Phosphorus ylide as a precursor for the formation of new high-valent tantalum phosphonio methylidyne complexes

Article abstract of DOI:10.1021/om061068b

Two new high-valent tantalum(V) phosphonio methylidyne complexes, [CpTa(C-PPh₃)(CH-PPh₃)-Cl] (4) and [CpTa(C-PPh ₃)(CH-PPh₃)₂] (5), have been obtained respectively via transylidation reactions of CpTaCl₄ with 5 and 7 equiv of the phosphorus ylide Ph₃P=CH₂. Complex 4 was structurally analyzed with X-ray diffraction. The possible formation mechanism has been discussed. To our knowledge this presentation is the first example of a stable tantalum complex with a terminal [M≡C-PPh₃] function.

Full text of DOI:10.1021/om061068b

Organometallics 2007, 26, 1411-1413
1411
Phosphorus Ylide as a Precursor for the Formation of New
High-Valent Tantalum Phosphonio Methylidyne Complexes
Xiaoyan Li,*,† Aichen Wang,† Liang Wang,† Hongjian Sun,† 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 NoVember 21, 2006
Two new high-valent tantalum(V) phosphonio methylidyne complexes, [CpTa(C-PPh3)(CH-PPh3)-
Cl] (4) and [CpTa(C-PPh3)(CH-PPh3)2] (5), have been obtained respectively via transylidation reactions
of CpTaCl4 with 5 and 7 equiv of the phosphorus ylide Ph3PdCH2. Complex 4 was structurally analyzed
with X-ray diffraction. The possible formation mechanism has been discussed. To our knowledge this
presentation is the first example of a stable tantalum complex with a terminal [MtC-PPh3] function.
The topic of high-valent methylidene and methylidyne
complexes with d0 electron configurations is an important and
interesting one, because they can be highly reactive catalysts
for the alkene and alkyne metathesis reactions, respectively.1-6
Recently, we have successfully used a phosphorus ylide as a
precursor for the formation of phosphonio methylidyne com-
plexes of tungsten,7 rhenium,8 and niobium9 with d0 electron
configurations. The rhenium phosphonio methylidyne complex,
by reacting with diphenylketene through a Wittig reaction, gives
rise to an allenylidene complex,10 which is a novel class of
compounds in organometallic chemistry11,12 and can be used
as precursors of new carbene complexes,13 as metal-containing
polymers,14,15 and as intermediates for organic synthesis.16 In
order to increase the yield and the stability of the phosphonio
methylidyne complex, we have introduced amino and cyclo-
pentadienyl (C5H5, Cp) groups.
Owing to the isolobal relationship between CpTaCl4 and
W(NR)Cl4 (Scheme 1), these two complexes should have similar
reactivities toward (triphenylmethylene)phosphorane. The tran-
sylidation reaction of CpTaCl4 (1) with 7 equiv of (triphenyl-
methylene)phosphorane gave the complex [CpTa(C-PPh3)-
(CH-PPh3)2] (5) (Scheme 2). Complex 5 is also isolobal with
[W(NMes)(C-PPh3)(CH-PPh3)2] and [W(NDip)(CH-PPh3)2-
(C-PPh3)].7 To our knowledge this presentation is the first
example of a stable tantalum complex with a terminal [MtC-
PR3] function.
By careful investigation of the stoichiometry of this trans-
formation and by characterization of some intermediates and
byproducts, a reaction mechanism is proposed in Scheme 3:
the first intermediate is the hexacoordinate ylide adduct 2, which
can be isolated in good yield when the parent compound 1 is
treated with 1 equiv of Ph3PdCH2 in toluene. Compound 2 is
stable as a solid, but in solution it is deprotonated by 6 equiv
of Ph3PdCH2 to provide complex 5 and phosphonium chloride.
