Effect of different bases and phosphorus ylide on the selective deprotonation of phosphorus ylide adduct Cp*TaCl4(CH 2=PPh3)

Article abstract of DOI:10.1021/om0701266

The effect of different bases and phosphorus ylide on the selective deprotonation of phosphorus ylide adduct Cp*TaCl₄(CH ₂=PPh₃) (4) was studied. The acidity of the methylene hydrogen atoms in ylide adduct complex 4, [Cp*TaCl₄(CH ₂=PPh₃)], is weaker than those in the derivative complex [CpTaCl₄-(CH₂=PPh₃)]. Under the same conditions complex 4 cannot transylidate. With the strong, but weakly coordinating base bis(trimethylsilyl)amide a double deprotonation of two methyl groups on the pentamethylcyclopentadienyl ring occurs, and the novel ylide adduct complex 6, with an η³-ally-η⁴-butadiene ligand, is obtained. Only when elimination of three chloride ligands is compensated by at least three coordinating ylide molecules can the strong base bis(trimethylsilyl)amide selectively deprotonate in a Ta-CH position, affording the expected carbyne complex 5.

Full text of DOI:10.1021/om0701266

3456
Organometallics 2007, 26, 3456-3460
Effect of Different Bases and Phosphorus Ylide on the Selective
Deprotonation of Phosphorus Ylide Adduct Cp*TaCl4(CH2dPPh3)
Xiaoyan Li,*,† Aichen Wang,† Hongjian Sun,† Liang Wang,† Simone Schmidt,‡
Klaus Harms,‡ and Jo¨rg Sundermeyer‡
School of Chemistry and Chemical Engineering, Shandong UniVersity, Shanda Nanlu 27, 250100 Jinan,
People’s Republic of China, and Department of Chemistry, UniVersity of Marburg,
Hans-Meerwein-Strasse, 35032 Marburg, Germany
ReceiVed February 8, 2007
The effect of different bases and phosphorus ylide on the selective deprotonation of phosphorus ylide
adduct Cp*TaCl4(CH2dPPh3) (4) was studied. The acidity of the methylene hydrogen atoms in ylide
adduct complex 4, [Cp*TaCl4(CH2dPPh3)], is weaker than those in the derivative complex [CpTaCl4-
(CH2dPPh3)]. Under the same conditions complex 4 cannot transylidate. With the strong, but weakly
coordinating base bis(trimethylsilyl)amide a double deprotonation of two methyl groups on the
pentamethylcyclopentadienyl ring occurs, and the novel ylide adduct complex 6, with an η3-ally-η4-
butadiene ligand, is obtained. Only when elimination of three chloride ligands is compensated by at least
three coordinating ylide molecules can the strong base bis(trimethylsilyl)amide selectively deprotonate
in a Ta-CH position, affording the expected carbyne complex 5.
PPh3)(dCH-PPh3)Cl] (2) (eq 1) as the first example of a stable
tantalum complex with a terminal [MtC-PR3] function.7
Instead of the cyclopendienyl ligand (Cp), the pentamethylcy-
clopentadienyl ligand (Cp*) was introduced to increase the yield
and the stability of the phosphonio methylidyne complex.
Introduction
The synthesis of transition metal compounds containing
metal-carbon multiple bonds and their applications in olefin/
alkyne metathesis is a very important research field in organo-
metallic chemistry. Olefin metathesis reaction is a not only
simple but also efficient chemical method to recombine the
carbon-carbon bonds and has been widely applied in organic
synthesis, fine chemical industry, pharmaceutical chemistry,
material chemistry, green chemistry, etc. The development of
the chemistry of alkylidene complexes of tantalum was well
reviewed by Schrock, Schmidbaur, Johnson and Kolodiazhnyi.1
In 1986 the first bridged dinuclear four-valent titanium phos-
phonio carbyne compound was obained from titanium tetra-
chloride through transylidation reaction.2
In this paper we report the effect of the different bases
CH2dPPh3, (Me3Si)2N-, and pyridine on the different and
regioselective deprotonation in phosphorus ylide adduct Cp*TaCl4-
(CH2dPPh3) (4).
