Early transition metal complexes containing 1,2,4-triazolato and tetrazolato ligands: Synthesis, structure, and molecular orbital studies

Article abstract of DOI:10.1021/ic0109389

Several early transition metal complexes bearing 1,2,4-triazolato and tetrazolato ligands have been prepared by reaction of the pyrazolato complexes Ti(tBu₂pz)_4-xCl_x (tBu₂pz = 3,5-di-tert-butylpyrazolato; x = 1, 2) and M(tBu₂pz)_5-xCl_x (M = Nb, Ta: x = 2, 3) with the sodium or potassium salts derived from 1,2,4-triazoles and tetrazoles. The X-ray structure analysis of Ti(tBu₂pz)₂ (Me₂C₂N₃)₂ shows η²-coordination of the 1,2,4-triazolato ligands, while in Ti(tBu₂pz)₃(C₂H₂N₃) and Nb(tBu₂pz)₃ (Me₂C₂N₃)₂ the analogous groups are joined in a η¹fashion in the solid-state structure. Solution NMR studies at different temperatures suggest transition states involving η²-1,2,4-triazolato ligands for the complexes containing ??¹-1,2,4-triazolato ligands in the solid state. X-ray crystal structures of analogous tetrazolato complexes Ti(tBu₂pz)₃(PhCN₄) and Nb(tBu₂pz)₃(PhCN₄)₂ show η¹-coordination of the 2-nitrogen atoms of the tetrazolato ligands. Molecular orbital calculations have been carried out on several model titanium complexes and provide detailed insight into the bonding between early transition metal centers and 1,2,4-triazolato and tetrazolato ligands. The η²-coordination mode of 1,2,4-triazolato and tetrazolato ligands is predicted to be more stable than the η¹-coordination mode by 13.8-5.2 kcal/mol.

Full text of DOI:10.1021/ic0109389

Inorg. Chem. 2001, 40, 6451-6462
6451
Early Transition Metal Complexes Containing 1,2,4-Triazolato and Tetrazolato Ligands:
Synthesis, Structure, and Molecular Orbital Studies
Carlos Ye´lamos,† Karl R. Gust, Anwar G. Baboul, Mary Jane Heeg,
H. Bernhard Schlegel, and Charles H. Winter*
Department of Chemistry, Wayne State University, Detroit, Michigan 48202
ReceiVed August 30, 2001
Several early transition metal complexes bearing 1,2,4-triazolato and tetrazolato ligands have been prepared by
reaction of the pyrazolato complexes Ti(tBu2pz)4-xClx (tBu2pz ) 3,5-di-tert-butylpyrazolato; x ) 1, 2) and
M(tBu2pz)5-xClx (M ) Nb, Ta: x ) 2, 3) with the sodium or potassium salts derived from 1,2,4-triazoles and
tetrazoles. The X-ray structure analysis of Ti(tBu2pz)2(Me2C2N3)2 shows η2-coordination of the 1,2,4-triazolato
ligands, while in Ti(tBu2pz)3(C2H2N3) and Nb(tBu2pz)3(Me2C2N3)2 the analogous groups are joined in a η1-
fashion in the solid-state structure. Solution NMR studies at different temperatures suggest transition states involving
η2-1,2,4-triazolato ligands for the complexes containing η1-1,2,4-triazolato ligands in the solid state. X-ray crystal
structures of analogous tetrazolato complexes Ti(tBu2pz)3(PhCN4) and Nb(tBu2pz)3(PhCN4)2 show η1-coordination
of the 2-nitrogen atoms of the tetrazolato ligands. Molecular orbital calculations have been carried out on several
model titanium complexes and provide detailed insight into the bonding between early transition metal centers
and 1,2,4-triazolato and tetrazolato ligands. The η2-coordination mode of 1,2,4-triazolato and tetrazolato ligands
is predicted to be more stable than the η1-coordination mode by 13.8-5.2 kcal/mol.
Introduction
been reported recently include amidinate,17-22 pyrazolylborate,23-26
amido,27-30 and others.31-40 Our group has reported extensively
about the use of pyrazolato ligands41-44 among the transition,45-50
There is considerable interest in the development of new
nitrogen donor ligand sets for early transition metal complexes.
Motivations in this area are diverse and include the preparation
of new single-site olefin polymerization catalysts,1-6 attempts
to understand and mimic hydrodenitrogenation catalysts,7-14 and
the preparation of improved precursors to metal nitride phases,15,16
to name a few. Examples of nitrogen donor ligands that have
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† Current address: Departamento de Qu´ımica Inorga´nica, Edificio de
Farmacia-Campus Universitario, Universidad de Alcala´, Carretera Madrid-
Barcelona, Km 33.600, E28871, Alcala´ de Henares, Madrid, Spain.
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10.1021/ic0109389 CCC: $20.00 © 2001 American Chemical Society
Published on Web 11/07/2001

6452 Inorganic Chemistry, Vol. 40, No. 25, 2001
Ye´lamos et al.
lanthanide,51-54 and main group metals.55-58 In particular,
we45-49 and others59,60 have demonstrated that η2-coordination
of pyrazolato ligands is common in the early transition metals
and that complexes containing this coordination mode bear
significant structural and chemical resemblance to analogous
cyclopentadienyl and â-diketonate derivatives. As part of this
program, we sought to extend our exploration to complexes
containing 1,2,4-triazolato and tetrazolato ligands.
The coordination chemistry of 1,2,4-triazolato and tetrazolato
ligands has not been as widely studied as that of pyrazolato
ligands, and there is more variability in the binding modes due
to the increased number of nitrogen atoms and the attendant
possibilities for isomerism.61-92 Binding modes that have been
observed for 1,2,4-triazolato ligands include η1,62-64 1,2-µ:
η1,η1,65-69 1,4-µ:η1,η1,70-73 and 1,2,4-µ:η1,η1,η1.74-78 The bridg-
ing coordination modes are by far the most common with 1,2,4-
triazolato ligands; η1 coordination is rare. A review article on
the coordination chemistry of ligands derived from 1,2,4-
triazoles has recently appeared and gives a comprehensive listing
of known coordination modes.61 Structurally characterized
coordination modes among tetrazolato ligands include η1,79-82
1,2-µ:η1,η1,83 1,3-µ:η1,η1,84,85 2,3-µ:η1,η1,86 1,2,3-µ:η1,η1,η1,87
1,2,4-µ:η1,η1,η1,88 µ-1,2-η2,3-η1,89,90 µ-1,3-η1,2,3-η2,91 and
µ:η1,η1,η1,η1.92 The best documented coordination mode for
tetrazolato ligands is η1, although the number of crystallographi-
cally characterized complexes is small.
We are interested in the synthesis of complexes that possess
only nitrogen atoms in the coordination sphere and their
subsequent use as precursors for the deposition of thin films of
nitride materials.51-54,93 1,2,4-Triazolato and tetrazolato ligands
are potentially interesting for such applications, since they may
form complexes that are analogous to complexes containing
pyrazolato ligands. In addition, the higher nitrogen content in
triazolato and tetrazolato complexes, compared to pyrazolato
complexes, may lead to low film deposition temperatures and
highly efficient precursor decomposition pathways that are
driven by the formation of dinitrogen. Herein we describe the
synthesis, structure, and properties of titanium, niobium, and
tantalum complexes containing 1,2,4-triazolato and tetrazolato
ligands. This is the first description of early transition metal
complexes containing these ligands. Crystal structures of
representative complexes document η1- and η2-coordination of
1,2,4-triazolato ligands, depending on the degree of steric
crowding in the coordination sphere and η1-coordination of the
tetrazolato ligands. This study provides the first example of η2-
1,2,4-triazolato ligand coordination by any metal. NMR studies
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Metal Complexes Containing 1,2,4-Triazolato Ligands
Inorganic Chemistry, Vol. 40, No. 25, 2001 6453
suggest that the η1-1,2,4-triazolato ligands can access low-energy
η2-transition states that lead to site exchange of substituents in
the 3- and 5- positions of these ligands. Finally, molecular orbital
calculations demonstrate that η2-coordination of 1,2,4-triazolato
and tetrazolato ligands is more stable than the η1-coordination
mode, in the absence of steric effects.
is proposed on the basis of spectral and analytical data and the
similarity to 4-7. Structural speculation about 8 and 9 from
the low-temperature NMR spectra is described below.
Synthesis of Complexes with Tetrazolato Ligands. Treat-
ment of chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV) with
sodium 5-phenyltetrazolate in tetrahydrofuran at room temper-
ature for 48 h afforded the titanium tetrazolato derivative 10 as
yellow crystals in 74% yield after crystallization from hexane
at -20 °C (eq 3). The structure of 10 was established from the
spectral and analytical data. η1-Coordination to the 2-nitrogen
atom of the phenyltetrazolato ligand was determined from a
low precision X-ray crystallographic structure determination.
Results
Synthesis of Complexes with 1,2,4-Triazolato Ligands.
Treatment of dichlorobis(3,5-di-tert-butylpyrazolato)titanium-
(IV) or chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV) with
excess potassium 3,5-dimethyl-1,2,4-triazolate or sodium 1,2,4-
triazolate in tetrahydrofuran at room temperature for 48 h
afforded the titanium triazolato derivatives 1-3 as yellow
crystalline solids in 56-79% yields after workup (eq 1).
Compounds 1-3 were characterized by spectroscopic and
analytical techniques and by crystal structure determinations
(vide infra). Compound 1 possesses a structure with two η2-
di-tert-butylpyrazolato and two η2-dimethyl-1,2,4-triazolato
ligands. Consistent with this structure, the 1H NMR spectra of
1 are static between -80 and +20 °C in toluene-d8 solution.
Compounds 2 and 3 have structures with three η2-di-tert-
butylpyrazolato ligands and one η1-dimethyl-1,2,4-triazolato (2)
or one η1-1,2,4-triazolato (3) ligand. The variable-temperature
1H NMR spectra of 2 are described below.