As an intermediate the phosphonio methylidyne complex 4 can
be isolated when the parent compound 1 is treated with 5 equiv
of Ph3PdCH2 in toluene. The phosphonio methylidyne complex
3 cannot be isolated as an intermediate when 2 is treated with
2 equiv of Ph3PdCH2 in toluene. There is some collateral
evidence for intermediate 3, as transylidation reactions of
[CpNbCl4] with (triphenylmethylene)phosphorane afforded phos-
phonio methylidyne complexes (Scheme 4).9
* To whom correspondence should be addressed. Fax: 0086-531-
8564464. E-mail: xli63@sdu.edu.cn (X.L.).
† Shandong University.
‡ University of Marburg.
(1) (a) Schrock, R. R. Chem. Commun. 2005, 2773-2777. (b) Schrock,
R. R. Chem. ReV. 2002, 102, 145-179.
(2) (a) Jamison, G. M.; White, P. S.; Templeton, J. L. Organometallics
1991, 10, 1954. (b) Bruce, A. E.; Gamble, A. S.; Tonker, T. L.; Templeton,
J. L. Organometallics 1987, 6, 1350.
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8, 2010.
(4) Holmes, J. S.; Schrock, R. R.; Churchill, M. R.; Wasserman, H. J.
Organometallics 1984, 3, 476.
(5) Schmidbaur, H.; Mu¨ller, G.; Pichl, R. Angew. Chem. 1986, 98, 572;
Angew. Chem., Int. Ed. Engl. 1986, 25, 574.
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Chem. 1993, 32, 603; Angew. Chem., Int. Ed. Engl. 1993, 32, 554. (b)
Reynolds, K. A.; Dopico, P. G.; Sundermann, M. J.; Hughes, K. A.; Finn,
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Organometallics 2002, 21, 2356-2358.
Complexes 4 and 5 have been fully characterized by NMR
and elemental analysis. The 1H NMR spectra show one singlet
at 5.92 ppm (4) and 5.61 ppm (5) for the cyclopentadienyl
ligand, respectively. The 31P NMR spectra of 4 show two
(8) Li, X.; Stephan, J.; Harms, K.; Sundermeyer, J. Organometallics 2004,
23, 3359-3361.
(14) (a) Macomber, D.; Hung, M. H.; Liang, M.; Verma, A. G.;
Madhukar, P. Macromolecules 1988, 21, 1187. (b) Hagihara, N.; Songashira,
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Y.; Murata, E.; Sonogashira, K.; Hagihara, N. J. Polym. Sci.: Polym. Chem.
Ed. Engl. 1980, 18, 349-361.
(9) Li, X.; Sun, H.; Harms, K.; Sundermeyer, J. Organometallics 2005,
24, 4699-4701.
(10) Li, X.; Schopf, M.; Stephan, J.; Kippe, J.; Harms, K.; Sundermeyer,
J. J. Am. Chem. Soc. 2004, 126, 8660-8861.
(15) (a) Schrock, R. R.; Luo, S.; Lee, J. C.; Zanetti, N. C.; Davis, W.
M. J. Am. Chem. Soc. 1996, 118, 3883-3895. (b) Kishimoto, Y.; Eckerle,
P.; Miyatake, T.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1994, 116,
12131-12132. (c) Mizumoto, T.; Masuda, T.; Higashimura, T. Macromol.
Chem. Phys. 1995, 196, 1769-1771.
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I.; Swincer, A. G. AdV. Organomet. Chem. 1983, 22, 59-128. (c) Bruce,
M. I. Chem. ReV. 1991, 91, 197-257.
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E. F.; Roper, W. R. Organometallics 1992, 11, 809.
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10.1021/om061068b CCC: $37.00 © 2007 American Chemical Society
Publication on Web 02/07/2007

1412 Organometallics, Vol. 26, No. 6, 2007
Li et al.
Scheme 1. Isolobal Relationship
Scheme 2. Synthesis of Complex 5
Scheme 3. Proposed Mechanism for the Formation of
Complexes 4 and 5
Figure 1. X-ray crystal structure of 4. Selected bond distances
(Å) and angles (deg): Ta1-C1 ) 1.853(7), Ta1-C2 ) 2.040(6),
Ta1-C3 ) 2.385(7), Ta1-C4 ) 2.470(8), Ta1-C5 ) 2.555(6),
Ta1-C6 ) 2.521(6), Ta1-C7 ) 2.431(6), Ta1-Cl1 ) 2.4116-
(17), P1-C1 ) 1.700(7), P2-C2 ) 1.715(6); P1-C1-Ta1 )
164.9(4), P2-C2-Ta1 ) 136.3(4), Cl-Ta-Cl1 ) 102.3(2), C2-
Ta-Cl1 ) 103.9(2), C2-Ta-C1 ) 105.8(3).
