A new general method for the preparation of metal carbene complexes [13]

Full text of DOI:10.1021/ja0157393

5372
J. Am. Chem. Soc. 2001, 123, 5372-5373
Scheme 1
A New General Method for the Preparation of Metal
Carbene Complexes
Mark Gandelman, Boris Rybtchinski, Nissan Ashkenazi,
Re´gis M. Gauvin, and David Milstein*
Scheme 2
Department of Organic Chemistry
The Weizmann Institute of Science
RehoVot 76100, Israel
ReceiVed March 1, 2001
ReVised Manuscript ReceiVed April 19, 2001
The chemistry of late-transition-metal carbene complexes has
recently received much attention, primarily due to the high
catalytic activity of phosphine ruthenium carbene complexes in
olefin metathesis.1,2 The most useful Ru carbene in these series
is Grubbs’ catalyst, (PCy3)2Cl2RudCHPh, bearing a benzylidene
unit.1 Being highly active and remarkably tolerant to common
functional groups, this compound found broad applications in both
organic2b,c and polymer chemistry.2d,e Therefore, synthesis and
investigation of late-metal benzylidene complexes (MdCHPh)
is a topic of great interest.1-4a There are several synthetic
approaches toward alkylidene complexes,4 with the ones utilizing
the corresponding diazoalkane being the most popular.1,2,5 How-
ever, the instability of diazo compounds and the safety issues
involved in handling them seriously limit this method. Another
recent approach, involving the reaction of precursors to unstable
Ru(0) complexes with alkyl dihalides,6 is limited by the difficult
synthesis of the unstable Ru(COD)(COT) precursor.7 New ap-
proaches toward Ru-alkylidenes starting from Ru-hydride
complexes and utilizing alkyne or alkene functions were reported
recently.8 Here, we present a new, synthetically simple and safe
method toward carbene preparation by using sulfur ylides as
carbenoid precursors.9 Such ylides are extensively used in organic
chemistry.10 To our knowledge, there are no examples for the
synthesis of metal carbene complexes by using these compounds,
although metal complexes of sulfur ylides are reported.11,12 Also,
the “transylidation” reaction, transfer of a carbenoid unit between
heteroatom centers, is well-known among main group elements.13
The new synthetic route is general and can be applied to different
metals. Moreover, it can be used for the synthesis of carbene
complexes which could not be prepared by known methods.
The general pathway of metal carbene preparation is presented
in Scheme 1. Benzyldiphenylsulfonium tetrafluoroborate 1, the
precursor of the corresponding ylide compound, can be easily
prepared by a one-pot reaction of diphenylsulfide and benzyl
bromide in the presence of AgBF4.14 Deprotonation of this
sulfonium salt by base results in the formation of the benzyl ylide
2, that readily reacts with the appropriate metal complex to give
the metal carbene complex.
In continuation of our interest in pincer-type PCX complexes,15
we have studied the possibility of synthesis of rhodium PCX-
type (X ) P, N) carbene complexes by this approach. When the
sulfonium salt 1 was reacted with 1 equiv of KN(SiMe3)2 at
-30 °C in toluene, immediate formation of a yellow solution
and precipitation of KBF4 took place (Scheme 2). After filtration
of KBF4, the sulfur ylide 2 was reacted with complexes 316 at
(1) Schwab, P.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1996, 118,
100.
(2) For some reviews see: (a) Schuster, M.; Blechert, S. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 2036. (b) Grubbs, R. H.; Chang, S. Tetrahedron 1998,
54, 4413. (c) Randall, M. L.; Snapper, M. L. Strem Chem. 1998, 1. 36, 2036.
(d) Noels, A. F.; Demonceanu, A. J. Phys. Org. Chem. 1998, 11, 602. (e)
Buchmeiser, M. R. Chem. ReV. 2000, 100, 1565. (f) Dragutan, V.; Dragutan,
I.; Balaban, A. T. Platinum Met. ReV. 2000, 44, 58. (g) Trnka, T. M.; Grubbs,
R. H. Acc. Chem. Res. 2001, 34, 18.
(11) For example, see: (a) Schmidbaur, H. Acc. Chem. Res. 1975, 8, 62.
(b) Lai, J. S.; Wu, R. F.; Lin, I. J. B.; Cheng, M. C.; Wang, Y. J. Organomet.
Chem. 1990, 393, 431. (c) Lin, I. J. B.; Hwan, L.; Shy, H. C.; Chen, M. C.;
Wang, Y. J. Organomet. Chem. 1986, 315, 135. (d) Vicente, J.; Chicote, M.
T.; Abrisqueta, M. D.; Gonzalez-Herrero, P.; Guerrero, R. Gold Bull. 1998,
31, 126. (e) Weber, L.; Matzke, T.; Boese, R. Chem. Ber. 1990, 123, 739.
(12) Intermediacy of unobserved metal carbenes has been suggested in
reactions using R2S(O)CH2: (a) Fischer, H.; Weber, L. Chem. Ber. 1984, 117,
3340. (b) Weber, L.; Luecke, E. Organometallics, 1986, 5, 2114.
(13) For some examples see: (a) Hadjiarapoglou, L.; Varvoglis, A. Synthesis
1988, 11, 913. (b) Suzuki, H.; Murafuji, T. Bull. Chem. Soc. Jpn. 1990, 63,
950. (c) Yang, S.-Y.; Dai, L.-X.; Chen, C.-G. J. Chem. Soc., Chem. Commun.
1992, 1487.
(3) (a) Werner, H.; Stu¨er, W.; Laubender, M.; Lehmann, C.; Herbst-Irmer,
R. Organometallics 1997, 16, 2236. (b) Werner, H.; Stu¨er, W.; Wolf, J.;
Laubender, M.; Weberndo¨rfer, B.; Herbst-Irmer, R.; Lehmann, C. Eur. J. Inorg.
Chem. 1999, 1889.
(4) For example: (a) Brookhart, M.; Studabaker, W. B.; Humphrey, M.
B.; Husk, G. R. Organometallics 1989, 8, 133. (b) Nguyen, S. T.; Johnson,
L. K.; Grubbs, R. H.; Ziller, J. W. J. Am. Chem. Soc. 1992, 114, 3974. (c)
Spivak, G. J.; Caulton, K. G. Organometallics 1998, 17, 5260.
(5) For reviews see: (a) Putala, M.; Lemenovskii, D. A. Russ. Chem. ReV.
1994, 63, 1994. (b) Mizobe, Y.; Ishii, Y.; Hidai, M. Coord. Chem. ReV. 1995,
139, 281. (c) Herrmann, W. A. Angew. Chem., Int. Ed. Engl. 1978, 17, 800.
See also: (d) Polse, J. L.; Kaplan, A. W.; Andersen, R. A.; Bergman, R. G.
J. Am. Chem. Soc. 1998, 120, 6316.
(6) (a) Belderrain, T. R.; Grubbs, R. H. Organometallics 1997, 16, 4001.
(b) Olivan, M.; