70 °C). Attempts to isolate 12 on a preparative scale
were unsuccessful. The conversion of 12 to 11 is consistent with
the reaction of 1 with Ph2NNH2 to form 4 and tBuNH2. Unfort-
unately the conversion of 12 to 11 was not sufficiently clean at
temperatures suitable for practical kinetic measurements. DFT
calculations on models of 12 and 11 found that the latter was
5.7 kcal molꢀ1 more stable in terms of electronic energies. The
Gibbs free energy difference, ΔG = ꢀ5.0 kcal molꢀ1, further
confirms 11 as the most stable isomer.
Qualitatively, the rate of reaction did not appear to be signi-
ficantly affected by additional pyridine. To probe further the
implication that H atom migration takes place without pyridine
dissociation, DFT calculations were performed on the two pos-
sible pathways (i.e., with or without pyridine dissociation prior to H
atom transfer). These found a transition state (TS) for H transfer
with pyridine still coordinated to Ti (TS-12-11, see Figure 5) at ΔG
= 31.8 kcal molꢀ1 above 12, consistent with the slow experimental
rate of conversion of 12 to 11. The corresponding reaction pathway
proceeding via pyridine-free Cp*Ti(NtBu)(NHNPh2) (12-py),
which lies at ΔG = 6.5 kcal molꢀ1 above 12, had a much higher
energy rate-limiting TS, lying at 40.7 kcal molꢀ1 with respect to 12
(i.e., ca. 9 kcal molꢀ1 higher than TS-12-11). The DFT calcula-
tions thus indicate that the preferred mechanism keeps the
pyridine coordinated all along the transformation.
Sandwich Compounds. As mentioned, attempts to prepare
cyclopentadienyl titanium hydrazido complexes by reaction of
Ti(NNPh2)Cl2(py)3 (3) with LiCp* or NaCp gave mixtures of
unknown products. We therefore again chose a tert-butyl imide/
hydrazine exchange strategy to prepare titanium hydrazido sand-
wich complexes. The new chemistry is summarized in Scheme 3.
Reaction of Cp2Ti(NtBu)(py) (13) with Ph2NNH2 formed
the desired titanocene-hydrazido compound Cp2Ti(NNPh2)-
(py) (14). This reaction is rather sensitive to the conditions,
being best carried out in near-frozen (5 °C) benzene with careful
addition of Ph2NNH2 and rapid stirring. At the correct concen-
tration, compound 14 separates from solution in 58% yield. Longer
reaction times or higher temperatures lead to lower yields and
more side-reactions. In the presence of an excess of Ph2NNH2 14
also undergoes rapid decomposition. Once isolated, 14 is stable
in solution for at least several days. Diffraction-quality crystals
were grown by slow diffusion of pentane into a saturated
toluene solution of 14. The molecular structure is shown in
Figure 6, and selected distances and angles are given in Table 6.
The solution NMR and other data are consistent with the
solid-state structure, which is discussed in detail below along
with bonding considerations.
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Table 6. Selected Bond Lengths (Å) and Angles (deg) for
Cp2Ti(NNPh2)(py) (14)a
Table 7. Selected Bond Lengths (Å) and Angles (deg) for
CpTi(NHtBu)(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)TiCp-
(η1-Cp) (15)a
Ti(1)ꢀN(1)
1.757(2) N(1)ꢀN(2)
2.266(2) N(2)ꢀC(1)
1.351(3)
1.429(3)
1.418(3)
Ti(1)ꢀN(1)
Ti(1)ꢀN(2)
Ti(1)ꢀN(3)
Ti(1)ꢀN(4)
Ti(1)ꢀCpcent(1)
N(2)ꢀN(3)
1.9094(18) Ti(2)ꢀN(2)
2.0362(16) Ti(2)ꢀN(4)
2.1980(17) Ti(2)ꢀC(19)
2.0395(15) Ti(2)ꢀCpcent(2)
1.8163(16)
1.8589(15)
2.293(2)
2.06
Ti(1)ꢀN(3)
Ti(1)ꢀCpcent(1)
Ti(1)ꢀCpcent(2)
2.21
N(2)ꢀC(7)
2.15
Cpcent(1)ꢀTi(1)ꢀN(1)
Cpcent(2)ꢀTi(1)ꢀN(1)
Cpcent(1)ꢀTi(1)ꢀN(3)
Cpcent(2)ꢀTi(1)ꢀN(3)
113.1
115.1
104.8
102.8
N(1)ꢀTi(1)ꢀN(3) 89.5(1)
Ti(1)ꢀN(1)ꢀN(2) 175.9(2)
N(1)ꢀN(2)ꢀC(1)
N(1)ꢀN(2)ꢀC(7)
C(1)ꢀN(2)ꢀC(7)
2.08
N(1)ꢀH(1)
N(4)ꢀN(5)
0.81(4)
1.375(2)
1.414(2)
119.5(2)
119.2(2)
121.0(2)
Cpcent(1)ꢀTi(1)ꢀN(1) 117.3
Cpcent(1)ꢀTi(1)ꢀN(2) 129.8
Cpcent(1)ꢀTi(1)ꢀN(3) 112.7
Cpcent(1)ꢀTi(1)ꢀN(4) 112.8
Cpcent(2)ꢀTi(2)ꢀN(2) 122.9
Cpcent(2)ꢀTi(2)ꢀN(4) 121.7
Cpcent(2)ꢀTi(2)ꢀC(19) 117.9
Cpcent(1)ꢀTi(1)ꢀCpcent(2) 123.8
a Cpcent(1) and Cpcent(2) are the computed Cp ring carbon centroids for
“upper” and “lower” Cp rings, respectively, as depicted in Figure 6.
