Titanium Hydrazido and Imido Complexes: Synthesis, Structure, Reactivity, and Relevance to Alkyne Hydroamination

Article abstract of DOI:10.1021/ja038320g

Treatment of Ti(NMe₂)₂(dpma) (1) with aniline results in the protonation of the dimethylamido ligands, which are retained as dimethylamines, and generation of a titanium imido complex Ti(NPh)(NHMe ₂)₂-(dpma) (2) in 94% yield. The monomeric imido 2 is converted to the reactive dimeric μ-imido [Ti(NPh)-(dpma)]₂ (3) on removal of the labile dimethylamine donors. The dimer 3 is converted to monomeric terminal imido complexes in the presence of added donors, e.g., 4,4′-di-tert-butyl-2,2′-bipyridine (Bu^t-bpy) and DME. Compounds 1-3 exhibit the same rate constant for 1-phenylpropyne hydroamination by aniline and are all kinetically competent to be involved in the catalytic cycle. Attempts to use 1 as a catalyst for hydroaminations involving 1,1-dimethylhydrazine resulted in only a few turnovers under the best conditions. Consequently, the chemistry of 1 with hydrazines to generate hydrazido complexes was scrutinized for comparison with the imido species. Through these studies, titanium hydrazido complexes including Ti(η ²-NHNC₅H₁₀)₂(dpma) (5), Ti(η²-NHNMe₂)₂(dpma) (6), and [Ti(μ:η¹,η²-NNMe₂)(dpma)] ₂ (7) were characterized. In addition, a terminal hydrazido(2-) complex was available by addition of Bu^t-bpy to 1 prior to 1,1-dimethylhydrazine addition, which provided Ti(η¹-NNMe ₂)(Bu^t-bpy)(dpma) (8). Compound 8 was structurally characterized and compared to Ti(NPh)(Bu^t-bpy)(dpma) (4b), an imido derivative with the same ancillary ligand set. Compound 8 has a nucleophilic β-nitrogen consistent with a hydrazido(2-) formulation, as determined by reaction with Mel to form the ammonium imido complex [Ti(NNMe ₃)(Bu^t-bpy)(dpma)]l (9). Analogous pyridinium imido complexes [Ti(N-1-pyridinium)(Bu^t-bpy)(dpma)]⁺ (10) are available by addition of 1-aminopyridinium iodide to 1. From the investigations, some conclusions regarding the activity of titanium pyrrolyl complexes in hydroamination were drawn. The lack of conversion of the bis[μ-hydrazido(2-)] 7 to monomeric species in the presence of donor ligands is put forth as one explanation for the poor hydrazine hydroamination activity of 1. This problem was combated in the synthesis of Ti(NMe₂)₂(dap) ₂, which is an active catalyst for hydrazine hydroamination of alkynes.

Full text of DOI:10.1021/ja038320g

Published on Web 01/21/2004
Titanium Hydrazido and Imido Complexes: Synthesis,
Structure, Reactivity, and Relevance to Alkyne
Hydroamination
Yahong Li, Yanhui Shi, and Aaron L. Odom*
Contribution from the Department of Chemistry, Michigan State UniVersity,
East Lansing, Michigan 48824
Received September 3, 2003; E-mail: odom@cem.msu.edu.
Abstract: Treatment of Ti(NMe2)2(dpma) (1) with aniline results in the protonation of the dimethylamido
ligands, which are retained as dimethylamines, and generation of a titanium imido complex Ti(NPh)(NHMe2)2-
(dpma) (2) in 94% yield. The monomeric imido 2 is converted to the reactive dimeric µ-imido [Ti(NPh)-
(dpma)]2 (3) on removal of the labile dimethylamine donors. The dimer 3 is converted to monomeric terminal
imido complexes in the presence of added donors, e.g., 4,4′-di-tert-butyl-2,2′-bipyridine (But-bpy) and DME.
Compounds 1-3 exhibit the same rate constant for 1-phenylpropyne hydroamination by aniline and are all
kinetically competent to be involved in the catalytic cycle. Attempts to use 1 as a catalyst for hydroaminations
involving 1,1-dimethylhydrazine resulted in only a few turnovers under the best conditions. Consequently,
the chemistry of 1 with hydrazines to generate hydrazido complexes was scrutinized for comparison with
the imido species. Through these studies, titanium hydrazido complexes including Ti(η2-NHNC5H10)2(dpma)
(5), Ti(η2-NHNMe2)2(dpma) (6), and [Ti(µ:η1,η2-NNMe2)(dpma)]2 (7) were characterized. In addition, a terminal
hydrazido(2-) complex was available by addition of But-bpy to 1 prior to 1,1-dimethylhydrazine addition,
which provided Ti(η1-NNMe2)(But-bpy)(dpma) (8). Compound 8 was structurally characterized and compared
to Ti(NPh)(But-bpy)(dpma) (4b), an imido derivative with the same ancillary ligand set. Compound 8 has
a nucleophilic â-nitrogen consistent with a hydrazido(2-) formulation, as determined by reaction with MeI
to form the ammonium imido complex [Ti(NNMe3)(But-bpy)(dpma)]I (9). Analogous pyridinium imido
complexes [Ti(N-1-pyridinium)(But-bpy)(dpma)]+ (10) are available by addition of 1-aminopyridinium iodide
to 1. From the investigations, some conclusions regarding the activity of titanium pyrrolyl complexes in
hydroamination were drawn. The lack of conversion of the bis[µ-hydrazido(2-)] 7 to monomeric species in
the presence of donor ligands is put forth as one explanation for the poor hydrazine hydroamination activity
of 1. This problem was combated in the synthesis of Ti(NMe2)2(dap)2, which is an active catalyst for hydrazine
hydroamination of alkynes.
Introduction
nitrogens of the hydrazido. Third, the ligand may be terminal
to a single metal or bridging to two (µ2) or more metal centers.
A few of the various bonding modes available and all of the
In large part, investigation of hydrazido complexes has been
driven by studies of dinitrogen reduction to ammonia.1 Likely
intermediates in that process include N-N-bonded species (azo,
hydrazido, and hydrazine complexes), which can impart inter-
esting electronic and reactivity properties to metal complexes.2
Due to the composition of the nitrogenase active site, which
can incorporate both early and late transition metals (e.g.,
vanadium, molybdenum, and iron), studies on ligands bearing
N-N bonds have extended across the periodic table.
Hydrazido ligands may have several bonding modes to
transition metal centers.3 First, the coordination is classified by
the formal charge on the hydrazido ligand, which with the 1,1-
dialkylhydrazido ligands used here is limited to -1 or -2.
Second, the metal may be bound to either one (η1) or both (η2)
(2) Selected recent examples of dinitrogen reactivity, see: (a) Yandulov, D.
V.; Schrock, R. R. J. Am. Chem. Soc. 2002, 124, 6252-6253. (b) Laplaza,
C. E.; Johnson, M. J. A.; Peters, J.; Odom, A. L.; Kim, E.; Cummins, C.
C.; George, G. N.; Pickering, I. J. J. Am. Chem. Soc. 1996, 118, 8623. (c)
Smith, J. M.; Lachicotte, R. J.; Pittard, K. A.; Cundari, T. R.; Lukat-Rodgers,
G.; Rodgers, K. R.; Holland, P. L. J. Am. Chem. Soc. 2001, 123, 9222-3.
(d) Fryzuk, M. D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.; Mason, S.
A.; Koetzle, T. F. J. Am. Chem. Soc. 2001, 123, 3960-3973. (e) Odom,
A. L.; Arnold, P. L.; Cummins, C. C. J. Am. Chem. Soc. 1998, 120, 5836-
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K.; Mori, M. J. Am. Chem. Soc. 1998, 120, 7651-7652. (h) Solari, E.; Da
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P. Biology and Biochemistry of Nitrogen Fixation; Elsevier: Amsterdam,
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9
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10.1021/ja038320g CCC: $27.50 © 2004 American Chemical Society

Titanium Hydrazido and Imido Complexes
A R T I C L E S
Chart 1. Some Relevant Bonding Modes for 1,1-Dialkylhydrazido
described the synthesis and reactivity of titanium porphyrin
complexes of the type R2N-NdTi(TPP).10,11 In related chem-
istry, Leigh and co-workers published a series of papers12 on
titanium monocyclopentadienyl complexes bearing hydrazine-
derived ligands including bridging hydrazido(2-) containing
[Ti(µ-NNPh2)ClCp]2, which contains a µ2: η2,η1-hydrazido(2-)
and a µ2: η1,η1-hydrazido(2-) ligand.
