Synthesis, structures, and DFT bonding analysis of new titanium hydrazido(2-) complexes

Article abstract of DOI:10.1021/ic051271j

The reaction of 1,1-diphenylhydrazine with Ti(NMe₂) ₂Cl₂ produced the monomeric terminal titanium hydrazido(2-) species Ti(NNPh₂)Cl₂(HNMe₂) ₂ (1) in near-quantitative yield. The reaction of Ti(NMe ₂)₂Cl₂ with the less sterically demanding ligand precursors 1,1-dimethylhydrazine or N-aminopiperidine gave the dimeric μ-η²,η¹-bridged compounds Ti ₂(μ-η²,η¹-NNMe₂) ₂Cl₄(HNMe₂)₂ (2) and Ti ₂{μ-η²,η¹-NN(CH₂) ₅}₂Cl₄(HNMe₂)₃ (3). The X-ray structures of 2 and 3 showed the formation of N-H...Cl hydrogen bonded dimers or chains, respectively. The reaction of 1 with an excess of pyridine formed [Ti(NNPh₂)Cl₂(py)₂]_n (4, n = 1 or 2). The reaction of the tert-butyl imido complex Ti(N ^tBu)Cl₂(py)₃ with either 1,1-dimethylhydrazine or N-aminopiperidine again resulted in the formation of hydrazido-bridged dimeric complexes, namely Ti₂(μ-η², η¹-NNMe₂)₂Cl₄(py)₂ (5, structurally characterized) and Ti₂{μ-η², η¹-NN(CH₂)₅}₂Cl ₄(py)₂ (6). Compounds 1 and 4 are potential new entry points into terminal hydrazido(2-) chemistry of titanium. Compound 1 reacted with neutral fac-N₃ donor ligands to form Ti(NNPh₂)Cl ₂(Me₃[9]aneN₃) (7), Ti(NNPh₂)Cl ₂(Me₃[6]aneN₃) (8), Ti(NNPh₂)Cl ₂{HC(Me₂pz)₃} (9, structurally characterized), and Ti(NNPh₂)Cl₂{HC(ⁿBupz)₃} (10) in good yields (Me₃[9]aneN₃ = trimethyl-1,4,7- triazacyclononane, Me₃[6]aneN₃ = trimethyl-1,3,5- triazacyclohexane, HC(Me₂pz)₃ = tris(3,5- dimethylpyrazolyl)methane, and HC(ⁿBupz)₃ = tris(4- ⁿbutylpyrazolyl)-methane). DFT calculations were performed on both the model terminal hydrazido compound Ti(NNPh₂)Cl₂{HC(pz) ₃} (I) and the corresponding imido compounds Ti(NMe)Cl ₂{HC(pz)₃} (II) and Ti(NPh)Cl₂{HC(pz) ₃} (III). The NNPh₂ ligand binds to the metal center in an analogous manner to that of terminal imido ligands (metal≡ligand triple bond), but with one of the Ti=N_α π components significantly destabilized by a π* interaction with the lone pair of the N _β atom. The NR ligand σ donor ability was found to be NMe > NPh > NNPh₂, whereas the overall (σ + π) donor ability is NMe > NNPh₂ > NPh, as judged by fragment orbital populations, Ti-N atom-atom overlap populations, and fragment-charge analysis. DFT calculations on the hydrazido ligand in a μ-η², η¹-bridging mode showed involvement of the N=N π electrons in donation to one of the Ti centers. This TiN₂ interaction is best represented as a metallocycle.

Full text of DOI:10.1021/ic051271j

Inorg. Chem. 2005, 44, 8442−8458
Synthesis, Structures, and DFT Bonding Analysis of New Titanium
Hydrazido(2 ) Complexes
−
Thomas B. Parsons, Nilay Hazari, Andrew R. Cowley, Jennifer C. Green, and Philip Mountford*
Chemistry Research Laboratory, UniVersity of Oxford, Mansfield Road, Oxford OX1 3TA, U.K.
Received July 28, 2005
The reaction of 1,1-diphenylhydrazine with Ti(NMe2)2Cl2 produced the monomeric terminal titanium hydrazido(2
species Ti(NNPh2)Cl2(HNMe2)2 (1) in near-quantitative yield. The reaction of Ti(NMe2)2Cl2 with the less sterically
demanding ligand precursors 1,1-dimethylhydrazine or N-aminopiperidine gave the dimeric
1-bridged compounds
Ti2( 2Cl4(HNMe2)3 (3). The X-ray structures of 2 and 3
1-NNMe2)2Cl4(HNMe2)2 (2) and Ti2{µ 1-NN(CH2)5
showed the formation of N ‚‚‚Cl hydrogen bonded dimers or chains, respectively. The reaction of 1 with an
excess of pyridine formed [Ti(NNPh2)Cl2(py)2]n (4, n 1 or 2). The reaction of the tert-butyl imido complex Ti-
(NtBu)Cl2(py)3 with either 1,1-dimethylhydrazine or N-aminopiperidine again resulted in the formation of hydrazido-
bridged dimeric complexes, namely Ti2(
1-NNMe2)2Cl4(py)2 (5, structurally characterized) and Ti2{µ
NN(CH2)5 2Cl4(py)2 (6). Compounds 1 and 4 are potential new entry points into terminal hydrazido(2 ) chemistry
of titanium. Compound 1 reacted with neutral fac-N3 donor ligands to form Ti(NNPh2)Cl2(Me3[9]aneN3) (7), Ti-
(NNPh2)Cl2(Me3[6]aneN3) (8), Ti(NNPh2)Cl2 HC(Me2pz)3 (9, structurally characterized), and Ti(NNPh2)Cl2-
HC(nBupz)3
(10) in good yields (Me3[9]aneN3 trimethyl-1,4,7-triazacyclononane, Me3[6]aneN3 trimethyl-
1,3,5-triazacyclohexane, HC(Me2pz)3
tris(3,5-dimethylpyrazolyl)methane, and HC(nBupz)3 tris(4-nbutylpyrazolyl)-
methane). DFT calculations were performed on both the model terminal hydrazido compound Ti(NNPh2)Cl2 HC(pz)3
(I) and the corresponding imido compounds Ti(NMe)Cl2 HC(pz)3 (II) and Ti(NPh)Cl2 HC(pz)3 (III). The NNPh2
ligand binds to the metal center in an analogous manner to that of terminal imido ligands (metal ligand triple
* interaction with the lone pair of
donor ability was found to be NMe > NPh > NNPh2, whereas the overall (σ + π
N atom atom overlap populations,
and fragment-charge analysis. DFT calculations on the hydrazido ligand in a
1-bridging mode showed
−)
µ- ,η
η2
µ
-
η2
,
η
-
η2
,
η
}
−H
)
µ
-
η2
,
η
- , -
η2 η1
}
−
{
}
{
}
)
)
)
)
{
}
{
}
{
}
t
bond), but with one of the Ti
the Nâ atom. The NR ligand
d
NR π components significantly destabilized by a π
σ
)
donor ability is NMe > NNPh2 > NPh, as judged by fragment orbital populations, Ti
−
−
µ- ,η
η2
involvement of the N
dN
π
electrons in donation to one of the Ti centers. This TiN2 interaction is best represented
as a metallocycle.
Introduction
Group 4 metal4) terminal hydrazido(2-) complexes of the
type (L)TidNNR2 where (L) represents a supporting ligand
or ligand set and R is an alkyl or aryl group (note that reports
of titanium hydrazido(1-) compounds [(L)Ti(NR′NR2)]n are
comparatively abundant).5 This situation contrasts strongly
to the rather well-developed area of titanium imido chem-
istry.6
For over four decades the chemistry of transition metal
complexes containing hydrazido ligands has generated
considerable interest,1,2 particularly with regard to developing
models for the biological fixation of molecular nitrogen.3
However, despite the many advances in the field, there
remain few reports of terminal titanium (or indeed other
Binuclear titanium compounds containing bridging hy-
drazido(2-) ligands are fairly well established.2a,7 The earliest
report of a terminal titanium hydrazido(2-) compound was
by Wiberg and co-workers in 19788 for the pseudo-three-
coordinate titanocene complex, Cp2Ti{NN(SiMe3)2}. In 1999,
we described the synthesis and [2π + 2π] cycloaddition
reactions of the macrocycle-supported Ti(NNPh2)(Mentaa)
* To whom correspondence should be addressed. Email:
philip.mountford@chem.ox.ac.uk.
(1) For reviews of transition metal hydrazido chemistry, see: (a) Sutton,
D. Chem. ReV. 1993, 93, 995. (b) Johnson, B. F. G.; Haymore, B. L.;
Dilworth, J. D. In ComprehensiVe Coordination Chemistry; Wilkinson,
G., Gillard, R. D., McCleverty, J. A., Eds.; Pergamon Press: Oxford,
1987; Vol. 2, pp 100. (c) Nugent, W. A.; Mayer, J. M. Metal-Ligand
Multiple Bonds; Wiley-Interscience: New York, 1988.
8442 Inorganic Chemistry, Vol. 44, No. 23, 2005
10.1021/ic051271j CCC: $30.25
© 2005 American Chemical Society
Published on Web 10/13/2005

New Titanium Hydrazido(2-) Complexes
(n ) 4 or 8, H2Mentaa ) tetra- or octa-methyldibenzotetraaza-
[14]annulene) complexes with CO2.2g These were the first
reported reactions of a TidNNR2 bond. Subsequently, Woo
and Thorman described the synthesis of Ti(NNR2)(TTP) (R
) Me or Ph, H2TTP ) meso-tetra-p-tolylporphyrin) and its
reactions with p-chlorobenzaldehyde.2e Very recently, Odom
et al. reported the first crystallographically characterized
terminal titanium hydrazide(2-), namely Ti(NNMe2)(dpma)-
(tBu-bipy) (dpma ) N,N-di(pyrrolyl-R-methyl)-N-methyl-
referred to as “hydrazido”), together with a range of
macrocycle-supported and related derivatives and a density
functional theory (DFT) analysis of the bonding in terminal
diphenylhydrazido compounds and their alkyl- and phenyl-
imido analogues.9
Results and Discussion
New Entry Points to Titanium Hydrazido Chemistry.
NHMe2 Adducts. We previously showed that reactions of
primary amines RNH2 (R ) alkyl or aryl) with the readily
available Ti(NMe2)2Cl210 gave facile and high-yielding access
to a family of monomeric titanium imido synthons of the
type Ti(NR)Cl2(HNMe2)2.11 Such compounds have recently
been useful in the MOCVD synthesis of TiN thin films,12
the synthesis of calix[4]arene-supported terminal imido
complexes,13 and the preparation of a library of highly active
polymerization catalysts.14 We also showed11b that certain
complexes Ti(NR)Cl2(HNMe2)2 could be converted to the
bis- or tris-(pyridine) homologues [Ti(NR)Cl2(py)m]n (m )
3, n ) 1; m ) n ) 2), themselves very useful precursors to
new titanium imido chemistry.6a,f,15 We anticipated that 1,1-
disubstituted hydrazines would react with Ti(NMe2)2Cl2 in
a fashion similar to primary amines and that it would be
possible to use the resulting hydrazido complexes as new
starting materials in titanium hydrazido chemistry. For initial
studies in this area, three different commercially available
1,1-disubstituted hydrazines were chosen, namely, diphen-
ylhydrazine, dimethylhydrazine, and N-aminopiperidine. The
products of their reactions with Ti(NMe2)2Cl2 are sum-
marized in Scheme 1.
t
amine, Bu-bipy ) 4,4′-di-tert-butyl-2,2′-bipyridine) which
was used as a hydroammination catalyst.2a
These terminal titanium hydrazido(2-) complexes were
each prepared using different synthetic strategies. In this
contribution, we report new and potentially general entry
points to titanium hydrazido(2-) compounds (hereafter
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Kim, S.-J.; Jung, I. N.; Yoo, B. R.; Cho, S.; Ko, J.; Kim, S. H.; Kang,
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L. Dalton Trans. 2005, 225. (c) Bolton, P. D.; Mountford, P. AdV.
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42, 239.
H2NNPh2 reacted smoothly at room temperature with Ti-
(NMe2)2Cl2 to produce Ti(NNPh2)Cl2(HNMe2)2 (1) in a 91%
isolated yield. Compound 1 was characterized by elemental
1
analysis and NMR and IR spectroscopy. The H NMR
spectrum featured resonances corresponding to a NNPh2
moiety and two coordinated HNMe2 ligands by integration.
The solid-state IR spectrum (Nujol mull) showed an absorp-
tion at 3254 cm-1 corresponding to a ν(Ν-H) stretch. This
value lies within the range of frequencies (3320-3273 cm-1)
observed for the corresponding imido complexes Ti(NR)-
Cl2(NHMe2)2 which exist as N-H‚‚‚Cl hydrogen-bonded
chains in the solid state.11 Attempts to grow diffraction-
quality crystals of 1 were unsuccessful. However, a cryo-
scopic molecular weight determination in benzene gave a
(9) Although for the sake of convenience the titanium-imido and -hy-
drazido linkages herein are drawn as “TidNR”, it is most appropriate
to consider them as metal-ligand triple bonds.
(10) Froneman, M.; Cheney, D. L.; Modro, T. A. Phosphorus, Sulfur Silicon
Relat. Elem. 1990, 47.
(11) (a) Adams, N.; Cowley, A. R.; Dubberley, S. R.; Sealey, A. J.; Skinner,
M. E. G.; Mountford, P. Chem. Commun. 2001, 2738. (b) Adams, N.;
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A. J.; Cowley, A. R.; Skinner, M. E. G.; Mountford, P. Inorg. Chem.
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J.; Dubberley, S. R. J. Mater. Chem. 2003, 13, 84.
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U. Chem.sEur. J. 2003, 9, 3634.
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Friederichs, N.; Grant, C. M.; Kranenburg, M.; Sealey, A. J.; Wang,
B.; Wilson, P. J.; Cowley, A. R.; Mountford, P.; Schro¨der, M. Chem.
Commun. 2004, 434.
(7) (a) Hughes, D. L.; Latham, I. A.; Leigh, G. J. J. Chem. Soc., Dalton
Trans. 1986, 393. (b) Latham, I. A.; Leigh, G. J. J. Chem. Soc., Dalton
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(8) Wiberg, N.; Haering, H. W.; Huttner, G.; Friedrich, P. Chem. Ber.
1978, 111, 2708.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8443