Tetrazolato complexes of niobium and tantalum were pre-
pared through treatment of dichlorotris(3,5-di-tert-butylpyra-
zolato)metal(V) with sodium 5-phenyltetrazolate in refluxing
tetrahydrofuran for 40 h (eq 4). The complexes tris(3,5-di-tert-
butylpyrazolato)bis(5-phenyltetrazolato)niobium(V) (11) and
chlorotris(3,5-di-tert-butylpyrazolato)(5-phenyltetrazolato)tan-
talum(V) (12) were obtained as yellow crystals in 59 and 60%
yields, respectively, after workup. Despite extended reflux of
dichlorotris(3,5-di-tert-butylpyrazolato)tantalum(V) with excess
sodium 5-phenyltetrazolate, only one chlorine atom could be
replaced and 12 was the only product observed. The composi-
tions of 11 and 12 were established through spectral and
analytical data and from an X-ray crystal structure determination
of 11 (vide infra).
Analogous 1,2,4-triazolato derivatives of niobium and tan-
talum were prepared by reaction of dichlorotris(3,5-di-tert-
butylpyrazolato)metal(V) and trichlorobis(3,5-di-tert-butylpyra-
zolato)metal(V) complexes with potassium 3,5-dimethyl-1,2,4-
triazolate and potassium 3,5-diethyl-1,2,4-triazolate in tetrahydro-
furan at ambient temperature (eq 2). Complexes 4-9 were
obtained in 40-81% yields after crystallization from hexane at
-20 °C. These compounds were characterized by spectroscopic
and analytical techniques and by a crystal structure determination
of 4 (vide infra). On the basis of the crystal structure of 4 and
NMR studies described below on 4 and 6, 4-7 possess three
η2-di-tert-butylpyrazolato and two η1-dialkyl-1,2,4-triazolato
ligands. The formulation of 8 and 9 as monomeric complexes
Crystal Structures of 1, 2, 4, and 11. The X-ray crystal
structures of 1, 2, 4, and 11 were determined to establish the
geometries about the metal centers as well as the bonding modes
of the pyrazolato, 1,2,4-triazolato, and tetrazolato ligands.
Experimental crystallographic data are summarized in Table 1,
selected bond lengths and angles are given in Tables 2-5, and
perspective views are presented in Figures 1-4. Further data
are available in the Supporting Information. The X-ray crystal
structures of 3 and 10 are presented in the Supporting Informa-
tion. The molecular structure of 3 is very similar to that of 2,
while the structural data for 10 are of low precision (although
the structure is unambiguously established).
The molecular structure of 1 is presented in Figure 1. The
complex crystallizes with one and a half independent molecules
in the asymmetric unit. The molecule exhibits distorted dodeca-

6454 Inorganic Chemistry, Vol. 40, No. 25, 2001
Ye´lamos et al.
Table 1. Experimental Crystallographic Data for 1, 2, 4, and 11
1
2
4
11
empirical formula
fw
space group
a (Å)
b (Å)
c (Å)
â (deg)
V (Å3)
Z
C30H50N10Ti
598.70
C2/c
33.981(2)
16.2356(8)
23.0511(11)
121.6160(10)
10829.9(9)
12
C37H63N9Ti
681.86
P21/n
10.2054(11)
37.372(4)
10.8560(13)
96.506(2)
4113.8(8)
4
C41H69N12Nb
822.99
C2221 (No. 20)
14.2966(8)
23.9396(14)
14.7500(8)
90
C47H67N14Nb
921.06
P21
12.6843(2)
18.3911(3)
13.1692(3)
112.8500(10)
2831.00(9)
2
5048.3(5)
4
T (K)
295(2)
0.710 73
1.102
0.269
5.55
295(2)
0.710 73
1.101
0.243
5.49
295(2)
0.710 73
1.083
0.276
4.92
295(2)
0.710 73
1.081
0.253
5.23
λ (Å)
F
calcd (g cm3)
µ (mm-1
)
R(F) (%)
Rw(F) (%)
13.66
10.53
9.10
13.88
Table 2. Selected Bond Lengths (Å) and Angles (deg) for 1
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 4
Ti(1)-N(1)
Ti(1)-N(3)
Ti(1)-N(5)
Ti(1)-N(8)
N(1)-N(2)
N(5)-N(6)
2.019(2)
2.057(2)
2.059(2)
2.065(2)
1.370(3)
1.370(3)
Ti(1)-N(2)
Ti(1)-N(4)
Ti(1)-N(6)
Ti(1)-N(9)
N(3)-N(4)
N(8)-N(9)
2.054(2)
2.018(2)
2.098(2)
2.067(2)
1.361(3)
1.373(3)
Nb-N(1)
2.114(2)
2.094(3)
1.358(5)
1.403(4)
Nb-N(2)
Nb-N(4)
N(2)-N(3)
2.073(2)
2.194(3)
1.388(4)
Nb-N(3)
N(1)-N(1)#1
N(4)-N(5)
N(1)-Nb-N(2)
N(1)-Nb-N(4)
N(2)-Nb-N(3)
N(2)-Nb-N(2)′
N(2)-Nb-N(1)′
N(3)-Nb-N(3)′
N(3)-Nb-N(4)′
N(4)-Nb-N(2)′
Nb-N(4)-N(5)
Nb-N(2)-N(3)
91.23(13)
83.68(10)
38.90(10)
178.8(2)
89.95(13)
101.32(14)
84.73(10)
89.15(9)
N(1)-Nb-N(3)
N(1)-Nb-N(1)′
N(2)-Nb-N(4)
N(2)-Nb-N(3)′
N(3)-Nb-N(1)′
N(3)-Nb-N(4)
N(4)-Nb-N(1)′
N(4)-Nb-N(4)′
Nb-N(1)-N(1)′
Nb-N(3)-N(2)
126.24(13)
37.47(13)
90.58(9)
139.86(11)
127.55(12)
79.60(10)
121.14(10)
155.2(2)
N(1)-Ti(1)-N(2)
39.30(7)
N(1)-Ti(1)-N(3)
N(1)-Ti(1)-N(5)
94.47(9)
95.81(8)
N(1)-Ti(1)-N(4) 120.71(9)
N(1)-Ti(1)-N(6) 134.26(8)
N(1)-Ti(1)-N(8) 114.41(9)
N(1)-Ti(1)-N(9)
N(2)-Ti(1)-N(4)
89.53(9)
92.26(9)
N(2)-Ti(1)-N(3)
87.11(9)
N(2)-Ti(1)-N(5) 134.63(8)
N(2)-Ti(1)-N(6) 172.26(8)
N(2)-Ti(1)-N(8)
N(3)-Ti(1)-N(4)
N(3)-Ti(1)-N(6)
94.06(9)
39.01(8)
89.53(9)
N(2)-Ti(1)-N(9)
N(3)-Ti(1)-N(5)
92.92(9)
91.73(9)
112.9(2)
71.40(14)
71.26(7)
69.7(2)
N(3)-Ti(1)-N(8) 134.84(8)
N(3)-Ti(1)-N(9) 173.66(8)
Table 5. Selected Bond Lengths (Å) and Angles (deg) for 11
N(4)-Ti(1)-N(5) 114.48(9)
N(4)-Ti(1)-N(6)
N(4)-Ti(1)-N(9)
89.51(9)
134.69(8)
N(4)-Ti(1)-N(8)
N(5)-Ti(1)-N(6)
N(5)-Ti(1)-N(9)
N(6)-Ti(1)-N(9)
Ti(1)-N(1)-N(2)
Ti(1)-N(3)-N(4)
Ti(1)-N(5)-N(6)
Ti(1)-N(8)-N(9)
95.90(8)
38.47(7)
92.75(9)
91.19(9)
71.72(13) Ti(1)-N(2)-N(1)
68.95(12) Ti(1)-N(4)-N(3)
72.32(13) Ti(1)-N(6)-N(5)
70.67(13) Ti(1)-N(9)-N(8)
Nb-N(1)
2.092(5)
2.096(4)
2.056(4)
2.198(5)
1.377(6)
1.396(6)
1.306(6)
1.336(6)
1.346(6)
Nb-N(2)
2.054(4)
2.080(4)
2.093(4)
2.179(5)
1.368(6)
1.336(6)
1.338(7)
1.354(6)
N(5)-Ti(1)-N(8) 117.25(10)
Nb-N(3)
Nb-N(4)
N(6)-Ti(1)-N(8)
N(8)-Ti(1)-N(9)
93.26(9)
38.83(8)
68.97(13)
72.04(12)
69.21(13)
70.50(13)
Nb-N(5)
Nb-N(6)
Nb-N(7)
Nb-N(11)
N(3)-N(4)
N(7)-N(8)
N(9)-N(10)
N(11)-N(14)
N(1)-N(2)
N(5)-N(6)
N(7)-N(10)
N(11)-N(12)
N(13)-N(14)
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 2
N(1)-Nb-N(2)
N(1)-Nb-N(4)
N(1)-Nb-N(6)
N(2)-Nb-N(3)
N(2)-Nb-N(5)
N(2)-Nb-N(7)
N(3)-Nb-N(5)
N(3)-Nb-N(7)
N(4)-Nb-N(6)
N(5)-Nb-N(6)
N(6)-Nb-N(7)
Nb-N(2)-N(1)
Nb-N(4)-N(3)
Nb-N(6)-N(5)
Nb-N(7)-N(10)
Nb-N(11)-N(14)
38.8(2)
125.3(2)
101.1(2)
89.7(2)
178.4(2)
91.5(2)
91.9(2)
122.4(2)
128.1(2)
39.3(2)
83.7(2)
72.1(2)
71.5(2)
68.9(2)
125.2(3)
125.2(3)
N(1)-Nb-N(3)
N(1)-Nb-N(5)
N(1)-Nb-N(7)
N(2)-Nb-N(4)
N(2)-Nb-N(6)
N(3)-Nb-N(4)
N(3)-Nb-N(6)
N(4)-Nb-N(5)
N(4)-Nb-N(7)
N(5)-Nb-N(7)
Nb-N(1)-N(2)
Nb-N(3)-N(4)
Nb-N(5)-N(6)
Nb-N(7)-N(8)
Nb-N(11)-N(12)
127.5(2)
139.7(2)
78.5(2)
92.2(2)
139.3(2)
38.2(2)
126.7(2)
89.9(2)
84.2(2)
87.6(2)
69.1(3)
70.2(2)
71.8(2)
123.0(3)
123.9(3)
Ti-N(1)
Ti-N(5)
Ti-N(7)
Ti-N(9)
N(4)-N(5)
N(8)-N(9)
2.020(4)
2.042(4)
2.036(4)
2.018(4)
1.362(4)
1.375(4)
Ti-N(4)
2.016(4)
1.986(4)
1.999(4)
1.392(5)
1.360(4)
Ti-N(6)
Ti-N(8)
N(1)-N(2)
N(6)-N(7)
N(1)-Ti-N(4)
N(1)-Ti-N(6)
N(1)-Ti-N(8)
N(4)-Ti-N(5)
N(4)-Ti-N(7)
N(4)-Ti-N(9)
N(5)-Ti-N(7)
N(5)-Ti-N(9)
N(6)-Ti-N(8)
N(7)-Ti-N(8)
N(8)-Ti-N(9)
Ti-N(4)-N(5)
Ti-N(6)-N(7)
Ti-N(8)-N(9)
94.78(15)
110.49(16)
115.25(16)
39.22(11)
101.07(15)
130.17(15)
85.86(15)
131.17(15)
109.54(14)
148.04(14)
40.02(13)
71.4(2)
N(1)-Ti-N(5)
N(1)-Ti-N(7)
N(1)-Ti-N(9)
N(4)-Ti-N(6)
N(4)-Ti-N(8)
N(5)-Ti-N(6)
N(5)-Ti-N(8)
N(6)-Ti-N(7)
N(6)-Ti-N(9)
N(7)-Ti-N(9)
Ti-N(1)-N(2)
Ti-N(5)-N(4)
Ti-N(7)-N(6)
Ti-N(9)-N(8)
130.90(15)
89.45(16)
87.92(15)
129.31(15)
96.91(15)
96.06(14)
91.76(16)
39.50(11)
95.06(14)
128.74(15)
111.0(3)
nitrogen-nitrogen bond in the ligands is considered to be a
monodentate donor. The titanium-nitrogen bond lengths
associated with the triazolato ligands (range 2.059-2.098 Å)
are slightly longer than the analogous values in the pyrazolato
ligands (range 2.018-2.057 Å). Within each pyrazolato ligand,
one titanium-nitrogen bond is 0.035-0.039 Å longer than the
other. Within the triazolato ligands, the ligand containing N(5)
and N(6) shows a similar asymmetric bonding to titanium
(difference 0.031 Å), while the ligand containing N(8) and N(9)
exhibits ideal η2-bonding. The nitrogen-nitrogen bond lengths
69.4(2)
68.3(2)
69.2(3)
72.2(2)
70.7(3)
hedral geometry, similar to that found in eight-coordinate
pyrazolato complexes of the formula Ti(R2pz)4 (R ) CH3, C6H5)
that we have previously reported.45 The titanium atom in 1 is
bound to two pyrazolato and two triazolato ligands with η2-
coordination to both types of ligands. The geometry about the
titanium center is distorted tetrahedral, if the center of each

Metal Complexes Containing 1,2,4-Triazolato Ligands
Inorganic Chemistry, Vol. 40, No. 25, 2001 6455
Figure 1. Perspective view of Ti(tBu2pz)2(Me2C2N3)2 (1) with thermal
ellipsoids at the 50% probability level.