Ligands and Associated Nomenclature
More common are reports of hydrazido(1-) complexes of
titanium.13 Fully characterized complexes in this genre usually
have incorporated cyclopentadienyl, tris(pyrazolyl)borate, or
halide supporting ligands.14
Using pyrrolyl-based ancillary ligands, we have been explor-
ing the catalytic chemistry of titanium complexes. Specifically,
Ti(NMe2)2(dpma) (1), where dpma is N,N-di(pyrrolyl-R-methyl)-
N-methylamine15 (dpma), is an effective hydroamination catalyst
for alkynes with primary amines16 (eq 1) and related transfor-
mations such as iminoamination.17
forms relevant to this work are shown in Chart 1. The usual
nomenclature for the structures, as used throughout the remain-
der of this paper, is shown below each structure.
In addition, terminal η1-hydrazido(2-) complexes may have
several resonance forms owing to the potential participation of
the lone pair on the â-nitrogen. Very strong donation from the
â-nitrogen lone pair and weak π-donation from the metal center
results in a dominant isodiazene resonance form, which is found
for many transition metal complexes.4 However, in circum-
stances where the metal complex would be strongly reducing
in the n - 2 formal oxidation state, e.g. titanium(II), the
hydrazido resonance form should dominate (vide infra).5
Consequently, a circumstance reminiscent of the electronic
structures of transition metal carbenes6 is found where the
carbene may be described as a Schrock-type, triplet carbene
with the metal in a high formal oxidation state, which is similar
to the terminal hydrazido(2-) resonance form. The alternative
description is a Fischer-type singlet carbene with the metal in
a low formal oxidation state, which is analogous to the
isodiazene resonance form with a strongly donating â-nitrogen
lone pair. Substantial reactivity differences are expected as one
proceeds through the spectrum of possible electronic structures
for the multiple-bond substituent.
While many hydrazido complexes have been generated and
characterized for the transition metals, the known hydrazido
complexes of titanium7 remain relatively limited. For example,
reports on η1-hydrazido(2-) complexes of titanium are restricted
to three systems. The earliest report belongs to Wiberg and co-
workers, who provided evidence for the titanocene complex
(Me3Si)2N-NdTiCp2.8 Utilizing the Schiff-base ligand TMTAA,
Mountford and co-workers described the synthesis and reactivity
of Ph2N-NdTi(TMTAA).9 Most recently, Woo and Thorman
In one attempt to broaden the scope of hydroamination
catalysis, a 1,1-disubstituted hydrazine was used in place of
(9) Blake, A. J.; McInnes, J. M.; Mountford, P.; Nikonov, G. I.; Swallow, D.;
Watkin, D. J. J. Chem. Soc., Dalton Trans. 1999, 379-391.
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Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 11649-11662. (b) Polse, J.
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A R T I C L E S
Li et al.
Scheme 1. Example of a Successful Hydroamination Reaction
with Hydrazines
primary amine for alkyne hydroamination. While titanium dpma
complexes were quite effective with primary amines, they
provided only a few turnovers with hydrazines as substrates
under the same conditions. Isolating the cause of the poor
catalytic activity of 1 led to the present study on the synthesis,
structure, and reaction chemistry of titanium hydrazido com-
plexes.
Figure 1. Simplified mechanistic scheme for alkyne hydroamination
(X ) aryl, alkyl, or NR2).
With the aid of the studies discussed here, we were able to
develop simple, effective catalysts for the desired transforma-
tion.18 With the improved titanium catalysts, hydrazones are
available directly from alkynes, and indoles can be prepared in
a one-pot procedure. An example of hydrazine hydroamination
with one of the catalysts developed is shown in Scheme 1, which
used bis(dimethylaminomethylpyrrolyl)bis(dimethylamido)-
titanium(IV), Ti(NMe2)2(dap)2. By analogy with the mechanism
for primary amine hydroamination (Figure 1),19,20 the titanium
system needs to access a titanium-nitrogen double-bond
complex (B), which can occur through reaction of the bis(amido)
precatalyst (A) with the H2NX species. The Ti-N multiple bond
can undergo [2 + 2] cycloaddition with alkynes to form a
metalloazacyclobutene intermediate and the new C-N bond.
Consequently, we sought to prepare and characterize terminal
hydrazido(2-) complexes of titanium with pyrrolyl-based ligands.
complexes, we first synthesized imido titanium species bearing
the dpma ancillary ligand. Titanium imido complexes21 are well-
known and better understood than their hydrazido analogues.22
Consequently, the imido compounds provide an important
framework for understanding hydrazido chemistry.
One of the key reactions that led to the discovery of the
hydroamination reactivity of the titanium dpma system is the
reaction of Ti(NMe2)2(dpma) (1) with aniline, which is shown
in eq 2. Treatment of the bis(dimethylamido) complex with
1 equiv of aniline generates a pseudo-octahedral terminal imido
Ti(NPh)(dpma)(NHMe2)2 (2) in 92% recrystallized yield. The
Results and Discussion
Synthesis and Reactivity of Titanium dpma Imido Com-
plexes. To better understand the reactivity of titanium hydrazido
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(20) For an excellent review of hydroamination chemistry, see: (a) Muller, T.
E.; Beller, M. Chem. ReV. 1998, 98, 675-703. For a unique perspective
on the field titanium hydroamination, see: (b) Bytschkov, I.; Doye, S. Eur.
J. Org. Chem. 2003, 935-946. (c) Pohlki, F.; Doye, S. Chem. Soc. ReV.
2003, 32, 104-114.
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Titanium Hydrazido and Imido Complexes
A R T I C L E S
Figure 2. ORTEP representation for the structure of Ti(NPh)(NHMe2)2-
(dpma) (2) from X-ray diffraction. Ellipsoids are at the 25% probability
level.
Figure 3. ORTEP representation for the structure of [Ti(NPh)(dpma)]2
(3) from X-ray diffraction. Ellipsoids are at the 25% probability level.
Table 1. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on Ti(NPh)(dpma)(NHMe2)2 (2)
Table 2. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on [Ti(NPh)(dpma)]2 (3)
Ti-N(1)
Ti-N(2)
Ti-N(3)
2.071(3)
2.080(2)
2.408(2)
Ti-N(4)
Ti-N(5)
Ti-N(6)
1.732(2)
2.221(3)
2.192(3)
Ti(1)-N(11)
Ti(1)-N(13)
Ti(1)-N(12)
Ti(1)-N(14)
Ti(1)-N(24)
2.005(2)
2.310(2)
2.038(2)
1.843(2)
1.890(2)
Ti(2)-N(21)
Ti(2)-N(22)
Ti(2)-N(23)
Ti(2)-N(24)
Ti(2)-N(14)
Ti(2)-C(141)
2.016(2)
2.017(2)
2.275(2)
1.915(2)
1.993(2)
2.477(3)
N(4)-Ti-N(1)
N(2)-Ti-N(1)
N(2)-Ti-N(5)
N(4)-Ti-N(3)
C(41)-N(4)-Ti
106.7(1)
147.6(1)
90.9(1)
177.0(1)
173.6(2)
N(4)-Ti-N(2)
N(4)-Ti-N(5)
N(1)-Ti-N(5)
N(6)-Ti-N(3)
N(4)-Ti-N(2)
105.3(1)
90.3(1)
150.8(1)
87.5(1)
105.3(1)
N(21)-Ti(2)-N(21)
N(11)-Ti(1)-N(12)
Ti(1)-N(14)-Ti(2)
148.5(1)
120.3(1)
93.9(1)
C(141)-N(14)-Ti(1)
C(241)-N(24)-Ti(1)
Ti(1)-N(24)-Ti(2)
174.0(2)
113.1(2)
94.9(1)
product retains the generated dimethylamine as donor ligands
in a mutually trans arrangement (Figure 2, Table 1). The labile
dimethylamines are both cis to the reactive imido bond.
Consequently, dimethylamine loss exposes the reactive func-
tional group to substrate.
Bergman and co-workers showed that Group-4 imido com-
plexes were the key intermediate in alkyne hydroamination by
zirconocene.19 The observation that titanium with a dpma
ancillary ligand has a propensity to stabilize imido ligands, in
association with the labile ligands adjacent to the reactive
multiple-bond functionality, led us to investigate similar ca-
talyses by the titanium dpma system.
The labile dimethylamine ligands of 2 are readily removed
on trituration with various noncoordinating solvents, e.g.,
toluene, to produce a µ-imido dimer [Ti(NPh)(dpma)]2 (3) with
some interesting structural features in the solid state (Figure 3,
Table 2). The molecule has one titanium bearing a dpma in a
fac-arrangement with relatively short Ti-N(imido) bond dis-
tances of 1.843(2) and 1.890(2) Å. The cohabitant titanium
center has a dpma with a mer-arrangement and much longer
Ti-N(imido) bond distances of 1.915(2) and 1.993(2) Å. The
phenyl groups of the imido ligands both lean toward the titanium
with the mer-dpma, and the ipso-carbon of one phenyl, the one
anti to the dpma methyl, has a close contact with a Ti-C
distance of 2.477(3) Å. From this, it appears that the titanium
center is electron-deficient and is seeking out additional
intramolecular interactions in an attempt to sate that deficiency.