Parsons et al.
Scheme 1. Reactions of Ti(NMe2)2Cl2 with 1,1-Disubstituted
Hydrazines
Figure 1. (a) Displacement ellipsoid plot (30% probablility) of Ti2(µ-
η2,η1-NNMe2)2Cl4(HNMe2)2 (2). Carbon-bound H atoms are omitted for
clarity, and the other H atoms are shown as spheres of arbitrary radius. (b)
Ball and stick view of the N-H‚‚‚Cl hydrogen bonded pairs of 2. Atoms
carrying the suffix A are related their counterparts by the operator [1 - x,
1 - y, -z].
value of 417 g mol-1 which is close to the expected value
(391.1 g mol-1) for the monomeric species depicted in
Scheme 1. The approximately trigonal-pyramidal geometry
proposed is based on that found crystallographically for
i
monomeric imido Ti(NR)Cl2(NHMe2)2 (R ) Pr, Ph, C6F5,
note the presence of the third NHMe2 coordinated to one of
the titanium centers in 3. This “extra” coordinated amine
(in contrast to the bis(dimethylamine) homologue 2) could
not be removed under vacuum. Odom has recently reported
the bis(hydrazido-bridged) dititanium compound Ti2(µ-η2,η1-
NNMe2)2(dpma)2 containing one seven-coordinate titanium
center and one six-coordinate one.2a Overall, the reactions
of Ti(NMe2)2Cl2 with 1,1-disubstituted hydrazines suggest
that terminal hydrazido compounds (e.g., 1) are accessible
provided that sufficient steric bulk is available to prevent
the formation of hydrazido-bridged dimers.
The molecular and supramolecular structures of 2 and 3
are shown in Figures 1 and 2, respectively, and selected
distances and angles are given in Tables 1 and 2. Both
compounds feature Ti2(µ-η2,η1-NNR2)2 units with the tita-
nium coordination spheres being completed by Cl and
NHMe2 ligands. In 2, the Ti-Cl bonds lie approximately
perpendicular to the plane containing the Ti2(µ-NN)2 moiety,
whereas in 3, two of the Cl ligands lie within this plane.
Atom Ti(1) in each case has an approximately octahedral
geometry, being coordinated to two Cl ligands, two NHMe2
ligands, and one nitrogen of each of the two bridging
hydrazido ligands. Ti(2) in 2 has a highly distorted octahedral
geometry, whereas in 3, Ti(2) has a distorted pentagonal
t
C6Cl4H, 2-C6H4CF3, and 2-C6H4 Bu) compounds.11 All
structurally characterized compounds of the type “M(NR)-
Cl2(NHMe2)2” (M ) Ti11 or V16) reported to date have
possessed monomeric structures.
The reaction of 1 equiv of either dimethylhydrazine or
N-aminopiperidine with Ti(NMe2)2Cl2 in benzene resulted
in the formation of dinuclear hydrazido-bridged Ti2(µ-η2,η1-
NNMe2)2Cl4(HNMe2)2 (2) or Ti2{µ-η2,η1-NN(CH2)5}2Cl4-
(HNMe2)3 (3) (Scheme 1). The solubility of both complexes
is substantially lower than that of 1. Their dimeric nature
was confirmed by X-ray diffraction (vide infra), and the 1H
NMR spectrum of 2 showed resonances for a NNMe2 ligand
and one NHMe2 ligand (per hydrazido moiety), consistent
with the proposed structures. Both compounds show ν(N-
H) bands in the expected region for N-H‚‚‚Cl hydrogen
bonding11 in their IR spectra, and this is consistent with the
solid-state structures as discussed later. It is interesting to
(15) (a) Nielson, A. J.; Glenny, M. W.; Rickard, C. E. F. J. Chem. Soc.,
Dalton Trans. 2001, 232. (b) Li, Y.; Banerjee, S.; Odom, A. L.
Organometallics 2005, 24, 3272. (c) Male, N. A. H.; Skinner, M. E.
G. Bylikin, S. Y.; Wilson, P. J.; Mountford, P.; Schro¨der, M. Inorg.
Chem. 2000, 39, 5483.
(16) Lorber, C.; Choukroun, R.; Donnadieu, B. Inorg. Chem. 2002, 41,
4217.
8444 Inorganic Chemistry, Vol. 44, No. 23, 2005

New Titanium Hydrazido(2-) Complexes
Figure 2. (a) Displacement ellipsoid plot (30% probablility) of Ti2{µ-η2,η1-NN(CH2)5}2Cl4(HNMe2)3 (3). Benzene molecules of crystallization and carbon-
bound H atoms are omitted for clarity, and all other H atoms are shown as spheres of arbitrary radius. (b) Ball and stick view of a portion of the N-H‚‚‚Cl
1
1
hydrogen-bonded chain of 3. Atoms carrying the suffixes A, B, and C are related their counterparts by the operators [1 - x, y - /2, /2 - z], [x, y + 1, z],
1
1
and [1 - x, y + /2, /2 - z], respectively.
Table 1. Selected Bond Lengths (Å) and Angles (deg) for
Ti2(µ-η2,1-NNMe2)2Cl4(HNMe2)2 (2)a
Table 2. Selected Bond Lengths (Å) and Angles (deg) for
Ti2{µ-η2,η1-NN(CH2)5}2Cl4(HNMe2)3 (3)a
Ti(1)-Cl(1)
Ti(1)-Cl(2)
Ti(1)-N(1)
Ti(1)-N(3)
Ti(1)-N(5)
Ti(1)-N(6)
N(1)-N(2)
H(1)‚‚‚Cl(1A)
2.4068(7)
2.3875(7)
1.8582(19)
1.858(2)
2.296(2)
2.300(2)
1.391(3)
2.67
Ti(2)-Cl(3)
Ti(2)-Cl(4)
Ti(2)-N(1)
Ti(2)-N(3)
Ti(2)-N(2)
Ti(2)-N(4)
N(3)-N(4)
2.2972(7)
2.2935(7)
1.922(2)
1.918(2)
2.198(2)
2.185(2)
1.386(3)
Ti(1)-Cl(1)
Ti(1)-Cl(2)
Ti(1)-N(1)
Ti(1)-N(3)
Ti(1)-N(5)
Ti(1)-N(6)
N(1)-N(2)
N(3)-N(4)
H(1A)‚‚‚Cl(4)
2.4907(7)
2.4956(7)
1.8574(19)
1.848(2)
2.220(2)
2.262(2)
1.398(3)
1.397(3)
2.56
Ti(2)-Cl(3)
Ti(2)-Cl(4)
Ti(2)-N(1)
Ti(2)-N(3)
Ti(2)-N(2)
Ti(2)-N(4)
Ti(2)-N(7)
H(3)‚‚‚Cl(2A)
2.3543(7)
2.3984(7)
1.947(2)
1.966(2)
2.210(2)
2.244(2)
2.311(2)
2.85
Cl(1)-Ti(1)-Cl(2)
N(1)-Ti(1)-N(3)
N(5)-Ti(1)-N(6)
Ti(1)-N(1)-Ti(2)
Ti(1)-N(1)-N(2)
164.54(3)
88.06(8)
85.56(8)
93.63(9)
Cl(3)-Ti(2)-Cl(4) 116.37(3)
N(1)-Ti(2)-N(3)
N(2)-Ti(2)-N(4)
Ti(1)-N(3)-Ti(2)
84.55(8)
161.16(8)
93.75(9)
Cl(1)-Ti(1)-Cl(2)
N(1)-Ti(1)-N(3)
N(5)-Ti(1)-N(6)
Ti(1)-N(1)-Ti(2)
Ti(1)-N(1)-N(2)
Ti(1)-N(3)-Ti(2)
85.68(3)
88.73(9)
153.67(9)
94.32(9)
175.15(16) Cl(4)-Ti(2)-N(7)
93.96(9) Ti(1)-N(3)-N(4)
Cl(3)-Ti(2)-Cl(4)
N(1)-Ti(2)-N(3)
N(2)-Ti(2)-N(4)
Cl(3)-Ti(2)-N(7)
159.19(3)
82.92(8)
159.60(8)
82.48(6)
77.03(6)
175.64(17)
166.20(17) Ti(1)-N(3)-N(4)
169.78(17)
N(5)-H(1)‚‚‚Cl(1A) 152
a Atoms carrying the suffix A are related their counterparts by the
operator [1 - x, 1 - y, -z].
N(7)-H(3)‚‚‚Cl(2A) 143
N(5A)-H(1A)‚‚‚Cl(4) 147
a Atoms carrying the suffixes A, B, and C are related their counterparts
by the operators [1 - x, y - 1/2, 1/2 - z], [x, y + 1, z], and [1 - x, y + 1/2,
1/2 - z], respectively.
bipyramidal geometry. The small N(1)-Ti(2)-N(3) or
N(2)-Ti(1)-N(4) angles are responsible for the major
deviations from the ideal geometries. Molecules of 2 exist
as N-H‚‚‚Cl hydrogen-bonded dimers in the solid state with
one NHMe2 and one Cl ligand of each Ti(1) center
participating in these interactions. The other NHMe2 and Cl
ligands are not involved in intermolecular contacts. Mol-
ecules of 3 form N-H‚‚‚Cl hydrogen-bonded chains because
of the participation of the Ti(2)-bound NHMe2 ligand. These
chains propagate along the crystallographic b axis. Again,
only one NHMe2 and one Cl ligand of Ti(1) are involved in
hydrogen bonding and only one of the Cl ligands bound
to Ti(2). The distances and angles associated with the
N-H‚‚‚Cl hydrogen bonds are comparable to those found
in the supramolecular structures of Ti(NR)Cl2(NHMe2)2 (R
i
t
) Pr, Ph, C6Cl4H, 2-C6H4CF3, and 2-C6H4 Bu)11b and
transition metal chloride compounds in general.17
The point of main interest in 2 and 3 are the Ti2(µ-η2,η1-
NNR2)2 moieties. The Ti(1)-N distances are equivalent
within error for the two compounds while the Ti(2)-N
distances differ slightly between 2 and 3, presumably because
(17) Aullo´n, G.; Bellamy, D.; Brammer, L.; Bruton, E. A.; Orpen, A. G.
Chem. Commun. 1998, 653.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8445