Figure 4. Perspective view of Nb(tBu2pz)3(PhCN4)2 (11) with thermal
ellipsoids at the 50% probability level.
best described as distorted trigonal bipyramidal, if the centers
of the nitrogen-nitrogen bonds of the η2-pyrazolato ligands are
considered as monodentate donors. The equatorial plane is
defined by two approximately coplanar di-tert-butylpyrazolato
ligands and one di-tert-butylpyrazolato ligand whose plane is
approximately perpendicular to the plane of the other two. We
have previously observed a similar arrangement of η2-pyrazolato
ligands in lanthanide complexes of the formula Ln(tBu2pz)3-
(py)2;51 such a disposition of these ligands is apparently due to
steric accommodation of the tert-butyl groups. The η1-triazolato
ligands occupy the axial positions. The N(4)-Nb-N(4)′ angle
is 155.2(2)° and is less than the idealized 180°, apparently due
to avoidance of steric interactions with the tert-butyl groups of
one of the pyrazolato ligands. The 3,5-di-tert-butylpyrazolato
ligands are symmetrically bound in a η2-fashion, with the
niobium-nitrogen distances ranging from 2.073(2) to 2.114(2)
Å. The values described thus far for 4 are very similar to the
related values for dichlorotris(3,5-di-tert-butylpyrazolato)nio-
bium(V), whose structure we have recently reported.48 The
niobium-nitrogen bond length for the η1-dimethyl-1,2,4-
triazolato ligand is 2.194(3) Å. The second nitrogen on each
triazolato ligand is clearly not coordinated to the niobium center.
The crowded coordination sphere that is present in 4 probably
causes the lengthening of the niobium-nitrogen bond for the
triazolato ligand compared to the pyrazolato ligands.
Figure 2. Perspective view of Ti(tBu2pz)3(Me2C2N3) (2) with thermal
ellipsoids at the 50% probability level.
The molecular structure of 11 is presented in Figure 4. The
coordination sphere contains two η1-tetrazolato and three η2-
pyrazolato groups. The coordination geometry is very similar
to those found in 4 and dichloro(3,5-di-tert-butylpyrazolato)-
niobium(V).48 Again, the equatorial plane is comprised of two
approximately coplanar pyrazolato ligands and a third pyrazolato
ligand whose five-membered ring approximately bisects the
plane of the other two. The angle between the coordinated
nitrogen atoms of the axial tetrazolato ligands is 152.2(2)°. The
niobium-nitrogen bond lengths for the pyrazolato ligands range
from 2.054(4) to 2.096(4) Å and are slightly shorter than those
found in 4. The niobium-nitrogen bond lengths in the η1-
tetrazolato groups (2.179(5) and 2.198(5) Å) are similar to the
related bond length for the η1-triazolato ligands in 4.
Variable-Temperature NMR Behavior. We sought to
explore solution structures and exchange processes that might
occur in the new compounds. Kinetics of methyl site exchange
in the dimethyl-1,2,4-triazolato ligands of 4 and 6 was studied
and is described below. In addition, solution structures for 8
and 9 are proposed on the basis of the low-temperature NMR
spectra. In 2, a single sharp resonance was observed at -80 °C
in toluene-d8 for the 1,2,4-triazolato ligand methyl groups,
Figure 3. Perspective view of Nb(tBu2pz)3(Me2C2N3)2 (4) with thermal
ellipsoids at the 50% probability level.
in the pyrazolato and triazolato groups are almost identical
(1.361(3)-1.373(3) Å).
Complex 2 crystallizes as a 7-coordinate monomer with three
η2-di-tert-butylpyrazolato ligands and one η1-dimethyl-1,2,4-
triazolato ligand (Figure 2). The geometry about the titanium
center is distorted tetrahedral, if the center of each nitrogen-
nitrogen bond in the 3,5-di-tert-butylpyrazolato ligands is
considered to be a monodentate donor. The titanium-nitrogen
bond length to the η1-triazolato ligand (2.020(4) Å) is similar
to the values for the η2-pyrazolato ligands (1.986(4)-2.042(4)
Å). The metal-nitrogen bond lengths in 2 are slightly shorter
than those found in 1, probably due to the less crowded
7-coordinate metal center in 2.
The molecular structure of 4 is presented in Figure 3. The
coordination sphere of 4 contains two η1-triazolato and three
η2-pyrazolato groups. The geometry about the niobium atom is

6456 Inorganic Chemistry, Vol. 40, No. 25, 2001
Ye´lamos et al.
afforded the activation parameters ∆Hq ) 11.4 ( 0.1 kcal/mol,
∆Sq ) -6.2 ( 0.1 cal/(K·mol), and ∆Gq(298 K) ) 13.2 ( 0.1
kcal/mol. The activation parameters for 6 were ∆Hq ) 10.0 (
0.2 kcal/mol, ∆Sq ) -14.6 ( 0.2 cal/(K·mol), and ∆Gq(298
K) ) 14.3 ( 0.2 kcal/mol. These data allow us to offer some
insight into the character of the transition states that interconvert
the triazolato methyl sites in 4 and 6. The transition state most
likely corresponds to a nine-coordinate structure 13 that contains
one η2-triazolato ligand. The more ordered nature of the
transition states, compared to the ground-state structures of 4
and 6, is reflected in the negative entropies of activation for
the kinetic processes. An ionic transition state that entails
dissociation of a dimethyl-1,2,4-triazolate ion, followed by
recoordination to the other nitrogen atom, is unlikely since such
a process should exhibit a large positive entropy of activation.
A transition state that involves substantial η1-pyrazolato ligand
character is also unlikely in view of the negative entropies of
activation.
Figure 5. Variable-temperature 1H NMR Spectra for 4. The resonance
at δ 2.08 corresponds to the residual hydrogen atoms on the methyl
group of toluene-d8, and the resonance denoted with an asterisk is an
impurity.
Table 6. Rate Constants Data for Interconversion of Triazolato
Ligand Methyl Sites for 4 and 6
temp (K)
rate const (s-1
(a) Data for 4
293.2
)
temp (K)
rate const (s-1
)
We have recently reported that the starting material used to
prepare 4, dichlorotris(3,5-di-tert-butylpyrazolato)niobium, un-
dergoes a Berry pseudorotation-type process in toluene-d8
between -50 and -30 °C that interconverts the separate sites
for the tert-butyl groups.48 In 4 and 6, three types of tert-butyl
sites were observed in toluene-d8 at temperatures up to about
60 °C. Between 60 and 100 °C, the tert-butyl resonances began
to broaden slightly, suggesting that the di-tert-butylpyrazolato
ligands in these complexes undergo an exchange process at
higher temperatures. However, even at 120 °C in o-xylene-d10,
line broadening had not occurred sufficiently to allow kinetics
determinations with gNMR. Accordingly, kinetics studies for
these processes were not carried out. The much higher temper-
atures required for a tert-butyl site interconversion in 4 and 6,
compared to the case for dichlorotris(3,5-di-tert-butylpyrazola-
to)niobium, is consistent with the much more crowded coordi-
nation spheres in the former complexes.
223.4
234.0
244.6
255.3
265.9
276.6
0.00
5.36
972
1600
2500
6610
13900
303.7
308.5
324.4
340.4
13.9
34.7
113
259
(b) Data for 6
247.6
259.2
270.9
282.5
288.3
298.8
7.2
12
26.4
67.5
104
148
305.8
311.6
317.5
323.3
329.1
259
462
590
972
1190
suggesting that there is a low barrier for exchange between the
two possible sites in the η1-3,5-dimethyl-1,2,4-triazolato ligand.