The dimer 3, while unsymmetrical in the solid state, exhibits
one set of resonances for the dpma and phenyl groups by NMR
in fluid solution, presumably due to rapid exchange processes
relative to that time scale.
bpy) results in formation of Ti(NPh)(DME)(dpma) (4a) and
Ti(NPh)(But-bpy)(dpma) (4b), respectively.
[Ti(NPh)(dpma)]2 + 2L f 2Ti(NPh)(L)2(dpma) (3)
2L ) DME 4a (47%)
2L ) But-bpy 4b (85%)
The investigation of hydroamination with Ti(NMe2)2(dpma)
(1), Ti(NPh)(dpma)(NHMe2)2 (2), or [Ti(NPh)(dpma)]2 (3)
added as catalyst led to the same observed rate constant. In other
words, all three species, including the imido dimer, are
kinetically competent to be involved under the catalytic condi-
tions.
Synthesis and Reactivity of Hydrazido(1-) and Hydrazido-
(2-) Titanium dpma Complexes. Only a few titanium com-
plexes bearing multiple hydrazido(1-) ligands have been fully
characterized.13b,s,t For example, Leigh and co-workers reported
the bis[η2-hydrazido(1-)] complex of titanium Ti(NMeNMe2)2-
Cl2 synthesized from trimethylhydrazine and titanium chloride.
As shown in Scheme 2, treatment of a room-temperature
solution of Ti(NMe2)2(dpma) (1) with excess 1-aminopiperidine
resulted in the generation of an unusual bis[η2-hydrazido(1-)]
complex Ti(NHNC5H10)2(dpma) (5). Seven-coordinate 5 was
readily purified and isolated in 67% yield as yellow micro-
crystals.
The solid-state structure of 5 determined by X-ray diffraction
is shown in Figure 4. The complex exhibits a pseudo-pentagonal
bipyramidal arrangement of ligands with two pyrrolyl rings
occupying the axial positions. Distances and angles (Table 3)
involving the dpma ligand are typical for titanium. Metrical data
for 5, such as NR-Ti distances and angles internal to the
Reactions with donors lead to cleavage of dimeric 3 to
terminal imido compounds (eq 3). For example, treatment of
the dimer with DME or 4,4′-di-tert-butyl-2,2′-bipyridine (But-
9
J. AM. CHEM. SOC. VOL. 126, NO. 6, 2004 1797

A R T I C L E S
Li et al.
Figure 4. ORTEP representation for the structure of Ti(NHNC5H10)2(dpma)
(5) from X-ray diffraction. Ellipsoids are at the 25% probability level.
Scheme 2. Reactions of Ti(NMe2)2(dpma) (1) with
1,1-Dialkylhydrazines
Figure 5. ORTEP representation of the structure of [Ti(NNMe2)(dpma)]2
(7) from X-ray diffraction. Ellipsoids are at the 25% probability level.
Treatment of Ti(NMe2)2(dpma) (1) with excess 1,1-dimeth-
ylhydrazine results in the formation of two compounds (Scheme
2). The major product is bis[η2-hydrazido(1-)] Ti(NHNMe2)2-
(dpma) (6) analogous to 5, which has been characterized
spectroscopically. A second product of bis[µ: η1,η2-hydrazido-
(2-)] containing [Ti(NNMe2)(dpma)]2 (7) is consistently present
in samples of 6 due to loss of H2NNMe2 and dimerization. The
dimer could be prepared in pure form by addition of a slight
excess of H2NNMe2 to 1 followed by repeated crystallization.
The structure of 7 determined by X-ray diffraction, which bears
many features in common with the structure of 3, is shown in
Figure 5. The complex contains one seven-coordinate titanium
center and one five-coordinate titanium. The seven-coordinate
metal center, Ti(A), bears a mer-dpma ligand and is structurally
similar to 5. The five-coordinate metal center, Ti(B), bears a
fac-dpma and is structurally similar to 1.23 Other bridging
hydrazido(2-) complexes exhibit this unsymmetrical bridging
structure, such as [ZrCp2(NNPh2)]2 reported by Walsh and
Bergman.7
Bis(hydrazido) 6 can be prepared in >90% purity, as
determined by NMR spectroscopy, through the rapid addition
of a large excess of 1,1-dimethylhydrazine to a room-temper-
ature ethereal solution of 1 (Scheme 2). The dimerization is
apparently irreversible as addition of 10 equiv of H2NNMe2 to
a pure sample of dimeric 7 did not afford amounts of monomeric
1
6 detectable by H NMR, even after heating at 50 °C for 12 h
Table 3. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on Ti(NHNC5H10)2(dpma) (5)
(eq 4).
Ti-N(4)
Ti-N(5)
Ti-N(1)
Ti-N(2)
Ti-N(3)
1.894(3)
1.911(3)
2.070(3)
2.082(3)
2.321(3)
Ti-N(41)
2.221(3)
2.192(3)
1.435(4)
1.432(4)
Ti-N(51)
N(4)-N(41)
N(5)-N(51)
Ti-N(4)-N(41)
Ti-N(5)-N(51)
N(4)-Ti-N(5)
N(4)-Ti-N(1)
N(5)-Ti-N(1)
N(4)-Ti-N(2)
Ti-N(41)-N(4)
82.45(19)
N(5)-Ti-N(2)
N(1)-Ti-N(2)
N(4)-Ti-N(3)
N(5)-Ti-N(3)
N(1)-Ti-N(3)
N(2)-Ti-N(3)
Ti-N(51)-N(5)
99.88(12)
147.61(13)
138.1(12)
132.37(12)
73.28(11)
74.34(11)
59.34(16)
80.50(18)
89.09(12)
100.05(13)
102.22(12)
103.70(13)
57.71(16)
A terminal hydrazido(2-) was not obtained on addition of
DME, pyridine, or 4,4′-di-tert-butyl-2,2′-bipyridine to bis-
[µ: η1,η2-hydrazido(2-)] 7. Fortunately, terminal hydrazido(2-)
complexes are available if But-bpy is added prior to addition
of 1,1-dimethylhydrazine (Scheme 3). Pseudo-octahedral
hydrazido ligands, are reminiscent of previously reported η2-
hydrazido(1-) complexes. For example, the Ti-Nâ-NR angles
are significantly smaller at 57.7(2)° and 59.3(2)° than the Ti-
NR-Nâ angles of 82.4(2)° and 80.5(2)°.
(23) Harris, S. A.; Ciszewski, J. T.; Odom, A. L. Inorg. Chem. 2001, 40, 1987-
1988.
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1798 J. AM. CHEM. SOC. VOL. 126, NO. 6, 2004

Titanium Hydrazido and Imido Complexes
A R T I C L E S
Figure 7. ORTEP representation of the structure of Ti(NPh)(But-bpy)-
(dpma) (4b) from X-ray diffraction. Ellipsoids are at the 25% probability
level.
Figure 6. ORTEP representation for the structure of Ti(NNMe2)(But-bpy)-
(dpma) (8) from X-ray diffraction with 25% ellipsoids.
Table 4. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on [Ti(NNMe2)(dpma)]2 (7)
Scheme 3. Synthesis of Terminal Hydrazido(2-) Titanium
Ti(A)-N(11)
Ti(A)-N(21)
Ti(A)-N(12)
Ti(A)-N(22)
Ti(A)-N(1A)
Ti(A)-N(2A)
1.947(4)
1.972(4)
2.185(4)
2.202(4)
2.058(4)
2.056(5)
Ti(B)-N(11)
Ti(B)-N(21)
Ti(B)-N(1B)
Ti(B)-N(2B)
Ti(B)-N(3B)
Ti(A)-N(3A)
1.837(4)
1.836(4)
2.019(4)
2.016(4)
2.303(4)
2.299(4)
Complexes
N(21)-Ti(B)-N(11)
N(11)-Ti(A)-N(21)
90.66(19) N(12)-N(11)-Ti(B) 171.9(4)
83.59(18) N(12)-N(11)-Ti(A) 79.5(3)
N(11)-Ti(A)-N(22) 122.48(17) N(22)-N(21)-Ti(B) 171.8(3)
N(12)-Ti(A)-N(22) 161.50(16) N(22)-N(21)-Ti(A)
N(2B)-Ti(B)-N(1B) 113.12(18) N(2A)-Ti(A)-N(1A) 149.34(18)
79.4(3)
Table 5. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on Ti(NNMe2)(But-bpy)(dpma) (8)
Ti-N(4)
1.708(3)
2.064(3)
2.242(3)
1.388(4)
Ti-N(1)
Ti-N(3)
Ti-N(5)
2.069(3)
2.415(3)
2.238(3)
Ti-N(2)
Ti-N(6)
N(4)-N(41)
Ti(NNMe2)(But-bpy)(dpma) (8) is prepared by treating 1 with
But-bpy followed by 1 equiv of H2NNMe2.