With the transylidation method we successfully prepared the
phosphonio methylidyne complex of tungsten,3 rhenium4 and
niobium5 with d0 electron configuration. The rhenium phos-
phonio methylidyne complex when reacted with diphenylketene
through a Wittig reaction gave rise to an allenylidene complex.6
Results and Discussion
Reaction of Cp*TaCl4with CH2dPPh3. When Cp* is used
instead of Cp, the ylide adduct could be obtained (eq 2).8 With
5 molar equiv of phosphorus ylide the transylidation reaction
fails to occur and the corresponding carbyne complex is not
obtained (eq 3). Compared with the cyclopentadienyl ligand,
the pentamethylcyclopentadienyl ligand has a stronger donor
strength with five methyl groups as electron-donating groups,
and the positive charge at the metal center in pentamethylcy-
clopentadienyl tantalum tetrachloride decreases. This leads to
a decrease of the acidity of the proton in the ylide adduct 4,
and finally the basicity of the ylide is not able to eliminate a
hydrogen chloride molecule.
The transylidation reaction of CpTaCl4 1 with 5 equiv of
triphenylmethylenephosphorane gave the complex [CpTa(tC-
* To whom correspondence should be addressed. Fax: 0086-531-
8564464. E-mail: xli63@sdu.edu.cn.
† Shandong University.
‡ University of Marburg.
(1) (a) Schrock, R. R. Acc. Chem. Res. 1979, 12, 98. (b) Schmidbaur,
H. Angew. Chem., Int. Ed. Engl. 1983, 22, 907. (c) Johnson, A. W. Ylide
and Imines of Phosphorus, 1st ed.; Wiley-Interscience: New York, 1993.
(d) Kolodiazhnyi, O. I. Phosphorus Ylides, Chemistry and Application in
Organic Synthesis; Wiley-VCH: New York, 1999.
(2) Schmidbaur, H.; Mu¨ller, G.; Pichl, R. Angew. Chem. 1986, 98, 572;
Angew. Chem., Int. Ed. Engl. 1986, 25, 574.
(3) Li, X.; Schopf, M.; Stephan, J.; Harms, K.; Sundermeyer, J.
Organometallics 2002, 21, 2356.
(4) Li, X.; Stephan, J.; Harms, K.; Sundermeyer, J. Organometallics 2004,
23, 3359.
Reaction of Ylide Adduct 4 with NaN(SiMe3)2. In trying
to deprotonate the relatively weaker ylide methylene protons
in complex 4 with a stronger base, the novel complex 6 was
(5) Li, X.; Sun, H.; Harms, K.; Sundermeyer, J. Organometallics 2005,
24, 4699.
(6) Li, X.; Schopf, M.; Stephan, J.; Kippe, J.; Harms, K.; Sundermeyer,
J. J. Am. Chem. Soc. 2004, 126, 8660.
(7) Li, X.; Wang, A.; Wang, L.; Sun, H.; Harms, K.; Sundermeyer, J.
Organometallics 2007, 26, 1411.
(8) Fandos, R.; Gomez, M.; Royo, P. Organometallics 1987, 6, 1581.
10.1021/om0701266 CCC: $37.00 © 2007 American Chemical Society
Publication on Web 05/27/2007

SelectiVe Deprotonation of Phosphorus Ylide Adduct
Organometallics, Vol. 26, No. 14, 2007 3457
Figure 1. Molecular structure of 6. The ellipsoids are drawn at
30% probability. Selected bond distances (Å) and angles (deg):
C1-C6 1.440(8), C2-C7 1.466(8), C1-C2 1.453(9), C2-C3
1.455(8), C3-C4 1.391(8), C4-C5 1.410(8), C1-C5 1.434(8),
C3-C8 1.512(8), C4-C9 1.498(8), C5-C10 1.507(9), C1-Ta1
2.154(5), C2-Ta1 2.173(5), C3-Ta1 2.436(5), C4-Ta1 2.572(5),
C5-Ta1 2.410(5), C6-Ta1 2.289(7), C7-Ta1 2.320(6), C11-Ta1
2.313(5), Cl1-Ta1 2.4319(14), Cl2-Ta1 2.4312(13), C11-P1
1.764(5); Cl1-Ta1-Cl2 94.99(6), Cl1-Ta1-C11 79.40(13), Cl2-
Ta1-C11 84.85(14), Ta1-C11-P1 131.5(3), C5-C1-C6 120.5-
(7), C3-C2-C7 118.8(6).
formed through the reaction of complex 4 with 2 equiv of
sodium bis(trimethylsilyl)amide (eq 4). This result shows that
the larger pentamethylcyclopentadienyl ligand likely hinders this
deprotonation of the ylide adduct in addition to the above-
mentioned electronic effect.
dimethylene groups, which can be considered a η3-allyl-η4-
butadien coordination. For this reason this mode is referred to
as a form of an η7-ligand containing a doubly “tucked-in”
Complex 6 as red crystals is stable in the air for several hours.