Ti(1)ꢀN(2)ꢀTi(2)
95.15(7)
Ti(1)ꢀN(4)ꢀTi(2)
93.73(7)
a Cpcent(1) and Cpcent(2) are the computed Cp ring carbon centroids for
Ti(1) and Ti(2), respectively.
moiety. The former is a base-free analogue of 14, whereas the
latter is related to Cp*Ti(NNPh2)(NHtBu)(py) (11). The
presence of the CpTi(NHtBu) moiety in 15 is an indication that
protonolysis by Me2NNH2 can occur both at a TiꢀC bond of 13
(or of an intermediate Cp2Ti(NNMe2)-type species) and at the
TidNimide bond. This chemistry is probably a manifestation of
the “π-loaded”25 nature of compounds of the type Cp2Ti(NR)
(R = tBu or NR2), as discussed below, which leads to incomplete
donation of ligand electron density to the metal centers and an
increase in the Brønsted basicity of the bonded atoms.
In an attempt to control the reactions of 13 with hydrazines,
we turned to the slightly bulkier Cp*CpTi(NtBu)(py) (16).10
Unfortunately, reaction with Me2NNH2 in C6D6 gave a complex
mixture of unknown products. The corresponding reaction with
Ph2NNH2 also formed a mixture among which could be identi-
fied CpH and Cp*Ti(NNPh2)(NHNPh2)(py) (10), formed by
protonolysis of the Cp ligand in 16. Bergman has reported some
related observations in the reactions of Cp2TiMe2 with anilines
leading to CpTi(NAr)(NHAr)(L).26 The other products formed
could not be identified, and a scale-up reaction was not attempted.
The reactions of 16 reflect the delicate balance of competing
reaction pathways in these π-loaded systems.
Figure 7. Displacement ellipsoid plot (20% probability) of CpTi-
(NHtBu)(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)TiCp(η1-Cp) (15).
Carbon-bound H atoms are omitted. H(1) is drawn as a sphere of
arbitrary radius.
Reaction of 13 with Me2NNH2 on the NMR tube scale in
C6D6 immediately gave a number of products. Scaling up in
benzene at 5 °C gave the binuclear complex CpTi(NHtBu)-
(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)TiCp(η1-Cp) (15) in 11%
yield among other species. Pure 15 decomposes fully over two
days in solution to an unknown mixture of compounds. The
molecular structure is shown in Figure 7, and selected distances
and angles are listed in Table 7. Molecules of 15 feature quite
distinct environments at the two titaniums. Ti(1) is bound to a
η5-Cp and tert-butyl amido ligand. It is also bonded to the NR
atoms of two bridging NNMe2 ligands and additionally to the Nβ
atom of one of them. Ti(2) is ligated by both an η5- and an η1-Cp
ligand and also to the NR atoms of the bridging NNMe2 ligands.
The solution NMR data for 15 are consistent with the solid-state
structure, showing resonances for a NHtBu and two equivalent
NNMe2 ligands, along with three 5H intensity singlets for the
different Cp ligands. Cooling to ꢀ70 °C in toluene-d8 did not
lead to decoalescence of any of the Cp ligand singlets, showing
that the sigmatropic shifts that average the environments for
C(19)ꢀC(23) have a low energy barrier.
Molecular Structure and Bonding Considerations for
Cp2Ti(NNPh2)(py) (14). As shown in Figure 6, molecules of 14
contain a bent Cp2Ti moiety coordinated to a terminal NNPh2
ligand and a pyridine donor. Compound 14 is the first structu-
rally characterized titanocene hydrazide and is a member of the
wider family of metalꢀligand multiply bonded group 4 metallo-
cene complexes of the type CpR M(E)(L) (M = Ti, Zr, Hf; E =
2
NR, PR, O, S, Se, Te; L = Lewis base).10,27 The Cp rings are
η5-coordinated to the metal with TiꢀC bonds in the range
2.423(3)ꢀ2.591(3) Å. The TiꢀCp centroid distances (av 2.18 Å)
are comparable to those in 13 (av 2.22 Å) but ca. 0.1 Å longer
than those found in general for titanocene complexes of the type
CpR TiX2 (X = Cl, alkyl).14 The TidNꢀNPh2 linkage is
2
approximately linear (175.9(2) Å), indicating sp hybridization
at NR. The environment at Nβ is trigonal planar, as is invariably
found for diphenyl hydrazido(2ꢀ) ligands due to stabilization
of the Nβ-based lone pair by conjugation with the phenyl
rings.9c,e,14 The TidNR bond length of 1.757(2) Å is equal
within error to that in the π-loaded diamide-amine complex
Ti(N2Npy)(NNPh2)(py) (1.759(2) Å, N2Npy = (2-NC5H4)CMe-
(CH2NSiMe3)2), which is the longest recorded to date.9c It is
The overall geometry of 15 is reminiscent of that of Cp*2Ti2-
(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)Cl2 (8), with Cp taking the
place of Cp*, and the NHtBu and η1-Cp groups substituting for
the Cl ligands. Compound 15 can also be viewed as an adduct
between a (ηx-Cp)2Ti(NNMe2) and CpTi(NNMe2)(NHtBu)
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Figure 8. (Left) The four highest occupied MOs of a C2v symmetric dianion [NNR2]2ꢀ with the π-donor orbitals highlighted in red. (Middle) Correct
orientation of the NNPh2 ligand for optimum match between πv and the frontier MOs of a Cp2Ti(py) fragment. (Right) Out-of-plane πh orbital that
must compete with the Cp2 SALCs for a 3dπ acceptor AO at titanium.
significantly longer than in Cp*Ti(NNPh2)Cl(py) (4) and also
longer than the TidNtBu bond length of 1.723(6) Å in 13 itself.
The phenyl substituents of NNPh2 are oriented “up” and
“down” with respect to the equatorial plane that contains Ti, NR,
and the NNPh2 πh MO (Figure 8, right). There is no correctly
aligned nonbonding acceptor MO on the Cp2Ti(py) fragment, and
so formally πh has to donate into a TiꢀCp antibonding orbital. In
effect this sets up a competition between πh and the SALCs of Cp2.