The Ta1-C1 distance of 1.853 Å in [TatC-PPh3] lies within
the range expected for a metal-carbon triple bond17-19 (1.850
Å in [Ta(CPh)(η5-C5Me5)(PMe3)2Cl],18 1.851 Å in [Ta(CCMe3)-
(H)(dmpe)2(ClAlMe3)]19) and compares perfectly with that of
the related d0 phosphonium methylidyne complexes7-9 (Re1-
C1 ) 1.758 Å in [Re(NtBu)(C-P(NEt2)3)Cl3],8 W-C ) 1.813
Å in [W(NDip)(CH-PPh3)2(C-PPh3)],7 Nb-C )1.829 Å in
[CpNb(C-PPh3)Cl2]).9
Scheme 4
The ylidic Cyl-P distances C1-P1 ) 1.700(7) and C2-P2
) 1.715(6) Å are substantially shorter than other Car-P
distances of the PPh3 group (1.806-1.830 Å), reflecting a
considerable contribution of the charged resonance form.8,9
The angle of the P1-C1-Ta1 ) 164.9(4)° deviates slightly
from the expected 180° for an sp hybridized C atom. This can
be explained by the significant steric repulsion between the two
triphenylphosphine groups in complex 4. The PPh3 group on
the carbyne carbon is pushed toward the C5 ring. As a
consequence of the strong trans influence of both phosphonio
methylidene and phosphonio methylidyne units, the distances
Ta-C5 ) 2.555(6) and Ta-C6 ) 2.521(6) Å in trans positions
are considerably longer than Ta1-C3 ) 2.385(7) Å in a cis
position, while the other two distances Ta1-C4 ) 2.470(8) and
Ta1-C7 ) 2.431(6) Å are close to the average value of these
five distances, 2.47 Å.
doublets for [TadCH-PPh3] and [TatC-PPh3] at 23.7 and
4
-21.7 ppm, respectively, with the coupling constant J(PP) )
5.0 Hz. The 31P NMR spectra of 5 reveal a triplet for [Tat
C-PPh3] at -27.7 ppm and a doublet at 19.7 ppm for the two
[TadCH-PPh3] functionalities (4J(PP) ) 4.0 Hz). The differ-
ences in metal-carbon bond orders are also reflected in the
13C NMR spectra of 4 and 5, showing resonances at 117.7 ppm
(4) and 79.2 ppm (5) for [TadCH-PPh3] and 208.0 ppm (4)
and 202.1 ppm (5) for [TatC-PPh3], which are comparable
with those for the related isolobal complexes of tungsten
[W(NMes)(C-PPh3)(CH-PPh3)2] and [W(NDip)(CH-PPh3)2-
(C-PPh3)].7
By recrystallization from pentane at 4 °C crystals of 4 as
yellow prisms suitable for X-ray diffraction analysis were
obtained. The molecular geometry is shown in Figure 1 with
selected bond distances and angles. The tantalum atom is found
in a slightly distorted pseudo-tetrahedral geometry, reminiscent
of a three-legged piano stool. The structure is related to that of
[CpNb(NtBt)(CH-PPh3)Cl]17 by formal replacement of an [Nt-
Bt] with an isoelectronic [C-PR3] ligand. The Ta1-C2 distance
of 2.040(6) Å in the [TadCH-PPh3] moiety is consistent with
a tantalum-carbon double bond1a and matches the bond length
of structurally and electronically related d0 phosphonium
methylidene complexes.7 (Nb-C6 ) 2.043 Å in [CpNb(NtBt)-
(CH-PPh3)Cl],17 W-C32 ) 1.994 Å and W-C51 ) 2.022 Å
in [W(NDip)(CH-PPh3)2(C-PPh3)]).