It was fully characterized by NMR (C6D6) and elemental
analysis. The 1H NMR spectrum reveals two methylene groups
1
cyclometalated Cp* ligand.11 In light of the H NMR data of
complex 6 the form 6B is a more appropriate representation,
2
because the coupling constant J(HH) ) 5.2 Hz is typical for
2
as doublets with couplings constant J(HH) ) 5.5 Hz at 0.74
the geminal hydrogen atoms at an sp2-hybridized carbon atom.
Similar results were reported for the tantalum dihydride [(η7-
C5Me3(CH2)2)Ta(H)2(PMe3)2]9 and [Cp*(η3:η4-C5Me3(CH2)2)-
Ti] complex.10
and 0.86 ppm, respectively, which implies that they are geminal
hydrogen atoms attached to an sp2-hybridized carbon atom.9 A
singlet at 1.85 ppm is found for the methyl group in the middle
of the allyl part, and a signal as a singlet was obtained at 2.16
ppm for the two methyl groups on the two sides of the allyl
part. The two methylene protons in ylide ligand are registered
The solution data were substantiated by an X-ray diffraction
analysis. In the structure of complex 6 (Figure 1) the tantalum
bears one phosphorus ylide ligand, two chloride ligands, and a
1,2,3-trimethyl-4,5-dimethylenecyclopentenyl ligand in an η3-
allyl-η4-diene coordination mode. The shorter CdCH2 bonds,
C2-C7 ) 1.466(8) and C1-C6 ) 1.440(8) Å, in comparison
with the other three carbon-carbon bonds, C3-C8 ) 1.512-
(8), C4-C9 ) 1.498(8), and C5-C10 ) 1.507(9) Å, the angles
H6A-C6-H6B ) 116° and H7A-C7-H7B ) 119°, and the
near-planarity of bonds C7-H7A, C7-H7B, and C2-C7, as
well as C6-H6A, C6-H6B, and C1-C6, indicate that C6 and
C7 are sp2-hybridized methylene carbon atoms. However, the
elongation of the CdCH2 unit in comparison with the normal
CdC bond in olefins12 also confirms the activation of both Cd
CH2 units through π-coordination (η2-bonding) of these two
groups to the metal, while the other three carbon-carbon bonds,
C3-C8 ) 1.512(8), C4-C9 1.498(8), and C5-C10 ) 1.507-
(9) Å, are in the range of lengths for normal carbon-carbon
single bonds. Comparing with the other three bonds, C3-Ta1
) 2.436(5), C4-Ta1 ) 2.572(5), and C5-Ta1 2.410(5) Å, the
especially short distances C1-Ta1 ) 2.154(5), C2-Ta1 )
2.173(5), C6-Ta1 ) 2.289(7), and C7-Ta1 ) 2.320(6) Å also
prove this interaction between tantalum and the CdCH2 units.
The relatively long C11-Ta1 ) 2.313(5) Å implies a weaker
2
at 3.16 ppm as a doublet with a coupling constant J(PH) )
16.5 Hz. This is typical for a phosphorus ylide ligand. The 31
P
NMR spectrum of 6 shows one singlet at 34.8 ppm, a
characteristic value for phosphorus ylide adducts. In the 13C
NMR spectrum, two sp2-methylene groups on the C5 ring appear
at 64.6 and 64.7 ppm as singlets, respectively, which are
comparable with the complex [Cp*(η3:η4-C5Me3(CH2)2)Ti].10
The bonding mode in complex 6 can be explained with two
possible resonance forms (Scheme 1):
Scheme 1. Two Resonance Forms of Complex 6
(η5-C5Me5)-substituted tantalum complex 6A with two σ-bonded
sp3-methylene groups, which are formed through the deproto-
nation of methyl groups of C5Me5, or in form 6B with trimethyl
(11) Wigley, D. E.; Gray, S. D. ComprehensiVe Organometallic Chem-
istry, A ReView of the Literarure 1982-1994; Abel, E. W., Stone, F. G.
A., Wilkinson, G., Eds.; pp 132-133.
(12) International Tables for Crystallography; Wilson, A. J. C., Ed.;
Kluwer Academic Publishers: Dordrecht, 1992; Vol. C, pp 694-695.
(9) Gibson, V. C.; Kee, T. P.; Carter, S. T.; Sanner, R. D.; Clegg, W. J.
