Synthesis, structure, and LLCT transitions in terminal hydrazido(2-) bipyridine complexes of titanium

Article abstract of DOI:10.1021/ic700426s

Addition of 2,2′-bipyridine and its derivatives to Ti(NMe ₂)₂(dpma), where dpma is N,N-di(pyrrolyl-α-methyl)- N-methylamine, followed by various hydrazine derivatives was used to generate a series of terminal hydrazido(2-) complexes. Among the new complexes is Ti[=NN(H)Ph](Bu^t-bpy)(dpma), which was structurally characterized, where Bu^t-bpy is 4,4′-tert-butyl-2,2′-bipyridine. Other new complexes reported are Ti(NNMe₂)(Me-bpy)(dpma), Ti-(NNMe ₂)(bpy)(dpma), Ti(NNMe₂)(Ph-bpy)(dpma), Ti[NN(Me)Ph](Bu^t-bpy)(dpma), Ti[NN(Me)p-tolyl](Bu^t-bpy) (dpma), and Ti[NN(Me)4-FC₆H₄](Bu^t-bpy)(dpma). Titanium hydrazido(2-) complexes bearing bpy substituents possess a low-energy transition, leading them to have blue or green colors, which is somewhat unusual for titanium(IV) species. Through absorption studies on the derivatives, it was determined that the low-energy transition is the result of an unusual ligand-to-ligand charge transfer where electron density residing on the hydrazido(2-) is transferred to the bpy μ* orbitals.

Full text of DOI:10.1021/ic700426s

Inorg. Chem. 2007, 46, 6373−6381
Synthesis, Structure, and LLCT Transitions in Terminal Hydrazido(2
Bipyridine Complexes of Titanium
−)
Sameer Patel, Yahong Li,† and Aaron L. Odom*
Michigan State UniVersity, Department of Chemistry, East Lansing, Michigan 48824
Received March 5, 2007
Addition of 2,2
methylamine, followed by various hydrazine derivatives was used to generate a series of terminal hydrazido(2
complexes. Among the new complexes is Ti[
NN(H)Ph](But-bpy)(dpma), which was structurally characterized,
where But-bpy is 4,4
-tert-butyl-2,2 -bipyridine. Other new complexes reported are Ti(NNMe2)(Me-bpy)(dpma), Ti-
(NNMe2)(bpy)(dpma), Ti(NNMe2)(Ph-bpy)(dpma), Ti[NN(Me)Ph](But-bpy)(dpma), Ti[NN(Me)p-tolyl](But-bpy)(dpma),
and Ti[NN(Me)4-FC6H4](But-bpy)(dpma). Titanium hydrazido(2
) complexes bearing bpy substituents possess a
′-bipyridine and its derivatives to Ti(NMe2)2(dpma), where dpma is N,N-di(pyrrolyl-R-methyl)-N-
−)
d
′
′
−
low-energy transition, leading them to have blue or green colors, which is somewhat unusual for titanium(IV) species.
Through absorption studies on the derivatives, it was determined that the low-energy transition is the result of an
unusual ligand-to-ligand charge transfer where electron density residing on the hydrazido(2−) is transferred to the
bpy
π* orbitals.
Introduction
metals,6 only a few terminal hydrazido(2-) complexes of
the Group 4 elements have been reported until quite recently.
The first report was that of (Me3Si)2N-NdTiCp2 by
Wiberg.7 With the Schiff-base ligand TMTAA, Mountford
and co-workers synthesized Ph2N-NdTi(TMTAA).8 Woo
and Thorman prepared the porphyrin complexes R2N-Nd
Ti(TPP).9 The synthesis and structure of Ph2N-NdZr-
(DMAP)Cp2 was reported by Bergman and co-workers.10
Hydrazido(2-) complexes are largely of interest due to
their intermediacy in dinitrogen reduction. For example, they
are known intermediates in the reductive cleavage of
dinitrogen to produce ammonia in the catalytic system of
Schrock.1 They are believed to be involved in the natural
nitrogenase2 enzymatic cycle as well, e.g., in the E4 and E5
states of the FeMo cofactor.3 In other applications, terminal
hydrazido(2-) ligands are believed to participate in alkyne
hydrohydrazination4 and iminohydrazination5 catalysis.
The first structurally characterized example of a terminal
titanium hydrazido(2-) complex appeared in 2004 with the
report of Me2N-NdTi(dpma)(But-bpy) (1).11 This complex
is readily prepared (Scheme 1) by addition of But-bpy (4,4′-
di-tert-butyl-2,2′-bipyridine) to Ti(NMe2)2(dpma), where
dpma is N,N-di(pyrrolyl-R-methyl)-N-methylamine. To this
solution is then added H2NNMe2 to generate 1. Since the
structure of this complex has appeared, Mountford and co-
workers have reported Ph2N-NdTiCl2(L)x complexes, where
While hydrazido(2-) complexes have a role in several
important catalytic cycles and are known for many transition
* To whom correspondence should be addressed. E-mail: odom@cem.
msu.edu.
† Current address: Suzhou University, Department of Chemistry, Suzhou,
Jiangsu Province 215006, Peoples Republic of China.
(1) (a) Yandulov, D. V.; Schrock, R. R. Inorg. Chem. 2005, 44, 1103.
(b) Yandulov, D. V.; Schrock, R. R. Science 2003, 301, 76. (c)
Yandulov, D. V.; Schrock, R. R.; Rheingold, A. L.; Ceccarelli, C.;
Davis, W. M. Inorg. Chem. 2003, 42, 796.
(6) For reviews see (a) Nugent, W. A.; Haymore, B. L. Coord. Chem.
ReV. 1980, 31, 123-175. (b) Nugent, W. A.; Mayer, J. M. Metal-
Ligand Multiple Bonds; John Wiley and Sons: New York, 1988. (c)
Sutton, D. Chem. ReV. 1993, 93, 995-1022.
(7) Wiberg, N.; Ha¨ring, H.-W.; Huttner, G.; Friedrich, P. Chem. Ber. 1978,
111, 2708-2715.
(2) Igarashi, R. Y.; Seefeldt, L. C. Crit. ReV. Biochem. Mol. Biol. 2003,
38, 351.
(3) Durrant, M. C. Biochemistry 2002, 41, 13934.
(4) (a) Cao, C.; Shi, Y.; Odom, A. L. Org. Lett. 2002, 4, 2853. (b)
Ackermann, L.; Born, R. Tetrahedron Lett. 2004, 45, 9541. (c)
Khedkar, V.; Tillack, A.; Michalik, M.; Beller, M. Tetrahedron Lett.
2004, 45, 3123.
(5) Banerjee, S.; Cao, C.; Shi, Y.; Odom, A. L. J. Organometallic Chem.
2005, 690, 5066.
(8) Blake, A. J.; McInnes, J. M.; Mountford, P.; Nikonov, G. I.; Swallow,
D.; Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999, 379-391.
(9) Thorman, J. L.; Woo, L. K. Inorg. Chem. 2000, 39, 1301-1304.
(10) Walsh, P. J.; Carney, M. J.; Bergman, R. G. J. Am. Chem. Soc. 1991,
113, 6343-6345.
(11) Li, Y.; Shi, Y.; Odom, A. L. J. Am. Chem. Soc. 2004, 126, 1794.
10.1021/ic700426s CCC: $37.00
Published on Web 07/11/2007
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 16, 2007 6373

Patel et al.
Scheme 1. Synthesis of Ti(NNMe2)(But-bpy)(dpma) (1)
Figure 1. Hydrazido(2-) (left) and isodiazene (right) resonance forms
for metal center M.
pyramidalization is unusual in terminal hydrazido(2-)
complexes as a whole, where the angles around the unco-
ordinated nitrogen are typically more indicative of sp2
hybridization.6,15 A planar geometry in dialkylhydrazido(2-)
complexes can be attributed, in some cases, to significant
participation by the isodiazene resonance form, which can
be considered the result of â-N lone pair donation into the
MdN double bond. The resulting electronic structure at one
extreme can be drawn as shown in Figure 1 where the ligand
becomes a neutral donor and the formal oxidation state is
reduced by 2 relative to the hydrazido(2-) resonance form.