N(4)-Ti-N(2)
N(2)-Ti-N(1)
N(2)-Ti-N(5)
N(4)-Ti-N(3)
N(41)-N(4)-Ti
101.1(1)
103.6(1)
90.9(1)
173.2(1)
177.3(2)
N(4)-Ti-N(1)
N(4)-Ti-N(5)
N(1)-Ti-N(5)
N(6)-Ti-N(3)
100.0(1)
101.9(1)
150.8(1)
86.0(1)
The terminal hydrazido(2-) complex Ti(NNMe2)(But-bpy)-
(dpma) (8) was characterized by X-ray diffraction (Figure 6).24
One interesting feature of the structure is the highly pyrami-
dalized â-nitrogen of the hydrazido(2-). The angles around N(41)
add to 337(1)°, only slightly larger than expected for a
tetrahedral nitrogen. The pyramidal â-nitrogen suggests that the
contribution from the isodiazene resonance form (Chart 1) is
only modest. However, the significance of the interaction
between the two nitrogens of the hydrazido(2-) group may be
better told by the N(4)-N(41) distance of 1.388(4) Å, which is
slightly shorter than a typical N-N single bond distance (see
the structure of [Ti(NNMe3)(But-bpy)(dpma)]+ (9) below). The
hydrazido(2-) ligand is linear with a Ti-N(4)-N(41) angle of
177.3(2)°.
Table 6. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on Ti(NPh)(But-bpy)(dpma) (4b)
Ti(1)-N(4)
Ti(1)-N(2)
Ti(1)-N(5)
1.721(6)
2.036(6)
2.230(6)
Ti(1)-N(1)
Ti(1)-N(6)
Ti(1)-N(3)
2.055(6)
2.227(6)
2.408(6)
N(4)-Ti(1)-N(2)
N(2)-Ti(1)-N(6)
N(4)-Ti(1)-N(6)
N(4)-Ti(1)-N(5)
C(40)-N(4)-Ti(1)
97.9(3)
N(4)-Ti(1)-N(1)
N(2)-Ti(1)-N(1)
N(1)-Ti(1)-N(6)
N(4)-Ti(1)-N(3)
103.7(3)
104.2(3)
151.2(2)
171.7(3)
92.6(2)
96.9(3)
96.9(3)
171.9(6)
For comparison with 8, the imido complex Ti(NPh)(But-bpy)-
(dpma) (4b), which bears the same ancillary ligands as 8, was
structurally characterized (Figure 7, Table 6). The compound
is available from the dimer (eq 3) or directly by addition of
aniline and But-bpy to Ti(NMe2)2(dpma) (1) as shown in Scheme
4. The titanium-imido bond distance of 1.721(6) Å is typical
for this functional group and the same within error as the Ti-N
multiple bond in 8.
We are beginning to probe the effects of substituents on Ti-N
bonding in terminal hydrazido(2-) complexes, a feature that may
be of paramount importance in designing and understanding
successful catalysts for hydrazine hydroamination. The terminal
(24) No terminal titanium hydrazido(2-) complexes are found in the latest
Cambridge Structural Database at the time of this writing. For examples
of structurally characterized terminal hydrazido(2-) compounds of the
Group-5 elements, see: (a) Veith, M. Angew. Chem., Int. Ed. Engl. 1976,
15, 387. (b) Green, M. L. H.; James, J. T.; Chernega, A. N. J. Chem. Soc.,
Dalton Trans. 1997, 1719. (c) Davies, S. C.; Hughes, D. L.; Janas, Z.;
Jerzykiewicz, L.; Richards, R. L.; Sanders, J. R.; Sobota, P. Chem. Commun.
1997, 1261. (d) Davies, S. C.; Hughes, D. L.; Janas, Z.; Jerzykiewicz, L.
B.; Richards, R. L.; Sanders, J. R.; Silverston, J. E.; Sobota, P. Inorg. Chem.
2000, 39, 3485. (e) Green, M. L. H.; James, J. T.; Saunders, J. F.; Souter,
J. J. Chem. Soc., Dalton Trans. 1997, 1281. There are many structurally
characterized examples of terminal hydrazido(2-) complexes for molyb-
denum and tungsten.
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A R T I C L E S
Li et al.
Scheme 4. Synthesis of Terminal Imido and Pyridinium Imido
Titanium Complexes
Figure 8. ORTEP representation of the structure of [Ti(NNMe3)(But-bpy)-
(dpma)]I (9) from X-ray diffraction. Anion is not shown. Ellipsoids are at
the 25% probability level.
Table 7. Selected Bond Distances (Å) and Angles (deg) from the
X-ray Diffraction Study on [Ti(NNMe3)(But-bpy)(dpma)]I (9)
hydrazido(2-) complexes exhibit a relatively low-energy transi-
tion in their absorption spectra that is related to the lone pair
on the â-nitrogen. For 8, the transition is at 547 nm with an
absorption coefficient of 1100 M-1 cm-1. The low-energy
absorption results in a dark blue color for 8, which is quite
unusual for a titanium(IV) complex. For example, imido
complex 4b with a very similar ligand set is pale yellow. A
study to detail the electronic structure of these metal-ligand
multiple-bond complexes and its possible relevance to hy-
drazido(2-) reactivity is underway.
Ti-N(4)
1.702(10)
2.052(8)
2.221(8)
1.429(13)
Ti-N(1)
Ti-N(6)
Ti-N(3)
2.041(9)
2.230(8)
2.349(14)
Ti-N(2)
Ti-N(5)
N(4)-N(41)
N(4)-Ti-N(2)
N(2)-Ti-N(6)
N(4)-Ti-N(6)
N(4)-Ti-N(5)
N(41)-N(4)-Ti
99.6(4)
86.4(3)
100.5(4)
97.2(4)
N(4)-Ti-N(1)
N(2)-Ti-N(1)
N(1)-Ti-N(6)
N(4)-Ti-N(3)
98.9(4)
105.2(3)
155.4(3)
170.8(4)
173.2(7)
The N-N bond distance in 9 is 0.06 Å longer than in hydrazido-
(2-) 8, suggesting a change in N-N multiple-bond character.
On methylation of the lone pair, the blue complex 8 becomes
the pale yellow of the ammonium imido, also signifying a
significant change in electronic structure.
Even though the isodiazene resonance form (Chart 1) will
participate, 8 is expected to bear a functional group more closely
resembling a hydrazido(2-) (vide supra). Considering the two
resonance forms may differ significantly in nucleophilicity of
Nâ, we investigated the reaction of 8 with an electrophiles
methyl iodide (Scheme 3). The N-trimethylammonium imido
complex [Ti(NNMe3)(But-bpy)(dpma)]I (9) was prepared, the
structure of which is shown in Figure 8.25 The Ti-N(4)-N(41)
bond angle in 9 is 173.2(7)° (Table 7). This linearity has been
noted in all of the structurally characterized N-ammonium imido
complexes, whether the â-nitrogen is sp2 or sp3 hybridized. One
of the few other N-ammonium imido compounds to be analyzed
by X-ray diffraction where the â-nitrogen is sp3-hybridized is
[MoCp*Me3(NNMe3)][OTf] prepared by Vale and Schrock.25d
The N-N bond distance in 9 is 1.429(13) Å; the N-N bond
distance in [MoCp*Me3(NNMe3)]+ is 1.426(5) Å, which is very
similar to the typical N-N single-bond length of 1.451 Å.26 In
addition, the Ti-N multiple bond measures 1.702(10) Å, which
is in the typical titanium-nitrogen double to triple bond range.
As shown in Scheme 4, N-pyridinium imido complexes25a
are readily accessed using a transamination route similar to the
hydrazido(2-) syntheses. Addition of 1-aminopyridinium iodide
to a solution of Ti(NMe2)2(dpma) (1) and But-bpy in acetonitrile
results in the formation of N-pyridinium imido [Ti(N-NC5H5)-
(But-bpy)(dpma)]I (10-I) in 94% recrystallized yield. While 10-I
has not been structurally characterized, its spectroscopic and
chemical properties are consistent with the salt formulation. For
example, the iodide is readily exchanged with other counterions
through reaction with AgOTf and AgBF4 to form [Ti(N-
NC5H5)(But-bpy)(dpma)]OTf (10-OTf) and [Ti(N-NC5H5)-
(But-bpy)(dpma)]BF4 (10-BF4), respectively. Also in support
of the salt formulation, 10-OTf and 10-BF4 have absorption
spectra very similar to 10-I. Interestingly, 10-I exhibits an
emission with a maximum at 469 nm on excitation at 303 nm.