Parsons et al.
Scheme 2. Selected Reactions of Ti(NtBu)Cl2(py)3 with
1,1-Disubstituted Hydrazines
of the different hydrazide R-substituents and Ti(2) coordina-
tion numbers. In each compound, the Ti(1)-N-NR2 linkages
are approximately linear (av Ti(1)-N-NR2 ) 168.0° and
175.4° for 2 and 3, respectively) with an average N-N
distance of 1.393 Å which is approaching that of a single
N-N bond distance (1.451 ( 0.005 Å) for compounds of
the type R2N-NR2.18 The Ti(1)-N(1) and Ti(1)-N(3)
distances (av 1.855 Å) are somewhat shorter than those to
Ti(2) for these atoms (av 1.938 Å). The Ti(2)-N(2) and
Ti(2)-N(4) distances are longest of all (av 2.209 Å) in the
Ti2(µ-η2,η1-NNR2)2 moieties, reflecting the neutral, sp3-
hybridized nature of the N(2) and N(4) atoms.
Compounds containing a structurally characterized M(µ-
η2,η1-NNR2)M unit are not common, and only five have been
reported to date (av N-N distance 1.400 Å, range 1.383-
1.424 Å).19 Only one has two µ-η2,η1-bridging ligands, this
being Odom’s Ti2(µ-η2,η1-NNMe2)2(dpma)2.2a The only other
examples from Group 4 contain one µ-η2,η1-coordinated
ligand and one that is µ-η1,η1-coordinated; these are CpTiCl-
(µ-η2,η1-NNPh2)(µ-η1,η1-NNPh2)TiCpCl7a and Cp2Zr(µ-
η1,η1-NNPh2)(µ-η2,η1-NNPh2)ZrCp2.4 The different coordi-
nation modes in the latter two compounds may reflect the
increased steric demands of bridging 1,1-diphenylhydrazido
ligands as opposed to the less sterically demanding ones
present in Ti2(µ-η2,η1-NNMe2)2(dpma)2, 2 and 3 (and also
5, vide infra).
Pyridine Adducts. As mentioned, the pyridine-supported
compound Ti(NtBu)Cl2(py)320 allows general access to new
titanium tert-butyl imido compounds through chloride or
pyridine ligand metathesis. In certain cases, the use of this
pyridine adduct instead of the bis(dimethylamino) homologue
Ti(NtBu)Cl2(NHMe2)211 is preferred (for example when other
reagents present could react with the amino N-H bond or
if a good Lewis base such as pyridine is required for
stabilizing the target product). Furthermore, Ti(NtBu)Cl2(py)3
undergoes tert-butyl imide/amine exchange reactions (tBuNH2
elimination) with anilines15a,20 or other amines15b,c to give
new monomeric imido compounds or their halide-bridged
terminal imido analogues Ti2(NR)2Cl2(µ-Cl)2(py)4, both also
useful reagents in titanium imido chemistry. In a previous
paper,2g we showed that the macrocycle-supported compound
Ti(NtBu)(Mentaa) reacted with H2NNPh2 to give the corre-
sponding terminal hydrazido derivatives Ti(NNPh2)(Mentaa).
It was of interest, therefore, to explore the reactions of Ti-
(NtBu)Cl2(py)3 with 1,1-disubstituted hydrazines.
H2NNPh2 (1 equiv) produced a complex mixture of products
(including the expected BuNH2 side product). Similarly,
t
reaction of Ti(NNPh2)Cl2(NHMe2)2 (1) with several equiva-
lents of pyridine in benzene gave a mixture of products which
appeared to contain coordinated pyridine and NHMe2.
However, heating (70 °C) a solution of 1 in neat pyridine
for 16 h gave clean conversion to [Ti(NNPh2)Cl2(py)2]n (4,
eq 1). An analogous method was used previously11b for the
conversion of the imido compounds Ti(NR)Cl2(NHMe2)2 (R
t
) Bu, C6F5, or 4-C6H4Cl) to the corresponding pyridine
adducts Ti2(NtBu)2Cl2(µ-Cl)2(py)4 or Ti(NR)Cl2(py)3 (R )
C6F5 or 4-C6H4Cl). The loss of pyridine (that nominally
coordinated trans to the TidNR bond) from compounds of
the type Ti(NR)Cl2(py)3 under vacuum is well-known15a,20
and has been attributed to the strong trans influence of the
imido ligand.
Compound 4 was characterized by spectroscopic methods
and elemental analysis, but unfortunately, it was too insoluble
to allow an accurate solution molecular weight determination.
However, we consider it to be very likely (at least in the
solid state) that 4 exists as a chloride-bridged terminal
hydrazido dimer Ti2(NNPh2)2Cl2(µ-Cl)2(py)4 of the type
found to date in the solid state for all the related structurally
characterized11b,15a,b,21 bis(pyridine) titanium imido com-
pounds “Ti(NR)Cl2(py)2” (note that Odom has found that
“Ti(NSiPh3)Cl2(py)2” is a chloride-bridged dimer in the solid
state but monomeric in solution15b). The following indirect
evidence points to a terminal hydrazido structure for 4. First,
(18) Gordon, A. J.; Ford, R. A. The Chemist’s Companion; Wiley-
Interscience: New York, 1972; p 107.
(19) For the Cambridge Structural Database, see: (a) Allen, F. H.; Kennard,
O. Chem. Des. Autom. News 1993, 8, 1 & 31. (b) Fletcher, D. A.;
McMeeking, R. F.; Parkin, D. J. Chem. Inf. Comput. Sci. 1996, 36,
746.
(20) Blake, A. J.; Collier, P. E.; Dunn, S. C.; Li, W.-S.; Mountford, P.;
Shishkin, O. V. J. Chem. Soc., Dalton Trans. 1997, 1549.
Although H2NNMe2 and N-aminopiperidine undergo clean
tert-butyl imide exchange reactions with Ti(NtBu)Cl2(py)3
(vide infra and Scheme 2), the corresponding reaction with
8446 Inorganic Chemistry, Vol. 44, No. 23, 2005

New Titanium Hydrazido(2-) Complexes
error. Unlike 2 and 3, molecules of 5 show no significant
intermolecular interactions.
Titanium η1-Hydrazido Complexes with fac-N3 Donor
Ligands. We have recently been developing the stoichio-
metric and catalytic chemistry of titanium imido compounds
supported by tridentate fac-N3 donor ligands.14,15c,22 The
compounds of the type Ti(NR)X2(fac-N3) (R ) alkyl or aryl,
X ) Cl or alkyl) are isolobal analogues of metallocenes Cp2-
MX2 (for X ) Cl) and are accessible via the reaction of the
imido synthons Ti(NR)Cl2(py)3 or Ti(NR)Cl2(NHMe2)2 with
the appropriate fac-N3 donor ligand. It was therefore of
interest to explore the parallel reactions of representative fac-
N3 donor ligands with compounds Ti(NNPh2)Cl2(NHMe2)2
(1) and Ti(NNPh2)Cl2(NHMe2)2 (4) to establish a framework
for future studies.
Figure 3. Displacement ellipsoid plot (30% probablility) of Ti2(µ-η2,η1-
NNMe2)2Cl4(py)2 (5). H atoms are omitted for clarity. Atoms carrying the
suffix A are related their counterparts by the operator [1 - x, y, /2 - z].
1
The reactions of 1 with the fac-N3 donor ligands Me3[9]-
aneN3 (trimethyl-1,4,7-triazacyclononane), Me3[6]aneN3 (tri-
methyl-1,3,5-triazacyclohexane), HC(Me2pz)3 (tris(3,5-di-
methylpyrazolyl)methane), and HC(nBupz)3 (tris(4-nbutyl-
pyrazolyl)methane) are summarized in Scheme 3. The
reaction with 1 equiv of the appropriate fac-N3 donor
proceeded smoothly in a 68-81% yield in benzene to give
Ti(NNPh2)Cl2(Me3[9]aneN3) (7), Ti(NNPh2)Cl2(Me3[6]aneN3)
(8), Ti(NNPh2)Cl2{HC(Me2pz)3} (9), and Ti(NNPh2)Cl2{HC-
(nBupz)3} (10) as analytically and spectroscopically pure
solids. They are proposed to be six-coordinate monomeric
η1-hydrazido compounds on the basis of the available data
and the X-ray crystal structure of 9 (vide infra). Reaction of
4 on the NMR-tube scale with Me3[9]aneN3, Me3[6]aneN3,
HC(Me2pz)3, and HC(nBupz)3 also resulted in the quantitative
formation of complexes 7-10, demonstrating that 4 can also
be used as a titanium hydrazido synthon. In contrast, neither
2 nor 3 react with these fac-N3 donor ligands, implying that
the µ-η2,η1-hydrazido bridges in 2 and 3 are not readily
cleaved.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for
Ti2(µ-η2,η1-NNMe2)2Cl4(py)2 (5)
Ti(1)-Cl(1)
Ti(1)-N(1)
Ti(1)-N(3)
N(1)-N(2)
2.3950(6)
1.867(2)
2.277(2)
1.379(3)
Ti(2)-Cl(2)
Ti(2)-N(1)
Ti(2)-N(2)
2.2889(8)
1.920(2)
2.206(2)
Cl(1)-Ti(1)-Cl(1A) 164.10(4)
Cl(2)-Ti(2)-Cl(2A) 117.27(5)
N(1)-Ti(1)-N(1A)
N(3)-Ti(1)-N(3A)
Ti(1)-N(1)-Ti(2)
87.91(13) N(1)-Ti(2)-N(1A)
84.94(13)
159.97(12)
165.12(18)
86.59(12) N(2)-Ti(2)-N(2A)
93.58(10) Ti(1)-N(1)-N(2)
the EI mass spectra of the structurally characterized dimers
2 and 3 (Scheme 1) and of the corresponding dimeric
pyridine compounds Ti2(µ-η2,η1-NNR2)2Cl4(py)2 (R ) Me
(5), R2 ) (CH2)5 (6), vide infra and Scheme 2) feature well-
defined dimeric fragment ions [Ti2(NNR2)2]+ with the correct
m/z ratio and isotope patterns, whereas 4 shows a well-
defined envelope only for the monomeric [TiNNPh]+ frag-
ment. Furthermore, while 1 (monomeric) and 4 react readily
with a range of fac-N3 donor ligands to form six-coordinate
terminal hydrazido Ti(NNPh2)Cl2(fac-N3) compounds (vide
infra), the dimeric compounds 2 and 3 and 5 and 6 do not
react at all (consistent with them possessing unreactive Ti2-
(µ-η1,η2-NNR2)2 cores).
As mentioned, Ti(NtBu)Cl2(py)3 reacts smoothly with H2-
NNMe2 or N-aminopiperidine to yield dimeric pyridine Ti2-
(µ-η2,η1-NNR2)2Cl4(py)2 (R ) Me (5), R2 ) (CH2)5 (6))
compounds. Compound 5 features resonances for NNMe2
and coordinated pyridine ligands (1:1 ratio) and has been
crystallographically characterized. Compound 6 was too
insoluble to obtain NMR data (cf. 3) but on the basis of
elemental analysis appears to contain two pyridine ligands
as indicated in Scheme 2. The molecular structure of 5 is
shown in Figure 3, and selected bond distances and angles
are given in Table 3. Molecules of 5 lie on crystallographic
2-fold rotation axes which pass through the Ti(1)‚‚‚Ti(2)
vector. The molecular structure of 5 is very similar to that
of Ti2(µ-η2,η1-NNMe2)2Cl4(NHMe2)2 (2) with the NHMe2
ligands formally replaced by pyridines (the Ti(1)-N(3)
distance is typical for a Ti-bound pyridine ligand19). The
distances and angles associated with the Ti2(µ-η2,η1-NNMe2)2
cores in the two compounds are equivalent with experimental
1
The H NMR spectra of compounds 7-10 all feature
characteristic resonances in the region of 6.8-7.5 ppm
corresponding to the diphenylhydrazido ligand. The reso-
nances for the coordinated fac-N3 donor ligands were as
expected on the basis of previous studies and were consistent
with the Cs symmetry proposed in Scheme 3 (see Experi-
mental Section for further details). As was found in the
corresponding imido compounds Ti(NR)(Me3[6]aneN3)X2 (X
t
i
t
) Cl, R ) Bu or 2,6-C6H3 Pr2; X ) CH2Ph, R ) Bu),22d
the Me3[6]aneN3 ligand in 8 undergoes a slow fluxional
process at room temperature interpreted as a trigonal twist
rearrangement that exchanges the macrocyclic ring N-methyl
groups and each of the “up” and each of the “down” (with
respect to the titanium center) methylene H atoms (no
exchange is seen between any of the “up” with any of the
(21) Hazari, N.; Cowley, A. R.; Mountford, P. Acta Crystallogr. 2004, E60,
m1844.
(22) (a) Bolton, P. D.; Clot, E.; Cowley, A. R.; Mountford, P. Chem.
Commun. 2005, 3313. (b) Lawrence, S. C.; Skinner, M. E. G.; Green,
J. C.; Mountford, P. Chem. Commun. 2001, 705. (c) Gardner, J. D.;
Robson, D. A.; Rees, L. H.; Mountford, P. Inorg. Chem. 2001, 40,
820. (d) Wilson, P. J.; Blake, A. J.; Mountford, P.; Schro¨der, M. J.
Organomet. Chem. 2000, 600, 71. (e) Wilson, P. J.; Blake, A. J.;
Mountford, P.; Schro¨der, M. Chem. Commun. 1998, 1007. (f) Dunn,
S. C.; Mountford, P.; Shishkin, O. V. Inorg. Chem. 1996, 35, 1006.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8447