This isodiazene form is the major contributor for many
complexes. For example, Mansuy, Weiss, and co-workers
reported an isodiazene iron porphyrin complex with an N-N
bond distance of 1.232(5) Å,16 indicating a bond order of
∼2.0.17 Mo¨ssbauer and other techniques indicated the
complex was best described as iron(II).
Scheme 2. Preparation of Ti[NN(R2)R3](R1-bpy)(dpma) Complexes
L is a donor ligand and x ) 2-3.12 In the same report, DFT
was used to study the bonding of titanium hydrazido(2-)
complexes relative to the better known imido.
In the case of the titanium complexes, there is some
indication that the isodiazene resonance form participates.
For example, the N-N distance in 1 was determined to be
1.388(4) Å by X-ray diffraction. Hydrazido 1 reacts with
methyliodide to methylate the â-nitrogen forming [Ti-
(NNMe3)(But-bpy)(dpma)]I (1-MeI),11 which removes the
possibility of the isodiazene resonance form. The N-N
distance in this complex was determined as 1.429(13) Å,
similar to a typical N-N single bond distance of 1.451 (
0.05 Å in hydrazine.14 Consequently, some small participa-
tion of the isodiazene resonance form in 1 is suggested by
the experimental data for these complexes, but the participa-
tion is quite small. By the strongly pyramidalized â-nitrogen
angles, typical Ti-N double to triple bond distances, and
only slightly shortened N-N distances, the hydrazido(2-)
form is the major contributor in these titanium derivatives.
By contrast, â-nitrogen pyramidalization is not observed
in titanium and zirconium complexes where the â-nitrogen
bears aromatic groups.10,12 This suggests that the nitrogen
lone pair is delocalized by pendant aromatic groups in these
systems, a suggestion consistent with the DFT calculations
of Mountford and Green12 and consistent with the experi-
mental work in this study (vide infra).
The hydrazido pyrrolyl complex 1 has an optical transition
leading to the complex appearing blue, an unusual color for
a Ti(IV) complex. Here, we report a study on the nature of
that transition and the synthesis of several related terminal
hydrazido(2-) complexes of titanium and discuss what may
be gleaned from the electronic structure of these compounds
from these electronic transitions. There are multiple signs
of the hydrazido(2-) π system being strongly delocalized
with a pendant â-aryl group. In addition to explaining some
of the transition energy effects below, this delocalization is
likely the cause for the planarity of aryl-containing hy-
drazido(2-) ligands on titanium and zirconium complexes
as opposed to the dimethylhydrazido(2-) titanium com-
plexes, which are usually strongly pyramidalized.
Results and Discussion
Synthesis and Structure. For this study, we prepared a
series of 2,2′-bipyridine complexes with various substituents
(R1) in the 4,4′ positions (R1-bpy). The substituents on the
â-nitrogen were also altered to observe the effects on the
electronic structure. To this end, complexes containing a
variety of groups R2 and R3 such as methyl, aryl, and
hydrogen groups on the â-nitrogen were all prepared and
characterized. The syntheses were all analogous to that shown
in Scheme 1 for 1. The variety of complexes Ti[NN(R2)R3]-
(R1-bpy)(dpma) prepared is shown in Scheme 2.
Synthesized in the course of this work was a hydrazido-
(2-) complex of titanium bearing a hydrogen on the
â-nitrogen, Ti[NN(H)Ph](But-bpy)(dpma) (8). While these
types of protio complexes are known for other groups, they
have not been previously reported in Group 4. Their synthesis
The â-nitrogen in all the structurally characterized titanium
dimethylhydrazido(2-) complexes11,13 are pyramidalized to
typical angles for an sp3-hybridized nitrogen.14 This type of
(15) Kahlal, S.; Saillard, J.-S.; Hamon, J.-R.; Manzur, C.; Carrillo, D. Dalton
Trans. 1998, 1229.
(16) Mahy, J.-P.; Battioni, P.; Mansuy, D.; Fisher, J.; Weiss, R.; Mispelter,
J.; Morgenstern-Badarau, I.; Gans, P. J. Am. Chem. Soc. 1984, 106,
1699.
(17) Allman, R. Structural Chemistry. In The Chemistry of the Hydrazo,
Azo, and Azoxy Groups; Patai, S., Ed.; John Wiley and Sons: London,
1975; Part 1, p 23.
(12) Parsons, T. B.; Hazari, N.; Cowley, A. R.; Green, J. C.; Mountford,
P. Inorg. Chem. 2005, 44, 8442-8458.
(13) Banerjee, S.; Odom, A. L. Organometallics 2006, 25, 3099.
(14) Gordon, A. J.; Ford, R. A. The Chemist’s Companion; John Wiley
and Sons: New York, 1972.
6374 Inorganic Chemistry, Vol. 46, No. 16, 2007

LLCT Transitions in Titanium Hydrazido(2-) Complexes
Figure 3. Absorption spectra for (a) Ti(NNMe2)(But-bpy)(dpma) (1) with
expansion of the 450-800 nm region and (b) [Ti(NNMe3)(But-bpy)(dpma)]I
(1 + MeI).
Figure 2. ORTEP structural drawing of Ti[NN(H)Ph](But-bpy)(dpma) (8).
Selected bond lengths (Å) and angles (deg): Ti-N(6) 1.712(4), Ti-N(1)
2.079(4), Ti-N(2) 2.073(4), Ti-N(3) 2.396(4), Ti-N(4) 2.237(4), Ti-
N(5) 2.251(4), N(6)-N(61) 1.350(5), N(6)-Ti-N(2) 95.68(17), N(6)-
Ti-N(1) 103.82(18), N(2)-Ti-N(1) 101.94(15), N(6)-Ti-N(4) 100.13-
(16), N(2)-Ti-N(4) 157.97(14), N(1)-Ti-N(4) 89.13(14), N(6)-Ti-N(5)
97.39(17), N(2)-Ti-N(5) 91.60(15), N(1)-Ti-N(5) 153.41(14), N(4)-
Ti-N(5) 71.30(14), N(6)-Ti-N(3) 170.20(16), N(2)-Ti-N(3) 74.60(15),
N(1)-Ti-N(3) 77.49(16), N(4)-Ti-N(3) 89.58(13), N(5)-Ti-N(3) 84.35-
(15).
Scheme 3. Reactions of Ti[NN(H)Ph](But-bpy)(dpma) (8) with MeI
and HOTf
Figure 4. Plot of the low-energy transition energy versus the ionization
energy of the corresponding tertiary amine derivatives, MeN(R′)R.
low-energy band in the 400-800 nm region leading to their
blue or green colors in solution with extinction coefficients
from about 900 to 2200 M-1 cm-1.19 As shown, there are
solvent effects on the energy of the transition, which are
discussed in a later section.
Several of these compounds were also examined for
emission both at room temperature and in liquid-nitrogen-
cooled toluene glasses. However, the emission is either too
weak to observe or shifted outside of our observation
window.
To discover the nature of the transition, the effect on the
energy of the band caused by changing the structure in
several ways was observedsmethylation of the â-nitrogen
lone pair, altering the substituents R1 on the bpy, and altering
the substituents R2 and R3 on the â-nitrogen.
Methylation of the â-nitrogen extinguishes the low-energy
transition of the complex. For example, blue 1 exhibits a
band in the absorption spectrum at 550 nm (Figure 3a). On
methylation of the â-nitrogen, the complex becomes yellow
with the low-energy absorption no longer present (Figure
3b). Consequently, the low-energy band is likely related to
the lone pair on the â-nitrogen.
was sought because current catalysts for hydrohydrazination
have not been reported to be effective with monosubstituted
hydrazines such as phenylhydrazine. However, the synthesis
of 8 suggests that the cause for these problematic reactions
is not pandemic instability across all titanium complexes,
and catalysts for these monosubstituted hydrazine transfor-
mations may yet be accessible.18
The complex prepared from phenylhydrazine has been
structurally characterized (Figure 2). This complex, like the
others described, has a Ti-N(hydrazido) distance typical of
a double to triple bond at 1.712(4) Å. The N-N distance is
indicative of a small amount of double-bond character at
1.350(5) Å.