Investigating the nature of this emission was the initial impetus
behind the synthesis of 10-OTf and 10-BF4. While 10-OTf and
10-BF4 have an absorption spectrum similar to 10-I, no emission
is observed for the complexes. In addition, [Ti(NNMe3)-
(But-bpy)(dpma)]I (9) does not emit, which suggests that bpy
is not the acceptor for the charge transfer. Consequently, the
transition leading to emission is likely due to an iodide to
pyridinium imido charge transfer. Consistent with this assertion,
1-aminopyridinium iodide also emits under the same conditions,
albeit at a substantially shifted wavelength from the emission
of 10-I.
(25) A few complexes with a metal-nitrogen multiple bond bearing a cationic
nitrogen of the type MdN-NR3 are known. They have been given the
moniker “hydrazidium” previously, which misleadingly has the “ium”
ending for a ligand with an overall negative charge. Consequently, we chose
an alternative nomenclature derived from N-ammonium imido. The only
N-ammonium imido titanium complexes in the literature are pyridinium
imido derivatives, see: (a) Retbøll, M.; Ishii, Y.; Hidai, M. Organometallics
1999, 18, 150-155. For ammonium imido complexes of other transition
metals, see: (b) Ishii, Y.; Tokunaga, S.; Seino, H.; Hidai, M. Inorg. Chem.
1999, 38, 2489-2496. (c) Ishino, H.; Tokunaga, S.; Seino, H.; Ishii, Y.;
Hidai, M. Inorg. Chem. 1999, 38, 2489-2496. (d) Vale, M. G.; Schrock,
R. R. Inorg. Chem. 1993, 32, 2767-2772. (e) Glassman, T. E.; Vale, M.
G.; Schrock, R. R. J. Am. Chem. Soc. 1992, 114, 8098-8109. (f) Galindo,
A.; Hills, A.; Hughes, D. L.; Richards, R. L.; Hughes, M.; Mason, J. J.
Chem. Soc., Dalton Trans. 1990, 283-288. (g) Glassman, T. E.; Vale, M.
G.; Schrock, R. R. J. Am. Chem. Soc. 1992, 114, 8098-8109. (h)
Wagenknecht, P. S.; Norton, J. R. J. Am. Chem. Soc. 1995, 117, 1841. (i)
Seino, H.; Ishii, Y.; Sasagawa, T.; Hidai, M. J. Am. Chem. Soc. 1995, 117,
12181-12193. (j) Ishii, Y.; Tokunaga, S.; Seino, H.; Hidai, M. Inorg. Chem.
1996, 35, 5118-5119.
(26) Gordon, A. J.; Ford, R. A. The Chemist’s Companion: A Handbook of
Practical Data, Techniques, and References; John Wiley & Sons: New
York, 1972.
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(JADE Scientific), and benzene (EM Science) were distilled from purple
sodium benzophenone ketyl. Dichloromethane (EM Science) and
acetonitrile (Spectrum Chemical) were distilled from calcium hydride.
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 and VXR-500
spectrometers. 1H and 13C assignments were confirmed when necessary
with the use of two-dimensional 1H-1H and 13C-1H correlation NMR
experiments. All spectra were referenced internally to residual protio-
solvent (1H) or solvent (13C) resonances. Chemical shifts are quoted in
ppm and coupling constants in Hz. H2dpma15 and Ti(NMe2)2(dpma)
(1)23 were prepared as previously described.
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 SAINT-
PLUS supplied by Bruker AXS. The structures were solved by direct
methods (SHELXTL v5.1, Bruker AXS) in conjunction with standard
difference Fourier techniques.
Concluding Comments and Relevance to
Hydroamination
For successful hydroamination activity, it appears necessary
for the titanium catalyst to access terminal multiple-bond
species. Reaction of Ti(NMe2)2(dpma) (1) with primary amines,
e.g., aniline, results in the formation of isolable dimeric [Ti(µ-
NPh)(dpma)]2 (3), which readily reacts with many different
donor ligands, such as DME and But-bpy, to provide mono-
meric, terminal imido titanium complexes 4. Examination of
the reactions between 1 and H2NNMe2 led to the synthesis and
isolation of dimeric hydrazido(2-) [Ti(NNMe2)(dpma)]2 (7).
Because neither 1,1-dimethylhydrazine nor But-bpy can prompt
conversion of dimeric 7 to a monomeric species, it is postulated
that the formation of 7 is one cause for inefficient alkyne
hydroamination catalysis by 1 with dimethylhydrazine.18 Since
terminal hydrazido(2-) complexes are likely necessary for
hydroamination activity,19 catalysis terminates on conversion
of the available titanium to dimeric 7. Indeed, reexamination
1
by H NMR spectroscopy of hydroamination reactions with 1
as catalyst confirms the presence of 7 (eq 5). Attempts to use
dimeric 7 or monomeric bis[dimethylhydrazido(1-)] 6 as catalyst
provided no hydroamination product (eq 6).
Collection of Emission Spectra. Emission spectra were collected
on a Fluorolog-3 spectrofluorometer made by the Spex Fluorescence
Group of Jobin Yvon Horiba equipped with a 450 W Xe excitation
lamp and a 1527 PMT. The spectra were taken in THF at room
temperature. Sample spectra can be found in the Supporting Information.
Ti(NPh)(NHMe2)2(dpma) (2). To a frozen solution of Ti(NMe2)2-
(dpma) (1) (323 mg, 1.00 mmol) in CH2Cl2 (5 mL) was added PhNH2
(91 µL, 1.00 mmol). The reaction mixture was allowed to stand at
-35 °C for 24 h. Onto the resulting red solution was layered 2 mL of
pentane. The vial was then stored at -35 °C, which yielded 2 as a red
1
crystalline solid in 94% yield (0.391 g). H NMR (300 MHz, C6D6):
δ ) 7.88 (2 H, d, J ) 1 Hz, 5-C4H3N), 7.23-7.11 (4 H, m, 2,3-C6H5N),
6.78 (1 H, m, 4-C6H5N), 6.62 (2 H, dd, 4-C4H3N), 6.20 (2 H, d, J )
2 Hz, 3-C4H3N), 3.15 (4 H, s, C4H3NCH2N), 2.04 (12 H, br s,
HN(CH3)2), 1.68 (3 H, s, C4H3NCH2NCH3), 1.4 (2 H, br s,
HNMe2).13C{1H} NMR (300 MHz, CDCl3): δ ) 158.7 (1-C6H5N),
137.6 (2-C4H3N), 130.4 (5-C4H3N), 128.5 (3-C6H5N), 124.9 (4-C6H5N),
120.3 (2-C6H5N), 107.3 (4-C4H3N), 102.5 (3-C4H3N), 60.8 (C4H3NCH2-
NCH3), 45.4 (C4H3NCH2NCH3), 41.9 (HN(CH3)2). Elemental analysis
for C21H32N6Ti, found (calcd): C, 60.28 (60.57); H, 7.81 (7.74); N,
19.97 (20.18).
Consequently, it is apparent that the additional dative interac-
tions between the â-nitrogens of the hydrazido ligands and
titanium limit the catalytic activity. To destabilize these dative
interactions and allow conversion of the dimeric hydrazido(2-)
complex to terminal hydrazido species, one can alter the
ancillary ligand set to add more bulk, make the metal center
more electron-rich, or both. The strategy behind the design of
the catalyst in Scheme 1 was to increase the coordination
number by one and add an additional donor amine. The dpma
ligand can be regarded as an X2L ancillary ligand;27 whereas,
the more active Ti(NMe2)2(dap)2 possesses an X2L2 ancillary
ligand set. It is the desire to weaken the dative interactions in
µ-hydrazido(2-) intermediates that led to the design of the
successful hydrazine hydroamination catalyst shown in
Scheme 1.28
[Ti(NPh)(dpma)]2 (3). To a solution of Ti(NMe2)2(dpma) (1) (0.323
g, 1 mmol) in toluene (5 mL) cooled to -50 °C was added a solution
of PhNH2 (182 µL, 2 mmol) in toluene (2 mL). The reaction mixture
was stirred at room temperature for 12 h, after which time volatiles
were removed under reduced pressure. The solid was dissolved in CH2-
Cl2 and recrystallized at -35 °C, yielding 0.323 g (98%) of [Ti(dpma)-
1
(NPh)]2 as a black solid. H NMR (300 MHz, C6D6): δ ) 7.71 (4 H,
d, J ) 1 Hz, 5-C4H3N), 6.83-6.43 (4 H, m, 4-C4H3N, C6H5), 6.07 (4
H, d, J ) 2 Hz, 3-C4H3N), 3.36 (4 H, d, J ) 14 Hz, C4H3NCH2N),
3.18 (4 H, d, J ) 14 Hz, C4H3NCH2N), 1.74 (6 H, s, NCH3).13C{1H}
(300 MHz, CDCl3): 138.0 (2-C4H3N), 134.1 (1-C6H5N), 130.2 (5-
C4H3N), 129.5 (5-C4H3N), 125.8 (4-C6H5N), 122.7 (2-C6H5N), 108.5
(4-C4H3N), 103.0 (3-C4H3N), 59.8 (C4H3NCH2N), 45.4 (NCH3).