Parsons et al.
Scheme 3. Reactions of Ti(NNPh2)Cl2(NHMe2)2 (1) with fac-N3 Donor Ligands
“down” methylene hydrogens showing (just as for the imido
analogues) that this is an in-place rather than dissociative
process). The fluxional process for 8 was readily confirmed
by spin saturation transfer (SST) experiments between the
cis and trans (with respect to TidNNPh2) macrocycle N-Me
groups at 298 K, and the process is frozen out by 260 K (in
CD2Cl2). The rate constants for exchange between the ring
methyl groups were measured by SST at seven temperatures
in the range of 283-307 K, and an Eyring analysis23 gave
the activation parameters ∆Hq ) 54.9 ( 1.7 kJ mol-1 and
∆Sq ) -42 ( 6 J mol-1 K-1 (∆Gq298 ) 67.3 ( 2.4 kJ mol-1).
These values are comparable with those found previously
for the imido systems Ti(NR)(Me3[6]aneN3)X2 (∆Hq ) 46.7
( 3.3 to 66.2 ( 1.3 kJ mol-1, ∆Sq ) 11 ( 5 to -40 ( 13
J mol-1 K-1).22d
The molecular structure of Ti(NNPh2)Cl2{HC(Me2pz)3}
(9) is shown in Figure 4, and selected bond lengths and
angles are given in Table 4. Molecules of 9 contain an
approximately octahedral Ti center ligated by a fac-
coordinated HC(Me2pz)3 group, two cis-chloride ligands, and
a terminal linear diphenylhydrazido ligand (Ti(1)-N(1)-
N(2) ) 176.03(16)°). Compound 9 is the second structurally
characterized terminal hydrazido complex of titanium (the
first being Odom’s recent dimethylhydrazide Ti(NNMe2)-
(dpma)(tBu-bipy)).2a Only one other terminal hydrazido
compound of Group 4 is known, namely, Cp2Zr(NNPh2)(4-
NC5H4NMe2).4 However, terminal diphenylhydrazido com-
pounds of the 2nd and 3rd row Groups 6 (especially) and 7
metals have been extensively structurally characterized (ca.
40 such compounds are recorded in the Cambridge Structural
Database).19
The Ti(1)-N(1) bond length of 1.718(2) Å in 9 is
equivalent, within experimental error, to the corresponding
Figure 4. Displacement ellipsoid plot (25% probablility) of Ti-
(NNPh2)Cl2{HC(Me2pz)3} (9). Benzene molecules of crystallization and
H atoms are omitted for clarity.
(23) Sandstro¨m, J. Dynamic NMR Spectroscopy; Academic Press: London,
1992.
8448 Inorganic Chemistry, Vol. 44, No. 23, 2005

New Titanium Hydrazido(2-) Complexes
Figure 5. The model compounds Ti(NNPh2)Cl2{HC(pz)3} (I) and Ti(NR)Cl2{HC(pz)3} (R ) Me (II) or Ph (III)) used in the DFT calculations.9
Table 4. Selected Bond Lengths (Å) and Angles (deg) for
possibly indicating more N-N multiple-bond character in 9
Ti(NNPh2)Cl2{HC(Me2Pz)3} (9)a
(note that the NNMe2 nitrogen in Ti(NNMe2)(dpma)(tBu-
bipy) is rather strongly pyramidalized (formally sp3 hybrid-
ized), whereas N(2) in 9 is trigonal planar (sum of the angles
subtended at N(2) is 359.9(6) °). The average N-NPh2
distance in Cp2Zr(NNPh2)(4-NC5H4NMe2) is 1.363 Å (two
independent molecules in the asymmetric unit with N-NPh2
values of 1.350(3) and 1.376(3) Å), which is experimentally
identical to that in 9. However, for diphenylhydrazido
compounds in general the average N-NPh2 distance is 1.317
Å (range 1.275-1.376 Å).
Ti(1)-Cl(1)
Ti(1)-N(1)
Ti(1)-N(5)
N(1)-N(2)
2.4013(7)
1.718(2)
2.242(2)
1.369(3)
Ti(1)-Cl(2)
Ti(1)-N(3)
Ti(1)-N(7)
2.3962(7)
2.364(2)
2.208(2)
Cl(1)-Ti(1)-Cl(2)
Cl(2)-Ti(1)-N(1)
Cl(2)-Ti(1)-N(3)
Cl(1)-Ti(1)-N(5)
N(1)-Ti(1)-N(5)
Cl(1)-Ti(1)-N(7)
Cl(2)-Ti(1)-N(7)
N(3)-Ti(1)-N(7)
Ti(1)-N(1)-N(2)
101.38(3)
97.01(7)
86.80(5)
157.32(5)
100.12(8)
89.59(6)
162.55(5)
81.11(7)
176.03(16)
Cl(1)-Ti(1)-N(1)
Cl(1)-Ti(1)-N(3)
N(1)-Ti(1)-N(3)
Cl(2)-Ti(1)-N(5)
N(3)-Ti(1)-N(5)
Cl(2)-Ti(1)-N(7)
N(1)-Ti(1)-N(7)
N(5)-Ti(1)-N(7)
Ti(1)-N(1)-N(2)
99.06(7)
82.73(5)
175.35(8)
88.18(5)
77.27(7)
162.55(5)
94.58(8)
76.94(7)
176.03(16)
Density Functional Theory Analysis of Ti(NNPh2)Cl2-
{HC(pz)3} (I) and a Comparison with Imido Compounds
Ti(NMe)Cl2{HC(pz)3} (II) and Ti(NPh)Cl2{HC(pz)3} (III).
Computational studies of the bonding in transition metal
hydrazido complexes are rare in comparison to those of the
related imido systems.25,26 Previous computational studies27
of metal-hydrazido(2-) bonding were based on extended
Hu¨ckel calculations for hypothetical mono- and bis-hydrazido
complexes, along with some ab initio calculations exploring
the structure of [Li(NNH2)]q (q ) +1, 0, or -1). In particular,
these studies examined the bonding of the terminal hydrazido
ligand in the model compound [MoH5(NNH2)]3- and com-
pared the bonding between NNR end-on complexes with η1-
bound NNR2 species. No reports of DFT-based studies of
terminal hydrazido complexes have appeared, and neither
have direct comparisons been made between the electronic
structures of hydrazido complexes and those of the corre-
sponding imido complexes. Therefore, we describe in this
contributionaDFTstudyofthebondinginTi(NNPh2)Cl2{HC(Me2-
pz)3} (9), together with a comparison of that in the related
imido complexes Ti(NtBu)Cl2{HC(Me2pz)3} (10) and Ti-
a Atoms carrying the suffix A are related their counterparts by the
operator [1 - x, y, /2 - z].
1
Table 5. Electron Occupancies of Selected NR Fragment Orbitals in
Ti(NR)Cl2{HC(pz)3} (NR ) NNPh2 (I), NMe (II), or NPh (III))a
NR ) NNPh2 (I)
orbital (type)
occupancy
35A (π)
34A (π)
33A (π)
23A (σ)
1.24
1.48
1.97
1.80
NR ) NMe (II)
NR ) NPh (III)
orbital (type)
occupancy
9A (π)
8A (π)
7A (σ)
1.31
1.35
1.59
orbital (type)
occupancy
18A (π)
17A (π)
15A (π)
14A (σ)
1.41
1.40
1.96
1.74
(24) (a) Sealey, A. J. PhD Thesis, University of Oxford, 2004. (b) Lawrence,
S. C. PhD Thesis, University of Oxford, 2003.
(25) For a recent review of computational studies of transition metal-
main group multiple bonding, see: Cundari, T. R. Chem. ReV. 2000,
100, 807.
a The fragment orbital numbers correspond to those given in Figures 6
(I), 8 (II), and 9 (III), and the “type” given in parentheses refers to the
generic symmetry of the interaction formed between the NR fragment orbital
and the Ti center in TiCl2{HC(pz)3}.
(26) For examples of recent calculations of titanium terminal imido systems,
see, in addition to refs 22a and b: (a) Boyd, C. L.; Clot, E.; Guiducci,
A. E. Mountford, P. Organometallics 2005, 24, 2347. (b) Blake, A.
J.; Cowley, A. R.; Dunn, S. C.; Green, J. C.; Hazari, N.; Jones, N.
M.; Moody, A. G.; Mountford, P. Chem.sEur. J. 2005, 11, 2111. (c)
Kaltsoyannis, N.; Mountford, P. J. Chem. Soc., Dalton Trans. 1999,
781. (d) Mountford, P.; Swallow, D. J. Chem. Soc., Chem. Commun.
1995, 2357. (e) Zambrano, C. H.; Profilet, R. D.; Hill, J. E.; Fanwick,
P. E.; Rothwell, I. P. Polyhedron 1993, 12, 689. (f) Cundari, T. R.
Organometallics 1993, 12, 4971.
distance of 1.708(3) Å in Ti(NNMe2)(dpma)(tBu-bipy) and
is also comparable to that typically found for titanium imido
compounds (the usual TidNR range is 1.69-1.74 Å19).
Several imido analogues of 9 have been reported,22b,24 and
in particular, we mention Ti(NtBu)Cl2{HC(Me2pz)3} (10) and
Ti(NPh)Cl2{HC(Me2pz)3} (11) which have TidNR distances
of 1.703(2) and 1.719(2) Å.24 The N(1)-N(2) distance of
1.369(3) Å in 9 is marginally shorter than the corresponding
N-NMe2 bond in Ti(NNMe2)(dpma)(tBu-bipy) (1.388(4) Å),
(27) (a) Kahlal, S.; Saillard, J.; Hamon, J.; Manzur, C.; Carrillo, D. J. Chem.
Soc., Dalton Trans. 1998, 1229. (b) Kahlal, S.; Saillard, J.; Hamon,
J.; Manzur, C.; Carrillo, D. New J. Chem. 2001, 25, 231.
Inorganic Chemistry, Vol. 44, No. 23, 2005 8449