The â-nitrogen in 8 is also nucleophilic, and adducts with
methyl iodide (8 + MeI) and triflic acid (8 + HOTf) have
been prepared (Scheme 3).
Structural Effects and the Nature of the Electronic
Transition. The absorption transitions for compounds 1-8
are shown in Table 1. All the complexes exhibit a single
(19) During data analysis, the oscillator strengths (f) for compounds 1, 5,
6, and 7 were calculated from Gaussian fits to the peak shapes in
benzene. The values varied from 0.02 to 0.04, as would be expected
for compounds with extinction coefficients of this order. Figgis, B.
N.; Hitchman, M. A. Ligand Field Theory and its Applications; Wiley-
VCH: New York 2000; Chapter 8.
(18) The authors’ research group has recently developed a 6-coordinate
precatalyst effective for hydrohydrazination with monosubstituted
hydrazines. Banerjee, S.; Barnea, E.; Odom, A. L. Manuscript in
preparation.
Inorganic Chemistry, Vol. 46, No. 16, 2007 6375

Patel et al.
Table 1. Absorption Spectra Data for Complexes 1-8
νjmax × 10-3 (cm-1) [ꢀ × 10-2 (M-1 cm-1)]
complex
C6H5CN
CH3CN
THF
C6H6
Ti(NNMe2)(But-bpy)dpma (1)
Ti(NNMe2)(Me-bpy)dpma (2)
Ti(NNMe2)(bpy)dpma (3)
19.23 [9.60]
19.01 [11.1]
18.18 [9.90]
17.27 [12.4]
16.89 [16.8]
16.53 [21.5]
17.06 [10.4]
17.70 [12.6]
19.92 [8.57]
19.88 [6.44]
19.05 [7.26]
18.08 [13.3]
17.45 [13.5]
17.15 [11.8]
17.70 [10.2]
18.18 [10.8]
18.28 [10.9]
18.28 [10.4]
17.76 [11.3]
16.70 [12.1]
16.18 [14.0]
15.82 [15.3]
16.53 [12.4]
16.52 [15.5]
17.27 [9.44]
17.69 [9.18]
16.64a
Ti(NNMe2)(Ph-bpy)dpma (4)
15.87 [14.2]
15.02 [14.4]
14.66 [19.6]
15.20 [16.0]
16.13 [10.2]
Ti[NN(Me)Ph](But-bpy)dpma (5)
Ti[NN(Me)(p-tolyl)](But-bpy)dpma (6)
Ti[NN(Me)(p-FC6H4)](But-bpy)dpma (7)
Ti[NN(H)Ph](But-bpy)dpma (8)
a Low solubility limited ability to get an accurate measurement of the extinction coefficient.
Changing the substituents on the bpy ligand, R1, has a
dramatic effect on the energy of the transition. As the
substituents are made more electron donating, the energy of
the absorption increases. That the energy of the transition
changes significantly on altering the bpy suggests that the
bipyridine is also involved in the transition. The increasing
energy with greater electron-donating ability indicates that
the ligand is acting as an acceptor of electron density.
The substituents on the â-nitrogen greatly alter the energy
of the transition as well. The dimethylhydrazido complexes
have the highest energy bands. If an aromatic group is added
to the â-nitrogen, the transition red-shifts significantly. If
an electron-donating group is added to the aromatic group,
like in the p-tolyl complex 6, the absorption red-shifts relative
to the phenyl containing 5. In other words, a donor on the
â-nitrogen makes the transition more energetically accessible,
which is consistent with this group acting as an electron
donor. Consistent with this, addition of an electron-
withdrawing group, as in p-fluoro-containing 7, causes the
transition to blue-shift relative to the phenyl derviative.
That the energy of the absorption is strongly affected by
the inductive effects of substituents as far away from the
â-nitrogen as a p-methyl on a phenyl group indicates that
the important nitrogen lone pair is delocalized with the arene
π system. Consistent with this, the â-nitrogens of hydrazido-
(2-) ligands bearing aromatic groups are generally planar
regardless of the metal center.10,12,15 Naturally, this is
consistent with the structures usually obtained for simple
aniline derivatives, which are often near planar at nitrogen
due to delocalization.
the fluoro derivative is off the line is consistent with it acting
as a better donor in the charge transfer than anticipated from
its ionization potential. The equation for the line not including
the fluoro data, albeit with only four points, is y ) -4565
+ 3113x with R ) 0.995.
The red-shift on addition of aromatic rings to the â-ni-
trogen is readily explained using the one-electron argument
given above. In this explanation, the HOMO is shifted
upward in energy relatively to the LUMO by the presence
of the aromatic ring as indicated by the ionization energies
of the corresponding aniline derivatives. An alternative and
perhaps more appealing resonance explanation for the red-
shifting of the transition on addition of an aromatic ring
involves stabilization of the transition state, which will have
a positive or partial positive charge on the hydrazido(2-)
ligand. In other words, the stabilization of the incipient
cationic charge on the â-nitrogen by the aromatic ring would
lower the transition energy associated with the LLCT. This
delocalization between the â-nitrogen and the aromatic ring
is supported by the planar structure of the aryl-substituted
derivatives and the calculations (vide infra).
From the results above, we suggest that the low-energy
transition is assignable to a ligand-to-ligand charge transfer
(LLCT), where the donor is located on the hydrazido(2-)
ligand and the acceptor is the π* orbital of the bipyridine.
LLCT transitions22 have been extensively explored since their
early observation in beryllium complexes by Coates and
Green.23 In only a couple of instances have absorption bands
for Group 4 complexes been assigned to LLCT bands, and
these systems involved zirconium.24
One could argue that the transition could be assigned as
an MLCT with the metal acting as the donor being attenuated
by the hydrazido ligand, which would depend on the metal
having electron density (formally titanium is d0) through the
isodiazene resonance form (Figure 1). However, the authors
prefer the LLCT assignment because the structural data
suggest that the hydrazido(2-) resonance form is strongly
favored and because the presence of the transition is
dependent upon the existence of a â-nitrogen lone pair (vide
supra). This having been said, the transfer of electron density
is mediated by the metal, as it often will be in LLCT
For the donor in the charge transfer, the ionization energy
of the fragment should correlate with the transition energy
if the donor is kept constant.20 For the donor fragment, which
we believe to be the hydrazido(2-), we used the ionization
energies21 for the aniline derivatives of the hydrazido(2-)
complexes essentially replacing the “Ti(dpma)(But-bpy)”
fragment with Me, e.g., using the ionization energy of Me2-
NPh for Ti(NN(Me)Ph)(But-bpy)(dpma) in the plot (Figure
4). The trend observed is consistent with the electron density
for the charge transfer originating with the hydrazido(2-)
unit in these complexes (Figure 4). The most anomalous point
is for the p-fluoro derivative, which is unique as a potential
π donor among this small set of compounds. The direction
(22) For recent reviews see (a) Vogler, A.; Kunkely, H. Top. Curr. Chem.
2001, 213, 143. (b) Vogler, A.; Kunkely, H. Comment. Inorg. Chem.
1997, 19, 283.
(20) McConnell, H.; Ham, J. S.; Platt, J. R. J. Chem. Phys. 1953, 21, 66.
(21) The ionization energies are from the NIST Webbook found at http://
webbook.nist.gov/chemistry/.
(23) Coates, Y. E.; Green, S. I. E. J. Chem. Soc. 1962, 3340.
(24) (a) Kunkely, H.; Vogler, A. Inorg. Chem. Commun. 2004, 7, 35. (b)
Kunkely, H.; Vogler, A. Eur. J. Inorg. Chem. 1998, 1863.
6376 Inorganic Chemistry, Vol. 46, No. 16, 2007

LLCT Transitions in Titanium Hydrazido(2-) Complexes
transitions, and the best description is probably one that
involves the TidN-N(R2)R3 delocalized system acting as
the donor with the π* orbital of the bipyridine acting as the
acceptor.