Organomet. Chem. 1991, 418, 197.
(10) Pattiasina, J. W.; Hissink, C. E.; de Boer, J. L.; Meetsma, A.; Teuben,
J. H. J. Am. Chem. Soc. 1985, 107, 7758.

3458 Organometallics, Vol. 26, No. 14, 2007
Li et al.
interaction between the tantalum center and the ylide ligand,
but corresponds to a single bond and is comparable with the
other tantalum phosphorus ylide adduct: Ta-C(ylide) ) 2.35
Å in [η5-C5Me5]Cl4Ta(CH2dPMePh2)].8
avoid the appearance of complex 6, CH2dPPh3 and LiN(SiMe3)2
were employed in different ratios. When the reaction was carried
out in a ratio of Cp*TaCl4:CH2dPPh3:LiN(SiMe3)2 of 1:3:1,
the in situ 31P NMR spectrum of the mother solution indicates
the existence of complex 5 and complex 6 with a ratio of 1:1.
We could also selectively obtain only complex 5 using a ratio
of Cp*TaCl4:CH2dPPh3:LiN(SiMe3)2 of 1:3:3 (eq 6).
Reaction of Cp*TaCl4 with CH2dPPh3 and LiN(SiMe3)2.
In this case it is considered that sodium bis(trimethylsilyl)amide
is a too strong base for this purpose. In order to investigate the
effect of different bases upon the deprotonation reaction, lithium
bis(trimethylsilyl)amide was selected because it has a basicity
between sodium bis(trimethylsilyl)amide and triphenylphos-
phorus ylide. The larger sodium cation can more strongly
activate the chloride ligand at the tantalum center than the
smaller lithium cation. This size-dependent counterion effect
could be understood from the difference of solubility in organic
solvents between sodium chloride and lithium chloride. It was
found that under the same reaction conditions apart from the
same product complex 6 as in eq 4, the in situ 31P NMR
spectrum of the mother solution indicates the existence of the
less (<5%) expected phosphino carbyne complex 5 (eq 5).
Complex 5 was fully characterized by NMR and elemental
analysis. The 1H NMR spectrum of 5 shows one singlet at 2.31
ppm for the five methyl groups on the cyclopentadienyl ring.
The carbene hydrogen atom is recorded at 4.72 ppm. In
comparison with the corresponding value (5.28 ppm) in complex
2, this shift to high field is attributed to the five electron-donating
methyl groups on the cyclopentadienyl ring, resulting in the
weaker acidity of the carbene proton in complex 4. The 31P
NMR spectrum of 5 consists of two doublets for the [TadCH-
PPh3] and [TatC-PPh3] moieties at 22.2 and -30.0 ppm,
4
respectively, with a coupling constant J(PP) ) 5.2 Hz. In
comparison with complex 2 these signals are shifted to high
field, indicating stronger shielding and a reduced electronega-
tivity of the tantalum center. This difference is also reflected in
the 13C NMR spectrum of 5 and 2 for [TatC-PPh3], showing
resonances at 198.6 ppm for 5 and 208.0 ppm for 2.
After changing the experimental conditions, it was found that
reacting Cp*TaCl4 4 with 3 equiv of phosphorus ylide affords
a carbyne compound not only with lithium salt but also with
sodium salt. In order to improve the yield of complex 5 and to
The formation of complex 6 can be explained as in Scheme
2. The sodium salt and lithium salt are stronger bases than the
ylide, but the bis(trimethylsilyl)amide anion is a weaker
coordination ligand. After the addition of the sodium salt or
Scheme 2. Formation of Complex 6

SelectiVe Deprotonation of Phosphorus Ylide Adduct
Organometallics, Vol. 26, No. 14, 2007 3459
Scheme 3. Formation Mechanism of Complex 5
lithium salt, sodium chloride or lithium chloride precipitates;
at the same time, one coordination cation forms, in which the
tantalum center is unsaturated because of no coordination of
the bis(trimethylsilyl)amide anion. This anion stays in the outer
sphere. The C-H bond of the methyl group on the C5 ring
will be activated by this active “naked” tantalum center with
high positive charge. Complex 6 is finally formed with the
formation of HN(SiMe3)2.
under the same reaction conditions, the in situ 31P spectrum
indicates the existence of 5 and 6 with a ratio of 1:1.
With the existence of the other phosphorus ylide molecules,
the coordination of the ylide shields the naked metal center.
This makes it impossible for the positive tantalum to attack the
C-H bonds of the methyl group on the C5 ring. Then the whole
transformation is a transylidation reaction with the formation
of final carbyne compound 5 (Scheme 3).