Complexes 4 and 5 are formally 18- and 20-electron species,
respectively, with a polar tantalum-carbon triple bond. They
are very reactive toward CO, CH3NC, and Ph2dCdCdO.
Currently we are investigating these reactions. We will report
the results in the near future.
Experimental Section
General Procedures and Materials. Standard vacuum tech-
niques were used in manipulations of volatile and air-sensitive
materials. CpTaCl4 and H2CdPPh3 were synthesized according to
literature procedures. Infrared spectra (4000-400 cm-1), as obtained
from Nujol mulls between KBr disks, were recorded on a Nicolet
5700 instrument. NMR spectra were recorded on a Bruker AV 400
(18) Churchill, M. R.; Youngs, W. J. Inorg. Chem. 1979, 18, 171-176.
(19) Churchill, M. R.; Wasserman, H. J.; Turner, H. W.; Schrock, R. R.
J. Am. Chem. Soc. 1982, 104, 1710-1716.
(17) Schmidt, S.; Sundermeyer, J.; Moeller, F. J. Organomet. Chem.
1994, 475, 157.

Tantalum Phosphonio Methylidyne Complexes
Organometallics, Vol. 26, No. 6, 2007 1413
MHz spectrometer. 13C and 31P NMR resonances were obtained
with broad-band proton decoupling.
turned red-brown. The filtrate was concentrated to 50 mL under
reduced pressure and layered with pentane (50 mL). At -30 °C
the orange product precipitated as a powder. Yield: 0.52 g (21%).
Anal. Calcd for C62H52TaP3 (5; 1070.8 g/mol): C, 69.54; H, 4.89.
Synthesis of 2. To 0.84 g (2.16 mmol) of CpTaCl4 (1) in 50 mL
of toluene was added 0.60 g (2.16 mmol) of Ph3PdCH2 in 10 mL
of toluene at 0 °C. After it was stirred for 2 h at ambient
temperature, the yellow suspension was filtered, reduced in volume,
layered with pentane, and stored at 4 °C. The product precipitated
as a yellow powder. Yield: 1.0 g (59%). Anal. Calcd for C24H22-
Cl4PTa (2; 664.17 g/mol): C, 45.21; H, 3.34. Found: C, 45.25; H,
1
Found: C, 69.39; H, 4.50. H NMR (400.1 MHz, C6D6, 300 K):
δ 3.46 (dd, 2J(PH) ) 4.0 Hz, 4J(PH) ) 1.2 Hz, 2H, TaCHP), 5.61
(s, 5H, C5H5), 7.02-8.07 (m, 45 H, P(C6H5)3). 13C NMR (125.8
1
MHz, C6D6, 300 K) δ 79.2 (d, J(PC) ) 48.5 Hz, TaCHP), 103.6
(s, C5H5), 129.3 (d, 4J(PC) ) 2.7 Hz), 129.7 (d, 4J(PC) ) 2.7 Hz),
132.6 (d, 3J(PC) ) 9.3 Hz), 133.1 (d, 2J(PC) ) 9.7 Hz), 133.9 (d,
1
2
3.48. H NMR (400.1 MHz, C6D6, 300 K): δ 4.05 (d, J(PH) )
16.2 Hz, 2H, TaCH2PPh3), 6.35 (s, 5H, C5H5), 6.93-7.73 (m, 15H,
PC6H5). 13C NMR (100.6 MHz, C6D6, 300 K): δ 123.98 (s, C5H5),
134.35 (d, 1J(PC) ) 9.6 Hz, TaCH2PPh3), 128.53 (d, 3J(PC) ) 12.0
1
1
2J(PC) ) 8.8 Hz), 136.5 (d, J(PC) ) 81.4 Hz), 137.5 (d, J(PC)
) 80.4 Hz), 202.1 (s br, TaCP). 31P NMR (81.0 MHz, C6D6, 300
K): δ 19.7(d, J(PP) ) 4.0 Hz, 2P, TaCHP), -27.7 (t, J(PP) )
4.0 Hz, 1P, TaCP).
4
4
4
Hz, Ph Cmeta), 132.11 (d, J(PC) ) 2.6 Hz, Ph Cpara), 134.35 (d,
2J(PC) ) 9.6 Hz, Ph Cortho). 31P NMR (162.0 MHz, C6D6, 300 K):
δ 33.1 (s, TaCH2PPh3).