Another possible interpretation of the above data would
be to assign the transition to an LMCT transition from the
hydrazido(2-) ligand to the titanium metal center. In this
interpretation, the hydrazido again acts as electron donor to
the metal where the electron density at the metal is attenuated
by electronics of the bpy. However, the electron would not
interact strongly with the π system of the bpy. While this is
difficult to exclude completely, there are several results that
make it seem unlikely. First, other hydrazido(2-)-terminal
titanium(IV) complexes not bearing bpy co-ligands and even
bearing pyrrolyl ancillaries do not have this low-energy
transition. For example, the recently reported13 Ti(NNMe2)-
(nacnac)(dap), where dap is dimethylaminomethylpyrrolyl,
is a more typical red color associated with LMCT transitions
to titanium(IV). Second, the transition is strongly effected
by substituents on the bpy.25 If the LMCT transition occurs
from the hydrazido(2-) to titanium in such a way that it
strongly interacts with the bpy π system, it again becomes
a semantic issue as to whether it is better to call it an LMCT
with some interaction with a bpy π system or an LLCT
mediated by the metal center. The calculations suggest the
LUMO (the most likely acceptor) is largely bpy-based (vide
infra), again favoring the LLCT designator.
DFT Calculations on Titanium Hydrazido(2-) Com-
plexes. The experimental results may be explained by
transitions resulting in electron transfer from hydrazido(2-)
to bpy π*.26 Calculations at the B3LYP/6-31G(d/p) level on
the dimethylhydrazido bpy containing 3 provide evidence
that the transition is one from HOMO to LUMO, which have
hydrazido and bpy π* character, respectively (Figure 5). The
HOMO is comprised largely of hydrazido(2-) character,
with the Ti-NR π bonding and NR-Nâ π antibonding. Also
in the HOMO are found some minor mixing with the bpy
and pyrrolyl π systems. The LUMO is largely bpy π* in
character with some mixing of the hydrazido π system.
Similar calculations were carried out on Ti[NN(Me)Ph]-
(But-bpy)(dpma) (5). The overall character of the HOMO
and LUMO between this complex bearing a phenyl-
substituted â-nitrogen and the dimethylhydrazido(2-) com-
plexes were similar except for the expected contributions of
the aromatic group to the hydrazido(2-) electronic structure
Figure 5. Kohn-Sham orbitals for the LUMO (top) and HOMO (bottom)
of Ti(NNMe2)(bpy)(dpma) (3).
(Figure 6). In other words, the HOMO in this case is largely
hydrazido(2-)-based with significant delocalization in the
π system of the phenyl group and some mixing with other
ligands on the metal as well. The LUMO is largely bpy π*
in character with some smaller contributions from other
ligands, most notably the hydrazido(2-). The HOMO of the
phenyl-substituted hydrazido, not surprisingly, is the apparent
combination of the HOMO of an aniline fragment and a
hydrazido(2-) orbital of similar character to the HOMO of
3. There are other subtle differences between the dialkyl-
hydrazido and the phenyl-substituted derivative, e.g., rotation
around the TidN vector which alters the nature of the [Ph-
(Me)N-NdTi]-N(bpy) interactions in the HOMO. The
LUMO exhibits modest participation of the phenyl ring.
The overall effect of the arene π system’s participation in
both the HOMO and the LUMO of 5 is to decrease the
energy of the HOMO-LUMO gap (EHLcalc) relative to the
dimethylhydrazido derivatives. This is consistent with the
(25) If one plots the energy of the transition in Pt(R-bpy)Cl2 versus the
one in the titanium complexes in this paper with various R (unfortu-
nately only three overlapping examples), one gets a straight line (R )
0.983) with a slope of 0.56 for the two systems. In other words, the
effect of the substituents in the titanium system is to change the energy
of the absorbance by about 1.8× more than in this known platinum
system, where the transition is a well-established MLCT with the bpy
as the acceptor. McInnes, E. J. L.; Farley, R. D.; Rowlands, C. C.;
Welch, A. J.; Rovatti, L.; Yellowless, L. J. Dalton Trans. 1999, 4203.
(26) TD-DFT calculations on 3 have been carried out using Gaussian at
the B3LYP/6-31G** level. However, the number, intensity, and energy
of the bands at this level did not seem to match well with experiment.
A full TD-DFT study on the entire series would be interesting and
may be enlightening as to the nature of the transitions. However,
limitations of this technique have been noted. (a) Neese, F. J. Biol.
Inorg. Chem. 2006, 11, 702. (b) Deeth, R. J. Faraday Discuss. 2003,
124, 378.
calc
red-shift found experimentally. For 3, EHL was 15 810
cm-1 versus the experimental energy for the transition in
benzene of 16 640 cm-1. For 5, EHL was 14 549 cm-1
calc
versus the experimental energy of 15 020 cm-1 for the
transition in benzene. The agreement is remarkable consider-
ing the lack of consideration for solvent effects and the one-
electron nature of this transition energy calculation. This
Inorganic Chemistry, Vol. 46, No. 16, 2007 6377

Patel et al.
Figure 7. Plot of transition energy versus dielectric constant of the solvent
for 1.
more polar solvents that were better organized by the charges
of the ground state lead to a higher-energy transition by being
poorly organized to support the charges of the excited state.
As a result, the energy of transition correlates fairly well to
the static dielectric constant of the solvent (Figure 7).29
Concluding Remarks
Titanium hydrazido(2-) complexes can be readily pre-
pared in circumstances where the dimerization processes can
be avoided, and we have prepared a series varying in
structure and electronics. The delocalization along the Ti-
N-N bonding vector leads to some unique electronic
features. In the presence of a bpy co-ligand, a rare example
of a Group 4 LLCT band results, which stretches well into
the visible absorption region and leads to observed colors
in solution from green to blue. Using structural modifications,
it was also possible to discern that the charge transfer likely
occurs with electron density moving from the hydrazido-
(2-) to the bpy π* orbitals.
The dramatic effects on the energy of the transition with
changing the para substituent of a phenyl group on the
hydrazido(2-) indicate the electronics of the system are very
sensitive to the nitrogen substituents and may suggest
delocalization from the metal-ligand multiple-bond π system
through the aromatic ring π system.12 The planarity of
terminal Group 4 hydrazido(2-) complexes bearing aryl
groups10,12 is likely due to this delocalization, and this
explains the disparity with pyrrolyl-bearing dimethylhy-
drazido(2-) complexes, which have been uniformly pyra-
midalized.11,13
Figure 6. Kohn-Sham orbitals for the LUMO (top) and HOMO (bottom)
of Ph(Me)NNdTi(But-bpy)dpma (5). (Derivative without tert-butyl groups
shown.)
seems consistent with the assertion of the HOMO-LUMO
nature of the transition.
Solvent Effects. As shown in Table 1, changing the
solvent has a dramatic effect on the energy of the transition.
The energy of the band blue-shifts over 2000 cm-1 on
moving from low-dielectric benzene to high-dielectric ac-
etonitrile for all of the complexes. The increase in energy
of the transition tracks roughly with the increasing dielectric
constant of the medium consistent with the above arguments
on the nature of the excited state. In this case, there is no
apparent correlation with acceptor number of the solvents,
which has been noted for other systems, e.g., cyano
complexes of ruthenium(II).27
In the ground state, the hydrazido(2-) ligand will be
negatively charged.28 On excitation some of that electron
density will shift to the bpy ligand. If the medium is polar,
it is aligned to interact with the negatively charged hydrazido
ligand in the ground state. On excitation, the charge density
shifts to the bpy, leaving the solvent “out of position” to
stabilize the molecular charge density. Consequently, the
(29) An attempt at a more thorough analysis on the complexes using the
Marcus-Hush equations gave results that were unreliable due to
incompatibilities between the model and the system being studied.
Namely, the “two sphere” model for the electron transfer may be
breaking down due to interpenetration of the spheres describing the
donor and acceptor. See the Supporting Information for more details.