1
In the H NMR spectra in toluene-d8, the methyl groups of
the 3,5-dimethyl-1,2,4-triazolato ligands in 4 and 6 undergo site
exchange between -50 and 60 °C. To gain further insight into
the dynamic processes, the line-broadening kinetics was studied
for these events. Details of the analyses are presented in the
Experimental Section and in the Supporting Information. Rate
The 1H and 13C{1H} NMR spectra of complexes 8 and 9 were
complicated and temperature dependent. Spectra obtained for
8 and 9 in toluene-d8 between -90 and +60 °C were virtually
identical, and only the spectra for 9 are discussed herein. At 60
1
1
°C, the H NMR spectrum of 9 revealed sharp resonances for
constants were determined by simulating the H NMR spectra
at various temperatures using the program gNMR.94 Figure 5
one type of pyrazolato ligand (δ 6.44 (2 CH), 1.11 (4 C(CH3)3))
and one type of triazolato ligand (δ 2.03 (6 CH3)). Upon cooling
of the sample to -65 °C, each of these resonances gradually
broadened and coalesced into new resonances. Between -65
1
shows the H NMR spectra for 4 that were taken at various
temperatures. Consistent with these spectra, the process was
modeled as a two-site AB exchange. Rate constants are
1
1
and -90 °C, the H NMR spectra were essentially static with
presented in Table 6. The H NMR spectra for 6 were very
only small chemical shift differences. At -90 °C, the 1H NMR
spectrum revealed resonances for two equal intensity pyrazolato
methine groups (δ 6.53, 6.34), six equal intensity methyl groups
(δ 2.76, 2.64, 2.48, 2.24, 2.02, 1.28), and four equal intensity
similar to those for 4, and a kinetics analysis was performed in
an analogous fashion. Eyring analysis of the rate data for 4
(94) gNMR; version 4; Cherwell Scientific Publishing: Oxford, U.K., 1997.

Metal Complexes Containing 1,2,4-Triazolato Ligands
Inorganic Chemistry, Vol. 40, No. 25, 2001 6457
tert-butyl groups (δ 1.29, 1.20, 1.18, 0.75). In particular, the
methyl resonance at δ 1.28 and the tert-butyl resonance at δ
0.75 are shifted substantially upfield from the normal chemical
shifts for these groups. The upfield shifts suggest that these
groups are positioned in the shielding region of an aromatic
pyrazolato or triazolato ligand. A monomeric structure consistent
with these spectral data is represented by 14. The proposed
structure possesses approximate trigonal pyramidal geometry,
with η2-pyrazolato, η2-triazolato, and η1-triazolato ligands in
the equatorial plane. The axial ligands comprise η2-pyrazolato
and η1-triazolato ligands. If the η2-pyrazolato and η2-triazolato
ligands are approximately coplanar in the equatorial plane, then
it is likely that the equatorial η1-triazolato ligand will lie
approximately perpendicular to the equatorial plane. Such a
disposition would place one methyl group from the η2-triazolato
ligand and one tert-butyl group from the η2-pyrazolato ligand
within the shielding cone of the equatorial η1-triazolato ligand
and could account for the observed unusually large upfield shifts.
It is necessary to propose an axial η2-pyrazolato ligand to arrive
Figure 6. Calculated Structures for trichloro(3,5-dimethyl-1,2,4-
triazolato)titanium(IV) (15; Ti-N and N-N bond lengths in Å, charges
on Ti, Cl, and the ring in italics, relative energies in bold). The η1-
structure 15b is not a minimum, since the Ti-N-N bond angle was
constrained to 126°.
1
at a structure that fits the low-temperature H NMR spectrum.
We caution that we have only considered monomeric structures.
While the crowded coordination spheres of 8 and 9 are likely
to disfavor oligomeric structures, we cannot rule out such species
at low temperature.
1
The H NMR spectra of 11 in toluene-d8 were recorded
1
between +40 and -80 °C. At or below -60 °C, the H NMR
spectra of 11 showed three different tert-butyl group sites
(δ 1.15, 1.12, 0.92 at -60 °C) and two different CH fragments
of the pyrazolato rings (δ 6.98 and 6.45 at -60 °C in a 2:1
proportion). Between -60 and -50 °C the tert-butyl resonances
at δ 1.15 and 1.12 merged to a single resonance, while warming
to between -50 and -30 °C led to coalescence of the two
remaining tert-butyl resonances into a single broad peak at δ
1.08. Between -50 and -30 °C the pyrazolato C-H resonances
at δ 6.98 and 6.45 gradually broadened. At -20 °C, a broad
pyrazolato C-H resonance was centered at δ 6.8. At 40 °C,
sharp singlets for tert-butyl and pyrazolato C-H groups were
observed at δ 1.07 and 6.83, respectively. Such dynamic
behavior for 11 is very similar to the pseudorotation-type process
that we have previously reported for dichlorotris(3,5-di-tert-
butylpyrazolato)niobium.48 It is particularly striking that the
pseudorotation rate constant for 11 is qualitatively similar to
that of dichlorotris(3,5-di-tert-butylpyrazolato)niobium,48 while
the related process for 4 and 6 is significantly slower. A possible
explanation is that the low energy η2-triazolato ligand transition
states for 4 and 6 lead to more steric congestion about the metal
centers than is present in 11 and dichlorotris(3,5-di-tert-
butylpyrazolato)niobium. Such a proposal suggests that a similar
η2-tetrazolato ligand transition state is not accessible for 11.
Along these lines, the tetrazolato phenyl resonances of 11
appeared at multiplets centered at δ 8.2 (4H), 7.15 (4 H), and
7.05 (2H) between +40 and -80 °C. These resonances did not
undergo any changes other than small chemical shift differences
with temperature ((δ 0.1 over 100 °C).
Figure 7. Calculated structures for trichloro(5-methyltetrazolato)-
titanium(IV) (16 and 17; Ti-N and N-N bond lengths in Å, charges
on Ti, Cl, and the ring in italics, relative energies in bold). The η1-
structures 16b and 17b are not minima, since the Ti-N-N bond angles
were constrained to 126°.
and tetrazolato ligands, we carried out a series of ab initio
molecular orbital calculations on model compounds containing
a single 3,5-dimethyltriazolato or methyltetrazolato ligand
complexed with the trichlorotitanium(IV) fragment. Thus con-
sidered were the 1,2-η2- and 1-η1-3,5-dimethyltriazolato (15),
2,3-η2- and 2-η1-methyltetrazolato (16), and 1,2-η2- and 1-η1-
3,5- methyltetrazolato (17) complexes. The optimized geom-
etries are shown in Figures 6 and 7. In each case, the equilibrium
geometry is η2. To simulate η1 bonding, the titanium-nitrogen-
nitrogen angle was constrained to 126° and the remaining
coordinates were reoptimized. We have carried out similar
calculations previously on trichloro(3,5-dimethylpyrazolato)-
titanium(IV).45 The two η2 isomers 16a and 17a differ in energy
by less than 0.8 kcal/mol, with the 2,3-isomer 16a being more
stable. Since these structures are separated by the η1 structure
Molecular Orbital Calculations. To help in understanding
the bonding between the titanium(IV) center and the triazolato

6458 Inorganic Chemistry, Vol. 40, No. 25, 2001
Ye´lamos et al.
Figure 8. Calculated occupied orbitals for (a) trichloro(3,5-dimethyl-1,2,4-triazolato)titanium(IV) and (b, c) two isomers of trichloro(5-
methyltetrazolato)titanium(IV) showing the interaction of the antisymmetric combination of the nitrogen lone pairs with the titanium dxz orbital.
16b that is only 5.2 kcal/mol higher in energy, interconversion
between 16a and 17a should be rapid at temperatures that are
accessible in normal NMR solvents.
the η1-η2 energy difference is about 3 kcal/mol less. Thus,
electronic factors must make a significant contribution.
Figure 8 shows the molecular orbitals for 15a, 16a, and 17a
consisting of bonding between the antisymmetric combination
of the nitrogen lone pairs and the empty titanium dxz orbital. A
similar bonding arrangement occurs between the symmetric
2
combination of the lone pairs and the titanium dz orbital, but
this interaction mixes with several other orbitals and is cor-
respondingly difficult to visualize. The related molecular orbitals
for trichloro(3,5-dimethylpyrazolato)titanium(IV) have been
reported previously.45 The shapes of these orbitals are very
similar and do not immediately supply an explanation for the
observed trends. However, an inspection of the lone pair orbital
energies does reveal the necessary differences. As expected from
the increased electronegativity, the lone pair orbitals on the ring
become more stable as the number of nitrogens increases. This
increases the energy difference between the occupied nitrogen
lone pair orbitals and the empty titanium d orbitals and,
consequently, the stabilizing interaction becomes weaker. The
weaker interaction is manifested by longer and weaker titanium-
nitrogen bonds: 1.991, 2.010, 2.044, and 2.046 Å for the average
titanium-nitrogen bond lengths in trichloro(3,5-dimethylpyra-
zolato)titanium(IV),45 15a, 16a, and 17a, respectively. The trend
in the bond strengths can be gauged by the energy needed to
break one of the η2 titanium-nitrogen bonds to form the η1
structure: 16.5 kcal/mol for pyrazolato; 13.8 kcal/mol for 16a;
5.2-8.6 kcal/mol for 16a and 17a. The weaker orbital inter-
action also diminishes the sharing of charge between the ring
and the trichlorotitanium(IV) fragment, thus accounting for the
trend in the charges as well.
The calculated titanium-nitrogen bond lengths for the
triazolato complexes 15 are about 0.06 Å shorter than in the
crystal structure for 1; a similar trend was found previously for
the analogous pyrazolato complex.45 The difference can probably
be attributed to the use of chloride for three of the ligands in
the computational models. Chloride is a less sterically demand-
ing ligand than those that are present in 1, and it is likely that
the trichlorotitanium(IV) fragment is a stronger Lewis acid than
the related fragment in 1. Both of these factors would lead to
shorter titanium-nitrogen bond lengths in the model complex
15a. The average titanium-nitrogen bond lengths calculated
for the η2 complexes are ca. 0.1 Å longer than for the η1
structures; a similar trend is also observed in the crystal
structures, but the change is at the limit of experimental error
(0.05 Å). The titanium-nitrogen bond lengths increase in going
from triazolato to tetrazolato ligands, and this increase is larger
for the η2 complexes than for the η1 structures. The charge on
the ring also increases in the series. The charge on the ring in
the η1 structures is slightly higher than for η2, presumably
because of a greater opportunity to share charge through bonding
in the latter.