Elemental analysis for C34H36N8Ti2: found (calcd) C, 61.85 (62.20);
H, 5.58 (5.53); N, 17.07 (17.07).
Ti(NPh)(DME)(dpma) (4a). To a 250 mL round-bottom flask
equipped with a stir bar was added dark red [Ti(NPh)(dpma)]2 (424
mg, 0.65 mmol) and 40 mL of DME. After stirring at room temperature
for 4 h, volatiles of the reaction mixture were removed in vacuo to
yield a dark orange solid. The solid was recrystallized from CH2Cl2/
pentane at -35 °C, which provided 253 mg of product. Yield: 47%.
1H NMR (300 MHz, CDCl3): δ ) 7.34 (2 H, s, 5-C4H3N), 7.28 (2 H,
m, 2-C6H5), 7.18 (2 H, m, 3-C6H5), 6.96 (1 H, m, 4-C6H5), 6.15 (2 H,
Experimental Section
General Considerations. All manipulations of air-sensitive com-
pounds were carried out in an MBraun drybox under a purified nitrogen
atmosphere. Anhydrous ether was purchased from Columbus Chemical
Industries Inc. and freshly distilled from purple sodium benzophenone
ketyl. Toluene was purchased from Spectrum Chemical Mfg. Corp.
and purified by refluxing over molten sodium under nitrogen for at
least 2 days. Pentane (Spectrum Chemical Mfg. Corp.), tetrahydrofuran
(27) Green, M. L. H. J. Organomet. Chem. 1995, 500, 127-148.
(28) Investigation of other ancillaries for hydrazine hydroamination led to the
synthesis of Ti(SC6F5)2(NMe2)2(NHMe2), which bears two electron-deficient
thiolates, as an alternative hydrazine hydroamination catalyst, see ref 18.
9
J. AM. CHEM. SOC. VOL. 126, NO. 6, 2004 1801

A R T I C L E S
Li et al.
m, 4-C4H3N), 5.96 (2 H, s, 3-C4H3N), 3.78 (4 H, s, C4H3NCH2N), 3.59
(4 H, d, CH3OC2H4OCH3), 3.44 (6 H, s, CH3OC2H4OCH3) 2.22 (3 H,
s, NCH3). 13C{1H} NMR (CDCl3): δ ) 138.1 (2-C4H3N), 134.2 (5-
C4H3N), 130.3 (1-C6H5), 129.5 (2-C6H5), 129.3 (3-C6H5), 125.8 (4-
C6H5), 108.5 (4-C4H3N), 103.0 (3-C4H3N), 71.8 (CH3OC2H4OCH3), 59.8
(C4H3NCH2N), 59.1 (CH3OC2H4OCH3), 45.4 (C4H3NCH2NCH3). El-
emental analysis for C21H28N4O2Ti, found (calcd): C, 60.33 (60.59);
H, 6.85 (6.73); N, 13.18 (13.47).
[Ti(µ-NNMe2)(dpma)]2 (7). To Ti(NMe2)2(dpma) (1) (298.6 mg,
0.92 mmol) in 10 mL of Et2O cooled to -100 °C was added H2NNMe2
(84 µL, 1.10 mmol) in 2 mL of Et2O dropwise. The mixture was
allowed to warm to room temperature and stir for 16 h. The solution
was filtered away from a yellow solid, which was recrystallized from
CH2Cl2 to yield the orange dimer 7 (71 mg, 26%). 1H NMR (300 MHz,
CDCl3): δ ) 7.02 (2 H, s, 5-C4H3N), 6.10 (2 H, s, 3-C4H3N), 6.07 (2
H, m, 4-C4H3N), 5.98 (2 H, s, 5-C4H3N), 5.77 (2 H, s, 3-C4H3N), 5.75
2
(2 H, m, 4-C4H3N), 4.50 (2 H, d, J ) 14 Hz, C4H3NCH2N), 4.25 (2
Ti(NPh)(dpma)(But-bpy) (4b). Method A: To a dark red solution
of [Ti(NPh)(dpma)]2 (215 mg, 0.33 mmol) in CH2Cl2 (5 mL) was added
a solution of But-bpy in CH2Cl2 (3 mL) dropwise. After stirring at room
temperature overnight, volatiles of the reaction mixture were removed
in vacuo to yield an orange solid. Yield: 335 mg (85%). Method B:
To a near frozen solution of Ti(NMe2)2(dpma) (1) (323 mg, 1.00 mmol)
and But-bpy (268 mg, 1.00 mmol) in Et2O (10 mL) was added a solution
of PhNH2 (93 mg, 1.00 mmol) in Et2O (5 mL) dropwise. After stirring
at room temperature overnight, volatiles were removed in vacuo to yield
an orange solid. The solid was recrystallized from CH2Cl2, yielding
crystals suitable for X-ray diffraction. Yield: 366 mg (62%). 1H NMR
(300 MHz, CDCl3): δ ) 8.02 (2 H, s, 3,3′-[But-bpy]), 7.70 (2 H, s,
5-C4H3N), 7.45 (2 H, m, 6,6′-[But-bpy]), 7.38 (2 H, m, 5,5′-[But-bpy]),
6.89 (2 H, m, 3-C6H5), 6.69 (2 H, d, 2-C6H5), 6.58 (1 H, m, 4-C6H5),
2
2
H, d, J ) 13.7 Hz, C4H3NCH2N), 4.18 (2 H, d, J ) 13.7 Hz, C4H3-
NCH2N), 4.01 (2 H, d, 2J ) 13.7 Hz, C4H3NCH2N), 3.22 (6 H, s,
NNMe2), 3.20 (3 H, s, C4H3NCH2NCH3), 3.09 (3 H, s, C4H3NCH2-
NCH3), 2.49 (6 H, s, NNMe2). 13C{1H} NMR (CDCl3): δ ) 138.4
(2-C4H3N), 137.5 (2-C4H3N), 129.6 (5-C4H3N), 127.4 (5-C4H3N), 108.1
(4-C4H3N), 107.9(4-C4H3N), 103.5 (3-C4H3N), 101.7 (3-C4H3N), 63.0
(C4H3NCH2N), 58.8 (C4H3NCH2N), 52.3 (NNMe2), 51.9 (NNMe2), 50.2
(C4H3NCH2NCH3). 48.7 (C4H3NCH2NCH3). Elemental analysis for
C26H38N10Ti2, found (calcd): C, 52.74 (53.21); H, 6.58 (6.48); N, 23.32
(23.88).
Ti(dpma)(But-bpy)(NNMe2) (8). To Ti(NMe2)2(dpma) (1) (1.018
g, 3.15 mmol) and But-bpy (845 mg, 3.15 mmol) in Et2O (10 mL)
cooled to -100 °C was added H2NNMe2 (189 mg, 3.15 mmol) in Et2O
(5 mL) dropwise. After stirring at room temperature overnight, volatiles
were removed in vacuo, resulting in a purple solid, which was washed
with pentane. Yield: 1.27 g (72%). 1H NMR (300 MHz, CDCl3): δ )
8.03 (2 H, s, 3,3′-[But-bpy]), 7.70 (2 H, s, 5-C4H3N), 7.67 (2 H, m,
6,6′-[But-bpy]), 7.38 (2 H, m, 5,5′-[But-bpy]), 6.26 (2 H, dd, 4-C4H3N),
2
6.26 (2 H, dd, 4-C4H3N), 5.94 (2 H, s, 3-C4H3N), 3.80 (2 H, d, J )
2
13.7 Hz, C4H3NCH2N), 3.12 (2 H, d, J ) 13.6 Hz, C4H3NCH2N),
1.52 (3 H, s, C4H3NCH2NCH3), 1.39 (18 H, s, 4,4′-di-tert-butyl). 13C-
{1H} NMR (CDCl3): δ ) 164.3 (2,2′-[But-bpy]), 152.6 (4,4′-[But-bpy]),
151.6 (6,6′-[But-bpy]), 136.8 (2-C4H3N), 129.8 (5,5′-[But-bpy]), 127.8
(1,4-C6H5), 124.2 (2,3-C6H5), 123.7 (5-C4H3N), 119.4 (4-C6H5), 117.1
(3,3′-[But-bpy]), 107.3 (4-C4H3N), 102.5 (3-C4H3N), 58.5 (C4H3NCH2N),
44.5 (C(CH3)3-[But-bpy]), 35.5 (C4H3NCH2NCH3), 30.3 (C(CH3)3-[But-
bpy]). Elemental analysis for C35H42N6Ti, found (calcd): C, 69.84
(70.58); H, 7.18 (7.06); N, 13.84 (14.13).