Attempts to access additional information through electrochemical
measurements in these systems were thwarted by a consistent lack of
reversibility on oxidation. For some relevant references see the
following and references therein. (a) Goldsby, K. A.; Meyer, T. J.
Inorg. Chem. 1984, 23, 3002. (b) Chen, P.; Meyer, T. J. Chem. ReV.
1998, 98, 1439. (c) Blackbourn, R. L.; Hupp, J. T. J. Phys. Chem.
1990, 94, 1788. (d) Hupp, J. T.; Dong, Y.; Blackbourn, R. L.; Lu, H.
J. Phys. Chem. 1993, 97, 3278.
(27) Timpson, C. J.; Bignozzi, C. A.; Sullivan, B. P.; Kober, E. M.; Meyer,
T. J. J. Phys. Chem. 1996, 100, 2915-2925.
(28) This charge distribution is certainly what would be expected for
nitrogen bound to titanium considering the differences in anticipated
electronegativities for the two fragments. For further conformation,
see ref 12, especially footnote 28.
6378 Inorganic Chemistry, Vol. 46, No. 16, 2007

LLCT Transitions in Titanium Hydrazido(2-) Complexes
03M program35 as implemented on a G5 Macintosh desktop with
dual processors.
Experimental
General Considerations. All manipulations of air-sensitive
compounds were carried out in an MBraun drybox under a purified
nitrogen atmosphere. Anhydrous ether, pentane, and tetrahydrofuran
were purchased from Jade Scientific. Toluene was purchased from
Spectrum Chemical Mfg. Corp. Benzene was purchased from EMD
chemicals. Acetonitrile was purchased from Fischer chemicals.
Solvents were purified by sparging with dry N2; then, water was
removed by running through activated alumina systems purchased
from Solv-Tek. Benzonitrile was purchased from ACROS and
distilled over P2O5. Solvents were transferred under vacuum or N2
to vacuum tight glass vessels and stored in the glove box.
Synthesis and Characterization. Ti(dpma)(4,4′-dimethyl-2,2′-
bipyridine)(NNMe2) (2). To a mixture of Ti(dpma)(NMe2)2 (85
mg, 0.26 mmol) and 4,4′-dimethyl-2,2′-bipyridine (48 mg, 0.26
mmol) in Et2O (5 mL) cooled to -100 °C was added a colorless
solution of H2NNMe2 (16 mg, 0.26 mol) in Et2O (1 mL) dropwise.
After stirring at room temperature overnight, the color of the mixture
changed from yellow to purple. The volatiles of the reaction mixture
were removed in vacuo, resulting in a purple solid that was washed
with pentane. The solid was dried under reduced pressure to yield
42 mg of product (33%). 1H NMR (300 MHz, CDCl3): 7.91 (2 H,
s, 3.3′-[4,4′-dimethyl-2,2′-bipyridine]), 7.70 (2 H, s, 5-C4H3N), 7.62
(2 H, m, 6,6′-[4,4′-dimethyl-2,2′-bipyridine]), 7.19 (2 H, m, 5,5′-
[4,4′-dimethyl-2,2′-bipyridine]), 6.26 (2 H, dd, 4-C4H3N), 5.94 (2
H, s, 3-C4H3N), 3.68 (2 H, d, C4H3NCH2N), 3.00 (2 H, d, C4H3-
NCH2N), 2.55 (6 H, s, TiNN(CH3)2), 2.51 (6 H, s, 4,4′-dimethyl),
1.36 (3 H, s, C4H3NCH2N(CH3)). 13C NMR (CDCl3): 151.9 (2,2′-
[4,4′-dimethyl-2,2′-bipyridine]), 151.2 (4,4′-[4,4′-dimethyl-2,2′-
bipyridine]), 150.7 (6,6′-[4,4′-dimethyl-2,2′-bipyridine]), 137.0 (2-
C4H3N), 131.5 (5,5′-[4,4′-dimethyl-2,2′-bipyridine]), 126.7 (5-
C4H3N), 121.3 (3,3′-[4,4′-dimethyl-2,2′-bipyridine]), 107.0 (4-
C4H3N), 102.2 (3-C4H3N), 58.4 (C4H3NCH2N), 48.0 (TiNN(CH3)2),
44.1 (C4H3NCH2N(CH3)), 21.4 (4,4′-dimethyl). Anal. Found for
C25H31N7Ti (Calcd): C, 62.64 (62.89); H, 6.63 (6.54); N, 20.42
(20.53).
Deuterated solvents were dried over purple sodium benzophenone
ketyl (C6D6) or phosphoric anhydride (CDCl3) and distilled under
nitrogen. 1H and 13C spectra were recorded on Inova-300 or VXR-
500 spectrometers. H and 13C assignments were confirmed when
1
necessary with the use of 2-dimensional 1H-1H and 13C-1H
correlation NMR experiments. All spectra were referenced internally
to residual protiosolvent (1H) or solvent (13C) resonances. Chemical
shifts are quoted in ppm and coupling constants in Hz. Typical
coupling constants in 13C NMR are not listed. H2dpma,30 Ti(NMe2)2-
(dpma),31 and Ti(NNMe2)(But-bpy)(dpma)11 were prepared as
previously described. The hydrazines H2NN(Me)(4-CH3C6H4) and
H2NN(Me)(4-FC6H4) were prepared using the published procedure32
(except that the final extraction was done with ethyl acetate in place
of diisopropylether) from the arylhydrazine hydrochloride salts,
which were purchased from Aldrich Chemical Co. The arylhydra-
zine hydrochloride salts were converted to the free base form by
addition of NaOH.33
Ti(dpma)(2,2′-bipyridine)(NNMe2) (3). To a mixture of Ti-
(dpma)(NMe2)2 (345 mg, 1.07 mmol) and 2,2′-bipyridine (167 mg,
1.07 mmol) in Et2O (10 mL) cooled to -100 °C was added a
colorless solution of H2NNMe2 (64 mg, 1.07 mol) in Et2O (5 mL)
dropwise. After stirring at room temperature overnight, the color
of the mixture changed from yellow to purple. The volatiles of the
reaction mixture were removed in vacuo, and the resulting purple
powder was washed with pentane. The powder was dried under
reduced pressure to yield 316 mg of product (66%). 1H NMR (300
MHz, CDCl3): 8.10 (2 H, d, 3,3′-[2,2′-bipyridine]), 7.95 (2 H, m,
4,4′-[2,2′-bipyridine]), 7.81 (2 H, d, 6,6′-[2,2′-bipyridine]), 7.70 (2
H, s, 5-C4H3N), 7.39 (2 H, m, 5,5′-[2,2′-bipyridine]), 6.26 (2 H, s,
General Considerations for X-ray Diffraction. Crystals grown
from concentrated solutions at -35 °C quickly were moved from
a scintillation vial to a microscope slide containing Paratone N.
Samples were selected and mounted on a glass fiber in wax and
Paratone. The data collections were carried out at a sample
temperature of 173 K on a Bruker AXS platform three-circle
goniometer with a CCD detector. The data were processed and
reduced utilizing the program SAINTPLUS supplied by Bruker
AXS. The structures were solved by direct methods (SHELXTL
v5.1, Bruker AXS) in conjunction with standard difference Fourier
techniques.
2
4-C4H3N), 5.93 (2 H, s, 3-C4H3N), 3.79 (2 H, d, J ) 13.7 Hz,
2
C4H3NCH2N), 2.98 (2 H, d, J ) 13.5 Hz, C4H3NCH2N), 2.56 (6
H, s, TiNN(CH3)2, 1.34 (3 H, s, C4H3NCH2N(CH3)). 13C NMR
(CDCl3): 151.9 (2,2′-[2,2′-bipyridine]), 138.8 (3,3′, 5,5′-[2,2′-
bipyridine]), 136.9 (2-C4H3N), 131.6 (4,4′-[2,2′-bipyridine]), 125.9
(5-C4H3N), 120.6.0 (6,6′-[2,2′-bipyridine]), 107.2 (4-C4H3N), 102.4
(3-C4H3N), 58.4 (C4H3NCH2N), 47.9 (TiNN(CH3)2), 44.1 (C4H3-
NCH2N(CH3)). EI MS low res.; found (calcd): 449 (449). Anal.