This leads to incomplete donation from both the Cp2 and NNPh2
moieties and results in a ligand-based nonbonding MO, as discussed
below. Although this bonding pattern has not been assessed
previously in a metallocene-hydrazido complex, it has been analyzed
in detail using theoretical, spectroscopic, and structural methods for
and Npy, as quantified by the CipsoꢀNβ TiꢀNpy dihedral
3 3 3
angles of 85° and 88o. This orientation of the Nβ substituents in
14 is analogous to that found in Cp2Zr(NNPh2)(DMAP) (17),7a
Cp2Nb(NNMe2)Cl (18),28 and Cp2Ta(NNPh2)Cl (19).29 It is
also reminiscent of the TadCHPh moiety in Cp2Ta(CHPh)-
CH2Ph30 and related metallocene- and metallocene-like alkyli-
dene compounds.18,31 The orientation of the alkylidene ligand in
these systems is well understood in terms of matching both the σ-
donor AO and (single) 2pπ bonding AO of CHPh with the
frontier MOs of a bent Cp2M fragment.32 These three MOs (two
having a1 and one b2 symmetry) lie in the equatorial plane of the
C2v bent Cp2M fragment. Thus the alkylidene 2pπ bonding AO is
aligned to maximize TaꢀC 5dπꢀ2pπ bonding. However,
whereas Cp2Ta(CHPh)CH2Ph and its homologues are formally
18 valence electron compounds, compound 14 and the other
metallocene hydrazides 17ꢀ19 are formally 20-electron compounds
if the NNR2 ligands are capable of acting as four-electron33 donors,
as is suggested by the sp hybridization at NR in all four instances.
The preferred orientation of the β-NPh2 group in 14 can be
explained by considering the frontier MOs of both the Cp2Ti-
(py) fragment and the hydrazide ligand. Cp2Ti(py) has two Ti-
based nonbonding MOs for forming the TidNR interaction, and
these lie in the equatorial plane.32b,c Figure 8 shows schematically
a number of group 4ꢀ6 complexes of the type CpR M(E)(L) (E =
2
O or NR; L = two- or one-electron donor or none).32b,35
We have carried out DFT calculations on Cp2Ti(NtBu)(py)
(13_Q) and Cp2Ti(NNPh2)(py) (14_Q), models of the real
complexes 13 and 14. Details of the geometries, which are in
good agreement with experiment, are given in the SI. The
HOMO and HOMOꢀ1 in each case are shown in Figure 9.
The HOMO of 13_Q lies at ꢀ4.4 eV and is an almost entirely
ligand-based nonbonding MO, as expected based on previous
studies of base-free CpR M(NR) (M = Ti36 or Mo35b) systems.
2
The HOMOꢀ1 is the in-plane TidN π-bonding MO at ꢀ5.8
eV. The hydrazido analogue 14_Q likewise has a ligand-based
MO at ꢀ4.6 eV, close in energy to that of the HOMO in 13_Q.
The πh MO of NNPh2 contributes to this, as can be seen in
Figure 9. However, this orbital is the HOMOꢀ1 of 14_Q since
the HOMO is now the in-plane TidN π-bonding MO formed
using πv of NNPh2 and is at ꢀ4.2 eV. The destabilization of this
MO compared to its counterpart in 13_Q is due to the π*
antibonding interaction between the TidNR π bond and the
Nβ lone pair, as has been noted previously.6,9c,34a
the four highest occupied MOs of planar, dianionic [NNR2]2ꢀ 6,34
.
The 1a1 MO is suitable for MdNR σ bonding, and the 1b2 MO is
NRꢀNβ π bonding and does not interact to any significant extent
with a metal center.6,34a The 1b1 MO (generically labeled πh) is
NRꢀNβ nonbonding and could in principle form a MdNR π
bond. The 2b2 MO (labeled πv) is the HOMO of [NNR2]2ꢀ and
is significantly higher in energy (g1 eV6,34a) than πh because of
its NRꢀNβ π* antibonding nature. Of these two π donor MOs,
πv has the better energy match with the metal acceptor orbitals.
The consistent orientation of the β-NPh2 moiety in 14 and 17ꢀ19
is therefore understood in terms of providing the best interaction
between the πv MO of NNPh2 and the metal, which preferably takes
place in the equatorial plane (see Figure 8, center). The TiꢀNR σ
interaction is cylindrical and has no orientational preference.
The relatively long TidNR and TiꢀCp distances in 14 are
explained by the second π interaction formed between titanium
A 90o rotation of the NPh2 group about the NRꢀNβ bond of
14_Q gives the isomer 14_Q_rot with πv now oriented
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Figure 9. DFT-computed HOMO and HOMOꢀ1 and their energies for Cp2Ti(NtBu)(py) (13_Q, top) and Cp2Ti(NNPh2)(py) (14_Q, bottom).
The value for the isodensity surface is 0.04 au.
approximately perpendicular to the equatorial plane (see also
Figure S4 in the SI). This isomer is 3.0 kcal molꢀ1 less stable than
14_Q and has one η5-bound Cp (TiꢀC = 2.40ꢀ2.49; TiꢀCpcent
= 2.13 Å) and one best approximated as an η3-bound Cp (TiꢀC
η3-coordination for one of the Cp ligands. Further details
are given in the SI (Figure S5).