The energy difference between the η1 and η2 structures is
largest for trichloro(3,5-dimethylpyrazolato)titanium(IV) (16.5
kcal/mol)45 and triazolato complexes 15 (13.8 kcal/mol) and
smallest for tetrazolato complexes 16 and 17 (5.2 and 8.6 kcal/
mol). This is in accord with the fact that sterically crowded
complexes 1 and 2 are observed to have both η2 and η1 bonding
of the triazolato ligands, but 11 has only η1 bonding of the
tetrazolato ligand. However, the trend in the η1-η2 energy
difference in 15-17 is not merely the result of sterics, since 15b
has steric interactions that are essentially the same as in the η1
structure of trichloro-3,5-dimethylpyrazolatotitanium(IV), but
Discussion
The complexes described herein are the first early transition
metal compounds that contain 1,2,4-triazolato and tetrazolato
ligands. Our initial synthetic attempts to prepare homoleptic
1,2,4-triazolato and tetrazolato complexes led to insoluble or
poorly soluble, intractable products. The tractable complexes
described herein were only obtained when bulky 3,5-di-tert-
butylpyrazolato ligands were included in the coordination
spheres. Thus, very bulky ligands appear to be required to
disfavor bridging coordination modes of 1,2,4-triazolato and
tetrazolato ligands. It is likely that 3,5-disubstituted 1,2,4-
triazolato ligands with large alkyl or aryl groups should also
provide sufficient steric bulk to allow the formation of homo-
leptic monomeric early transition metal complexes. Since
tetrazolato ligands contain only one group attached to carbon,
as opposed to the two substituents in 3,5-disubstituted pyrazolato

Metal Complexes Containing 1,2,4-Triazolato Ligands
Inorganic Chemistry, Vol. 40, No. 25, 2001 6459
and 1,2,4-triazolato ligands, a very bulky group is probably
required to obtain tractable homoleptic early transition deriva-
tives. Finally, because bulky ligands are required to obtain
monomeric complexes, as noted above, it is very likely that
both η1- and η2-1,2,4-triazolato and tetrazolato ligands are higher
in energy than bridging coordination modes of these ligands,
in the absence of steric effects. Accordingly, we predict that
η1- and η2-coordination of these ligands will only be observed
in early transition metal complexes when bulky substituents are
present in the coordination sphere to disfavor bridging ligands.
The theoretical results demonstrate that there is a strong
thermodynamic driving force for η2-coordination of 1,2,4-
triazolato and tetrazolato ligands over the η1-coordination mode.
On the basis of the theoretical results described herein, the
similarity between orbital interactions of η2-1,2,4-triazolato and
η2-tetrazolato ligands with those of η2-pyrazolato ligands45 and
the widespread occurrence of η2-pyrazolato ligands among early
transition metal complexes,44-49,59,60 we predict that η2-
coordination of 1,2,4-triazolato and tetrazolato ligands will be
common in early transition metal complexes. At the same time,
the energy difference between η2- and η1-coordination is smaller
for 1,2,4-triazolato and tetrazolato ligands (13.8-5.2 kcal/mol)
than for pyrazolato ligands (16.5 kcal/mol), and therefore, η2-
coordination of 1,2,4-triazolato and tetrazolato ligands should
be much more sensitive to steric crowding than are pyrazolato
ligands. Complexes 1-12 reflect the fine balance between η2-
and η1-coordination modes. Consistent with the higher calculated
bond energies, the pyrazolato ligands in 2-4, 10, and 11 are
η2-bonded. Apparently, the tris(η2-3,5-di-tert-butylpyrazolato)-
metal fragment is too bulky to allow a fourth or fifth ligand to
bond in a η2-fashion, so η1-coordination of the 1,2,4-triazolato
and tetrazolato ligands is observed. We have previously noted
that only three 3,5-di-tert-butylpyrazolato ligands can be placed
around a titanium(IV) center57 and that pentakis(3,5-dimeth-
ylpyrazolato)tantalum(V) contains three η2- and two η1-pyra-
zolato ligands.46
kcal/mol. In a study relevant to this work, Chisholm and Extine
prepared complexes of the formula M(O2CN(CH3)2)5 (M ) Nb,
Ta) and found that the niobium complex possessed a structure
with three η2- and two η1-dimethylcarbamato ligands.96 Such a
structure is similar to 4 and 6. M(O2CN(CH3)2)5 was found to
undergo dynamic exchange of the η2- and η1-dimethylcarbamato
ligands with interconversion barriers of 11-12 kcal/mol, and
the exchange was suggested to entail a bidentate transition state
or intermediate. These exchanges are remarkably similar to those
documented herein for 4 and 6 and suggest considerable
similarity between five membered heterocyclic ligands and
dialkylcarbamato ligands in group 5 metal(V) complexes.
As described herein, 1 contains the first example of terminal
η2-1,2,4-triazolato ligand coordination to any metal, while 2-4
provide additional examples of the rare η1-coordination mode
of this ligand. We were unable to prepare and characterize
crystallographically any complexes containing η2-tetrazolato
ligands, since the bulky pyrazolato ligand spheres required for
monomeric complexes also promoted η1-coordination. A search
of the Cambridge Crystallographic Database did not reveal any
examples of η2-bonding interactions within bridging 1,2,4-
triazolato ligands. Crystallographically characterized tetrazolato
complexes containing η2-bonding interactions within a bridging
coordination mode are limited to two examples. The 1- and
2-nitrogen atoms of each phenyltetrazolato ligand in the dimeric
complexes [(C5H4(CH3))2Ln(PhCN4)]2 (Ln ) Yb, Er) are η2-
bonded to each lanthanide(III) center, while the 3-nitrogen atom
bridges to the other lanthanide(III) ion of the dimeric unit with
a η1-interaction.88,89 The 2- and 3-nitrogen atoms in cesium
5-cyanotetrazolate are bonded to the cesium ion in a η2-
fashion.90 The bonding of cesium and lanthanide(III) ions to
nitrogen donor ligands is predominately ionic, so the interaction
of tetrazolato ligands with these metals is different than the more
covalent bonding observed in d-block metal complexes. Ac-
cordingly, the observation of a η2-1,2,4-triazolato ligand in 1
and the prediction that η2-coordination of 1,2,4-triazolato and
tetrazolato ligands should be common among the early transition
metals represent novel and unexpected findings given the current
state of the literature in this area.
The calculated charges on the η2-heterocyclic ligands in
trichloro(η2-dimethylpyrazolato)titanium45 and 15-17 follow the
order pyrazolato < 1,2,4-triazolato < tetrazolato. This order
reflects the ability of the ligands to stabilize a negative charge
and also follows the order of pKas of the parent heterocycles.95
The calculated charges also predict that the order of electron-
withdrawing character for these ligands will follow the order
pyrazolato < 1,2,4-triazolato < tetrazolato. Accordingly, 1,2,4-
triazolato and tetrazolato ligand sets in early transition metal
complexes should confer unique electronic character to the metal
centers. Such ideas may contribute to the development of new
ancillary ligand sets that can support useful reactivity in early
transition metal complexes.1-39
The long-term goal of our research is to explore new nitrogen
source compounds that can be used to grow metal nitride phases
by chemical vapor deposition techniques. While ammonia is
by far the most widely used nitrogen source compound in film
growth, the high stability of ammonia and concomitant high
film deposition temperatures has led to increasing consideration
of alternative nitrogen source compounds in the past several
years within the context of GaN and TiN film growth.86,97-107
Hydrazine and alkylhydrazines have been the focus of most of
(96) Chisholm, M. H.; Extine, M. W. J. Am. Chem. Soc. 1977, 99, 782.
(97) Auvray, L.; Dumont, H.; Dazord, J.; Monteil, Y.; Bouix, J.; Bru-
Chevallier, C.; Grenoullet, L. Mater. Sci. Semicond. Process. 2000,
3, 505.
(98) Friedman, D. J.; Norman, A. G.; Geisz, J. F.; Kurtz, S. R. J. Cryst.
Growth 2000, 208, 11.
(99) Nakamura, K.; Sasaki, T. J. Solid State Chem. 2000, 154, 101.
(100) Sussek, H.; Stark, O.; Devi, A.; Pritzkow, H.; Fischer, R. A. J.
Organomet. Chem. 2000, 602, 29.
(101) Peters, D. W.; Bourret, E. D.; Power, M. P.; Arnold, J. J. Organomet.
Chem. 1999, 582, 108.
(102) Sato, S.; Satoh, S. J. Cryst. Growth 1998, 192, 381.
(103) Beaumont, B.; Vaille, M.; Lorenzini, P.; Gibart, P. Internet J. Nitride
Semicond. Res. 1997, 1, 17.
(104) Hill, M.; Jegier, J.; Munoz-Hernandez, M. A.; Rutherford, D.; Singer,
A.; Atwood, D. Phosphorus, Sulfur, Silicon Relat. Elem. 1997, 125,
183.
The NMR kinetics studies of 4 and 6 suggest that methyl
site exchange in these complexes occurs through 9-coordinate
transition states that contain η2-dimethyl-1,2,4-triazolato ligands.
The enthalpy of activation for these processes (10.0-11.4 kcal/
mol) must represent the upper limit for the energy difference
between the ground state and the transition state for methyl site
exchange. Hence, the η1-dimethyl-1,2,4-triazolato ligands in 4
and 6 are stabilized by up to 11 kcal/mol compared to the η2-
ligand. In sterically unencumbered 15, the η2-coordination mode
is 13.8 kcal/mol more stable than the η1-ligand. Accordingly,
the tris(η2-3,5-di-tert-butylpyrazolato)metal(V) fragment in 4
and 6 may destabilize the η2-coordination mode by up to 25
(95) Grimmett, M. R. In ComprehensiVe Organic Chemistry; Barton, D.,
Ollis, W. D., Eds.; Pergamon Press: Oxford, U.K., 1979; Vol. 4, p
365.
(105) Amato-Wierda, C.; Wierda, D. A. J. Mater. Res. 2000, 15, 2414.
(106) Juppo, M.; Ritala, M.; Leskela, M. J. Electrochem. Soc. 2000, 147,
3377.

6460 Inorganic Chemistry, Vol. 40, No. 25, 2001
Ye´lamos et al.
Preparation of Tris(3,5-di-tert-butylpyrazolato)(1,2,4-triazolato)-
titanium(IV) (3). In a fashion similar to the preparation of 1, treatment
of chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV) (0.60 g, 0.97
mmol) with (1,2,4-triazolato)sodium (0.13 g, 1.43 mmol) in tetrahy-
drofuran (60 mL) afforded 3 as yellow crystals (0.50 g, 79%): mp
247 °C; IR (Nujol, cm-1) 1507 (m), 1481 (m), 1364 (s), 1287 (w),
1251 (s), 1233 (m), 1205 (w), 1175 (m), 1141 (w), 1064 (m), 1019
(m), 988 (m), 955 (w), 861 (m), 816 (m), 809 (s), 716 (w), 670 (m);
1H NMR (C6D6, 22 °C, δ) 8.43 (s, 2 H, triazolato ring CH), 6.48 (s, 3
H, pyrazolato ring CH), 1.13 (s, 54 H, C(CH3)3); 13C{1H} NMR (C6D6,
22 °C, ppm) 159.65 (s, CC(CH3)3), 150.34 (s, triazolato ring CH),
111.76 (s, pyrazolato ring CH), 32.31 (s, C(CH3)3), 30.31 (s, C(CH3)3).
the effort; however, nitrogen heterocycles such as those
described herein are potentially useful source compounds.86,104
Experimental Section
General Considerations. All manipulations were carried out under
argon using Schlenk line or glovebox techniques. Hexane and toluene
were distilled from sodium, while diethyl ether and tetrahydrofuran
were distilled from purple solutions of sodium benzophenone ketyl
immediately prior to use. Potassium hydride (35% dispersion in mineral
oil) and sodium hydride (60% dispersion in mineral oil) were purchased
from Aldrich Chemical Co. and were washed with hexane prior to use
to remove the mineral oil. (1,2,4-Triazolato)sodium was purchased from
Aldrich Chemical Co. and was used as received. 3,5-Dimethyl-1,2,4-
triazole was prepared according to a published procedure.108,109 3,5-
Diethyl-1,2,4-triazole was prepared in 49% yield in a similar fashion
using propionamide and hydrazine hydrate. Potassium 3,5-dimethyl-
1,2,4-triazolate, potassium 3,5-diethyl-1,2,4-triazolate, and sodium
5-phenyltetrazolate were prepared by treatment of 3,5-dimethyl-1,2,4-
triazole, 3,5-diethyl-1,2,4-triazole, and 5-phenyl-1H-tetrazole (Aldrich
Chemical Co.) with 1 equiv of potassium hydride or sodium hydride
in tetrahydrofuran and were isolated as a white solids after removing
the volatile components under vacuum. The insoluble salts were used
without further purification or characterization. Ti(tBu2pz)4-xClx (x )
1, 2), and M(tBu2pz)5-xClx (M ) Nb, Ta; x ) 2, 3) were prepared
according to our previously reported procedures.48
Anal. Calcd for C35H59N9Ti: C, 64.30; H, 9.10; N, 19.28. Found:
C, 64.21; H, 9.09; N, 19.20.
Preparation of Tris(3,5-di-tert-butylpyrazolato)bis(3,5-dimethyl-
1,2,4-triazolato)niobium(V) (4). A 100-mL Schlenk flask was charged
with dichlorotris(3,5-di-tert-butylpyrazolato)niobium(V) (0.50 g, 0.71
mmol), potassium 3,5-dimethyl-1,2,4-triazolate (0.24 g, 1.8 mmol), and
tetrahydrofuran (80 mL). The reaction mixture was stirred for 3 days
at room temperature, and the volatile components were removed under
reduced pressure. The resultant orange solid was extracted with hexane
(90 mL), and the hexane extract was filtered through a 2-cm pad of
Celite on a coarse glass frit. Crystallization at -20 °C for 24 h afforded
4 as orange crystals (0.45 g, 76%): mp: 210 °C dec; IR (Nujol, cm-1
)
3080 (m), 1522 (m), 1500 (m), 1402 (m), 1306 (m), 1261 (m), 1232
(m), 1204 (w), 1100 (s), 1020 (s), 965 (m), 902 (w), 800 (s), 752 (w),
722 (w); 1H NMR (C6D6, 22 °C, δ) 6.60 (s, 2 H, pyrazolato ring CH),
6.54 (s, 1 H, pyrazolato ring CH), 1.91 (s broad, 12 H, triazolato CH3),
1.14 (s, 18 H, C(CH)3)3), 1.08 (s, 18 H, C(CH)3)3), 1.01 (s, 18 H,
C(CH3)3; 13C{1H} NMR (C6D6, 22 °C, ppm) 161.58 (s, triazolato
CCH3), 160.25 (s, CC(CH3)3), 158.69 (s, CC(CH3)3), 156.04 (s, CC-
(CH3)3), 118.38 (s, 2 pyrazolato ring CH), 116.06 (s, 1 pyrazolato ring
CH), 32.47 (s, C(CH3)3), 32.25 (s, C(CH3)3), 32.15 (s, C(CH3)3), 30.03
(s, C(CH3)3), 29.98 (s, C(CH3)3), 29.98 (s, C(CH3)3), 12.94 (broad s,
triazolato CH3).
Infrared spectra were recorded as Nujol mulls. 1H and 13C{1H} NMR
spectra were determined at 500, 300, 125, or 75 MHz in the indicated
solvents. Chemical shifts (δ, ppm) are given relative to residual protons
or the carbon atoms of solvent. Melting points were determined in sealed
capillary tubes under argon and are uncorrected. Microanalyses were
performed by Midwest Microlab, Indianapolis, IN.
Preparation of Bis(3,5-di-tert-butylpyrazolato)bis(3,5-dimethyl-
1,2,4-triazolato)titanium(IV) (1). A 100-mL Schlenk flask was charged
with dichlorobis(3,5-di-tert-butylpyrazolato)titanium(IV) (1.00 g, 2.09
mmol), potassium 3,5-dimethyl-1,2,4-triazolate (0.71 g, 5.25 mmol),
and tetrahydrofuran (70 mL). The reaction mixture was stirred at room
temperature for 48 h. The volatile components were removed under
reduced pressure, and the resultant yellow solid was extracted with
hexane (90 mL). Filtration of the hexane extract through a 2-cm pad
of Celite on a coarse glass frit gave a yellow solution. Cooling the
solution to -20 °C afforded 1 as yellow crystals (0.70 g, 56%): mp
154 °C dec; IR (Nujol, cm-1) 1523 (m), 1498 (s), 1407 (w), 1364 (s),
1242 (s), 1206 (w), 1130 (w), 1016 (m), 1002 (w), 806 (s), 738 (m),
688 (w); 1H NMR (C6D6, 22 °C, δ) 6.25 (s, 2 H, pyrazolato ring CH),
2.32 (s, 12 H, triazolato CH3), 1.31 (s, 36 H, C(CH3)3); 13C{1H} NMR
(C6D6, 22 °C, ppm) 157.12 (s, CC(CH3)3), 154.25 (s, triazolato CCH3),
108.88 (s, pyrazolato ring CH), 32.26 (s, C(CH3)3), 30.70 (s, C(CH3)3),
13.89 (s, triazolato CH3).
Anal. Calcd for C41H69N12Nb: C, 59.84; H, 8.45; N, 20.42. Found:
59.60; H, 8.41; N, 20.34.
Preparation of Tris(3,5-di-tert-butylpyrazolato)bis(3,5-diethyl-
1,2,4-triazolato)niobium(V) (5). In a fashion similar to the preparation
of 4, treatment of dichlorotris(3,5-di-tert-butylpyrazolato)niobium(V)
(0.50 g, 0.71 mmol) with potassium 3,5-diethyl-1,2,4-triazolate (0.29
g, 1.78 mmol) in tetrahydrofuran (80 mL) afforded 5 as orange crystals
(0.51 g, 81%): mp 227-229 °C dec; IR (Nujol, cm-1) 3079 (m), 1522
(m), 1492 (s), 1415 (s), 1365 (s), 1351 (m), 1260 (m), 1232 (m), 1204
1
(w), 1027 (m), 967 (s), 812 (m), 727 (m); H NMR (C6D6, 22 °C, δ)
6.61 (s, 2 H, pyrazolato ring CH), 6.54 (s, 1 H, pyrazolato ring CH),
2.20 (broad s, 8 H, CCH2CH3), 1.34 (t, J ) 7.5 Hz, 12 H, CCH2CH3),
1.15 (s, 18 H, C(CH)3)3), 1.07 (s, 18 H, C(CH)3)3), 1.03 (s, 18 H,
C(CH3)3); 13C{1H} NMR (toluene-d8, 80 °C, ppm) 163.27 (s, triazolato
CCH2CH3), 161.59 (s, CC(CH3)3), 160.26 (s, CC(CH3)3), 156.29 (s,
CC(CH3)3), 118.12 (s, 2 pyrazolato ring CH), 115.78 (s, 1 pyrazolato
ring CH), 32.18 (s, C(CH3)3), 32.08 (s, C(CH3)3), 31.62 (s, C(CH3)3),
29.97 (s, 3 C(CH3)3 overlapped), 20.36 (s, CH2CH3), 12.97 (s, CH2CH3).
Anal. Calcd for C30H50N10Ti: C, 60.19; H, 8.42; N, 23.40. Found:
C, 59.86; H, 8.42; N, 23.67.
Preparation of Tris(3,5-di-tert-butylpyrazolato)(3,5-dimethyl-
1,2,4-triazolato)titanium(IV) (2). In a fashion similar to the preparation
of 1, treatment of chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV)
(0.60 g, 0.97 mmol) with potassium 3,5-dimethyl-1,2,4-triazolate (0.21
g, 1.55 mmol) in tetrahydrofuran (60 mL) afforded 2 as yellow crystals
(0.38 g, 58%): mp 291 °C dec; IR (Nujol, cm-1) 1507 (m), 1398 (w),
1365 (s), 1291 (m), 1252 (m), 1233 (m), 1204 (w), 1112 (w), 1019
(m), 989 (m), 843 (w), 810 (m), 802 (s), 754 (w), 722 (m), 693 (w);
1H NMR (C6D6, 22 °C, δ) 6.41 (s, 3 H, pyrazolato ring CH), 2.32 (s,
6 H, triazolato CCH3), 1.21 (s, 54 H, C(CH3)3; 13C{1H} NMR (C6D6,
22 °C, δ) 158.63 (s, CC(CH3)3), 156.06 (s, triazolato CCH3), 110.48
(s, pyrazolato ring CH), 32.32 (s, C(CH3)3), 30.55 (s, C(CH3)3), 14.18
(s, triazolato CH3).
Anal. Calcd for C45H77N12Nb: C, 61.48; H, 8.83; N, 19.12. Found:
C, 62.68; H, 9.21; N, 18.10.
Preparation of Tris(3,5-di-tert-butylpyrazolato)bis(3,5-dimethyl-
1,2,4-triazolato)tantalum(V) (6). In a fashion similar to the preparation
of 4, treatment of dichlorotris(3,5-di-tert-butylpyrazolato)tantalum(V)
(0.50 g, 0.63 mmol) with potassium 3,5-dimethyl-1,2,4-triazolate (0.21
g, 1.58 mmol) in tetrahydrofuran (80 mL) afforded 6 as colorless
crystals (0.36 g, 62%): dec pt 112 °C; IR (Nujol, cm-1) 3085 (m),
1525 (s), 1511 (m), 1403 (s), 1365 (s), 1308 (s), 1263 (m), 1233 (s),
1203 (w), 1158 (w), 1105 (w), 1068 (w), 1033 (w), 999 (w), 967 (s),
901 (m), 811 (s), 752 (m), 723 (w), 697 (w), 619 (w); 1H NMR (C6D6,
22 °C, δ) 6.74 (s, 1 H, pyrazolato ring CH), 6.68 (s, 2 H, pyrazolato
ring CH), 2.25 (broad s, 6 H, triazolato CH3), 1.62 (broad s, 6 H,
triazolato CH3), 1.14 (s, 18 H, C(CH)3)3), 1.07 (s, 18 H, C(CH)3)3),
1.01 (s, 18 H, C(CH3)3; 13C{1H} NMR (toluene-d8, 60 °C, ppm) 160.95
(s, triazolato CCH3), 161.18 (s, CC(CH3)3), 159.56 (s, CC(CH3)3),
156.98 (s, CC(CH3)3), 117.34 (s, 2 pyrazolato ring CH), 115.51 (s, 1
Anal. Calcd for C37H63N9Ti: C, 65.18; H, 9.31; N, 18.49. Found:
C, 65.14; H, 9.35; N, 18.56.
(107) Amato-Wierda, C.; Norton, E. T.; Wierda, D. A. Electrochem. Solid
State Lett. 1999, 2, 613.
(108) Jones, R. E.; Rees, C. W. J. Chem. Soc. C 1969, 2251.
(109) Macleod, I. T.; Tiekink, E. R. T.; Young, C. G. J. Organomet. Chem.
1996, 506, 301.

Metal Complexes Containing 1,2,4-Triazolato Ligands
Inorganic Chemistry, Vol. 40, No. 25, 2001 6461
pyrazolato ring CH), 32.30 (s, C(CH3)3), 32.12 (s, C(CH3)3), 32.02 (s,
C(CH3)3), 29.85 (s, 3 C(CH3)3 overlapped), 12.46 (broad s, triazolato
CH3).
Anal. Calcd for C41H69N12Ta: C, 54.05; H, 7.63; N, 18.45. Found:
C, 53.80; H, 7.57; N, 18.85.
22 °C, ppm) 161.45 (s, CPh), 159.23 (s, CC(CH3)3), 129.96 (s, ipso-C
of Ph ring), 128.41 (s, para-CH of Ph ring), 128.36 (s, meta-CH of Ph
ring), 126.86 (s, ortho-CH of Ph ring), 112.63 (s, pyrazolato ring CH),
32.15 (s, C(CH3)3), 30.06 (s, C(CH3)3).
Anal. Calcd for C40H62N10Ti: C, 65.73; H, 8.55; N, 19.16. Found:
C, 65.61; H, 8.57; N, 18.79.
Preparation of Tris(3,5-di-tert-butylpyrazolato)bis(3,5-diethyl-
1,2,4-triazolato)tantalum(V) (7). In a fashion similar to the preparation
of 4, treatment of dichlorotris(3,5-di-tert-butylpyrazolato)tantalum(V)
(0.50 g, 0.63 mmol) with potassium 3,5-diethyl-1,2,4-triazolate (0.26
g, 1.6 mmol) in tetrahydrofuran (70 mL) afforded 7 as colorless crystals
(0.26 g, 43%): dec pt. 273-275 °C; IR (Nujol, cm-1) 3083 (m), 1524
(m), 1494 (m), 1415 (m), 1261 (m), 1233 (w), 1026 (s), 968 (m), 801
Preparation of Tris(3,5-di-tert-butylpyrazolato)bis(5-phenyltet-
razolato)niobium(V) (11). A 100-mL Schlenk flask was charged with
dichlorotris(3,5-di-tert-butylpyrazolato)niobium(V) (0.52 g, 0.74 mmol),
sodium 5-phenyltetrazolate (0.36 g, 2.14 mmol), and tetrahydrofuran
(70 mL). After being stirred at ambient temperature for 2 h, the reaction
mixture was refluxed for 40 h. The volatile components were removed
under reduced pressure, and the resultant yellow solid was extracted
with toluene (50 mL). Filtration of the toluene extract through a 2-cm
pad of Celite on a coarse glass frit gave a yellow solution. Removal of
the toluene under reduced pressure afforded 11 as a yellow solid (0.40
g, 59%). An analytical sample was obtained by recrystallization from
hexane at -20 °C: dec pt 216 °C; IR (Nujol, cm-1) 1522 (m), 1507
(m), 1257 (m), 1232 (m), 1165 (w), 1068 (w), 1026 (s), 962 (m), 800
(m), 731 (s), 693 (m); 1H NMR (C6D6, 22 °C, δ) 8.38 (m, 4 H, ortho-
CH of Ph ring), 7.17 (m, 4 H, meta-CH of Ph ring), 7.04 (m, 2 H,
para-CH of Ph ring), 6.85 (s, 3 H, pyrazolato ring CH), 1.08 (s, 54 H,
C(CH3)3); 13C{1H} (C6D6, 22 °C, ppm) 163.17 (s, CPh), 159.20 (s,
CC(CH3)3), 130.63 (s, ipso-C of Ph ring), 128.85 (s, meta-CH of Ph
ring), 128.29 (s, para-CH of Ph ring), 126.78 (s, ortho-CH of Ph ring),
119.53 (s, pyrazolato ring CH), 32.35 (s, C(CH3)3), 30.07 (s, C(CH3)3).
Anal. Calcd for C47H67N14Nb: C, 61.29; H, 7.33; N, 21.29. Found:
C, 61.30; H, 7.37; N, 21.28.
Preparation of Chlorotris(3,5-di-tert-butylpyrazolato)(5-phen-
yltetrazolato)tantalum(V) (12). In a fashion similar to the preparation
of 11, treatment of dichlorotris(3,5-di-tert-butylpyrazolato)tantalum-
(V) (0.60 g, 0.76 mmol) with sodium 5-phenyltetrazolate (0.38 g, 2.26
mmol) in tetrahydrofuran (70 mL) afforded 12 as pale-yellow crystals
(0.43 g, 60%) after crystallization from hexane at -20 °C: dec pt 196
°C; IR (Nujol, cm-1) 1524 (s), 1485 (m), 1365 (s), 1283 (w), 1256 (s),
1235 (s), 1201 (w), 1173 (w), 1126 (w), 1075 (w), 1035 (m), 1001
(w), 973 (s), 842 (w), 822 (m), 815 (m), 732 (m), 722 (w), 694 (m);
1H NMR (C6D6, 22 °C, δ) 8.35 (m, 2 H, ortho-CH of Ph ring), 7.17
(m, 2 H, meta-CH of Ph ring), 7.02 (m, 1 H, para-CH of Ph ring),
6.88 (s, 3 H, pyrazolato CH), 1.20 (s, 54 H, C(CH3)3; 13C{1H} (C6D6,
22 °C, ppm) 163.55 (s, CPh), 158.12 (s, CC(CH3)3), 130.92 (s, ipso-C
of Ph ring), 128.80 (s, meta-CH of Ph ring), 128.67 (s, para-CH of Ph
ring), 126.64 (s, ortho-CH of Ph ring), 116.77 (s, pyrazolato ring CH),
32.31 (s, C(CH3)3), 30.37 (s, C(CH3)3).
1
(s), 727 (m); H NMR (C6D6, 22 °C, δ) 6.73 (s, 1 H, pyrazolato ring
CH), 6.70 (s, 2 H, pyrazolato ring CH), 2.69 (broad s, 4 H, CH2CH3),
1.53 (broad s, 4 H, CH2CH3), 1.34 (broad s, 12 H, CH2CH3), 1.15 (s,
18 H, C(CH)3)3), 1.06 (s, 18 H, C(CH)3)3), 1.02 (s, 18 H, C(CH3)3);
13C{1H} NMR (toluene-d8, 50 °C, ppm) 164.42 (s, triazolato CCH2-
CH3), 160.80 (s, CC(CH3)3), 159.97 (s, CC(CH3)3), 156.84 (s, CC-
(CH3)3), 117.43 (s, 2 pyrazolato ring CH), 115.42 (s, 1 pyrazolato ring
CH), 32.34 (s, C(CH3)3), 32.16 (s, C(CH3)3), 32.07 (s, C(CH3)3), 29.96
(s, CC(CH3)3), 29.92 (s, 2 C(CH3)3 overlapped), 22.64 (s, CH2CH3),
12.96 (broad s, CH2CH3).
Anal. Calcd for C45H77N12Ta: C, 55.89; H, 8.03; N, 17.38. Found:
C, 55.91; H, 8.21; N, 17.22.