Found for C23H27N7Ti (Calcd): C, 61.60 (61.47); H, 6.19 (6.06);
N, 21.57 (21.82).
Collection of UV-Vis Absorption Spectra. The room-temper-
ature absorption spectra were recorded on a Shimadzu UV 3101
PC. The extinction coefficients were obtained from Beer’s law
studies and were determined from at least four points. Solutions
for all the complexes were made in the dry box using freshly
distilled solvents. Determination of the absorption maxima for the
LLCT transition was accomplished by fitting the spectral data to a
Gaussian function. The details for the fits and plots are found in
the Supporting Information.
(35) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Montgomery, J. A., Jr.; Vreven, T.; Kudin,
K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone,
V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G.
A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.;
Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai,
H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.;
Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R.
E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J.
W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.;
Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.;
Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari,
K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.;
Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.;
Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.;
Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.;
Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A.
Gaussian 03, revision C.02; Gaussian, Inc.: Wallingford, CT, 2004.
Computational Details. The calculated molecular structure of
3 was obtained by geometry optimizations using DFT with the
B3LYP functional and Gaussian’s “Ultrafine” grid size.34 The
6-31G(p,d) basis set was used on all atoms, and the calculation
was done in restricted mode. All calculations used the Gaussian-
(30) Li, Y.; Turnas, A.; Ciszewski, J. T.; Odom, A. L. Inorg. Chem. 2002,
41, 6298.
(31) Harris, S. A.; Ciszewski, J. T.; Odom, A. L. Inorg. Chem. 2001, 40,
1987-1988.
(32) Lerch, U.; Ko¨nig, J. Synthesis 1983, 157-8.
(33) Yudina, L. N.; Bergman, J. Tetrahedron 2003, 59, 1265-75.
(34) Becke, A. D. J. Chem. Phys. 1993, 98, 1372.
Inorganic Chemistry, Vol. 46, No. 16, 2007 6379

Patel et al.
Ti(dpma)(4,4′-diphenyl-2,2′-bipyridine)(NNMe2) (4). To a
mixture of Ti(dpma)(NMe2)2 (73 mg, 0.23 mmol) and 4,4′-diphenyl-
2,2′-bipyridine (70 mg, 0.23 mmol) in toluene (8 mL) cooled to
-100 °C was added a colorless solution of H2NNMe2 (16 mg, 0.26
mmol) in toluene (1 mL) dropwise. After stirring at room
temperature overnight, the color of mixture changed from yellow
to dark blue. The volatiles of the reaction mixture were removed
in vacuo, and the resulting dark blue solid was washed with pentane.
The solid was dried under reduced pressure to yield 92 mg of
7.60 (2 H, d, 5-C4H3N), 7.57 (2 H, m, 6,6′-[4,4′-di-tert-butyl-2.2′-
bipyridine]), 7.38 (2 H, m, 5,5′-[4,4′-di-tert-butyl-2,2′-bipyridine]),
2
2
6.68 (2 H, d, J ) 7.7 Hz, 3-[4-CH3C6H4]), 6.50(2 H, d, J ) 7.7
Hz, 2-[4-CH3C6H4]), 6.20(2 H, m, 4-C4H3N), 5.94 (2 H, s,
3-C4H3N), 3.74 (2 H, d, 2J ) 13.5 Hz, C4H3NCH2N), 3.32 (3 H, s,
TiNN(CH3)(4-CH3C6H4)), 3.08 (2 H, d, 2J ) 13.5 Hz, C4H3-
NCH2N), 2.12 (3 H, s, TiNN(CH3)(4-CH3C6H4)); 1.47 (3 H, s, C4H3-
NCH2N(CH3)), 1.40 (18 H, s, 4,4′-di-tert-butyl). 13C NMR
(CDCl3): 164.0, (2,2′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 152.6
(4,4′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 151.8 (6,6′-[4,4′-di-tert-
butyl-2,2′-bipyridine]), 137.2 (2-C4H3N), 130.9 (5,5′-[4,4′-di-tert-
butyl-2.2′-bipyridine]), 128.9 (2,3,4,5,6-(4-CH3C6H4), 123.6 (5-
C4H3N), 117.0 (3,3′-[4,4′-di-tert-butyl-2.2′-bipyridine]), 110.7 (1-
(4-CH3C6H4),(107.5(4-C4H3N),102.6(3-C4H3N),58.9(C4H3NCH2N),
44.8 (C4H3NCH2N(CH3)), 40.7 (TiNN(CH3)(4-CH3C6H4)), 35.6
(C(CH3)3-[4,4′-di-tert-butyl-2,2′bipyridine]), 30.6 (C(CH3)3-[4,4′-
di-tert-butyl-2,2′-bipyridine]), 20.5 (4-CH3C6H4). Anal. Found for
C37H47N7Ti (Calcd): C, 69.80 (69.69); H, 7.34 (7.43); N, 15.49
(15.39).
1
product (68%). H NMR (300 MHz, CDCl3): 8.36 (2 H, s, 3,3′-
[2,2′-bipyridine]), 7.88 (2 H, s, 5-C4H3N), 7.77 (6 H, m, 6,6′, 4,4′-
[2,2′-bipyridine]) and [4,4′-diphenyl), 7.60 (8 H, m, [4,4′-diphenyl]),
6.26 (2 H, dd, 4-C4H3N), 5.94 (2 H, s, 3-C4H3N), 3.76 (2 H, d, 2J
) 13.4 Hz, C4H3NCH2N), 3.08 (2 H, d, 2J ) 13.7 Hz, C4H3-
NCH2N), 2.64 (6 H, s, TiNN(CH3)2, 1.48 (3 H, s, C4H3NCH2N-
(CH3)). 13C NMR (CDCl3): 152.4 (2,2′-[4,4′-diphenyl-2,2′-
bipyridine]), 152.1 (4,4′-[4,4′-diphenyl-2,2′-bipyridine]), 151.4 (6,6′-
[4,4′-diphenyl-2,2′-bipyridine]), 136.9 (2-C4H3N), 131.6 (5,5′-[4,4′-
diphenyl-2.2′-bipyridine]), 130.3 (1,1′-diphenyl), 129.5 (2,2′-
diphenyl), 129.0 (3,3′-diphenyl), 127.1 (4,4′-diphenyl), 123.7 (5-
C4H3N), 118.4 (3,3′-[4,4′-diphenyl-2,2′-bipyridine]), 107.2 (4-
C4H3N), 102.4 (3-C4H3N), 58.4 (C4H3NCH2N), 48.0 (TiNN(CH3)2),
44.3 (C4H3NCH2N(CH3)). Anal. Found for C35H35N7Ti (Calcd): C,
69.73 (69.88); H, 5.72 (5.86); N, 16.44 (16.30).
Ti(dpma)(4,4′-di-tert-butyl-2,2′-bipyridine)(NN(Me)(4-
FC6H4)) (7). To a mixture of Ti(dpma)(NMe2)2 (200 mg, 0.619
mmol) and 4,4′-di-tert-butyl-2,2′-bipyridine (169 mg, 0.63 mmol)
in Et2O (5 mL) cooled to -100 °C was added dropwise a solution
of H2N-N(Me)(4-FC6H4) (90 mg, 0.642 mmol) in Et2O (2 mL).
After stirring at room temperature overnight, the color of the
reaction mixture changed from yellow to green. The volatiles of
the reaction mixture were removed under reduced pressure, and
the resulting green solid was washed with pentane (3 × 3 mL).