The hypothetical compounds 20_Q and 20_Q_rot are mod-
els of Wiberg’s Cp2Ti{NN(SiMe3)2} (21), for which no crystal-
lographic data were reported.4 On the basis of our DFT
calculations, Wiberg’s compound would be expected to have a
geometry like that of 20_Q. However, Veith has reported the
structurally characterized vanadium analogue Cp2V{NN(SiMe3)2}
(22), which has the β-N(SiMe3)2 group lying in the equatorial
plane (cf. 20_Q_rot) with a short VdNR bond distance
(1.666(6) Å) and Cp rings that are tending toward η3-coordi-
nation.37 To probe this apparent discrepancy, we carried out
DFT geometry optimizations of Cp2Ti{NN(SiMe3)2} (21_Q,
Figure S6 of the SI) and Cp2V{NN(SiMe3)2} (22_Q, Figure S7
of the SI). In the case of 21_Q the optimal geometry corresponds
to a structure where the NN(SiMe3)2 ligand is slightly out of the
equatorial plane (CpcentꢀTiꢀNβꢀSi ≈ 62°). The TiꢀNR and
NRꢀNβ bond distances (1.695 and 1.367 Å, respectively) in
21_Q have similar values to those obtained for 20_Q_rot (1.699
and 1.370 Å), and the orientation of the N(SiMe3)2 moiety
results from destabilizing steric interactions between the Cp rings
and the SiMe3 substituents in the electronically preferred or-
ientation. This tendency is further confirmed by the calculated
geometry of Veith’s compound 22, where the NN(SiMe3)2
= 2.41ꢀ2.56; Ti C = 2.76 and 2.80; TiꢀCpcent = 2.30 Å). The
3 3 3
TidNR distance shortens from 1.743 in 14_Q to 1.718 Å in
14_Q_rot, while the NRꢀNβ lengthens from 1.337 to 1.357 Å.
The shift of one Cp from η5- to η3-coordination is due to more
effective donation into one of the TiꢀCp antibonding MOs as πv
is brought into alignment. The HOMO (see Figure S4) of
14_Q_rot lies at ꢀ3.9 eV and represents the out-of-plane
TidNR π-bonding MO formed using πv. The HOMOꢀ1
(ꢀ5.4 eV) is again a ligand-based MO but is more localized on
the Cp2 fragment because of the reduced average hapticity of the
Cp ligands. The destabilization of the HOMO on going from
14_Q to 14_Q_rot is because the metal-based, π-acceptor MO
used in the latter is at a higher energy.
ligand lies again approximately in the equatorial plane (Cpcent
ꢀ
VꢀNβꢀSi ≈ 82o), in agreement with the experimental observa-
tion. Test calculations failed to locate in each case an extremum
geometry (either local minimum or transition state) with the
NN(SiMe3)2 ligand perpendicular to the equatorial plane (i.e.,
analogous to 20_Q). For 21_Q and 22_Q, the HOMO is the
orbital associated with the donation from πv into a MꢀCp
antibonding orbital, hence accounting for the tendency to adopt
η3-Cp coordination.
We also carried out calculations on base-free model com-
pounds Cp2Ti(NNMe2) with the NMe2 group either oriented
perpendicular to the equatorial plane (20_Q) or lying within
it (20_Q_rot). As expected, 20_Q is 3.6 kcal molꢀ1 more
stable than 20_Q_rot. The TidNR bond is longer (1.726 vs
1.699 Å) and the NRꢀNβ shorter (1.328 vs 1.370 Å) in 20_Q,
as expected on the basis of the differences between 14_Q
and 14_Q_rot. Similarly, the two TiꢀCp centroid distances
are equal in 20_Q (2.12 Å), whereas they are different in
20_Q_rot (2.09 and 2.19 Å) with a tendency toward
’ CONCLUSIONS
Imide/hydrazine exchange routes have allowed access to new
sandwich and half-sandwich terminal hydrazido(2ꢀ) compounds.
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However, these reactions are very sensitive to the precise
substitution patterns and bonding situation in the starting
materials. Thus Cp*Ti(NtBu)Cl(py) (1) reacted with Ph2NNH2
to give the terminal hydrazide Cp*Ti(NNPh2)Cl(py) (4),
whereas reaction of CpTi(NtBu)Cl(py) with Ph2NNH2 or of 1
with Me2NNH2 gave dimeric hydrazido-bridged products. Like-
wise Cp2Ti(NNPh2)(py) was readily formed from Cp2Ti-
(NtBu)(py) (13), whereas reaction of 13 with Me2NNH2 or
of Cp*CpTi(NtBu)(py) with Ph2NNH2 gave mixtures among
which were products of TiꢀCp protonolysis. This latter reactiv-
ity is a consequence of the π-loaded nature of bis(cyclopentadienyl)
titanium imido and hydrazido complexes. Further studies of
the reactions of 1 with Me2NNH2 gave a rare example of a
structurally authenticated bis(η2-hydrazido(1ꢀ)) compound,
namely, 7. Reaction of 4 with LiNHNPh2 gave the first group
4 mixed hydrazido(2ꢀ)/hydrazido(1ꢀ) compound. DFT stud-
ies of Cp2Ti(NNPh2)(py) (14) and associated model complexes
showed that the bonding situation in this compound is largely
analogous to those reported elsewhere in metallocene oxo and
imido compounds. However, the precise orientation of the β-
NR2 group is important in the hydrazido systems, and the
electronically preferred arrangement is that which places the πv
donor MO of NNR2 in the Cp2Ti equatorial plane. This
electronic preference can be overridden by steric repulsions
developing between the Nβ R groups and the Cp ring, as
illustrated by the preferred geometries for Cp2Ti{NN(SiMe3)2}
and Cp2V{NN(SiMe3)2}.
of the appropriate hydrazine and n-butyllithium. Pyridine was dried
over freshly ground CaH2 and distilled before use. All other compounds
and reagents were purchased, degassed, and used without further
purification.