Crystallographic Data for 4: C43H36ClP2Ta, Mr ) 831.06,
crystal dimensions 0.20 × 0.16 × 0.05 mm, monoclinic, space
group C2/c, a ) 40.635(3) Å, b ) 10.1305(5) Å, c ) 18.5388(15)
Å, â ) 107.268(6)°, V )7287.6(9) Å3, T ) 193(2) K, Z ) 8, Dc
) 1.515 g cm-3, µ ) 3.207 mm-1, total reflections collected 39 754,
6396 unique reflections (Rint ) 0.0788), θmax ) 25.00°, semiem-
pirical absorption correction, R1 ) 0.0397 (for 4552 reflections
with I > 2σ(I)), wR2 ) 0.0920 (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 anisotropic.
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-226534. Copies of the data can be obtained free
of charge on application to the CCDC, 12 Union Road,
Cambridge CB2 1EZ, U.K. (fax, (+44)1223-336-033; e-mail,
deposit@ccdc.cam.ac.uk).
Synthesis of 4. A 1.19 g portion (3.06 mmol) of CpTaCl4 (1)
was dissolved in 50 mL of toluene, and 4.24 g (15.26 mmol) of
Ph3PdCH2 in 50 mL of toluene was added dropwise with stirring
at 0 °C. The reaction mixture was warmed to ambient temperature
and stirred for 4 days. During this period, the reaction mixture
turned orange. After removal of the solvent at reduced pressure,
the solid residue was extracted with pentane (80 mL) and diethyl
ether (2 × 80 mL), respectively. Repeated recrystallization from
pentane at 4 °C yielded yellow single crystals suitable for X-ray
diffraction. Yield: 0.85 g (33.9%). Anal. Calcd for C43H36ClP2Ta
(4; 831.0 g/mol): C, 62.14; H, 4.37; Cl, 4.26. Found: C, 62.02;
1
H, 4.50; Cl, 4.16. H NMR (400.1 MHz, CDCl3, 300 K): δ 5.28
2
(d, J(PH) ) 3.0 Hz, 1H, TaCHPPh3), 5.92 (s, 5H, C5H5), 6.94-
7.94 (m, 30 H, PC6H5). 13C NMR (100.6 MHz, CDCl3, 300 K): δ
1
105.2 (s, C5H5), 117.7 (d, J(PC) ) 46.6 Hz, TaCHP), 130.2 (d,
4J(PC) ) 2.2 Hz), 130.3 (d, 4J(PC) ) 2.2 Hz), 133.1 (d, 3J(PC) )
10.0 Hz), 134.2 (d, 3J(PC) ) 9.0 Hz), 134.9 (d, 1J(PC) ) 84.6 Hz),
Acknowledgment. This work was supported by the NSFC
(Nos. 20572062 and 20372042), by the Doctoral Program of
the MOE (Nos. 20050422010 and 20050422011), and by the
Deutsche Forschungsgemeinschaft (No. SFB 260).
1
135.7 (d, J(PC) ) 84.5 Hz), 208.0 (s br, TaCP). 31P NMR (81.0
4
MHz, C6D6, 300 K): δ 23.7 (d, J(PP) ) 6.0 Hz, 1P, TaCHP),
4
-21.7 (d, J(PP) ) 6.0 Hz, 1P, TaCP).
Synthesis of 5. A 0.90 g portion (2.31 mmol) of CpTaCl4 (1)
was dissolved in 50 mL of toluene, and 4.49 g (16.16 mmol) of
Ph3PdCH2 in 50 mL of toluene was added dropwise with stirring
at 0 °C. The reaction mixture was warmed to ambient temperature
and stirred for 3 days. During this period, the reaction mixture
Supporting Information Available: Tables containing full
X-ray crystallographic data for 4. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM061068B