The solid was dried under reduced pressure to yield 0.34 g of
product (85.4%). 1H NMR (500 MHz, CDCl3): 8.02 (2 H, s, 3,3′-
[4,4′-di-tert-butyl-2,2′-bipyridine]), 7.57 (2 H, d, 5-C4H3N), 7.52
(2 H, m, 6,6′-[4,4′-di-tert-butyl-2.2′-bipyridine]), 7.38 (2 H, m, 5,5′-
[4,4′-di-tert-butyl-2,2′-bipyridine]), 6.60-6.55 (4H, m, 4-CH3C6H4),
Ti(dpma)(4,4′-di-tert-butyl-2,2′-bipyridine)(NNMePh) (5). To
a mixture of Ti(dpma)(NMe2)2 (413 mg, 1.28 mmol) and 4,4′-di-
tert-butyl-2,2′-bipyridine (343 mg, 1.28 mmol) in Et2O (10 mL)
cooled to -100 °C was added a colorless solution of H2NN(Me)-
(Ph) (156 mg, 1.28 mol) in Et2O (5 mL) dropwise. After stirring at
room temperature overnight, the color of mixture changed from
yellow to dark green. The volatiles of the reaction mixture were
removed in vacuo, and the resulting dark green solid was washed
with pentane three times. The solid was dried under reduced
1
2
pressure to yield 501 mg of product (63%). H NMR (300 MHz,
6.20 (2 H, m, 4-C4H3N), 5.94 (2 H, s, 3-C4H3N), 3.76 (2 H, d, J
CDCl3): 8.03 (2 H, s, 3,3′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 7.59
(2 H, m, 5-C4H3N), 7.59 (2 H, m, 6,6′-[4,4′-di-tert-butyl-2.2′-
bipyridine]), 7.39 (2 H, m, 5,5′-[4,4′-di-tert-butyl-2,2′-bipyridine]),
6.88 (2 H, m, 3-C6H5), 6.57 (2 H, d, 2-C6H5), 6.46 (1 H, m, 4-C6H5),
6.22 (2 H, dd, 4-C4H3N), 5.96 (2 H, s, 3-C4H3N), 3.77 (2 H, d, 2J
) 13.5 Hz, C4H3NCH2N), 3.37 (3 H, s, TiNNCH3Ph), 3.11 (2 H,
d, 2J ) 13.5 Hz, C4H3NCH2N), 1.49 (3 H, s, C4H3NCH2N(CH3)),
1.41 (18 H, s, 4,4′-di-tert-butyl). 13C NMR (CDCl3): 163.9 (2,2′-
[4,4′-di-tert-butyl-2,2′-bipyridine]), 152.4 (4,4′-[4,4′-di-tert-butyl-
2,2′-bipyridine]), 151.5 (6.6′-[4,4′-di-tert-butyl-2,2′-bipyridine]),
136.9 (2-C4H3N), 130.6 (5,5′-[4,4′-di-tert-butyl-2,2′-bipyridine]),
128.1 (3-C6H5), 123.5 (5-C4H3N), 117.0 (3,3′-[4,4′-di-tert-butyl-
2,2′-bipyridine]), 116.2 (2-C6H5), 110.2 (4-C6H5), 107.3 (4-C4H3N),
102.4 (3-C4H3N), 58.7 (C4H3NCH2N), 44.6 (TiNNCH3), 40.2
(C(CH3)3-[4,4′-di-tert-butyl-2,2′-bipyridine]), 35.4 (C4H3NCH2N-
(CH3)), 30.3 (C(CH3)3-[4,4′-di-tert-butyl-2,2′-bipyridine]). EI MS
low res.; found (calcd): 623 (623). Anal. Found for C36H45N7Ti
(Calcd): C, 69.53 (69.27); H, 7.12 (7.20); N, 15.49 (15.71).
) 13.5 Hz, C4H3NCH2N), 3.30 (3 H, s, TiNN(CH3)(4-FC6H4)),
3.09 (2 H, d, J ) 13.5 Hz, C4H3NCH2N), 1.47 (3 H, s, C4H3-
2
NCH2N(CH3)), 1.40 (18 H, s, 4,4′-di-tert-butyl). 13C NMR
(CDCl3): 164.3, (2,2′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 152.6
(4,4′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 151.8 (6,6′-[4,4′-di-tert-
butyl-2,2′-bipyridine]), 137.2 (2-C4H3N), 130.8 (5,5′-[4,4′-di-tert-
butyl-2.2′-bipyridine]), 123.6 (5-C4H3N), 117.4 (3,3′-[4,4′-di-tert-
butyl-2.2′-bipyridine]), 114.7 (splitting, 2,3,5,6-(4-FC6H4), 111.7
(splitting, 1-(4-FC6H4)), 107.6 (4-C4H3N), 102.8 (3-C4H3N), 58.9
(C4H3NCH2N), 44.8 (C4H3NCH2N(CH3)), 41.0 (TiNN(CH3)(4-
FC6H4), 35.6 (C(CH3)3-[4,4′-di-tert-butyl-2,2′-bipyridine]), 30.6
(C(CH3)3-[4,4′-di-tert-butyl-2,2′-bipyridine]). 19F NMR (300 MHz,
CDCl3): -130.5 (1F, s, 4-FC6H4). GC-MS direct probe found
(calcd): 641 (641). Anal. Found for C36H44N7FTi (Calcd): C, 67.18
(67.36); H, 6.82 (6.86); N, 14.56 (15.28).
Ti(dpma)(4,4′-di-tert-butyl-2,2′-bipyridine)(NNHPh) (8). To
a mixture of Ti(dpma)(NMe2)2 (539 mg, 1.67 mmol) and 4,4′-di-
tert-butyl-2,2′-bipyridine (447.4 mg, 1.67 mmol) in Et2O (10 mL)
cooled to -100 °C was added a colorless solution of H2NN(H)Ph
(180 mg, 1.67mmol) in Et2O (5 mL) dropwise. After stirring at
room temperature overnight, the color of mixture changed from
yellow to dark green. The volatiles of the reaction mixture were
removed in vacuo, and the resulting dark green solid was washed
with pentane three times. The solid was dried under reduced
Ti(dpma)(4,4′-di-tert-butyl-2,2′-bipyridine)(NN(Me)(4-
CH3C6H4)) (6). To a mixture of Ti(dpma)(NMe2)2 (112 mg, 0.347
mmol) and 4,4′-di-tert-butyl-2,2′-bipyridine (93 mg, 0.347 mmol)
in Et2O (5 mL) cooled to -100 °C was added dropwise to a solution
of H2N-N(Me)(4-CH3C6H4) (47 mg, 0.346 mmol) in Et2O (2 mL).
After stirring at room temperature overnight, the color of mixture
changed from yellow to green. The volatiles of the reaction mixture
were removed under reduced pressure, and the resulting green solid
was washed with pentane (3 × 3 mL). The solid was dried under
reduced pressure to yield 0.18 g of product (82.6%). 1H NMR (500
MHz, CDCl3): 8.01 (2 H, s, 3,3′-[4,4′-di-tert-butyl-2,2′-bipyridine]),
1
pressure to yield 691 mg of product (68%). H NMR (300 MHz,
CDCl3): 8.22 (1 H, s, Ti(NNHPh), 8.04 (2 H, s, 3,3′-[4,4′-di-tert-
butyl-2,2′-bipyridine]), 7.61 (2 H, m, 5-C4H3N), 7.59 (2 H, m, 6,6′-
[4,4′-di-tert-butyl-2,2′-bipyridine]), 7.42 (2 H, m, 5,5′-[4,4′-di-tert-
butyl-2,2′-bipyridine]), 6.94 (2 H, m, 3-C6H5), 6.54 (3 H, m, 2-C6H5
6380 Inorganic Chemistry, Vol. 46, No. 16, 2007

LLCT Transitions in Titanium Hydrazido(2-) Complexes
Table 2. Structural Parameters for the X-ray Diffraction Studies of
8‚CH2Cl2
(4,4′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 151.0 (6,6′-[4,4′-di-tert-
butyl-2,2′-bipyridine]), 137.3 (2-C4H3N), 129.2 (5,5′-[4,4′-di-tert-
butyl-2,2′-bipyridine]), 128.0 (3-C6H5), 125.3 (5-C4H3N), 124.5
(3,3′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 120.9 (2-C6H5), 120.1 (4-
C6H5), 109.1 (4-C4H3N), 103.0 (3-C4H3N), 60.8 (C4H3NCH2N), 46.9
(TiNNCH3), 36.1 (C(CH3)3-[4,4′-di-tert-butyl-2,2′-bipyridine]), 30.5
(C(CH3)3-[4,4′-di-tert-butyl-2,2′-bipyridine]). Anal. Found for C36H46-
IN7Ti (Calcd): C, 57.26 (57.54); H, 6.02 (6.13); N, 13.16 (13.05).