Cp*Ti(NNPh2)Cl(py) (4). To a stirred solution of Cp*Ti(NtBu)Cl-
(py) (1.02 g, 2.76 mmol) in benzene (20 mL) was added a solution of
Ph2NNH2 (0.55 g, 3.00 mmol) in benzene (10 mL). The resultant dark
brown solution was stirred for 16 h. The volatiles were removed under
reduced pressure to give a light brown powder, which was washed with
pentane (3 ꢁ 10 mL) and dried under reduced pressure to give 4 as a
brown solid. Yield: 1.10 g (83%). Diffraction-quality crystals were grown
from a saturated pentane solution. 1H NMR (C6D6, 299.9 MHz, 293 K):
δ 8.36 (2 H, d, 3J = 5.3 Hz, o-NC5H5), 7.49 (4 H, d, 3J = 8.8 Hz, o-C6H5),
7.21 (4 H, app. t, app. 3J = 8.0 Hz, m-C6H5), 6.87 (2 H, t, 3J = 7.4 Hz,
p-C6H5), 6.75 (1 H, t, 3J = 7.6 Hz, p-NC5H5), 6.44 (2 H, app. t, app. 3J =
6.8 Hz, m-NC5H5), 1.88 (15 H, s, C5Me5). 13C{1H} NMR (C6D6, 75.4
MHz, 293 K): δ 150.8 (o-NC5H5), 146.7 (i-C6H5), 138.4 (p-NC5H5),
129.5 (m-C6H5), 124.6 (m-NC5H5), 122.9 (p-C6H5), 120.4 (o-NC5H5),
118.5 (C5Me5), 12.0 (C5Me5). IR (NaCl plates, Nujol mull, cmꢀ1): ν
1603 (m), 1593 (s) 1584 (s) 1486 (s) 1444 (s) 1310 (s) 1281 (m) 1239
(s) 1214 (w) 1169 (m) 1152 (m) 1069 (m) 1014 (m) 989 (m) 875 (w)
746 (s) 692 (s) 640 (w) 518 (s). Anal. Found (calcd for
C27H31ClN3Ti): C, 67.5 (67.4); H, 6.3 (6.5); N, 8.7 (8.7).
NMR Tube Scale Reaction of CpTi(NtBu)Cl(py) with Ph2NNH2.
To a stirred solution of CpTi(NtBu)Cl(py) (0.30 g, 1.00 mmol) in benzene
(10 mL) was added a solution of Ph2NNH2 (0.22 g, 1.20 mmol) in benzene
(10 mL). The resultant dark red solution was stirred for 16 h. The volatiles
were removed under reduced pressure to give a dark red powder, which was
washed with pentane (3 ꢁ 10 mL) and dried under reduced pressure to give
5 as a red solid. Yield: 0.12 g (36%). Analysis by 1H NMR indicated that a
reaction had occurred immediately and quantitatively to give the previously
reported Cp2Ti2(μ2-η1:η1-NNPh2)(μ2-η2:η1-NNPh2)Cl2 (5) and free
pyridine.15
’ EXPERIMENTAL SECTION
General Methods and Instrumentation. All manipulations
were carried out under an inert atmosphere of argon or dinitrogen
using standard Schlenk-line or drybox procedures. Solvents were pre-
dried over activated 4 Å molecular sieves and refluxed over sodium
(toluene), sodium/potassium (pentane, diethyl ether), or calcium
hydride (dichloromethane) under a dinitrogen atmosphere and col-
lected by distillation. Alternatively, solvents were degassed by sparging
with dinitrogen and dried by passing through a column of activated
alumina.38 Deuterated solvents were dried over potassium (C6D6),
sodium (toluene-d8), or P2O5 (CD2Cl2), distilled under reduced
pressure, and stored under dinitrogen in Young’s Teflon valve ampules.
NMR samples were prepared under a dinitrogen atmosphere in a
drybox, in 5 mm Wilmad NMR tubes equipped with Young’s Teflon
valves. 1H and 13C NMR spectra were recorded on a Varian Mercury 300
spectrometer or a Bruker AVII 500 spectrometer with a 13C cryoprobe.
1H and 13C{1H} spectra were referenced internally to residual protio-
solvent (1H) or solvent (13C) resonances and are reported relative to
tetramethylsilane (δ = 0 ppm). Chemical shifts are quoted in δ (ppm)
and coupling constants in Hz. Where necessary, 1H and 13C assignments
NMR Tube Scale Synthesis of Cp*Ti(NHtBu)(η2-NHNMe2)Cl
(6). To a solution of Cp*Ti(NtBu)Cl(py) (0.020 g, 51.7 μmol) in C6D6
(0.4 mL) was added H2NNMe2 (3.9 μL, 51.7 μmol). An immediate color
change to pale yellow was observed, and after 1 h the 1H NMR spectrum
showed quantitative conversion to 6 and free pyridine. 1H NMR (C6D6,
299.9 MHz, 293 K): δ 5.40 (1 H, s, NHCMe3), 5.10 (1 H, s, NHNMe2),
2.41 (6 H, NHNMe2), 1.39 (C5Me5), 1.24 (NHCMe3). 13C{1H} NMR
(C6D6, 75.4 MHz, 293 K): δ 121.1 (C5Me5), 58.9 (NHCMe3) 50.6
(NHNMe2), 33.1 (NHCMe3), 11.8 (C5Me5).
Cp*Ti(η2-NHNMe2)2Cl (7). To a stirred solution of Cp*Ti-
(NtBu)Cl(py) (0.50 g, 1.35 mmol) in toluene (20 mL) at ꢀ78 °C
was added Me2NNH2 (20 μL, 2.70 mmol) in toluene (5 mL) over
10 min. The resultant brown solution was allowed to warm to RT and
stirred for 16 h. The volatiles were removed under reduced pressure to
give a tan powder, which was washed with hexanes (3 ꢁ 10 mL) and
dried under reduced pressure to give 7 as a pale yellow solid. Yield: 0.28 g
(62%). Diffraction-quality crystals were grown by slow cooling of a
saturated hexanes solution. 1H NMR (C6D6, 299.9 MHz, 293 K): δ 5.05
(2 H, s, NHNMe2), 2.45 (12 H, s, NHNMe2), 1.88 (15 H, s, C5Me5).
13C{1H} NMR (C6D6, 75.4 MHz, 293 K): δ 120.3 (C5Me5), 51.32
(NHNMe2), 12.4 (C5Me5). IR (NaCl plates, Nujol mull, cmꢀ1): ν 3241
(s), 1456 (s), 1398 (w), 1378 (s), 1292 (w), 1261 (w), 1201 (w), 1088
(w), 1073 (w), 1023 (s), 821 (w), 805 (w), 773 (w), 737 (m), 665 (m).