Parsons et al.
Figure 6. Fragment orbital-interaction diagram for Ti(NNPh2)Cl2{HC(pz)3}. The double arrows indicate the HOMO in the fragments and resultant complex.28
(NPh)Cl2{HC(Me2pz)3} (11).24 Finally, we also describe a
DFT analysis of Ti2(µ-η2,η1-NNMe2)2Cl4(HNMe2)2 (2).
The complex Ti(NNPh2)Cl2{HC(pz)3} (I, Figure 5) was
used as model for Ti(NNPh2){HC(Me2pz)3}Cl2 (9). Ti(NMe)-
Cl2{HC(pz)3} (II) and Ti(NPh)Cl2{HC(pz)3} (III) were used
as models for the real compounds Ti(NtBu)Cl2{HC(Me2pz)3}
(10) and Ti(NPh)Cl2{HC(Me2pz)3} (11), in a similar fashion.
Except for hydrogen atoms, the experimental coordinates
determined from the solid-state structure of 9 were used to
describe the geometry of I. The positions of the hydrogen
atoms were determined using a geometry optimization
calculation in which all non-hydrogen atoms were fixed (no
symmetry restraints were imposed on this calculation).
Compound I was divided into a neutral d2 TiCl2{HC(pz)3}
fragment and a neutral NNPh2 fragment, and a fragment
analysis performed. An orbital interaction diagram for I
constructed from these fragments is shown in Figure 6.28
Table 5 presents Mulliken populations (electron occupancies)
of selected hydrazido fragment orbitals in complex I.
(28) Note than when NNPh2, NMe, or NPh bond to Ti{HC(pz)3}Cl2 there
is a net electron transfer from TiCl2{HC(pz)3} to NR which becomes
partially negatively charged. In the fragment analysis, a neutral NR
ligand is taken as one of the fragments (not a charged species) and as
a result the energies of the NR orbitals increase upon bonding to the
Ti{HC(pz)3}Cl2 fragment.
8450 Inorganic Chemistry, Vol. 44, No. 23, 2005

New Titanium Hydrazido(2-) Complexes
Figure 7. Representations of selected orbitals of Ti(NNPh2)Cl2{HC(pz)3} (I).
The bonding in the neutral d2 TiCl2{HC(pz)3} fragment
is typical for a pseudo C4V ML5 fragment.29 The tris-
(pyrazolyl)methane ligand forms three low-lying σ bonds
with the titanium center through one in-phase and two out-
of-phase combinations of the lone pairs of the nitrogen atoms
of the pyrazolyl rings (orbitals 38A, 39A, and 40A). The
two chlorine atoms also form σ bonds with the titanium
center (46A and 48A). This leaves four titanium-based
orbitals which are available for bonding to another ligand
(53A-56A). As a neutral d2 Ti fragment is being considered,
the lowest-energy orbital (53 A) of these four orbitals is
occupied.
As noted previously,27 the NNPh2 ligand has four frontier
orbitals. Two of these (23A (σ type) and 34A (π type)) are
associated with formal lone pairs on NR (the N bound to Ti)
and the other two represent the πNN and π*NN orbitals (33A
and 35A). Orbital 33A contains an antibonding interaction
between the 2pπ AO of Nâ and a π-bonding orbital of the
phenyl rings. In the neutral fragment analysis, the π*NN
orbital (35A) is unoccupied and represents the LUMO of
the hydrazido fragment.
The principal interactions on formation of I from these
fragments concern orbitals 38A, 39A, 40A, 53A, 54A, and
55A of TiCl2{HC(pz)3} and orbitals 23A, 34A, and 35A of
NNPh2 (Figure 6). Representations of the 59A, 86A, and
87A MOs of I are shown in Figure 7. Orbital 59A represents
the principal σ interaction between Ti and the σ symmetry
lone pair (orbital 23A) of the NNPh2. However, in the low
symmetry of I, orbital 23A competes with the in-phase
combination of the lone pairs of the HC(pz)3 ligand for the
same titanium 3d orbitals. The resultant MO (59A) is
therefore a combination of titanium-hydrazido σ bonding and
titanium-tris(pyrazolyl)methane σ bonding. MOs 86A and
87A (Figure 7) represent the principal π interactions between
NNPh2 and Ti and are formed between two titanium-based
orbitals (53A and 54A) of TiCl2{HC(pz)3} and the NNPh2
fragment orbitals 34A (2pπ lone pair on NR) and 35A (π*NN
antibonding). Interestingly, however, the gap between the
resulting π-bonding MOs, 87A and 86A, is rather large (1.38
eV). This is the result of of the unfavorable antibonding
interaction between NR and Nâ in 87A which is not present
in 86A.
The NNPh2 fragment orbital (33A, πNN bonding), which
is lower in energy than 34A and 35A, does not interact
significantly with the metal and is Ti-N nonbonding in I
(forming MO 78A). This is clearly seen from the 33A
fragment orbital occupancy of 1.97 (Table 5) indicating
negligible electron donation to titanium. Orbital 78A is thus
responsible for the residual multiple-bond character of the
N-N bond in I. However, the partial population of the
NNPh2 fragment N-N π*-antibonding orbital 35A in I
(occupancy 1.24, Table 5), reduces the N-N bond order and
explains why the experimental N-N bond distance in the
real complex 9 lies between typical N-N and NdN bond
distances. The LUMO (orbital 88A) in the 16 valence
electron compound I is based mainly on titanium and is
nonbonding.
The TidNNPh2 bonding description for I is in general
agreement with the previous studies of metal-hydrazido
bonding.27 Overall, the hydrazido ligand formally donates 4
electrons to the metal (in a neutral electron-counting formal-
ism) and forms one σ and two π bonds in an analogous
fashion to that found for metal-imido bonding.25,26 However,
it is clear that the presence of the NPh2 moiety in I has a
dramatic effect on the relative energies of the two TidNR
π-bonding orbitals (86A and 87A) because of unfavorable
N-N π* interactions in one of them (87A).
We turn now to a comparison of the bonding in I with
that in the model alkyl- and aryl-imido compounds Ti(NMe)-
Cl2{HC(pz)3} (II) and Ti(NPh)Cl2{HC(pz)3} (III). Electronic-
structure calculations for transition metal imido compounds
in general25 and for titanium specifically26 have been
described in detail previously. We note, especially, a recent
DFT analysis (focusing in particular on trans influence
trends) of the six-coordinate imido complexes Ti(NR)Cl2-
(29) Albright, T. A.; Burdett, J. K.; Whangbo, M.-H. Orbital Interactions
in Chemistry; Wiley-Interscience: New York, 1985.
t
(NH3)3 (R ) Bu, Ph, or 4-C6H4NO2) as models of the real
Inorganic Chemistry, Vol. 44, No. 23, 2005 8451

Parsons et al.
Figure 8. Fragment orbital-interaction diagram for Ti(NMe)Cl2{HC(pz)3} (II). The double arrows indicate the HOMO in the fragments and resultant
complex.28
complexes Ti(NR)Cl2(py)3.26c In our present contribution,
therefore, we focus specifically on the similarities and
differences in the TidNR bonding and NR ligand donor
ability in titanium-hydrazido (I) and -imido (II and III)
systems.
To ensure that the analysis would be based only on
electronic factors, we used the same supporting ligand-metal
distances in all three systems. The coordinates obtained for
the TiCl2{HC(pz)3} fragment in I were used to define the
position of these atoms in calculations on II and III. The
TidNimide bond distance was fixed at 1.716 Å (the experi-
mental value in 9 and that used in the calculations for I).
The Nimido-C bond lengths in II and III were, however,
taken from the experimental structures of the real compounds
t
Ti(NR)Cl2{HC(Me2pz)3} (R ) Bu (N-CMe3 ) 1.448(3)
Å) or Ph (N-Cipso ) 1.378(3) Å)). The positions of all other
atoms in compounds II and III were obtained through
geometry optimization calculations (no symmetry restraints
were imposed). Fragment analyses were performed on
compounds II and III which were divided into neutral d2
TiCl2{HC(pz)3} and NR (R ) Me or Ph) fragments.
Fragment orbital-interaction diagrams for II and III are
8452 Inorganic Chemistry, Vol. 44, No. 23, 2005

New Titanium Hydrazido(2-) Complexes
Figure 9. Fragment orbital-interaction diagram for Ti(NPh)Cl2{HC(pz)3} (III). The double arrows indicate the HOMO in the fragments and resultant
complex.28
shown in Figures 8 and 9, respectively.28 Table 5 lists
selected NR fragment orbital occupancies (based on Mulliken
analyses) for II and III.
bond (generic σ2, π4 configuration) with the metal center.
The main difference between the orbital interaction diagrams
for compounds II and III relates to the relative energies of
the two TidNR π-bonding orbitals. These are essentially
isoenergetic in II (orbitals 58A and 59A, separation 0.06
eV) but are separated by 0.32 eV in III (orbitals 69A and
70A). This difference in energy in III is the result of an
unfavorable π*-antibonding interaction in 70A between the
2pπ orbital of the nitrogen and one of the π-bonding orbitals
of the phenyl ring. Orbital 69A lies in the plane of the phenyl
The interactions between the TiCl2{HC(pz)3} and NR
fragment orbitals in II (Figure 8) and III (Figure 9) are totally
analogous to those in hydrazido compound I (i.e., metal
fragment orbitals 38A-40A mix with the NR σ-donor
fragment orbital while the 3dπ-acceptor orbitals 53A and 54A
interact well with the 2pπ-donor orbitals). Therefore, in both
II and III, the imido ligand forms the expected25,26 triple
Inorganic Chemistry, Vol. 44, No. 23, 2005 8453