Ti(dpma)(4,4′-di-tert-butyl-2,2′-bipyridine)(NNH2Ph)-
(CF3SO3) (8 + HOTf). To dark green Ti(dpma)(4,4′-di-tert-butyl-
2,2′-bipyridine)(NNHPh) (256 mg, 0.42 mmol) in toluene (10 mL)
cooled to near frozen in a liquid nitrogen cold well was added a
yellow solution of CF3SO3H (63 mg, 0.42 mmol) in toluene (5 mL)
dropwise. The color of the mixture changed from green to red after
addition. The reaction was stirred at room temperature for 2 h, and
the volatiles were removed in vacuo. The resulting red solid was
recrystallized from dichloromethane/pentane, and 74 mg of product
8
empirical formula
fw
C36H45Cl2N7Ti
694.59
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
P1h
11.467(12)
12.308(13)
15.270(16)
95.438(17)
1794(3)
2
µ (mm-1
calcd (g cm-3
total reflns
)
0.423
1.286
15 167
D
)
uniq. reflns (Rint
extinction
)
5182 (0.0656)
0.0014
R(F0)(I > 2σ)
0.0560
0.1365
2
Rw(F0 )(I > 2σ)
1
was obtained (32%). H NMR (300 MHz, CDCl3): 8.28 (2 H, s,
and 4-C6H5), 6.24 (2 H, dd, 4-C4H3N), 5.98 (2 H, s, 3-C4H3N),
3.79 (2 H, d, 2J ) 13.6 Hz, C4H3NCH2N), 3.14 (2 H, d, 2J ) 13.6
Hz, C4H3NCH2N), 1.52 (3 H, s, C4H3NCH2N(CH3)), 1.43 (18 H,
s, 4,4′-di-tert-butyl). 13C NMR (CDCl3): 164.1 (2,2′-[4,4′-di-tert-
butyl-2,2′-bipyridine]), 152.6 (4,4′-[4,4′-di-tert-butyl-2,2′-bipyri-
dine]), 151.8 (6.6′-[4,4′-di-tert-butyl-2.2′-bipyridine]), 137.2 (2-
C4H3N), 130.5 (5,5′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 128.8 (3-
C6H5), 123.8 (5-C4H3N), 117.9 (3,3′-[4,4′-di-tert-butyl-2,2′-
bipyridine]), 117.5 (2-C6H5), 109.8 (4-C6H5), 107.6 (4-C4H3N),
102.6 (3-C4H3N), 58.9 (C4H3NCH2N), 44.9 (C(CH3)3-[4,4′-di-tert-
butyl-2,2′-bipyridine]), 35.7 (C4H3NCH2N(CH3)), 30.6 (C(CH3)3-
[4,4′-di-tert-butyl-2,2′-bipyridine]). Satisfactory analysis on this
complex was not obtained after multiple attempts. However, the
salts derived from the compound were readily obtained as analyti-
cally pure compounds, and the compound’s composition has been
confirmed by X-ray diffraction and NMR spectroscopy.
3,3′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 7.35 (6 H, m, 5-C4H3N,
6,6′-[4,4′-di-tert-butyl-2,2′-bipyridine] and Ti(NNH2Ph)), 7.03 (1
H, m, 4-C6H5), 6.92 (2 H, d, 3-C6H5), 6.76 (2 H, m, 2-C6H5), 6.01
(2 H, m, 5,5′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 5.98 (2 H, dd,
2
4-C4H3N), 5.67 (2 H, s, 3-C4H3N), 4.25 (2 H, d, J ) 13.9 Hz,
2
C4H3NCH2N), 3.62 (2 H, d, J ) 13.7 Hz, C4H3NCH2N), 2.02 (3
H, s, C4H3NCH2N(CH3)), 1.43 (18 H, s, 4.4′-di-tert-butyl). 13C
NMR (CDCl3): 163.0 (2,2′-[4,4′-di-tert-butyl-2,2′-bipyridine]),
153.1 (4,4′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 150.6 (6,6′-[4,4′-
di-tert-butyl-2,2′-bipyridine]), 137.3 (2-C4H3N), 129.3 (5,5′-[4,4′-
di-tert-butyl-2,2′-bipyridine]), 128.0 (3-C6H5), 125.1 (5-C4H3N),
124.6 (3,3′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 120.3 (2-C6H5),
109.2(4-C6H5),104.0(4-C4H3N),102.4(3-C4H3N),60.8(C4H3NCH2N),
40.2 (C(CH3)3-[4,4′-di-tert-butyl-2,2′-bipyridine]), 36.1 (C4H3-
NCH2N(CH3)), 30.6 (C(CH3)3-[4,4′-di-tert-butyl-2,2′-bipyridine]).
Anal. Found for C36H44N7F3SO3Ti (Calcd): C, 56.73 (56.89); H,
5.88 (5.79); N, 12.74 (12.91).
Ti(dpma)(4,4′-di-tert-butyl-2,2′-bipyridine)(NNHMePh)I (8 +
MeI). To dark green Ti(dpma)(4,4′-di-tert-butyl-2,2′-bipyridine)-
(NNHPh) (207 mg, 0.34 mmol) in toluene (10 mL) cooled to near
frozen in a liquid nitrogen cold well was added a colorless solution
of MeI (100 mg, 0.70 mmol) in toluene (5 mL) dropwise. After
stirring at room temperature overnight, the color of the mixture
changed from dark green to brown. The volatiles of the reaction
mixture were removed in vacuo, and the resulting brown solid was
recrystallized from dichloromethane/pentane to yield 74 mg of red
Acknowledgment. The authors greatly appreciate the
financial support of the National Science Foundation,
Department of Energy-Defense Programs, and Michigan
State University. A.L.O. is an Alfred P. Sloan Fellow. A.L.O.
thanks Jim McCusker, Ned Jackson, Tom Meyer, and Richie
Eisenberg for helpful discussions.
1
product (29%). H NMR (300 MHz, CDCl3): 8.24 (2 H, s, 3,3′-
Supporting Information Available: Crystallographic details
and tabular material on positional and displacement parameters,
bond length, and angles are available for compound 8 in CIF format.
Gaussian fits, fitting parameters, tabular material for ∆E° calcula-
tions and plots of Eop - ∆E° vs 1/Dop - 1/Ds are available in pdf
[4,4′-di-tert-butyl-2,2′-bipyridine]), 7.33 (6 H, m, 5-C4H3N; 6,6′-
[4,4′-di-tert-butyl-2,2′-bipyridine]; 5,5′-[4,4′-di-tert-butyl-2,2′-
bipyridine]), 6.97 (3 H, m, TiNNMeHPh and 3-C6H5), 6.78 (2 H,
d, 2-C6H5), 6.01 (6 H, m, 4-C6H5, 4-C4H3N, and 3-C4H3N), 4.23
2
2
(2 H, d, J ) 13.9 Hz, C4H3NCH2N), 3.59 (2 H, d, J ) 13.9 Hz,
C4H3NCH2N), 2.00 (3 H, s, Ti(NNMeHPh)), 1.43 (18 H, s, 4.4′-
di-tert-butyl), 1.39 (3 H, s, C4H3NCH2N(CH3)). 13C NMR
(CDCl3): 166.7 (2,2′-[4,4′-di-tert-butyl-2,2′-bipyridine]), 153.1
1
format. H NMR spectra for 7 and 8. This material is available
free of charge via the Internet at http://pubs.acs.org.
IC700426S
Inorganic Chemistry, Vol. 46, No. 16, 2007 6381