Anal. Found (calcd for C14H27ClN4Ti): C, 49.8 (50.2); H, 8.1 (8.1); N,
16.7 (16.7).
1
13
were assisted by the use of two-dimensional 1Hꢀ H and 1Hꢀ C
correlation experiments. IR spectra were recorded on a Perkin-Elmer
1710 or Nicolet Magna 560 FTIR spectrometer. Samples were prepared
in a drybox as Nujol mulls between NaCl plates. IR data are quoted as
wavenumbers (cmꢀ1) within the range 4000ꢀ400 cmꢀ1. Elemental
analyses were carried out by Stephen Boyer at the London Metropolitan
University.
Starting Materials. The compounds Cp*Ti(NtBu)Cl(py) (1),
CpTi(NtBu)Cl(py) (2), Cp2Ti(NtBu)(py) (13), and Cp*CpTi(NtBu)-
(py) (16) were prepared according to the literature methods.10 Diphen-
yl hydrazine was obtained from Sigma-Aldrich as the hydrogen chloride
salt, from which the free hydrazine was obtained by basification, drying,
and removal of residual solvent, followed by distillation under inert
atmospheric conditions. Lithiated hydrazines were obtained by reaction
Cp*2Ti2(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)Cl2 (8). To a stir-
red solution of Cp*Ti(NtBu)Cl(py) (0.40 g, 1.08 mmol) in toluene
(20 mL) at ꢀ78 °C was added Me2NNH2 (8.10 μL, 1.08 mmol) in
toluene (5 mL) over 10 min. The resultant brown solution was allowed
to warm slowly to RT and stirred for 72 h. The volatiles were removed
under reduced pressure to give a gray powder, which recrystallized from
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benzene, washed with hexanes (3 ꢁ 10 mL), and dried under reduced
pressure to give 8 as a pale green powder. Yield: 0.15 g (50%).
Diffraction-quality crystals were grown from slow cooling of a hot
benzene solution. 1H NMR (C6D6, 299.9 MHz, 293 K): δ 2.82 (12 H, s,
After 4 h the 1H NMR spectrum showed quantitative conversion to 12.
3
1H NMR (C6D6, 299.9 MHz, 293 K): δ 8.25 (2 H, d, J = 6.4 Hz,
o-NC5H5), 7.42 (4 H, d, 3J = 8.8 Hz, o-C6H5), 7.13 (4 H, app. t, app. 3J =
8.0 Hz, m-C6H5), 6.79 (2 H, t, 3J = 7.1 Hz, p-C6H5), 6.72 (1 H, t, 3J =
7.5 Hz, p-NC5H5), 6.64 (1 H, s, NHNPh2), 6.34 (2 H, app. t, app. 3J =
6.8 Hz, m-NC5H5), 1.98 (15 H, s, C5Me5), 1.17 (9 H, s, CMe3).
13C{1H} NMR (C6D6, 75.4 MHz, 293 K): δ 152.1 (o-NC5H5), 151.0 (i-
C6H5), 137.6 (p-NC5H5), 128.9 (m-C6H5), 123.7 (m-NC5H5), 121.1
(p-C6H5), 120.1 (o-NC5H5), 116.0 (C5Me5), 67.1 (CMe3), 33.5
(CMe3), 12.3 (C5Me5).
Cp2Ti(NNPh2)(py) (14). To a vigorously stirred solution of Cp2Ti-
(NtBu)(py) (1.50 g, 4.60 mmol) in benzene (10 mL) cooled to 5 °C was
added dropwise a solution of Ph2NNH2 (0.84 g, 0.91 mmol) in benzene
(10 mL) over 10 min. The resultant brown solution was allowed to warm
to RT and stirred for 4 h, in which time a light brown solid formed. The
solid was filtered and washed with pentane (3 ꢁ 20 mL) and dried under
reduced pressure to give 14 as a brown powder. Yield: 1.16 g (58%).
Diffraction-quality crystals were grown from slow diffusion of pentane
into a concentrated toluene solution. 1H NMR (C6D6, 299.9 MHz, 293
K): 8.39 (2 H, d, 3J = 6.5 Hz, o-NC5H5), 7.25 (4 H, d, 3J = 8.8, o-C6H5),
7.15 (4 H, app. t, app. 3J = 8.2 Hz, m-C6H5), 6.88 (2 H, t, J = 7.7 Hz, p-
C6H5), 6.66 (1 H, t, 3J = 7.6 Hz, p-NC5H5), 6.23 (2H, app. t, app. 3J =
7.0 Hz, m-NC5H5), 5.88 (10 H, s, C5H5). 13C{1H} NMR (C6D6, 75.5
MHz, 293 K): δ 155.0 (o-NC5H5), 146.5 (i-C6H5), 137.0 (p-NC5H5),
129.9 (m-C6H5), 123.8 (m-NC5H5), 123.3 (p-C6H5), 120.8 (o-C6H5),
110.0 (C5H5). IR (NaCl plates, Nujol mull, cmꢀ1): ν 1592 (m), 1584
(m), 1440 (s), 1291 (w), 1261 (s), 1214 (w), 1151 (m), 1075 (s, br), 795
(s), 782 (s), 760 (m), 628 (m). Anal. Found (calcd) for C27H25N3Ti: C,
73.8 (73.8); H, 5.6 (5.7); N, 9.5 (9.6).
1
NNMe2), 2.07 (30 H, s, C5Me5). H NMR (toluene-d8, 299.9 MHz,
243 K): δ 2.86 (6 H, s, br, NNMe2), 2.75 (6 H, s, br, NNMe2), 2.13
(15 H, s, br, C5Me5), 2.01 (15 H, s, br, C5Me5).13C{1H} NMR (C6D6,
75.4 MHz, 293 K): δ 120.8 (C5Me5), 52.9 (NNMe2), 13.5 (C5Me5). IR
(NaCl plates, Nujol mull, cmꢀ1): ν 1304 (w), 1259 (m), 1156 (w), 1121
(m), 1086 (m), 1053 (s), 1022 (s), 988 (w) 869 (w), 796 (m), 774 (w),
665 (m), 644 (w), 580 (m). Anal. Found (calcd for C24H42Cl2N4Ti2):
C, 51.9 (52.1); H, 7.8 (7.7); N, 9.9 (10.1).