Parsons et al.
Table 6. Net Extent of NR Ligand σ and π Donation (electrons),
Ti-N Mulliken Overlap Populations (OPs) and Hirshfeld30 NR
Fragment Charges in Ti(NR)Cl2{HC(pz)3} (NR ) NNPh2 (I), NMe (II),
or NPh (III))
σ donation
π donation
total
OP
charge NR
I
II
III
0.20
0.41
0.26
1.28
1.34
1.19
1.58
1.75
1.45
0.34
0.39
0.27
-0.49
-0.48
-0.55
Table 7. Electron Occupancies of Selected NNMe2 Fragment Orbitals
in Ti2(µ-η2,η1-NNMe2)2Cl4(HNMe2)2 (2) for Both NNMe2 Fragments
occupancy
fragment 1
occupancy
fragment 2
orbital
type
13A
12A
11A
10A
N-N antibonding (π)
NR lone pair (π)
N-N bonding (π)
NR lone pair (σ)
1.22
1.46
1.83
1.80
1.23
1.46
1.84
1.80
Figure 10. Representations of the Ti-N π-bonding orbitals 69A and 70A
in Ti(NPh)Cl2{HC(pz)3} (III). Note the N-Ph antibonding interaction in
70A.
above, the occupancy of 1.97 electrons for orbital 33A (NR-
Nâ π bonding) of I and 1.96 electrons for orbital 15A (N-
phenyl π bonding) of III show that the contribution of these
fragment orbitals to Ti-NR π bonding is negligible. An
analysis of the σ-orbital occupancies shows that the σ-donor
ability of the three fragments decreases in the order NMe >
NPh > NNPh2. For the corresponding π-donor abilities, one
should consider all of the π fragment orbitals and Table 6
summarizes these data in terms of total electrons formally
donated (i.e., ∑(2 - orbital occupancy)). In terms of π-donor
ability, the order is NMe > NNPh2 > NPh, and for overall
σ and π donation combined, NMe is best donor, followed
by NNPh2, with NPh being the poorest electron donor for
the systems under consideration. The donor ability inferred
from the orbital occupancy analysis is supported by the Ti-N
atom-atom overlap populations listed in Table 6 (Ti-N(R)
for R ) Me > NPh2 > Ph) and the NR fragment charges
(least negative for NR ) NMe followed by NNPh2 and then
NPh). This order of NR-group donor ability is consistent
with the bond lengths found in the real complexes Ti(NR)-
ring and experiences no such destabilization. Representations
of orbitals 69A and 70A of compound III are shown in
Figure 10
. We have recently noted the same destabilizing feature
i
of titanium-arylimido bonding in Ti(η8-C8H8)(N-2,6-C6H3 -
Pr2).26b As expected, the fragment 2pπ-donor orbitals of NPh
(17A and 18A in Figure 9) are also separated in energy
because of this unfavorable N-phenyl antibonding interac-
tion. The NPh fragment orbital 15A represents the corre-
sponding N-phenyl π-bonding combination. In complex III,
this latter orbital (which lies low in energy compared to 17A
and 18A) has an occupancy of 1.96 electrons (Table 5)
showing that it contributes little to the Ti-NPh bonding.
The destabilizing effect of the N-phenyl π* interaction
present in the 70A molecular orbital (HOMO) of III is
analogous to the NR-Nâ π*-antibonding contribution to 87A
molecular orbital (HOMO) in the hydrazido complex I. In
I, the destabilizing effect is much more significant (∆(HOMO)
- (HOMO-1) ) 1.38 eV in I vs 0.32 eV in III). Therefore
of the three Ti(NR)Cl2{HC(pz)3} compounds studied, only
the alkyl imide II has a Ti-NR bond that is free of π*-
antibonding contributions from the R substituent (R ) NPh2
or Ph).
t
Cl2{HC(Me2pz)3} (R ) Bu < Ph ≈ NNPh2), and with the
general observation26c that, for homologous pairs of com-
pounds, M ) NtBu bond lengths are typically significantly
shorter than the corresponding M ) NPh bond lengths.
DFT Analysis of Ti2(µ-η2,η1-NNMe2)2Cl4(HNMe2)2 (2).
The electronic structure of the crystallographically character-
ized Ti2(µ-η2,η1-NNMe2)2Cl4(HNMe2)2 (2) was compared
with that of compound 9. Except for hydrogen atoms, the
experimental coordinates determined from the solid-state
structure of 2 were used to describe its geometry. The
positions of the hydrogen atoms were determined using a
geometry optimization calculation in which all non-hydrogen
atoms were fixed (no symmetry restraints were imposed).
A fragment analysis was performed where 2 was divided
into two equivalent NNMe2 fragments (each fragment
representing one of the bridging hydrazides) and into a TiCl2
and a TiCl2(HNMe2)2 fragment. Table 7 lists selected NNMe2
fragment orbital occupancies (based on Mulliken analyses)
for 2.
To evaluate the relative donor abilities of the hydrazido
and imido ligands in the three compounds, I-III, we
considered the Mulliken populations (occupancies) of the σ-
and π-donor orbitals of the NR fragments, as well as the net
(atom-atom) Ti-N overlap populations and NR fragment
Hirshfeld charges.30
The NR fragment σ- and π-donor orbital occupancies in
I-III are summarized in Table 5. For these particular
fragment orbitals, an occupancy of 2 electrons in the resultant
complex indicates that the orbital is not involved in electron
donation to titanium. Correspondingly, an electron occupancy
of less than 2 represents donation of electron density to
titanium relative to the formally dianionic NR2- hydrazide
or imide and dicationic [TiCl2{HC(pz)3}]2+. As mentioned
In a fashion analogous to that of I, both the hydrazido
fragments of 2 have four orbitals each that are suitable for
bonding to the two titanium centers. Overall, this results in
eight hydrazido orbitals that are combinations of the two
(30) (a) Hirshfeld, F. L. Theor. Chim. Acta 1977, 44, 129. (b) Wiberg, K.
B.; Rablen, P. R. J. Comput. Chem. 1993, 14, 1504.
8454 Inorganic Chemistry, Vol. 44, No. 23, 2005

New Titanium Hydrazido(2-) Complexes
Figure 11. In-phase and out-of-phase combinations of the two π*NN orbitals of Ti2(µ-η2,η1-NNMe2)2Cl4(HNMe2)2 (2).
hydrazido fragments which can be used for bonding to the
metal centers. These eight orbitals consist of an in-phase and
out-of-phase combination for each of the two lone pairs on
the two NR atoms (two of these orbitals are σ and two are π
in symmetry) and an in-phase and out-of-phase combination
for the two πNN-bonding and two π*NN-antibonding orbitals.
Figure 12. Potential bonding modes of the bridging hydrazido ligand.
The σ lone pairs on the two NR atoms (both the in-phase
and out-of-phase combinations) only interact with one
titanium center (that with the two-coordinated amines). Both
of these orbitals mix with the amine ligands and the titanium
3d orbitals to form metal-ligand σ bonds in a fashion similar
to I. In contrast, the in-phase and out-of-phase combinations
of the π lone pairs on the two NR atoms form π bonds with
both metal centers. The πNN hydrazido-bonding orbitals mix
shown in Table 7, indicates a reduction in the N-N bond
order and provides further support for bonding mode b.
Conclusions
We have established a new class of titanium hydrazido-
(2-) complexes through synthetic, structural, and DFT
studies. The titanium terminal hydrazido compound Ti-
(NNPh)Cl2(HNMe2)2 (1) has been developed and shown to
undergo facile metathesis reactions with a number of fac-
N3 donor ligands to produce further new hydrazido com-
plexes. One of these, Ti(NNPh2)Cl2{HC(Me2pz)3} (9),
represents only the second crystallographically characterized
terminal hydrazido complex of titanium. A second potential
synthon [Ti(NNPh2)Cl2(py)2]n (4) has also been developed,
and it also undergoes methathesis reactions. Reduction of
the steric bulk on the hydrazido ligand leads to unsym-
metrical dimeric species with bridging µ-η2,η1-bound hy-
drazido ligands, and three of these have been crystallograph-
ically characterized. These dimeric species do not undergo
metathesis reactions with neutral fac-N3 donor ligands.
The DFT analysis of the electronic structures of the
terminal hydrazido and imido complexes Ti(NR)Cl2{HC-
(pz)3} (R ) NPh2, Me, or Ph) showed that the NNPh2 ligand
binds to the metal center in a manner analogous to that of
the terminal imido ligands but with one of the TidN π
components significantly destabilized by the formal lone pair
of the â-N atom. The NR σ-donor ability was found to be
NMe > NPh > NNPh2, whereas the overall (σ + π) donor
ability is NMe > NNPh2 > NPh as determined from
fragment orbital population, overlap population, and fragment
charge analysis. The principal difference in orbital occupancy
when the hydrazido ligand is bonding in a bridging mode is
donation of the NdN π-bonding electrons to one of the Ti
centers. The TiN2 interaction is best represented as a
metallocycle because back donation into the NdN π* orbital
is extensive.
with the π lone pairs on the two NR atoms and the two π*NN
-
bonding orbitals to interact with the metal centers. This is
clearly indicated in Table 7 which shows that the occupancies
of the πNN hydrazido-bonding orbitals in 2 are 1.83 and 1.84,
and this is the major difference between the bonding in 2
and the bonding in I (occupancy πNN in I is 1.96). The
occupancies of the other hydrazido-bonding orbitals in 2 are
very similar to their corresponding orbitals in I. Interestingly,
the in-phase and out-of-phase combinations of the two π*NN
-
bonding orbitals bond differently to the titanium centers. The
in-phase combination bonds to both of the titanium centers,
whereas the out-of-phase combination only bonds to one of
the titanium centers. Representations of these orbitals are
shown in Figure 11.
Overall, the electronic structure of 2 clearly shows the
asymmetric nature of the two bridging hydrazido ligands.
One of the titanium centers only bonds to NR (the center
with the coordinated amines), while the other center bonds
to both NR and Nâ. It is possible to describe the interaction
between the hydrazido fragment and the titanium center
which binds both NR and Nâ in two different ways as shown
in Figure 12. In mode a, the hydrazido ligands bond to the
metal center through a π interaction, whereas in mode b, a
three-membered metallocycle is formed. In complex 2, the
bonding is probably better described by mode b than by a.
There are clear σ-interactions between both NR and Nâ and
the Ti center as shown in Figure 11, suggesting a metallo-
cyclic structure. Also, the partial population of the π*NN, as
Inorganic Chemistry, Vol. 44, No. 23, 2005 8455