The overall reaction can be expressed as in eq 7.
Conclusions
Different bases and phosphorus ylide have a synergistic effect
on the regioselective deprotonation of the phosphorus ylide
adduct Cp*TaCl4(CH2dPPh3) 4. The acidity of the methylene
hydrogen atoms in complex [Cp*TaCl4(CH2dPPh3)], 4, is
weaker than those in complex [CpTaCl4(CH2dPPh3)]. Under
the same conditions complex 4 cannot transylidate. With the
strong, but weakly coordinating base bis(trimethylsilyl)amide,
a double deprotonation, i.e., a metal-induced C-H activation,
of two methyl groups on the pentamethylcyclopentadienyl ring
occurs, and the η5-pentamethylcyclopantadienyl group is con-
verted to an η3-ally-η4-butadiene ligand. Only when elimination
of three chloride ligands is compensated by at least three
coordinating ylide molecules can the strong base bis(trimeth-
ylsilyl)amide selectively deprotonate in a Ta-CH position in
the phosphrous ylide adduct.
Influence of the Coordinative Base Pyridine on the
Selectivity. In order to confirm the reaction mechanism (Scheme
3), a strong base, pyridine, with coordinative activity, was added
to the reaction system (eq 8). As expected, the coordination of
pyridine blocked the attack of the tantalum center on the methyl
group on the pentamethylcyclopentadienyl ring. In this case
Experimental Section
General Procedures and Materials. Standard vacuum tech-
niques were used in manipulations of volatile and air-sensitive

3460 Organometallics, Vol. 26, No. 14, 2007
Li et al.
14
materials. Cp*TaCl4 313 and H2CdPPh3 were synthesized ac-
added dropwise at -80 °C to the above mixture with the color
rapidly turning to red. The reaction mixture was allowed to warm
to ambient temperature and stirred for 2 h. Evaporation of the filtrate
under vacuum followed by washing with pentane resulted in a red
powder, which was crystallized from diethyl ether at -30 °C.
Complex 6 was obtained as red cubic crystals suitable for X-ray
diffraction. Yield: 1.20 g (60.0%). Anal. Calcd for C29H30TaPCl2
(661.38 g/mol)%) 6: C 52.67, H 4.57. Found: C 52.48, H 4.73.
1H NMR (300.1 MHz, C6D6, 300 K): δ 0.74 (d, 2J(HH) ) 5.5 Hz,
cording to literature procedures. NMR spectra were recorded using
a Bruker Avance 300 MHz spectrometer. 13C and 31P NMR
resonances were obtained with broad-band proton decoupling.
Synthesis of 5. Method a. To a suspension of 1.23 g (2.68 mmol)
of Cp*TaCl4 3 and 1.48 g (5.36 mmol) of H2CdPPh3 in 60 mL of
toluene was added dropwise 1.34 g (8.04 mmol) of LiN(SiMe3)2
dissolved in 20 mL of toluene with stirring at 0 °C. The reaction
mixture immediately changed from yellow to brown. After 3 h at
room temperature the reaction solution was filtered. The solid
residue was dried and extracted with pentane and diethyl ether,
respectively. Complex 5 as an orange powder and complex 6 as
red crystals were obtained in yields of 28% (0.68 g) and 26% (0.49
g), respectively.
Method b. Cp*TaCl4 3 (1.23 g, 2.68 mmol) and 2.22 g (8.04
mmol) of H2CdPPh3, as well as 1.34 g (8.04 mmol) of LiN-
(SiMe3)2, were used under the same reaction conditions and with
the same workup as in method a. Only complex 5 was obtained in
52% yield (1.26 g).
Method c. Cp*TaCl4 3 (1.23 g, 2.68 mmol) and 2.22 g (8.04
mmol) of H2CdPPh3, as well as 1.47 g (8.04 mmol) of NaN-
(SiMe3)2, were used under the same reaction conditions and with
the same workup as in method a. Complex 5 was obtained in 45%
yield (1.10 g). Anal. Calcd for C48H46ClP2Ta (901.7 g/mol)%) 5:
C 63.94, H 5.14. Found: C 63.69, H 5.32. 1H NMR (300.1 MHz,
2
2H, CdCH2), 0.86 (d, J(HH) ) 5.5 Hz, 2H, CdCH2), 1.85 (s,
3H, CH3), 2.16 (s, 6H, CH3), 3.16 (d, 2J(PH) ) 16.5 Hz, 2H, TaCH2-
PPh3), 6.85-7.62 (m, 15 H, PC6H5). 13C NMR (75.5 MHz, C6D6,
300 K): δ 10.2 (s, CH3), 10.4 (s, CH3), 18.7 (d, 1J(PC) ) 25.0 Hz,
TaCH2P), 64.6 (s, CdCH2), 64.7 (s, CdCH2), 127.0 (s, C-CH3),
128.7 (d, 3J(PC) ) 11.6 Hz, Ph-Cmeta), 131.0 (s, C-CH3), 132.1 (d,
4J(PC) ) 2.6 Hz, Ph-Cpara), 133.8 (d, 4J(PC) ) 9.7 Hz, Ph-Cortho).