2
5.94 (2 H, s, 3-C4H3N), 3.72 (2 H, d, J ) 13.5 Hz, C4H3NCH2N),
3.02 (2 H, d, 2J ) 13.4 Hz, C4H3NCH2N), 2.57 (6 H, s, TiNN(CH3)2),
1.41 (18 H, s, tert-butyl), 1.38 (3 H, s, C4H3NCH2NCH3). 13C{1H} NMR
(CDCl3): δ ) 163.5 (2,2′-[But-bpy]), 152.2 (4,4′-[But-bpy]), 151.4 (6,6′-
[But-bpy]), 136.9 (2-C4H3N), 131.6 (5,5′-[But-bpy]), 123.1 (5-C4H3N),
117.0 (3,3′-[But-bpy]), 107.0 (4-C4H3N), 102.0 (3-C4H3N), 58.4
(C4H3NCH2N), 48.0 (TiNN(CH3)2), 44.1 (C4H3NCH2NCH3), 35.2
(C(CH3)3-[But-bpy]), 30.3 (C(CH3)3-[But-bpy]). Absorption spectrum:
λmax ) 547 nm, ꢀ ) 1100 cm-1 M-1. Elemental analysis for C31H43-
N7Ti, found (calcd): C, 66.31 (66.28); H, 7.99 (7.73); N, 17.23 (17.46).
Ti(dpma)(NHNC5H10)2 (5). To Ti(NMe2)2(dpma) (1) (234 mg, 0.72
mmol) in 5 mL of Et2O was quickly added 1-aminopiperidine (2 mL,
18.5 mmol, 26 equiv). After 1 h, a cloudy orange solution was obtained.
The solution was filtered, and the yellow precipitate was washed with
ether. The volatiles of the combined filtrates were removed under
reduced pressure to yield a yellow solid. The solid was dissolved into
CH2Cl2 and cooled to -35 °C, providing 210 mg (67%) of yellow
microcrystals. Single crystals suitable for X-ray diffraction were grown
from a saturated CH2Cl2 solution at -35 °C. 1H NMR (300 MHz,
CDCl3): δ ) 7.55 (2 H, s, TiNHNC5H10), 6.43 (2 H, s, 5-C4H3N),
[Ti(dpma)(But-bpy)(NNMe3)]I (9). To Ti(dpma)(But-bpy)(NNMe2)
(8) (700 mg, 1.25 mmol) in benzene (5 mL) at 0 °C was added MeI
(78 µL, 1.25 mmol) in benzene (3 mL) dropwise. The solution was
allowed to warm and stir after addition. The solution turned from the
blue of the starting material to yellow. After being stirred at room
temperature overnight, volatiles were removed in vacuo, yielding a
yellow solid. Recrystallization from ∼3 mL of CH2Cl2 at -35 °C
provided yellow microcrystals. Yield: 580 mg (66%). Single crystals
suitable for X-ray diffraction were grown by cooling a concentrated
solution of 9 in CH2Cl2. 1H NMR (300 MHz, d8-THF): δ ) 8.72 (2 H,
s, 3,3′-[But-bpy]), 7.49 (2 H, d, 6.6′-[But-bpy]), 7.40 (2 H, d, 5-C4H3N),
6.99 (2 H, d, 5,5′-[But-bpy]), 6.05 (2 H, dd, 4-C4H3N), 5.84 (2 H, d,
2
5.88 (2 H, m, 4-C4H3N), 5.74 (2 H, m, 3-C4H3N), 4.42 (2 H, d, J )
13.7 Hz, C4H3NCH2N), 4.04 (2 H, s, 2J ) 13.8 Hz, C4H3NCH2N), 2.91
(3 H, s, C4H3NCH2NCH3), 2.83-2.58 (6 H, m, TiNHNC5H10), 1.65-
1.32 (14 H, m, TiNHNC5H10). 13C{1H} NMR (CDCl3): δ ) 138.2 (2-
C4H3N), 126.8 (5-C4H3N), 106.8 (4-C4H3N), 100.6 (3-C4H3N), 62.7
(C4H3NCH2N), 58.3 (C4H3NCH2NCH3), 24.2 (2-C5H10N), 23.5 (4-
C5H10N), 22.4 (3-C5H10N). Elemental analysis for C21H35N7Ti, found
(calcd): C, 58.19 (58.22); H, 7.95 (8.14); N, 22.50 (22.62).
2
3-C4H3N), 3.82 (2 H, d, J ) 13.7 Hz C4H3NCH2N), 3.26 (2 H, d,
2J ) 13.4 Hz, C4H3NCH2N), 1.72 (9 H, s, TiNN(CH3)3), 1.65 (3 H, s,
C4H3NCH2NCH3), 1.45 (18 H, s, C(CH3)3-[But-bpy]). 13C{1H} NMR
(d8-THF): δ ) 165.8 (2,2′-[But-bpy]), 153.9 (4,4′-[But-bpy]), 150.6
(6,6′-[But-bpy]), 137.3 (2-C4H3N), 132.9 (5,5′-[But-bpy]), 130.8 (3,3′-
[But-bpy]), 124.8 (5-C4H3N), 108.7 (4-C4H3N), 103.8 (3-C4H3N), 60.3
(TiNN(CH3)3), 59.7 (TiNN(CH3)3), 45.18 (C(CH3)3-[But-bpy]), 36.5
(C4H3NCH2NCH3), 30.58 (C(CH3)3). Elemental analysis for C32H46N7-
ITi, found (calcd): C, 54.93 (54.62); H, 6.77 (6.60); N, 13.46 (13.94).
Ti(NHNMe2)2(dpma) (6). To an orange solution of Ti(dpma)-
(NMe2)2 (1) (231 mg, 0.71 mmol) in Et2O (10 mL) was quickly added
a solution of H2NNMe2 (1.580 g, 26.3 mmol) in 5 mL of Et2O. After
stirring at room temperature for 1 h, volatiles were removed in vacuo
to give a yellow solid. Unlike for 5, we were unable to purify the
complex due to irreversible formation of dimeric [Ti(µ-NNMe2)(dpma)]2
(7) during recrystallization. The complex formed using this preparation
1
1
[Ti(dpma)(But-bpy)(N-pyridinium imido)]I (10-I). To a near
frozen solution of Ti(NMe2)2(dpma) (1) (700 mg, 2.16 mmol) and But-
bpy (581 mg, 2.16 mmol) in CH3CN (10 mL) was added a solution of
1-aminopyridinium iodide (481 mg, 2.16 mmol) in CH3CN (5 mL)
dropwise. The reaction was stirred for 10 h at room temperature.
Volatiles were removed in vacuo to give a dark yellow solid. Yield:
1.48 g (94%). Single crystals were grown from CH3CN by slow
was >90% 6 by H NMR. H NMR (300 MHz, CDCl3) δ ) 6.81 (2
H, s, TiNHNMe2), 6.54 (2 H, s, 5-C4H3N), 5.97 (2 H, dd, 4-C4H3N),
2
5.86 (2 H, s, 3-C4H3N), 4.40 (2 H, d, J ) 13.6 Hz, C4H3NCH2N),
2
4.07 (2 H, d, J ) 13.7 Hz, C4H3NCH2N), 2.95 (3 H, s, C4H3NCH2-
NCH3), 2.64 (6 H, d, TiN(H)N(CH3)2, 2.10 (6 H, d, TiNHN(CH3)2).
13C{1H} NMR (CDCl3): δ ) 137.9 (2-C4H3N), 126.9 (5-C4H3N), 106.9
(4-C4H3N), 100.7 (3-C4H3N), 62.9 (C4H3NCH2N), 51.6 (TiNHNCH3),
51.0 (TiNHNCH3), 47.8 (C4H3NCH2NCH3).
1
evaporation. H NMR (300 MHz, CDCl3): δ ) 8.61 (2 H, m, 6,6′-
9
1802 J. AM. CHEM. SOC. VOL. 126, NO. 6, 2004

Titanium Hydrazido and Imido Complexes
A R T I C L E S
[But-bpy]), 8.39 (2 H, d, 2-C5H5N), 7.85 (4 H, m, 5,5′-[But-bpy] and
3,3′-[But-bpy]), 7.45 (2H, dd, 3-C5H5N), 7.21 (2H, s, 5-C4H5N), 7.07
(1 H, dd, 4-C5H5N), 6.19 (2 H, dd, 4-C4H5N), 6.00 (2 H, d, 3-C4H5N),
4.05 (2 H, d, 2J ) 13.9 Hz, C5H4NCH2N), 3.45 (2 H, d, 2J ) 13.9 Hz,
C5H4NCH2N), 1.86 (3 H, s, C5H4NCH2NCH3), 1.49 (18 H, s, C(CH3)3-
[But-bpy]). 13C{1H} NMR (CDCl3): δ ) 166.4 (2,2′-[But-bpy]), 152.7
(4,4′-[But-bpy]), 150.7 (6,6′-[But-bpy]), 141.0 (4-C5H5N), 136.8 (2-
C5H4N), 136.1 (5,5′-[But-bpy]), 127.8 (5-C4H5N), 124.7 (3-C5H5N),
119.8 (2-C5H5N), 109.0 (4-C4H5N), 103.6 (3-C4H5N), 59.4 (C5H4NCH2N),
45.7 (C5H4NCH2NCH3), 35.87 (C(CH3)3-[But-bpy]), 30.3 (C(CH3)3-
[But-bpy]). Absorption spectrum: λmax ) 346 nm, ꢀ ) 12 400 cm-1
M-1. Elemental analysis for C34H42IN7Ti, found (calcd): C, 56.88
(56.43); H, 5.94 (5.86); N, 13.29 (13.55).