Parsons et al.
145.3 (ipso-C), 129.6 (meta-C), 123.9 (para-C), 118.2 (ortho-C),
41.4 (NHMe2). IR (NaCl plates, Nujol mull, cm-1): ν 3254 (br,
w), 1588 (w), 1492 (w), 1092 (br, m), 1018 (br, m), 800 (w). EI-
MS: m/z 168 [NPh2]+ (73%), 105 [NNPh]+ (2%). Anal. Found
(calcd) for C16H24Cl2N4Ti: C, 49.0 (49.1); H, 6.1 (6.2); N, 14.3
(14.3).
The chemistry of the TidNR (imido) bond has been
developed in some detail over the past decade in particular,6
while that of the TidNNR2 (hydrazido) bond is virtually
unexplored.2a Much of the chemistry of the TidNR bond
involves [2 + 2] cycloaddition reactions with electrophilic
substrates. Our DFT analysis suggests that the TidNNR2
bond should, for otherwise analogous systems, be more
reactive in this regard because of the destabilizing effect of
the NR-Nâ π*-antibonding contribution to the HOMO. Our
future efforts in this area will be aimed at developing the
reaction chemistry of the TidNNR2 multiple bond.
Ti2(µ-η2,η1-NNMe2)2Cl4(HNMe2)2 (2). H2NNMe2 (0.25 g, 4.11
mmol) was added to a stirred brown solution solution of TiCl2-
(NMe2)2 (0.85 g, 4.11 mmol) in benzene (25 mL). The resultant
deep red mixture was left to stir for 2 h, after which a precipitate
had formed. The supernatant was decanted and the residues dried
1
in vacuo give 2 as a red powder. Yield: 0.60 g (66%). H NMR
(CD2Cl2, 500.0 MHz): δ 3.68 (2H, m, br, HNMe2), 3.45 (12H, s,
NNMe2), 2.47 (12H, d, 3J ) 5.9 Hz HNMe2). 13C-{1H} NMR (CD2-
Cl2, 125.8 MHz): δ 52.7 (NNMe2), 42.6 (HNMe2). IR (NaCl plates,
Nujol mull, cm-1): ν 3268 (w), 1632 (br, w), 1306 (w), 1260 (sh,
m), 1096 (br, m), 1019 (m), 987 (w), 896 (w), 803 (m), 722 (w).
EI-MS: m/z 354 [Ti2(NNMe2)2Cl4]+ (17%), 216 [Ti2(NNMe2)2]+
(5%), 58 [NNMe2]+ (100%). Anal. Found (calcd) for C8H26Cl4N6-
Ti2: C, 23.5 (23.5); H, 6.1 (6.0); N, 18.4 (18.4).
Experimental Section
General Methods and Instrumentation. All manipulations were
carried out using standard Schlenk line or drybox techniques under
an atmosphere of argon or dinitrogen. Solvents were predried over
activated 4 Å molecular sieves and were refluxed over appropriate
drying agents under a dinitrogen atmosphere and collected by
distillation. Deuterated solvents were dried over appropriate drying
agents, distilled under reduced pressure, and stored under dinitrogen
in Teflon valve ampules. NMR samples were prepared under
dinitrogen in 5 mm Wilmad 507-PP tubes fitted with J. Young
Teflon valves. 1H and 13C NMR spectra were recorded on a Varian
Mercury 500 spectrometer with a probe temperature of 298 K. 1H
and 13C assignments were confirmed when necessary with the use
of nOe and two-dimensional 1H-1H and 13C-1H NMR experiments.
All spectra were referenced internally to residual protio-solvent (1H)
or solvent (13C) resonances and are reported relative to tetrameth-
ylsilane (δ ) 0 ppm). Chemical shifts are quoted in δ (ppm) and
coupling constants in hertz. Infrared spectra were prepared as Nujol
mulls between NaCl plates and were recorded on Perkin-Elmer 1600
and 1700 series spectrometers. Infrared data are quoted in wave-
numbers (cm-1). Mass spectra were recorded by the mass spec-
trometry service of the University of Oxford’s Department of
Chemistry. Combustion analyses were recorded by the elemental
analysis service at the London Metropolitan University.
Ti2{µ-η2,η1-NN(CH2)5}2Cl4(HNMe2)3 (3). A solution of N-
aminopiperidine (0.24 g, 2.40 mmol) in benzene (15 mL) was added
to a stirred brown solution of TiCl2(NMe2)2 (0.49 g, 2.39 mmol)
in benzene (25 mL) over 10 min. The resultant crimson mixture
was left to stir for 16 h. The supernatant was decanted, and the
crimson solid washed with benzene (20 mL). Drying in vacuo
produced 3 as an orange powder. Yield: 0.42 g (62%). 1H and 13
C
NMR data could not be obtained as 3 was insoluble in nonreactive
NMR solvents. IR (NaCl plates, Nujol mull, cm-1): ν 3241 (w),
1613 (br, w), 1307 (w), 1260 (m), 1093 (br, m), 1022 (br, m), 898
(w), 851 (w), 801 (m), 722 (w), 683 (w). EI-MS: m/z 434 [Ti2-
{NN(CH2)5}2Cl4]+ (64%), 84 [N(CH2)5]+ (100%). Anal. Found
(calcd) for C16H41Cl4N7Ti2: C, 33.9 (33.8); H, 7.2 (7.3); N, 17.2
(17.2).
[Ti(NNPh2)Cl2(py)2]n (4). A solution of Ti(NNPh2)Cl2(HNMe2)2
(1) (1.01 g, 2.58 mmol) in pyridine (40 mL) was heated for 16 h
at 70 °C. The dark yellow-brown solution was filtered, and the
volatiles were removed under reduced pressure to yield crude 4 as
a yellow-green solid. This was washed with benzene (20 mL), and
the volatiles were removed under reduced pressure to give 4 as a
Starting Materials. The compounds Ti(NMe2)2Cl2,10 Me3[9]-
aneN3,31 Me3[6]aneN3,32 HC(Me2pz)3,33 HC(nBupz)3,34 and Ti(Nt-
20
Bu)Cl2(py)3 were prepared by literature methods. Diphenylhy-
1
yellow-green powder. Yield: 1.01 g (87%). H NMR (CD2Cl2,
drazine was purified as described previously.2g Dimethylhydrazine,
N-aminopiperidine, and pyridine were dried over freshly ground
CaH2 and distilled before use. Other reagents were obtained from
Sigma-Aldrich and used as received.
500.0 MHz): δ 9.01 (4H, app d, py ortho-H), 7.82 (2H, m, py
para-H), 7.43 (4H, m, ortho-H), 7.37 (4H, m, py meta-H), 7.26
(4H, m, meta-H), 6.99 (2H, m, para-H).13C-{1H} NMR (CD2Cl2,
125.8 MHz): δ 152.0 (py ortho-C), 149.7 (py para-C), 144.4 (ipso-
C), 129.1 (meta-C), 124.6 (py meta-C), 123.5 (para-C), 118.8
(ortho-C). IR (NaCl plates, Nujol mull, cm-1): ν 1601 (br, w),
1260 (m), 1092 (br, w), 1021 (br, m), 803 (m), 722 (m). EI-MS:
m/z 168 [NPh2]+ (100%), 153 [TiNNPh]+ (28%). Anal. Found
(calcd) for C22H20Cl2N4Ti: C, 57.5 (57.5); H, 4.3 (4.4); N, 12.3
(12.2).
Ti2(µ-η2η1-NNMe2)2Cl4(py)2 (5). H2NNMe2 (70.3 mg, 1.17
mmol) was added to a stirred orange solution of Ti(NtBu)Cl2(py)3
(0.50 g, 1.17 mmol) in benzene (40 mL). The dark reaction mixture
was stirred for 90 min, after which a precipitate had formed. The
solution was concentrated to approximately 20 mL and left to stir
for a further 30 min. Filtration yielded 5 as an orange powder, which
was dried in vacuo. Yield: 0.14 g (45%). 1H NMR (CD2Cl2, 500.0
MHz): δ 8.95 (4H, m, br, ortho-H), 7.87 (2H, m, para-H), 7.40
(4H, m, meta-H), 3.48 (12H, s, NNMe2). 13C-{1H} NMR (CD2Cl2,
125.8 MHz): δ 154.4 (ortho-C), 139.3 (para-C), 124.7 (meta-C),
51.4 (NNMe2). IR (NaCl plates, Nujol mull, cm-1): ν 1624 (br,
w), 1260 (sh, m), 1091 (br, m), 1019 (br, m), 800 (m), 722 (w).
Ti(NNPh2)Cl2(HNMe2)2 (1). A solution of H2NNPh2 (1.55 g,
8.43 mmol) in benzene (40 mL) was added to a stirred solution of
TiCl2(NMe2)2 (1.74 g, 8.43 mmol) in benzene (40 mL) over 30
min. The reaction mixture immediately turned a dark orange-brown
color and was left to stir for a further period during which time
there was no additional color change. The solution was filtered,
and the volatiles were removed under reduced pressure to give 1
1
as a brown-green powder. Yield: 3.00 g (91%). H NMR (C6D6,
500.0 MHz): δ 7.68 (4H, m, ortho-H), 7.22 (4H, m, meta-H), 6.86
(2H, m, para-H), 2.79 (2H, sep, 3J ) 6.3 Hz, NHMe2), 2.19 (12H,
3
d, J ) 6.3 Hz, NHMe2). 13C-{1H} NMR (C6D6, 125.8 MHz): δ
(31) Madison, S. A.; Batal, D. J.; Unilever PLC, U.K.; Unilever N. V.
U.S. Patent 5,284,944, 1994.
(32) Hoerr, C. W.; Rapkin, E.; Brake, A. E.; Warner, K. N.; Harwood, H.
J. J. Am. Chem. Soc. 1956, 78, 4667.
(33) Reger, D. L.; Grattan, T. C.; Brown, K. J.; Little, C. A.; Lamba, J. J.
S.; Rheingold, A. L.; Sommer, R. D. J. Organomet. Chem. 2000, 607,
120.
(34) Selby, J. D.; Mountford, P. Manuscript in preparation.
8456 Inorganic Chemistry, Vol. 44, No. 23, 2005

New Titanium Hydrazido(2-) Complexes
EI-MS: m/z 354 [Ti2(NNMe2)2Cl4]+ (17%), 216 [Ti2(NNMe2)2]+
(5%), 58 [NNMe2]+ (100%). Anal. Found (calcd) for C14H22Cl4N6-
Ti2: C, 32.7 (32.9); H, 4.4 (4.3); N, 16.4 (16.4).
solution of Ti(NNPh2)Cl2(HNMe2)2 (1) (0.50 g, 1.28 mmol) in
benzene (20 mL) over 15 min. The mixture was left to stir for a
further 3 h, after which the solution was a blue-green color and
some precipitate was present. The volume of solvent was reduced
to approximately 20 mL under reduced pressure, and the mixture
was left to stand for a further 2 h. The supernatant was decanted to
yield 9 as a yellow-green powder which was dried in vacuo.
Yield: 0.61 g (80%). 1H NMR (CD2Cl2, 500.0 MHz): δ 7.93 (1H,
s, apical H), 7.28 (4H, m, ortho-H), 7.13 (4H, m, meta-H), 6.88
(2H, m, para-H), 6.04 (2H, s, 4-pz Hcis), 5.89 (1H, s, 4-pz Htrans),
2.63 (3H, s, 3-pz Metrans), 2.62 (6H, s, 5-pz Mecis), 2.48 (3H, s,
5-pz Metrans), 2.21 (6H, s, 3-pz Mecis). 13C-{1H} NMR (CD2Cl2,
125.8 MHz): δ 157.1 (3-pztrans), 156.7 (3-pzcis), 145.0 (ipso-C),
140.3 (5-pzcis), 138.7 (5-pztrans), 129.7 (ortho-C), 123.0 (para-C),
120.1 (meta-C), 109.3 (4-pztrans), 108.9 (4-pzcis), 68.5 (apical-C),
15.6 (3-pz Mecis), 15.4 (3-pz Metrans), 11.8 (5-pz Mecis), 11.4 (5-pz
Metrans). IR (NaCl plates, Nujol mull, cm-1): ν 1594 (br, w), 1305
(w), 1260 (m), 1092 (br, w), 1020 (br, w), 803 (m), 722 (m). EI-
MS: m/z 503 [M - Me2pz]+ (7%), 203 [HC(Me2pz)2]+ (3%), 96
[Me2pz]+ (23%). Anal. Found (calcd) for C28H32Cl2N8Ti: C, 56.0
(56.1); H, 5.3 (5.4); N, 18.8 (18.7).
Ti2{µ-η2,η1-NN(CH2)5}2Cl4(py)2 (6). A solution of N-aminopi-
peridine (0.12 g, 1.15 mmol) in benzene (10 mL) was added to a
stirred orange solution of Ti(NtBu)Cl2(py)3 (0.49 g, 1.15 mmol) in
benzene (50 mL) over 10 min. The resultant bright red solution
was left to stir for 16 h, after which an orange solid had formed.
The supernatant was decanted, and the solid was washed with
benzene (20 mL) and dried in vacuo give 6 as an orange powder.
Yield: 0.24 g (68%). 1H and 13C NMR data could not be obtained
as 6 was insoluble in nonreactive NMR solvents. IR (NaCl plates,
Nujol mull, cm-1): ν 1652 (br, w), 1601 (w), 1260 (m), 1091 (br,
m), 1026 (br, m), 802 (br, w), 722 (w), 697 (w). EI-MS: m/z 434
[Ti2{NN(CH2)5}2Cl4]+ (100%), 84 [N(CH2)5]+ (90%). Anal. Found
(calcd) for C20H30Cl4N6Ti2: C, 40.6 (40.6); H, 5.0 (5.1); N, 14.4
(14.2).
Ti(NNPh2)Cl2(Me3[9]aneN3) (7). A solution of Me3[9]aneN3
(0.25 g, 1.46 mmol) in benzene (5 mL) was added to a stirred
solution of Ti(NNPh2)Cl2(HNMe2)2 (1) (0.57 g, 1.46 mmol) in
benzene (20 mL) over 15 min. On addition of the ligand, the
reaction mixture changed from an orange-brown solution to a yellow
suspension. The mixture was stirred for a further 90 min and then
filtered. Volatiles were removed under reduced pressure, giving 7
Ti(NNPh2)Cl2{HC(nBupz)3} (10). A solution of HC(nBupz)3
(0.19 g, 0.50 mmol) in benzene (15 mL) was added to a stirred
solution of Ti(NNPh2)Cl2(HNMe2)2 (1) (0.20 g, 0.50 mmol) in
benzene (20 mL) over 10 min. The solution was left to stir for 16
h, and the volatiles were then removed under reduced pressure to
1
as a light yellow-green powder. Yield: 0.56 g (81%). H NMR
(CD2Cl2, 500.0 MHz): δ 7.41 (4H, m, ortho-H), 7.32 (4H, m, meta-
H), 7.02 (2H, m, para-H), 3.15 (2H, m, NMecisCH2CH2NMetrans
down), 3.05 (2H, m, NMecisCH2CH2NMecis down), 3.01 (2H, m,
NMecisCH2CH2NMetrans down), 2.84 (6H, s, NMecis), 2.75 (2H, m,
NMecisCH2CH2NMecis up), 2.64 (2H, m, NMecisCH2CH2NMetrans
up), 2.56 (3H, s, NMetrans), 2.48 (2H, m, NMecisCH2CH2NMetrans
up). 13C-{1H} NMR (CD2Cl2, 125.8 MHz): δ 146.7 (ipso-C), 129.7
(ortho-C), 124.1 (para-C), 121.2 (meta-C), 57.4 (NMecisCH2CH2-
NMetrans), 57.1 (NMecisCH2CH2NMecis), 55.8 (NMecisCH2CH2-
NMetrans), 53.7 (NMetrans, partially obscured by solvent), 49.8
(NMecis). IR (NaCl plates, Nujol mull, cm-1): ν 1585 (w), 1260
(m), 1092 (br, w), 1020 (br, w), 802 (m), 722 (w). EI-MS: m/z
471 [M]+ (17%), 289 [M-NNPh2]+ (14%), 168 [NPh2]+ (39%). HR
EI-MS found (calcd) for C21H31Cl2N5Ti: m/z 471.1423 (471.1436).
Anal. Found (calcd) for C21H31Cl2N5Ti: C, 53.3 (53.4); H, 6.5 (6.6);
N, 14.7 (14.8).
1
give 10 as a bright green powder. Yield: 0.28 g (81%). H NMR
(CD2Cl2, 500.0 MHz, 298 K): δ 10.13 (1H, s, apical H), 8.52 (2H,
s, 5-pz Hcis), 8.32 (1H, s, 5-pz Htrans), 7.71 (2H, s, 3-pz Hcis), 7.60
(1H, s, 3-pz Htrans), 7.40 (4H, m, ortho-H), 7.24 (4H, m, meta-H),
6.98 (2H, m, para-H), 2.28 (6H, app t, 4-pz-CH2CH2CH2CH3), 1.38
(6H, m, 4-pz-CH2CH2CH2CH3), 1.23 (6H, m, 4-pz-CH2CH2CH2-
CH3), 0.82 (9H, m, 4-pz-CH2CH2CH2CH3). 13C-{1H} NMR (CD2-
Cl2, 125.8 MHz): δ 146.3 (3-pztrans), 144.8 (3-pzcis), 143.6 (ipso-
C), 129.3 (ortho-C), 123.5 (para-C), 123.4 (5-pzcis), 123.1 (5-pztrans),
119.5 (meta-C), 118.0 (4-pzcis), 117.8 (4-pztrans), 75.3 (apical-C),
32.9 (4-pz-CH2CH2CH2CH3trans), 32.7 (4-pz-CH2CH2CH2CH3cis),
23.7 (4-pz-CH2CH2CH2CH3trans) 23.7 (4-pz-CH2CH2CH2CH3cis),
22.7 (4-pz-CH2CH2CH2CH3trans), 22.7 (4-pz-CH2CH2CH2CH3cis),
13.9 (4-pz-CH2CH2CH2CH3cis), 13.9 (4-pz-CH2CH2CH2CH3trans). IR
(NaCl plates, Nujol mull, cm-1): ν 1595 (br, w), 1260 (w), 1091
(br, w), 1021 (br, w), 805 (w), 722 (w). Anal. Found (calcd) for
C34H44Cl2N8Ti: C, 59.7 (59.8); H, 6.4 (6.5); N, 16.2 (16.4).
Ti(NNPh2)Cl2(Me3[6]aneN3) (8). A solution of Me3[6]aneN3
(99.0 mg, 0.77 mmol) in benzene (5 mL) was added to a stirred
solution of Ti(NNPh2)Cl2(HNMe2) (1) (0.30 g, 0.77 mmol) in
benzene (20 mL) over 5 min to form a green precipitate. After 16
h, the supernatant was decanted to leave 8 as a green powder which
was dried in vacuo. Yield: 0.25 g (76%). 1H NMR (CD2Cl2, 500.0
MHz): δ 7.47 (4H, m, ortho-H), 7.32 (4H, m, meta-H), 6.99 (2H,
Alternative Syntheses of fac-N3 Donor-Supported Hydrazido
Complexes. Complexes 7, 8, 9, and 10 were synthesized on the
NMR tube scale from [Ti(NNPh2)Cl2(py)2]n (4) using the following
general method. A solution of the fac-N3 donor ligand (12.0 µmol)
in C6D6 (0.2 mL) was added to a solution of 4 (5 mg, 10.8 µmol)
in C6D6 (0.2 mL). A solid immediately precipitated out of the
reaction mixture. The volatiles were removed under reduced
2
m, para-H), 4.24 (2H, d, J ) 8.0 Hz, NMecisCH2NMetrans up),
4.03 (1H, d, 2J ) 7.7 Hz, NMecisCH2NMecis up), 3.40 (1H, d, 2J )
7.7 Hz, NMecisCH2NMecis down), 3.25 (2H, d, 2J ) 8.0 Hz,
NMecisCH2NMetrans down), 2.51 (6H, s, NMecis), 2.13 (3H, s,
NMetrans). 13C-{1H} NMR (CD2Cl2, 125.8 MHz): δ 145.3 (ipso-
C), 129.6 (ortho-C), 123.6 (para-C), 119.2 (meta-C), 78.9
(NMecisCH2NMetrans), 76.8 (NMecisCH2NMecis), 41.9 (NMetrans),
37.5 (NMecis). IR (NaCl plates, Nujol mull, cm-1): ν 1594 (w),
1260 (m), 932 (sw), 802 (m). EI-MS: m/z 429 [M]+ (2%), 168
[NPh2]+ (100%), 129 [Me3[6]aneN3]+ (5%). HR EI-MS found
(calcd) for C18H25Cl2N5Ti: m/z 429.0974 (429.0966). Anal. Found
(calcd) for C18H25Cl2N5Ti: C, 50.4 (50.3); H, 6.0 (5.9); N, 16.2
(16.3).
1
pressure and the sample redissolved in CD2Cl2. Analysis by H
NMR indicated that in all cases the reaction had occurred cleanly
to give the desired product.
Attempted Reaction of Ti2(µ-η2 η1-NNMe2)2Cl4(py)2 (2) and
,
Ti2(µ-η2η1-NNMe2)2Cl4(HNMe2)2 (3) with Me3[9]aneN3, Me3[6]-
aneN3, HC(Me2pz)3, and HC(nBupz)3. A solution of the fac-N3
donor ligand (25 µmol) in CD2Cl2 (0.2 mL) was added to a solution
of 2 or 3 (25 µmol) in CD2Cl2 (0.2 mL). After 5 days of heating at
70 °C, analysis by 1H NMR showed that in all cases only a mixture
of the starting materials were present.
Ti(NNPh2)Cl2{HC(Me2pz)3} (9). A solution of HC(Me2pz)3
(0.37 g, 1.28 mmol) in benzene (20 mL) was added to a stirred
Inorganic Chemistry, Vol. 44, No. 23, 2005 8457

