Synthesis and characterization of group 4 amidinate amide complexes M[CyNC(Me)NCy]2(NR2)2 (R = Me, M = Ti, Zr, Hf; R = Et, M = Zr)

Article abstract of DOI:10.1021/om900162b

Amidinate amide complexes M[CyNC(Me)NCy]₂(NR₂) ₂(M = Ti, R = Me (1); M = Zr, R = Me (2), R = Et, (3); M = Hf, R = Me (4); Cy = cyclohexyl) have been prepared, and their crystal structures show distorted-octahedral coordina

Full text of DOI:10.1021/om900162b

3
088
Organometallics 2009, 28, 3088–3092
Synthesis and Characterization of Group 4 Amidinate Amide
Complexes M[CyNC(Me)NCy] (NR ) (R ) Me, M ) Ti, Zr, Hf;
2
2 2
R ) Et, M ) Zr)
†
‡
‡
†
,†
Jia-Feng Sun, Shu-Jian Chen, Yuxi Duan, Yi-Zhi Li, Xue-Tai Chen,* and
,
‡
Zi-Ling Xue*
State Key Laboratory of Coordination Chemistry, Nanjing National Laboratory of Microstructures, School
of Chemistry and Chemical Engineering, Nanjing UniVersity, Nanjing 210093, People’s Republic of China,
and Department of Chemistry, UniVersity of Tennessee, KnoxVille, Tennessee 37996-1600
ReceiVed February 28, 2009
2 2 2
Amidinate amide complexes M[CyNC(Me)NCy] (NR ) (M ) Ti, R ) Me (1); M ) Zr, R ) Me (2),
R ) Et, (3); M ) Hf, R ) Me (4); Cy ) cyclohexyl) have been prepared, and their crystal structures
q
show distorted-octahedral coordination spheres. Variable-temperature NMR studies give ∆H ) 2.8(0.2)
-
1
q
q
-1
q
kcal mol , ∆S ) -36(1) eu and ∆H ) 0.5(0.3) kcal mol , ∆S ) -44(1) eu for interconversions in
2
and 3, respectively.
Amidinates are ligands containing two nitrogen donor atoms
Chart 1
that, like their isoelectronic analogues carboxylates, bind to a
1
wide range of metals and nonmetals in a bidentate fashion.
The fundamental chemistry of amidinate complexes and unique
properties of the metal complexes containing versatile amidinate
ligands have led to active studies of these complexes and their
1
-5
applications. Metal amidinate systems with lower electron
counts at the metals have shown, for example, enhanced
electrophilic behavior that leads to reactivities not observed in
6
7
more commonly studied cyclopentadienyl (Cp) analogs. Ap-
materials in microelectronic devices. MO (M ) Ti, Zr, Hf)
2
plications of amidinate complexes include catalysis in several
species have been prepared from their amide precursors
2
8,9
10
5b
reactions such as olefin polymerization, hydrosilylation of
M(NMe ) ,
precursors.
tetraamidinates (Chart 1), and guanidinate
2
n
3
4
alkenes, and hydroamination, as well as the use of the
complexes as precursors in chemical vapor deposition (CVD)/
atomic layer deposition (ALD) of metal-containing microelec-
There are few known group 4 mixed amidinate amide
1
h,l,m
complexes.
Triamide Ti and Zr complexes containing a
5
,7-10
tronic materials.
Thin films of group 4 metal oxides with
large dielectric constants are of particular interest as insulating
(5) (a) Lim, B. S.; Rahtu, A.; Park, J.-S.; Gordon, R. G. Inorg. Chem.
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008002546, 2008. (c) Sadique, A. R.; Heeg, M. J.; Winter, C. H. Inorg.
2
2
*
To whom correspondence should be addressed. E-mail: xue@utk.edu
Chem. 2001, 40, 6349. (d) Wu, J.; Li, J.; Zhou, C.; Lei, X.; Gaffney, T.;
Norman, J. A. T.; Li, Z.; Gordon, R.; Cheng, H. Organometallics 2007,
26, 2803. (e) Wilder, C. B.; Reitfort, L. L.; Abboud, K. A.; McElwee-
White, L. Inorg. Chem. 2006, 45, 263. (f) Hunks, W.; Chen, P. S.; Chen,
T.; Stender, M.; Stauf, G. T.; Maylott, L.; Xu, C.; Roeder, J. F. Mater.
Res. Soc. Symp. Proc. 2008, 1071, Paper No. 1071-F09-11. (g) P a¨ iv a¨ saari,
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(
Z.-L.X.).
†
Nanjing University.
‡
University of Tennessee.
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(
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1
0.1021/om900162b CCC: $40.75  2009 American Chemical Society
Publication on Web 04/24/2009

Group 4 Amidinate Amide Complexes
Organometallics, Vol. 28, No. 10, 2009 3089
Scheme 1
1
1,14
1
h,l
Table 1. Rate Constants of the Interconversions in 2 and 3
binucleating bis(amidinate) ligand and several bis(amidinate)-
bis(amide)titanium(IV) complexes supported by chiral amidi-
complex 2
complex 3
1m
a
k (s-1
a
k (s-1
)
nates (2-aminopyrrolines) have been prepared. To our knowl-
edge, group 4 bis(amidinate) bis(amide) complexes containing
simple amidinate ligands [RN(Me)NR] (Chart 1) have not been
reported. We have prepared and characterized such complexes
with bulky [CyN(Me)NCy] ligands. Our work is reported here.
T
∆V (Hz)
)
T
∆V (Hz)
2
53
243
33
223
13
05
0
293
245
164
133
313
303
293
286
276
266
201
0
520
490
457
437
410
385
-
36.1
54.5
58.7
63.0
39.5
56.0
63.8
72.1
78.8
2
-
2
2
85.7
0
65.9 (∆V )
Results and Discussion
117.2 (∆V
0
)
a
The Cy R-H resonances in
2
and -CH -
2
resonances in 3,
Synthesis and NMR Spectra of 1-4. The reaction of
TiCl (NMe ) (6) with 2 equiv of [CyNC(Me)NCy]Li (5)
2 2 2
respectively, were used in the kinetic studies.
(
Scheme 1) proceeds smoothly at 23 °C to yield dark red 1.
Repeated attempts to prepare 1 through the reaction of
Ti[CyNC(Me)NCy] Cl with 2 equiv of LiNMe did not yield
the product. The reaction of MCl with 2 equiv of 5 at 23 °C
gives M[CyNC(Me)NCy] Cl (M ) Zr, 7; M ) Hf, 8).
Subsequent treatment of 7 with 2 equiv of LiNR (R ) Me, Et)
yields pale yellow crystalline 2 or 3. Similar treatment of the
Hf complex 8 with 2 equiv of LiNMe gives 4. 2 and 3 are also
prepared in one pot by the reactions of ZrCl with 5 and LiNR
R ) Me, Et) in a 1:2:2 ratio at 23 °C.
are inequivalent. These observations suggested that the bulky
NEt groups slow down the fluxionality. In addition, several
2
2
2
2
broad Cy peaks are found in 1-4 and the signals of the CH
group attached to the central C atom appear at ca. 1.7 ppm.
3
4
2
2
To further clarify the fluxional behavior, a variable-temper-
2
1
11
ature H NMR experiment was carried out for 2. As the
temperature was lowered, the signal of Cy R-H starts to broaden;
at 253 K, the peak starts to decoalesce. At 205 K, two separate
signals appear at 3.20 and 3.03 ppm. The coalescence temper-
2
4
2
(
q
ature was 253 K and the ∆G 253 K value was calculated to be
1.9(0.5) kcal mol , which is very close to that found in a
1
H NMR spectra of 1 and 3 at 23 °C show two broad
-1 12
1
resonances at 3.28, 3.13 ppm and 3.15, 3.05 ppm, respectively,
for the Cy R-H atoms, suggesting the Cy groups are inequiva-
lent. However, 2 and 4 show one broad resonance at 3.10 and
six-coordinate Ti(IV) complex containing bis(2-pyridyl)amine
13
2
ligands. No splitting of the signals of the NMe group is
observed as a function of temperature until at least 205 K. The
rate constants of this interconversion of 2 at various temperatures
were calculated from eq 1
3
.22 ppm, respectively. The equivalence of the Cy R-H
resonances indicates that 2 and 4 are fluxional at 23 °C, since
the two rings are inequivalent in the solid state, as their X-ray
crystal structures below reveal. The only difference between 1
and 2 is the central metal atom: one is Ti and the other is Zr.
Because the atomic radius of Ti is smaller than that of Zr, the
environment around the Ti atom in 1 is more crowded,
2
2
k ) π 2(∆ν - ∆ν )
(1)
√
0
(where ∆ν and ∆ν
0
are frequency differences (Hz) between
exchange-broadened sites at temperature T and between the two
13
14
restricting its fluxionality. C NMR spectra of 2 show one signal
57.0 ppm) for the cyclohexyl R-C atom, while those of 3 show
sites at the slow exchange limit, respectively ), and they are
1
4
11
(
given in Table 1. An Eyring plot gives the activation
two signals (57.2 and 56.9 ppm) for its R-C atoms, indicating
that the Cy groups in 2 are equivalent and the Cy groups in 3
q
-1
parameters of the exchange: ∆H ) 2.8(0.2) kcal mol and
q
q
∆
S ) -36(1) eu. This fluxional process and small ∆H and
q
negative ∆S values can be explained by the Bailar twist
(
9) (a) Woods, J. B.; Beach, D. B.; Nygren, C. L.; Xue, Z.-L. Chem.
15
mechanism. At room temperature, two enantiomers intercon-
Vap Deposition 2005, 11, 289. (b) Wang, R.; Zhang, X.-H.; Chen, S.-J.;
Yu, X.; Wang, C.-S.; Beach, D. B.; Wu, Y.-D.; Xue, Z.-L. J. Am. Chem.
Soc. 2005, 127, 5204. (c) Chen, S.-J.; Zhang, X.-H.; Yu, X.; Qiu, H.; Yap,
G. P. A.; Guzei, I. A.; Lin, Z.; Wu, Y.-D.; Xue, Z.-L. J. Am. Chem. Soc.
(11) See the Supporting Information for details.
(12) Abrahams, R. J.; Fisher, J.; Loftus, P. Introduction to NMR
Spectroscopy; Wiley: New York, 1988.
(13) Fandos, R.; Hern a´ ndez, C.; Otero, A.; Rodr ´ı guez, A.; Ruiz, M. J.
J. Organomet. Chem. 2005, 690, 4828.
(14) (a) Macomber, R. S. A Complete Introduction to Modern NMR
Spectroscopy; Wiley: New York, 1998; pp 158-160. The rate constants
here are the chemical rate constants, and they differ from the observed
magnetization transfer rate constants by a factor of 2. See e.g.: (b) Green,
M. L. H.; Wong, L.-L.; Sella, A. Organometallics 1992, 11, 2660.
2
007, 129, 14408.
10) (a) Devi, A.; Bhakta, R.; Milanov, A.; Hellwig, M.; Barreca, D.;
Tondello, E.; Thomas, R.; Ehrhart, P.; Winter, M.; Fischer, R. Dalton Trans.
007, 1671. (b) Milanov, A.; Bhakta, R.; Baunemann, A.; Becker, H.-W.;
Thomas, R.; Ehrhart, P.; Winter, M.; Devi, A. Inorg. Chem. 2006, 45, 11008.
c) Thenappan, A.; Lao, J.; Nair, H. K.; Devi, A.; Bhakta, R.; Milanov, A.
(
2
(
PCT Int. Appl. WO 2007005088, 2007. (d) Thomas, R.; Bhakta, R.;
Milanov, A.; Devi, A.; Ehrhart, P. Chem. Vap. Deposition 2007, 13, 98.

3
090 Organometallics, Vol. 28, No. 10, 2009
Sun et al.
Scheme 2
Table 2. Selected Bond Distances (Å) and Bond Angles (deg) for
1
-3
1
Ti1-N2
2.275(3)
2.092(3)
1.952(3)
2.258(3)
2.088(3)
60.81(10)
146.23(10)
81.99(11)
94.61(12)
N1-C7
1.343(4)
1.967(3)
1.311(4)
1.316(4)
1.334(4)
60.73(10)
113.2(3)
112.3(3)
Ti1-N1
Ti1-N6
Ti1-N3
N2-C7
Ti1-N4
N4-C19
Ti1-N5
N5-C19
N1-Ti1-N2
N1-Ti1-N5
N2-Ti1-N4
N3-Ti1-N6
N4-Ti1-N5
N1-C7-N2
N4-C19-N5
vert rapidly on the NMR time scale via a trigonal-prismatic
intermediate (Scheme 2), where all the Cy groups are equivalent,
but they were distinguishable at lower temperatures. Such a
behavior has been suggested for six-coordinate Zr(IV) com-
2
3
Zr1-N1
Zr1-N2
Zr1-N3
Zr1-N4
Zr1-N5
Zr1-N6
N1-C13
N2-C13
N3-C27
N4-C27
2.331(2)
2.3469(14)
2.2446(18)
2.2330(17)
2.349(2)
2.0933(19)
2.0790(19)
1.322(3)
1.342(2)
1.353(2)
1.318(2)
58.18(6)
82.95(6)
142.12(6)
58.30(6)
94.12(7)
113.32(16)
113.55(16)
2.2520(14)
2.2269(14)
2.3687(14)
2.0761(14)
2.0587(15)
1.324(2)
1.334(2)
1.353(2)
1.315(2)
57.87(5)
80.06(5)
148.55(5)
57.97(5)
102.18(6)
113.73(14)
113.41(15)
15g,h,16
plexes with N-aryl-substituted ꢀ-diketiminato ligands.
C NMR spectra of 2 are also consistent with this dynamic
The
1
3
feature. For example, the R-C resonance appears at 57.0 ppm,
whereas at 205 K two sharp singlets at 56.9 and 56.3 ppm are
observed.
1
The VT H NMR spectrum of 3 at 23 °C displays two sets
of multiplets for the two chemically inequivalent methylene
N1-Zr1-N2
signals (3.80 and 3.68 ppm) of -NEt
3.15 and 3.05 ppm) for the ring R-H of Cy groups. No
splitting was found for the methyl protons of NEt groups, which
appear as a unique triplet centered at 1.11 ppm. In this case,
the larger steric demand of the -NEt groups further hinders
2
groups and two signals
N1-Zr1-N4
N2-Zr1-N3
N3-Zr1-N4
N5-Zr1-N6
N1-C13-N2
N3-C27-N4
1
1
(
2
2
the equilibration of the two enantiomers. Coalescence of the
cyclohexyl R-H resonances was observed at 333 K. The rate
constants of the interconversion in 3 were calculated from eq 1
(
(
2.275(3), 2.258(3) Å) are longer than the trans-Ti-N bonds
2.092(3), 2.088(3) Å), as a result of the strong π-donating effect
1
4
11
and are given in Table 1. An Eyring plot gives the activation
of the dialkylamide groups. The N-C bond lengths around the
central C7 and C19 atoms average 1.33 Å, indicating partial
double-bonding character and a π-conjugated NCN chelate.
The structures of 2 and 3 are shown in Figure 2. As in 1, the
Zr center is in a distorted-octahedral environment. Similarly,
the termini of the amidinate ligand can be divided roughly into
two types, and the two cis-Zr-N bonds (2.331(2), 2.349(2) Å
in 2, 2.3469(14), 2.3687(14) Å in 3) are longer than the trans-
Zr-N bonds (2.2446(18), 2.2330(17) Å in 2, 2.2520(14),
.2269(14) Å in 3). All Zr-N bond lengths are similar to the
amidinate complexes Zr[CyNC(Me)NCy] Cl and Zr[CyNC-
The bond distances around NCN chelate
average 1.33 Å, indicating partial double-bonding character. In
q
-1
parameters of the exchange: ∆H ) 0.5(0.3) kcal mol and
q
∆
∆
S ) -44(1) eu. At the coalescence temperature of 313 K,
q
-1
G
313 K ) 14.3(0.6) kcal mol . As in the interconversion in
q q
2
, small ∆H and negative ∆S values are consistent with the
1e,15f,g
Bailar twist mechanism.
The coalescence temperature is
q
higher than that in 2. The activation entropy ∆S here is more
negative than the -36(1) eu in 2. These could be attributed to
the greater steric demand of the -NEt groups in 3 as compared
2
16,17
to that of the -NMe
2
groups in 2.
This phenomenon is
2
16
similar to those found in ꢀ-diketiminato-based Zr complexes.
2
2
X-ray Crystal Structures of 1-3. Selected bond distances
and angles for 1-3 are given in Table 2. The Ti center in 1 is
in a distorted-octahedral environment, surrounded by the four
1d
(
2 2
Me)NCy] Me .
3
1
(
, the two cis-NEt
2
groups exhibit a N5-Zr1-N6 angle of
02.18(6)°, which is larger than that of the two cis-NMe
N atoms of the two amidinate anions and two cis-NMe
2
ligands
2
groups
(
Figure 1). The bonding parameters within the two amidinate
94.12(7)°) in 2.
ligands are not dramatically different. The two N and bridging
C atoms for each of the individual amidinate ligands lie in a
plane, which includes the Ti atom, resulting in a solid-state
2
molecular geometry with approximately C symmetry. The
nitrogen termini of the amidinate ligands can be divided roughly
into two types: cis-NCy groups (N2, N4) with a N2-Ti1-N4
angle of 81.99(11)° and trans-NCy groups (N1, N5) with a
N1-Ti1-N5 angle of 146.23(10)°. The two cis-Ti-N bonds
(15) (a) Bailar, J. C. J. Inorg. Nucl. Chem. 1958, 8, 165. (b) Wentworth,
R. A. D. Coord. Chem. ReV. 1972, 9, 171. (c) Fleischer, E. B.; Gebala,
A. E.; Swift, D. R.; Tasker, P. A. Inorg. Chem. 1972, 11, 2775. (d) Churchill,
M. R.; Reis, A. H. Inorg. Chem. 1972, 11, 1811. (e) Vanquickenborne,
L. G.; Pierloot, K. Inorg. Chem. 1981, 20, 3673. (f) Darensbonrg, D. J.;
Kump, R. L. Inorg. Chem. 1984, 23, 2993. (g) Rahim, M.; Taylor, N. J.;
Xin, S.; Collins, S. Organometallics 1998, 17, 1315. (h) Kakaliou, L.;
Scanlon, W. J.; Qian, B.; Baek, S. W.; Smith, M. R.; Motry, D. H. Inorg.
Chem. 1999, 38, 5964.
(
16) Franceschini, P. L.; Morstein, M.; Berke, H.; Schmalle, H. W. Inorg.
Chem. 2003, 42, 7273.
17) Bei, X.; Swenson, D. C.; Jordan, R. F. Organometallics 1997, 16,
282.
(
Figure 1. ORTEP diagram of 1 showing 30% probability thermal
ellipsoids.
3

Group 4 Amidinate Amide Complexes
Organometallics, Vol. 28, No. 10, 2009 3091
Figure 2. Molecular structures of 2 (left) and 3 (right).
The current work shows that amidinates are useful supporting
ligands, yielding six-coordinated group 4 complexes 1-4.
2 2 2
solution of TiCl (NMe ) (6; 1.000 g, 4.832 mmol) in hexanes (50
mL). The red solution was stirred for 20 h, filtered, concentrated,
Preparation of the Ti amidinate amide from TiCl
4
requires the
(6), followed by the replacement of
the two remaining Cl- by amidinate ligands. In comparison,
the Zr and Hf analogues were prepared from MCl by first
reacting with lithium amidinate to form M[CyNC(Me)NCy] Cl
M ) Zr, 7; M ) Hf, 8). The formation of the M-NR bonds
occurs in the second step. Dynamic NMR studies of
2 2
Zr[CyNC(Me)NCy] (NR ) (R ) Me, 2; R ) Et, 3) suggest
and cooled to -30 °C to give dark red crystals of 1 (0.304 g, 0.525
1
formation of TiCl
2
(NMe
2
)
2
mmol, 11% yield based on TiCl
2
(NMe
2
)
2
). H NMR (benzene-d
6
,
3
3
99.79 MHz, 23 °C): δ 3.46 (s, 12H, 2NMe
.13 (br, 2H, C 11), 1.88-1.29 (m, 40H, C
, 100.53 MHz, 23 °C) δ 171.5
11), 50.4 (NMe ), 11.4 (NC(Me)N).
Ti: C, 66.41; H, 10.80. Found: C, 66.49;
2
), 3.28 (br, 2H, C
6
H11),
6
H
6
H
11), 1.68 (s, 6H,
4
1
3
NC(Me)N). C NMR (benzene-d
NC(Me)N), 59.1-26.5 (m, C
6
2
2
(
6
H
2
(
2
Anal. Calcd for C32
62 6
H N
H, 11.01.
2
Synthesis of 2. To CyNdCdNCy (2.100 g, 10.18 mmol) in Et
40 mL) at -30 °C was added ca. 1 equiv of MeLi (6.4 mL, 1.6 M
in Et
2
O
that they undergo a Bailar twist interconversion in solution.
(
2
O, 10.2 mmol). After the solution was stirred at 23 °C for
Experimental Section
18 h, it was added to a THF solution of ZrCl (1.189 g, 5.102
4
mmol). The mixture was stirred at 23 °C for 20 h, followed by
All manipulations were carried out in either a nitrogen-filled
glovebox or under nitrogen using standard Schlenk-line techniques.
filtration. Volatiles were removed in vacuo to give a yellow-green
fluffy solid of ZrCl
This solid was added to a solution of LiNMe
in Et O (30 mL) at 0 °C. After it was stirred at 23 °C for 24 h, the
2
[CyNC(Me)NCy]
2
(7; 2.898 g, 4.780 mmol).
Solvents were dried using conventional methods and freshly distilled
(0.488 g, 9.56 mmol)
n
2
before use. MeLi (1.5-1.6 M in Et
LiNMe
Aldrich and used without further purification. Li[CyN(Me)NCy]
2
O), BuLi (2.5 M in hexane),
2
2
, and 1,3-dicyclohexylcarbodiimide were purchased from
solution was filtered and concentrated to give a solution containing
white solids. A few drops of THF were added to help dissolve the
white solids. The solution was cooled to -32 °C to give diamond-
1
k
(
5) was prepared by a modified literature procedure. MeLi (1
equiv) was added to a hexanes or Et O solution of 1,3-dicyclohexyl-
carbodiimide at room temperature. The resulting white precipitate
was collected on a frit under N and either washed with hexane or
directly used in the next step. LiNEt was obtained by addition of
BuLi to a hexanes solution of diethylamine and then evaporation
of the solvent. TiCl (NMe (6) was prepared by a literature
2
1
like crystals of 2 (1.070 g, 1.720 mmol, 36% yield based on 7). H
NMR (toluene-d
br, 4H, C 11), 1.80-1.26 (m, 40H, C
(Me)N). C NMR (toluene-d , 100.5 MHz, 23 °C): δ 174.6
NC(Me)N), 57.0, 35.8, 26.6, 26.5 (C 11), 46.2 (NMe ), 11.0
(NC(Me)N). Anal. Calcd for C H N Zr: C, 61.78; H, 10.05.
8
, 399.7 MHz, 23 °C): δ 3.22 (s, 12H, NMe
2
), 3.10
11), 1.70 (s, 6H, NC-
2
(
6
3
H
6
H
2
1
n
8
(
6
H
2
2
13
2 2
)
1
8
1
procedure. H and C NMR spectra were recorded on a Bruker
AMX-400 FT spectrometer. Elemental analyses were conducted
by Complete Analysis Laboratories, Inc., Parsippany, NJ.
32 62
6
Found: C, 61.68; H, 10.13. For the preparation of 2 in toluene, see
the Supporting Information.
q
q
Synthesis of 3. To CyNdCdNCy (2.100 g, 10.18 mmol) in Et O
The uncertainties in ∆H and ∆S were computed from the error
2
(
Et
40 mL) at 23 °C was added 1 equiv of MeLi (6.4 mL, 1.6 M in
propagation formulas derived by Girolami and co-workers from
1
1,19
2
O, 10 mmol). The mixture was stirred for 80 min and was added
the Eyring equation.
Synthesis of 1. Compound 5 was prepared in situ by the addition
of MeLi (6.5 mL, 1.5 M in Et O, 9.750 mmol) to CyNdCdNCy
1.994 g in 30 mL of hexanes, 9.664 mmol) at ambient temperature.
After it was stirred overnight, the cloudy solution was added to a
to a THF solution of ZrCl
4
(1.189 g, 5.102 mmol). The mixture
was filtered, and volatiles in the filtrate were removed to give a
yellow-green fluffy solid of 7 (2.893 g, 4.780 mmol). The solid
2
(
was dissolved in Et
2
O (30 mL), and 2 equiv of LiNEt
O (20 mL) was added. After it was stirred for
4 h, the solution was filtered, and volatiles were removed to give
2
(0.756 g,
9
.56 mmol) in Et
2
2
(
(
18) Benzing, E.; Kornicker, W. Chem. Ber. 1961, 94, 2263.
19) Morse, P. M.; Spencer, M. D.; Wilson, S. R.; Girolami, G. S.
a solid. The solid was dissolved in hexanes and kept at -30 °C to
Organometallics 1994, 13, 1646.
20) (a) Sheldrick, G. M. Program for Empirical Absorption Correction;
give crystalline solids of 3 (0.499 g, 0.731 mmol, 15% yield based
(
1
on 7). H NMR (toluene-d
8
, 399.7 MHz, 23 °C): δ 3.80 (br,
CH , 4H), 3.15 (br, C 11, 2H), 3.05
11, 2H), 1.85-1.17 (m, C 11, 40H), 1.69 (s, 6H, NC-
University of G o¨ ttingen, G o¨ ttingen, Germany, 2000. (b) Sheldrick, G. M.
Program for Crystal Structure Solution and Refinement; University of
G o¨ ttingen, G o¨ ttingen, Germany, 2000.
CH
2
CH
3
, 4H), 3.68 (br, CH
2
3
6
H
(br, C
6
H
6
H

3
092 Organometallics, Vol. 28, No. 10, 2009
, 12H). 13C NMR (toluene-d
Sun et al.
20a
SADABS program. The structures of 1 and 3 were solved by
direct methods. The structure of 2 was solved by the heavy-atom
method. The structures were refined on F against all reflections
by full-matrix least-squares methods with the SHELXTL (version
(Me)N), 1.11 (t, CH
2
CH
3
8
, 100.5 MHz,
CH ),
2
3
1
6
3 °C): δ 173.0 (NC(Me)N), 57.2, 56.9 (C 11), 41.4 (CH
6.6, 36.3, 35.6, 34.0 (C 11), 26.7, 26.6 (C 11), 26.4, 26.2 (C
3.4 (CH CH ), 11.6 (NC(Me)N). Anal. Calcd for C36 Zr: C,
3.76; H, 10.40. Found: C, 63.78; H, 10.47.
Synthesis of 4. To CyNdCdNCy (6.365 g, 30.85 mmol) in Et
30 mL) at -30 °C was added 1 equiv of MeLi (19.3 mL, 1.6 M
in Et O, 31 mmol). The mixture was stirred for 80 min and then
added to a THF solution (30 mL) of HfCl (4.940 g, 15.40 mmol)
at -60 °C. The mixture was stirred at 23 °C for 2 days. LiNMe
1.574 g, 30.85 mmol) in Et O (30 mL) was added to the mixture
6
H
2
3
2
6
H
6
H
6
H11),
2
3
70 6
H N
20b
6
.10) program. The hydrogen atoms in the three compounds were
2
O
positioned geometrically and refined in the riding-model ap-
proximation. All non-hydrogen atoms were refined with anisotropic
thermal parameters.
(
2
4
2
Acknowledgment. This work was supported by the
NationalBasicResearchProgramofChina(Nos.2006CB806104
and 2007CB925102), the Natural Science Grant of China
(No. 20721002), the National Science Foundation (No. CHE-
0516928), and the Changjiang Lecture Professor program
(
2
at 0 °C, and the mixture was stirred at 23 °C for another 20 h.
Filtration, concentration, and recrystallization gave crystals of 4
1
(
(
(
(
(
(
8.093 g, 11.41 mmol, 74% yield based on HfCl
4
). H NMR
benzene-d
6
, 399.8 MHz, 23 °C): δ 3.33 (s, 12H, 2NMe
11), 1.81-1.27 (m, 40H, C 11), 1.66 (s, 6H, NC-
, 100.5 MHz, 23 °C): δ 174.2
NC(Me)N), 67.8, 56.8, 26.5, 26.3 (C 11), 46.1 (NMe ), 11.3
NC(Me)N). Anal. Calcd for C32 Hf: C, 54.18; H, 8.81. Found:
2
), 3.22
br, 4H, C
6
H
6
H
(Z.-L.X.).
Me)N). 13C NMR (benzene-d
6
6
H
2
Supporting Information Available: Text, figures, tables, and
62 6
H N
CIF files giving details of the preparation of 2 and 3 in toluene,
crystal data and all bond lengths and angles in 1-3, and Eyring
plots of the interconversion in 2 and 3. This material is available
free of charge via the Internet at http://pubs.acs.org.
C, 53.94; H, 8.89.
X-ray Crystallography. Data were collected on a SMART
APEX CCD diffractometer (1 and 2) and a Bruker CCD-1000
diffractometer (3), both with graphite-monochromated Mo KR
radiation (λ ) 0.710 73 Å), and corrected for absorption using the
OM900162B