(5-C4H3N), 124.5 (3-C5H5N), 119.7 (2-C5H5N), 109.0 (4-C4H3N), 103.6
(3-C4H3N), 59.5 (C5H4NCH2N), 45.7 (C5H4NCH2NCH3) 35.8 (C(CH3)3-
[But-bpy]), 30.3 (C(CH3)3-[But-bpy]). Absorption spectrum: λmax
)
343 nm, ꢀ ) 12 700 cm-1 M-1. Elemental analysis for TiC34H42N7-
BF4, found (calcd): C, 58.69 (59.74); H, 6.14 (6.21); N, 14.11 (14.35).
Procedure for the Kinetic Experiments. All manipulations were
done in an MBraun inert atmosphere glovebox under an atmosphere
of dry nitrogen. In a 1 mL volumetric flask was loaded catalyst (0.1
Ti-equiv, 0.04 mmol Ti), aniline (3 equiv, 1.2 mmol), FeCp2 (0.2 M
solution in toluene, 250 µL), and alkyne (1 equiv, 0.4 mmol). The
solution was diluted to 1 mL with toluene and transferred to a J-Y
NMR tube. The tube was removed from the drybox and heated in an
oil bath at 100 °C, and the concentration of 1-phenylpropyne was
monitored as a function of time by 1H NMR spectroscopy. The observed
pseudo-first-order rate constants using this procedure for Ti(NMe2)2-
(dpma) (1), Ti(NPh)(NHMe2)2(dpma) (2), and [Ti(NPh)(dpma)]2 (3)
[Ti(dpma)(But-bpy)(N-pyridinium imido)]OTf (10-OTf). To a
suspension of AgOTf (81 mg, 0.31 mmol) in CH3CN cooled to -100
°C was added a cold solution of [Ti(dpma)(But-bpy)(N-1-pyridinium)]I
(10-I) (227 mg, 0.31 mmol) in CH3CN dropwise. The reaction mixture
was allowed to warm to room temperature and stir 16 h. After this, a
gray precipitate was filtered away from the yellow-brown solution. The
volatiles were removed in vacuo, yielding a brown solid. The solid
was recrystallized from CH3CN at -35 °C, which provided 115 mg
were 3.9 × 10-6, 3.6 × 10-6, and 3.6 × 10-6 s-1
.
Attempted Hydroamination of 1-Hexyne with 1,1-Dimethyl-
hydrazine Using 1, 6, and 7 as Catalyst. To a solution of H2NNMe2
(228 µL, 3 mmol) and 1-hexyne (115 µL, 1 mmol) in 30 mL of toluene
was added Ti(NMe2)2(dpma) (1) (65 mg, 0.2 mmol), Ti(NHNMe2)2-
(dpma) (6) (70 mg, 0.2 mmol), or [Ti(NNMe2)(dpma)]2 (7) (29 mg,
0.05 mmol). The reaction mixtures were sealed in a 50 mL pressure
tube and put in a 100 °C oil bath for 24 h. The vessels were returned
to the drybox. The generation of hydroamination product was probed
by GC/FID in comparison with authentic samples. The volatiles of the
reaction mixtures were removed in vacuo, and the resulting residues
were analyzed by 1H NMR for investigation of the titanium complexes
prepared. The reaction involving 1 had generated 7 as the major titanium
product observed. No hydroamination product was observed when either
6 or 7 were used. Trace amounts of hydroamination product were
observed with 1 as catalyst.
1
(49%) of 10-OTf. H NMR (300 MHz, CDCl3): δ ) 8.49 (2 H, m,
6.6′-[But-bpy]), 8.38 (2 H, d, 2-C5H5N), 7.78 (2 H, m, 5,5′-[But-bpy]),
7.66 (2 H, dd, 3,3′-[But-bpy]), 7.43 (2 H, dd, 3-C5H5N), 7.22 (2 H, s,
5-C4H5N), 7.04 (2 H, dd, 4-C5H5N), 6.20 (2 H, dd, 4-C4H5N), 5.95 (2
H, m, 3-C4H5N), 3.99 (2 H, d, 2J ) 13.9 Hz, C5H4NCH2N), 3.40 (2 H,
2
d, J ) 13.9 Hz, C5H4NCH2N), 1.85 (3 H, s, C5H4NCH2NCH3), 1.46
(18 H, s, C(CH3)3[But-bpy]). 13C{1H} NMR (CDCl3): δ ) 166.5 (2,2′-
[But-bpy]), 153.0 (4,4′-[But-bpy]), 150.5 (6,6′-[But-bpy]), 141.1 (4-
C5H5N), 136.8 (2-C5H4N), 136.9 (5,5′-[But-bpy]), 127.9 (5-C4H5N),
124.5 (3-C5H5N), 119.8 (2-C5H5N), 108.9 (4-C4H5N), 103.6 (3-C4H5N),
59.5 (C5H4NCH2N), 45.7 (C5H4NCH2NCH3), 35.8 (C(CH3)3-[But-bpy]),
30.2 (C(CH3)3-[But-bpy]). Absorption spectrum: λmax ) 347 nm, ꢀ )
19 200 cm-1 M-1. Elemental analysis for TiC35H42N7SF3O3, found
(calcd): C, 56.19 (56.32); H, 5.78 (5.63); N, 12.83 (13.14).
Acknowledgment. The authors gratefully acknowledge the
financial support of the Petroleum Research Fund administered
by the American Chemical Society, Center for Fundamental
Materials Research at MSU, Department of Energy-Defense
Programs, Office of Naval Research, and Michigan State
University. A.L.O. thanks Mitch Smith, Seth N. Brown, Dan
Nocera, Zhi-Heng Loh, and Jim McCusker for many interesting
and helpful discussions. The authors also appreciate the aid of
James T. Ciszewski with some of the X-ray diffraction studies.
[Ti(dpma)(But-bpy)(N-pyridinium imido)]BF4 (10-BF4). To a
suspension of AgBF4 (53.2 mg, 0.27 mmol) in CH3CN at -100 °C
was added a cold solution of [Ti(dpma)(But-bpy)(N-1-pyridinium)]I (10-
I) (200 mg, 0.276 mmol) in CH3CN dropwise. The mixture was allowed
to warm to room temperature and stirred for 16 h. The reaction was
filtered to remove a gray precipitate from the yellow-brown solution.
Volatiles were removed in vacuo, and the resulting solid was recrystal-
lized from CH3CN at -35 °C, yielding 112 mg (60%) of yellow
1
Supporting Information Available: Supporting Information
Available: Tables of crystallographic data including refinement
parameters, coordinates, bond distances, and bond angles.
Emission spectra for 10-I and 1-aminopyridinium iodide. This
material is available free of charge via the Internet at http://
pubs.acs.org. See any current masthead page for ordering
information and Web access instructions.
product. H NMR (300 MHz, CDCl3): δ ) 8.37 (4 H, m, 2-C5H5N,
3-C5H5N), 7.7 (1 H, m, 4-C5H5N) 7.65 (2 H, m, 6,6′-[But-bpy]), 7.41
(2 H, m, 5,5′-[But-bpy]), 7.22 (2 H, s, 5-C4H3N), 6.20 (2 H, m,
4-C4H3N), 6.00 (2 H, s, 3-C4H3N), 4.05 (2 H, d, 2J ) 14.2 Hz,
C5H4NCH2N), 4.03 (1 H, s, C4H3NCH2N), 3.47 (2 H, d, 2J ) 13.8 Hz,
C5H4NCH2N), 3.45 (1 H, s, C4H3NCH2N), 1.86 (3 H, s, C4H3NCH2-
NCH3), 1.40 (18 H, s, C(CH3)3). 13C{1H} NMR (CDCl3): δ ) 166.6
(2,2′-[But-bpy]), 153.0 (4,4′-[But-bpy]), 150.5 (6,6′-[But-bpy]), 140.9
(4-C5H5N), 136.8 (2-C4H3N), 136.1 (3,3′-5,5′-[But-bpy]), 128.0
JA038320G
9
J. AM. CHEM. SOC. VOL. 126, NO. 6, 2004 1803