Parsons et al.
Table 8. Crystal Data Collection and Processing Parameters for Ti2(µ-η2,η1-NNMe2)2Cl4(HNMe2)2 (2), Ti2{µ-η2,η1-NN(CH2)5}2Cl4(HNMe2)3‚C6H6
(3‚C6H6), Ti2(µ-η2,η1-NNMe2)2Cl4(py)2 (5), and Ti(NNPh2)Cl2{HC(Me2Pz)3}‚2C6H6 (9‚2C6H6)
2
3‚C6H6
5
9‚2C6H6
empirical formula
fw
C8H26Cl4N6Ti2
443.95
C27H47Cl4N7Ti
647.27
C14H22Cl4N6Ti2
511.98
C40H44Cl2N8Ti
755.65
temp (K)
wavelength (Å)
space group
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
150
0.71073
P 21/n
8.9547(2)
14.4471(3)
15.0142(4)
90
94.5104(9)
90
1936.36(8)
4
1.523
1.375
0.0310, 0.0357
150
0.71073
P 21/c
10.5306(2)
17.0858(3)
17.9110(3)
90
103.6204(7)
90
3131.98(10)
4
1.373
0.875
0.0329, 0.0369
150
0.71073
C 2/c
15.2735(4)
9.9708(3)
14.6349(4)
90
90.6119(13)
90
2228.61(11)
4
1.526
1.207
0.0581, 0.0484
150
0.71073
P1h
9.6913(2)
13.9790(3)
14.1852(3)
80.3636(9)
88.1593(9)
86.2151(11)
1890.05(7)
2
Z
d
calcd (Mg m-3
)
1.328
0.408
0.0390, 0.0452
abs coeff (mm-1
R indices
)
R1, Rw [I>3σ(I)]a
2
a R1 ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) {∑w (|Fo| - |Fc|)2/∑(w|Fo| )}1/2
.
Crystal-Structure Determination of Ti2(µ-η2,η1-NNMe2)2Cl4-
(HNMe2)2 (2), [Ti2{µ-η2,η1-NN(CH2)5}2Cl4(HNMe2)3‚C6H6 (3‚
C6H6), and Ti2(µ-η2,η1-NNMe2)2Cl4(py)2 (5) and Ti(NNPh2)Cl2-
{HC(Me2pz)3}‚2C6H6 (9‚2C6H6). Crystal data collection and
processing parameters are given in Table 8. Crystals were mounted
on a glass fiber using perfluoropolyether oil and cooled rapidly to
150 K in a stream of cold N2 using an Oxford Cryosystems
CRYOSTREAM unit. Diffraction data were measured using an
Enraf-Nonius KappaCCD diffractometer, and intensity data were
processed using the DENZO-SMN package.35 The structures were
solved using SIR9236 which located all non-hydrogen atoms.
Subsequent full-matrix least-squares refinement was carried out
using the CRYSTALS program suite.37 Coordinates and anisotropic
thermal parameters of all non-hydrogen atoms were refined. Carbon-
bound hydrogen atoms were positioned geometrically. Nitrogen-
bound hydrogens in 2 and 3‚C6H6 were located from Fourier
difference maps and isotropically refined (for the purposes of
estimating N-H‚‚‚Cl hydrogen bonding parameters in Tables 1 and
2 geometrically positioned (N-H ) 0.87 Å) atoms were used).
Weighting schemes were applied as appropriate. Full listings of
atomic coordinates, bond lengths and angles, and displacement
parameters have been deposited at the Cambridge Crystallographic
Data Centre.
and nonlocal correlation corrections by Perdew.41 TZP basis sets
were used with triple-ú accuracy sets of Slater-type orbitals and a
polarization function added to the main group atoms. The cores of
the atoms were frozen up to 1s for C and N and 2p for Ti and Cl.
Fragment analyses use the MOs of the chosen fragments as the
basis set for the molecular calculation. Initial spin-restricted
calculations are carried out on the fragments with the geometry
that they have in the molecule; thus, the fragments are in a prepared
singlet state. Neutral fragments were chosen as this assisted in
drawing up the MO diagrams.
Acknowledgment. This work was supported by funding
from the EPSRC and Rhodes Trust. Calculations were carried
out using the facilities of the Oxford Supercomputing Centre.
Supporting Information Available: X-ray crystallographic files
in CIF format for the structure determination of compounds 2, 3,
5, and 9 and optimized geometries in Cartesian (xyz) form for
compounds I, II, III, and 2. This material is available free of charge
via the Internet at http://pubs.acs.org.
IC051271J
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M.; Cavallo, L.; Chong, D. P.; Deng, L.; Dickson, R. M.; Ellis, D. E.;
Fan, L.; Fischer, T. H.; Fonseca Guerra, C.; Van Gisbergen, S. J. A.;
Groeneveld, J. A.; Gritsenko, O. V.; Gru¨ning, M.; Harris, F. E.; van
den Hoek, P.; Jacobsen, H.; van Kessel, G.; Kootstra, F.; Vanlenthe,
E.; Osinga, V. P.; Patchkovskii, S.; Phillipsen, P. H. T.; Post, D.; Pye,
C. C.; Ravenek, W.; Ros, P.; Schipper, P. R. T.; Schreckenbach, G.;
Snijders, J. G.; Sola, M.; Swart, M.; Swerhone, D.; te Velde, G.;
Vernooijis, P.; Versluis, L.; Visser, O.; van Wezenbeek, E.; Wie-
senekker, G.; Wolff, S. K.; Woo, T. K.; Ziegler, T. Scientific
Computing and Modelling NV; Vrije Universiteit: Amsterdam, 2002.
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(b) Becke, A. D. J. Chem. Phys. 1988, 88, 1053.
Density Functional Theory Calculations. DFT calculations
were carried out using the Amsterdam Density Functional program
suite ADF 2002.02.38 The generalized gradient approximation was
employed, using the local density approximation of Vosko, Wilk,
and Nusair,39 together with nonlocal exchange correction by Becke40
(35) Otwinowski, Z.; Minor, W. Methods Enzymol. 1997, 276, 307.
(36) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(37) Watkin, D. J.; Prout, C. K.; Carruthers, J. R.; Betteridge, P. W.; Cooper,
R. I. CRYSTALS, version 11; Chemical Crystallography Laboratory:
Oxford, UK, 2001.
(41) Perdew, J. P. Phys. ReV. B 1986, 33, 8800.
8458 Inorganic Chemistry, Vol. 44, No. 23, 2005