Cp*Ti(NNPh2)(NHNPh2)(py) (10). To a stirred solution of
Cp*Ti(NNPh2)Cl(py) (0.20 g, 0.42 mmol) in benzene (20 mL) was
added a solution of LiNHNPh2 (0.08 g, 0.45 mmol) in benzene (10 mL).
The solution darkened and was stirred for 4 h. The volatiles were
removed under reduced pressure, and the residue was extracted into
Et2O (20 mL) and filtered to yield a green solution. Et2O was removed
under reduced pressure, and the resultant solid was washed with hexanes
(3 ꢁ 10 mL) and dried under reduced pressure to give 10 as a brown
solid. Yield: 0.11 g (45%). Diffraction-quality crystals were grown by
1
slow cooling of a saturated hexanes solution. H NMR (C6D6, 299.9
MHz, 293 K): δ 7.85 (2 H, d, 3J = 6.5 Hz, o-NC5H5), 7.34 (4 H, d, 3J =
8.8 Hz, o-NNC6H5), 7.23 (4 H, d, 3J = 8.8 Hz, o-NHNC6H5), 7.08 (4 H,
app. t, app. 3J = 8.0 Hz, m-NNC6H5), 7.02 (4 H, app. t, app. 3J = 8.0 Hz,
3
m-NHNC6H5), 6.96 (1 H, s, NHNPh2), 6.84 (2 H, t, J = 7.1 Hz,
p-NNC6H5), 6.74 (2 H, t, 3J = 7.5 Hz, p-NHNC6H5), 6.66 (1 H, t, 3J =
7.7 Hz, p-NC5H5), 6.24 (2 H, dd, 3J = 7.7 and 6.5 Hz, m-NC5H5), 1.88
(15 H, s, C5Me5). 13C{1H} NMR (C6D6, 75.4 MHz, 293 K): δ 152.1
(o-NC5H5), 150.9 (i-NHNC6H5), 147.1 (i-NNC6H5), 137.4 (p-
NC5H5), 129.2 (m-NNC6H5), 128.9 m-NHNC6H5, 123.6 (m-NC5H5),
122.0 (p-NNC6H5), 121.0 (p-NHNC6H5), 120.3 (o-NC5H5), 116.2
(C5Me5), 11.9 (C5Me5). IR (NaCl plates, Nujol mull, cmꢀ1): ν 3259
(m, NHN(C6H5)2) 1585 (s), 1490 (s), 1459 (m), 1444 (m), 1377 (w),
1328 (m), 1311 (w), 1260 (w), 1213 (w), 1167 (w), 1069 (w), 1044
(w), 1024 (w), 989 (w), 838 (w), 792 (m), 744 (s), 696 (s), 665 (m),
640 (s). Anal. Found (calcd for C39H41N5Ti): C 74.5 (74.6), H 6.8
(6.6), N 11.1 (11.2).
CpTi(NHtBu)(μ-η1:η1-NNMe2)(μ-η2:η1-NNMe2)TiCp(η1-Cp)
(15). To a stirred solution of Cp2Ti(NtBu)(py) (0.30 g, 0.91 mmol)
in hexanes (30 mL) cooled to 5 °C was added Me2NNH2 (68 μL,
0.91 mmol). The resultant dark red solution was allowed to warm to RT
and stirred for 2 h, during which time dark browncrystals crystallized. The
solid was filtered and washed with hexanes (3 ꢁ 20 mL) and dried under
reduced pressure to give 15 as brown crystals. Yield: 0.05 g (11%).
Diffraction-quality crystals were grown from a concentrated hexanes
1
solution. H NMR (toluene-d8, 299.9 MHz, 243 K): δ 6.29 (5 H, s,
Cp*Ti(NNPh2)(NHtBu)(py) (11). To a stirred solution of Cp*Ti-
(NNPh2)Cl(py) (0.30 g, 0.63 mmol) in benzene (20 mL) was added a
solution of LiNHtBu (0.05 g, 0.63 mmol) in benzene (10 mL), and the
solution darkened and was stirred for 4 h. The volatiles were removed
under reduced pressure, and the residue was extracted into Et2O
(20 mL) and filtered to yield a green solution. Et2O was removed under
reduced pressure, and the resultant solid was washed with hexanes (3 ꢁ
10 mL) and dried under reduced pressure to give 11 as a brown solid.
Yield: 0.10 g (31%). 1H NMR (C6D6, 299.9 MHz, 293 K): δ 8.14 (2 H,
d, 3J = 6.6 Hz, o-NC5H5), 7.39 (4 H, d, 3J = 8.8 Hz, o-C6H5), 7.21 (4 H,
app. t, app. 3J = 8.4 Hz, m-C6H5), 6.89 (2 H, t, 3J = 7.1 Hz, p-C6H5), 6.70
(1 H, t, 3J = 7.6 Hz, p-NC5H5), 6.34 (2 H, app. t, app. 3J = 7.0 Hz, m-
NC5H5), 6.16 (1 H, s, NHCMe3), 1.90 (15 H, s, C5Me5), 1.50 (9 H, s,
CMe3). 13C{1H} NMR (C6D6, 75.4 MHz, 293 K): δ 152.3 (o-NC5H5),
147.2 (i-C6H5), 137.5 (p-NC5H5), 129.3 (m-C6H5), 123.6 (m-NC5H5),
121.6 (p-C6H5), 120.3 (o-NC5H5), 115.6 (C5Me5), 56.3 (CMe3), 35.4
(CMe3), 11.9 (C5Me5). IR (NaCl plates, Nujol mull, cmꢀ1): ν 3258 (m,
br, NH), 1600 (m), 1592 (s), 1585 (s), 1489 (s), 1462 (m), 1444 (w),
1376 (m), 1359 (w), 1349 (w), 1325 (s), 1302 (w), 1259 (w), 1214 (m),
1207 (m), 1168 (w), 1152 (w), 1068 (w), 1042 (w), 1022 (m), 987 (w),
972 (w), 840 (m), 793 (m), 752 (m), 740 (s), 697 (s), 666 (w). Anal.