Preparation of Bis(3,5-di-tert-butylpyrazolato)tris(3,5-dimethyl-
1,2,4-triazolato)niobium(V) (8). A 100-mL Schlenk flask was charged
with trichlorobis(3,5-di-tert-butylpyrazolato)niobium(V) (0.30 g, 0.55
mmol), potassium 3,5-dimethyl-1,2,4-triazolate (0.29 g, 2.15 mmol),
and tetrahydrofuran (50 mL). The mixture was stirred at room
temperature for 48 h to give a red suspension. The volatile components
were removed under reduced pressure, and the resultant solid was
extracted with hexane (90 mL). The hexane extract was filtered through
a 2-cm pad of Celite on a coarse glass frit. The red filtrate was
concentrated to a volume of about 10 mL. Crystallization at -20 °C
for 48 h afforded 8 as red blocks (0.24 g, 60%): dec pt 148 °C; IR
(Nujol, cm-1) 3081 (m), 1508 (vs), 1398 (vs), 1306 (s), 1286 (s), 1256
(w), 1238 (s), 1204 (w), 1143 (w), 1115 (w), 1103 (w), 1019 (m), 994
(m), 983 (m), 877 (w), 823 (m), 754 (m), 735 (m), 694 (w), 668 (w),
617 (s); 1H NMR (C6D6, 22 °C, δ) 6.41 (broad s, 2 H, pyrazolato ring
CH), 2.11 (broad s, 18 H, triazolato CH3), 1.10 (s, 36 H, C(CH3)3);
13C{1H} NMR (toluene-d8, 80 °C, ppm) 158.82 (s, CC(CH3)3), 157.11
(s, triazolato CCH3), 116.30 (s, pyrazolato ring CH), 32.22 (s, C(CH3)3),
29.68 (s, C(CH3)3), 12.91 (broad s, triazolato CH3).
Anal. Calcd for C34H56N13Nb: C, 55.20; H, 7.63; N, 24.61. Found:
55.11; H, 7.55; N, 24.60.
Anal. Calcd for C40H62ClN10Ta: C, 53.42; H, 6.95; N, 15.57.
Found: C, 53.52; H, 6.88; N, 15.54.
Preparation of Bis(3,5-di-tert-butylpyrazolato)tris(3,5-dimethyl-
1,2,4-triazolato)tantalum(V) (9). In a fashion similar to the preparation
of 8, treatment of trichlorobis(3,5-di-tert-butylpyrazolato)tantalum(V)
(0.60 g, 0.93 mmol) with potassium 3,5-dimethyl-1,2,4-triazolate (0.50
g, 3.72 mmol) in tetrahydrofuran (70 mL) afforded 9 as pale yellow
crystals (0.31 g, 40%): dec pt 162-164 °C; IR (Nujol, cm-1) 3085
(m), 1508 (s), 1399 (s), 1308 (m), 1292 (s), 1257 (m), 1238 (m), 1205
(w), 1108 (w), 1023 (w), 994 (m), 983 (w), 823 (w), 755 (m), 736 (w),
721 (m); 1H NMR (C6D6, 22 °C, δ) 6.50 (s, 2 H, pyrazolato ring CH),
2.12 (broad s, 18 H, triazolato CH3), 1.10 (s, 36 H, C(CH3)3); 13C{1H}
NMR (toluene-d8, 80 °C, ppm) 158.62 (s, CC(CH3)3), 158.03 (s,
triazolato CCH3), 115.19 (s, pyrazolato ring CH), 32.20 (s, C(CH3)3),
29.68 (s, C(CH3)3), 12.91 (broad s, triazolato CH3).
Kinetics Measurements on 4. A 5-mm NMR tube was charged
with 4 (0.015 g, 0.018 mmol) and toluene-d8 (0.80 mL) and was fitted
with a rubber septum. The tube was transferred to the NMR probe,
1
and the H NMR spectra were recorded between -50 and 67 °C. At
-50 °C the 3,5-dimethyl-1,2,4-triazolato methyl resonances were
observed at δ 2.34 and 1.63. Upon warming, the methyl resonances
became broad and coalesced into one peak at 20 °C to give a broad
peak at δ 1.86. At 67 °C, the 3,5-dimethyl-1,2,4-triazolato methyl
resonances were observed as a single peak at δ 1.82. The dynamic
process was modeled as an AB exchange using the program gNMR.94
The same coalescence temperatures were observed in a sample of 4
(0.008 g, 0.010 mmol) in toluene-d8 (0.80 mL) that was about half as
concentrated, suggesting that the observed kinetic event was intra-
molecular. For further data, see the Supporting Information. Errors in
kinetic data are reported at the 95% confidence level.
Anal. Calcd for C34H56N13Ta: C, 49.33; H, 6.82; N, 21.99. Found:
C, 48.36; H, 7.06; N, 21.29.
Preparation of Tris(3,5-di-tert-butylpyrazolato)(5-phenyltetra-
zolato)titanium(IV) (10). In a fashion similar to the preparation of 1,
treatment of chlorotris(3,5-di-tert-butylpyrazolato)titanium(IV) (0.52 g,
0.84 mmol) with sodium 5-phenyltetrazolate (0.21 g, 1.2 mmol) in
tetrahydrofuran (60 mL) afforded 10 as yellow crystals (0.45 g, 74%):
mp 201 °C dec; IR (Nujol, cm-1) 1559 (w), 1540 (w), 1508 (m), 1365
(s), 1256 (s), 1236 (m), 1205 (w), 1168 (w), 1073 (w), 1027 (m), 991
Kinetics Measurements on 6. A 5-mm NMR tube was charged
with 6 (0.015 g, 0.016 mmol) and toluene-d8 (0.80 mL) and was fitted
with a rubber septum. The tube was transferred to the NMR probe,
1
and the H NMR spectra were recorded between -60 and 70 °C. At
-60 °C the 3,5-dimethyl-1,2,4-triazolato methyl resonances were
observed at δ 2.40 and 1.65. Upon warming, the methyl resonances
became broad and coalesced into one peak at 38 °C to give a broad
peak at δ 1.84. At 70 °C, the 3,5-dimethyl-1,2,4-triazolato methyl
resonance was observed as a single peak at δ 1.84. The dynamic process
was modeled as an AB exchange using the program gNMR.94 The same
1
(w), 976 (w), 852 (w), 800 (s), 731 (m), 721 (w), 695 (m); H NMR
(C6D6, 22 °C, δ) 7.67 (m, 2 H, ortho-CH of Ph ring), 7.24 (m, 2 H,
meta-CH of Ph ring), 7.10 (m, 1 H, para-CH of Ph ring), 6.52 (s, 3 H,
pyrazolato ring CH), 1.16 (s, 54 H, C(CH3)3); 13C{1H} NMR (CDCl3,

6462 Inorganic Chemistry, Vol. 40, No. 25, 2001
Ye´lamos et al.
coalescence temperature was observed in a sample of 6 (0.008 g, 0.008
mmol) in toluene-d8 (0.80 mL) that was about half as concentrated.
For further data, see the Supporting Information. Errors in kinetic data
are reported at the 95% confidence level
Molecular Orbital Calculations. Electronic structure calculations
were carried out with the GAUSSIAN 98110 series of programs using
the B3LYP density functional method111-113 and the 6-311G(d) basis
set114-116 (for titanium, this corresponds to the Wachters-Hay basis
set117,118 augmented with an f-type Gaussian shell with an exponent of
0.690). Equilibrium geometries were optimized using redundant internal
coordinates. Charge distributions were obtained by Mulliken population
analysis.
temperature on a Bruker P4/CCD diffractometer equipped with Mo
radiation. For each collection, frames were collected at 10 s/frame with
0.3° between each frame. The frame data was integrated with the
manufacturer’s SMART and SAINT software. Absorption corrections
were applied with Sheldrick’s SADABS program, and the structure
was solved and refined using the programs of SHELX-97. Hydrogen
atoms were placed in calculated positions. All molecules crystallized
as neutral compounds with no associated ions or solvent. Complex 1
crystallized as irregular yellow fragments. 1390 frames yielded 52110
reflections, which averaged into 11478 unique data points. The
asymmetric unit contains 1.5 molecules; the half molecule occupies a
crystallographic 2-fold axis. Complex 2 crystallized as yellow rods.
1650 frames yielded 30 245 reflections, which averaged into 10 060
unique reflections. Three tert-butyl groups were badly disordered and
their best representation involved partial occupancy positions and
isotropic refinement. The asymmetric unit contains one general
molecule. Complex 4 crystallized as orange multifaceted crystals with
24 787 reflections measured on 1390 frames. The molecule occupies a
crystallographic 2-fold axis. Complex 11 crystallized as orange
rhomboids with 1470 frames of data yielding 16 587 integrated
intensities. The complex displays typical disorder in the position of
the tert-butyl groups; one of them is described in 0.5 occupancy
positions and isotropic.
Crystallographic Determinations. Crystalline samples were mounted
in sealed thin walled capillary tubes under a nitrogen atmosphere for
X-ray data collection. All crystal structures were collected at room
(110) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb,
M. A.; Cheeseman, J. R.; Zakrzewski, V. G.; Montgomery, J. A.;
Stratmann, R. E.; Burant, J. C.; Dapprich, S.; Millam, J. M.; Daniels,
A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J.; Barone,
V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo, C.;
Clifford, S.; Ochterski, J.; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J. B.; Cioslowski, J.; Ortiz, J. V.; Stefanov, B. B.; Liu,
G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin,
R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.;
Nanayakkara, A.; Gonzalez, C.; Challacombe, M.; Gill, P. M. W.;
Johnson, B. G.; Chen, W.; Wong, M. W.; Andres, J. L.; Head-
Gordon, M.; Replogle, E. S.; Pople, J. A. GAUSSIAN 98; Gaussian,
Inc.: Pittsburgh, PA, 1998.
Acknowledgment. We are grateful to the National Science
Foundation (Grant CHE-9807269) and the Ministerio de Edu-
cacio´n y Cultura of Spain (postdoctoral fellowship to C.Y.) for
support of this research.
(111) Becke, A. D. Phys. ReV. A 1988, 38, 3098.
(112) Lee, C.; Yang, W.; Parr, R. D. Phys. ReV. B 1988, 37, 785.
Supporting Information Available: Figures and tables presenting
kinetic data for 4 and 6, tables of Cartesian coordinates for 15-17,
and X-ray crystallographic files for 1-4, 10, and 11, in CIF
format. This material is available free of charge via the Internet at
http://pubs.acs.org.
(113) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(114) Krishnan, R.; Binkley, J. S.; Seeger, R.; Pople, J. A. J. Chem. Phys.
1980, 72, 650.
(115) McLean, A. D.; Chandler, G. S. J. Chem. Phys. 1980, 72, 5639.
(116) Wachters, A. J. H. J. Chem. Phys. 1970, 52, 1033.
(117) Hay, P. J. J. Chem. Phys. 1977, 66, 4377.
(118) Raghavachari, K.; Trucks, G. W. J. Chem. Phys. 1989, 91, 1062.
IC0109389