31P NMR (121.5 MHz, C6D6, 300 K): δ 35.2 (s, TaCH2PPh3).
Crystallographic data for (6 + Et2O): C33H40Cl2OPTa, Mr )
735.47, crystal dimensions 0.48 × 0.27 × 0.27 mm, monoclinic,
space group P21/n, a ) 11.6458(5) Å, b ) 13.1279(5) Å, c )
20.9329(10) Å, â ) 96.311(6)°, V ) 3180.9(2) Å3, T ) 193(2) K,
Z ) 4, Dc ) 1.536 g cm-3, µ ) 3.697 mm-1. A total of 24 697
reflections were collected, 6195 unique (Rint ) 0.0635), θmax
)
25.95°, semiempirical absorption correction. R1 ) 0.0397 (for 4741
reflections with I > 2σ(I)), wR2 ) 0.0874 (all data). The structure
was solved by direct methods and refined with full-matrix least-
squares on all F2 (SHELXL-97) with non-hydrogen atoms aniso-
tropic.
2
4
C6D6, 300 K): δ 2.31(s, 15H, CCH3, 4.72 (t′, | J(PH) + J(PH)|
) 3.0 Hz, TaCHP), 7.07-8.09 (m, 30H, PC6H5). 13C NMR (75.5
MHz, C6D6, 300 K): δ 11.1 (s,CH3), 113.1 (s,C5(CH3)5), 117.6
(d,1J(PC) ) 46.1 Hz), 128.5 (d,4J(PC) ) 2.3 Hz), 128.8 (d,4J(PC)
Crystallographic data (excluding structure factors) for the
structure reported in this paper have been deposited with the
Cambridge Crystallographic Data Center as supplementary publica-
tion no. CCDC-616486 (6). Copies of the data can be obtained
free of charge on application to CCDC, 12 Union Road, Cambridge
CB21EZ, UK (fax: (+44)1223-336-033; e-mail: deposit@
ccdc.cam.ac.uk).
3
3
) 2.3 Hz), 131.9 (d, J(PC) ) 9.8 Hz), 132.7 (d, J(PC) ) 9.1
1
1
Hz), 134.9 (d, J(PC) ) 83.8 Hz), 134.1 (d, J(PC) ) 83.1 Hz),
198.6 (t, | J(PC) + 4J(PC)| ) 7.5 Hz,TaCP). 31P NMR (121.5 MHz,
1
C6D6, 300 K): δ 22.2 (d, 4J(PP) ) 5.2 Hz, 1P, TaCHP), -30.0(d,
4J(PP) ) 5.2 Hz, 1P, TaCP).
Synthesis of 6. Cp*TaCl4 (1.31 g, 2.84 mmol) was dissolved in
50 mL of toluene, and 0.79 g (2.84 mmol) of Ph3PdCH2 in 20 mL
of toluene was added dropwise with stirring at 0 °C. The reaction
mixture was allowed to warm to ambient temperature and stirred
for 4 h. During this period, the reaction mixture turned orange in
color. NaN(SiMe3)2 (1.14 g, 5.72 mmol) in 10 mL of toluene was
Acknowledgment. This work was supported by NSFC No.
20572062 and 20372042, the Doctoral Program of MOE No.
20050422010 and 20050422011, and Shandong Scientific Plan
032090105.
Supporting Information Available: Tables containing full
X-ray crystallographic data for 4. This materials is available free
of charge via the Internet at http://pubs.acs.org.
(13) Cardoso, A. M.; Clark, R. J. H.; Moorhouse, S. J. Chem. Soc., Dalton
Trans. 1980, 1156.
(14) Schmidbaur, H.; Stuhler, H.; Vornberger, W. Chem. Ber. 1972, 105,
1084.
OM0701266