Found (calcd for C31H40N4Ti): C 71.6 (72.1); H 7.7 (7.8); N 11.1
(10.9).
η5-CpTi), 5.99 (5 H, s, η5-Cp(NHCMe3)Ti), 5.72 (5 H, s, η1-C5H5),
5.17 (1 H, s, NHCMe3), 2.42 (12 H, s, NNMe2), 0.89 (9 H, s, NHCMe3).
13C{1H} NMR (toluene-d8, 75.5 MHz, 243 K): δ 117.2 (C5H5), 116.2
(Cp(NHCMe3)Ti), 113.6 (η1-Cp), 62.0 (NHCMe3), 56.8 (NNMe2),
38.4 (NHCMe3). IR (NaCl plates, Nujol mull, cmꢀ1): ν 2955 (NHCMe3),
1432 (s), 1382 (s), 1362 (m), 1260 (s), 1245 (m), 1198 (w), 1023 (s),
1012 (m), 983 (w), 946 (w), 872 (w), 813 (s), 726 (m), 690 (w), 602 (w).
Anal. Found (calcd) for C23H37N5Ti2: C, 57.8 (57.6); H, 7.6 (7.8); N,
14.6 (14.6).
Crystal Structure Determinations of Cp*Ti(NNPh2)Cl(py)
(4), Cp*Ti(η2-NHNMe2)2Cl (7), Cp*2Ti2(μ-η1:η1-NNMe2)(μ-
η2:η1-NNMe2)2Cl2 (8), Cp*Ti(η2-NHNMe2)Cl2 (9), Cp*Ti
(NNPh2)(NHNPh2)(py) (10), Cp*Ti(NNPh2)(NHtBu)(py) (11),
Cp2Ti(NNPh2)(py) (14), and CpTi(NHtBu)(μ-η1:η1-NNMe2)-
(μ-η2:η1-NNMe2)TiCp(η1-Cp) (15). Crystal data collection and
processing parameters are given in Table S3 of the SI. Crystals were
mounted on glass fibers using perfluoropolyether oil and cooled
rapidly in a stream of cold N2 using an Oxford Cryosystems Cryo-
stream unit. Diffraction data were measured using an Enraf-Nonius
KappaCCD diffractometer. As appropriate, absorption and decay
corrections were applied to the data, and equivalent reflections were
merged.39 The structures were solved by direct methods (SIR9240),
and further refinements and all other crystallographic calculations were
performed using the CRYSTALS program suite.41 N-Bound H atoms
were located from Fourier difference syntheses and positionally refined
isotropically. C-Bound H atoms were placed geometrically and refined
NMR Tube Scale Synthesis of Cp*Ti(NtBu)(NHNPh2)(py)
(12). A solution of LiNHNPh2 (0.0052 mg, 27.1 μmol) in C6D6
(0.4 mL) was added to Cp*Ti(NtBu)Cl(py) (0.01 mg, 27.1 μmol).
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in a riding model. Details of the structure solution and refinements are
given in the Supporting Information (CIF data). A full listing of atomic
coordinates, bond lengths and angles, and displacement parameters
for all the structures have been deposited at the Cambridge Crystal-
lographic Data Centre. Copies of the data can be obtained, free of
charge, on application to the Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (fax: þ44-(0)1223-336033 or e-mail:
deposit@ccdc.cam.ac.uk).
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Computational Details. All the calculations have been performed
with the Gaussian03 package42 at the B3PW91 level.43 The titanium,
vanadium, and silicon atoms were represented by relativistic effective
core potentials from the Stuttgart group and the associated basis sets,44
augmented by an f (Ti, V) or d (Si) polarization function (R = 1.506, Ti;
R = 1.751, V; R = 0.284, Si).45 The remaining atoms (C, H, N) were
represented by a 6-31G(d,p) basis set.46 Full optimizations of geometry
without any constraint were performed, followed by analytical computa-
tion of the Hessian matrix to confirm the nature of the located extrema as
minima on the potential energy surface.
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’ ASSOCIATED CONTENT
S
Supporting Information. Data collection and processing
b
information and X-ray crystallographic data in CIF format for
the structure determinations of Cp*Ti(NNPh2)Cl(py) (4),
Cp*Ti(η2-NHNMe2)Cl (7), Cp*2Ti2(μ-η1:η1-NNMe2)(μ-η2:
η1-NNMe2)Cl2 (8), Cp*Ti(η2-NHNMe2)Cl2 (9), Cp*Ti-
(NNPh2)(NHNPh2)(py) (10), Cp*Ti(NNPh2)(NHtBu)(py)
(11), Cp2Ti(NNPh2)(py) (14), and CpTi(NHtBu)(μ-η1:η1-
NNMe2)(μ-η2:η1-NNMe2)TiCp(η1-Cp) (15). Details of the
synthesis, diagram of the molecular structure, and selected
distances and angles for 9. Additional information regarding
the DFT calculations. This information is available free of
charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: eric.clot@univ-montp2.fr; philip.mountford@chem.ox.ac.uk.
’ ACKNOWLEDGMENT
(10) Dunn, S. C.; Mountford, P.; Robson, D. A. J. Chem. Soc., Dalton
Trans. 1997, 293.
We thank the EPSRC, British Council, MESR, and the Spanish
Ministerio de Educaciꢀon y Ciencia for support. We thank
Andrew Cowley for help with some of the X-ray structures.
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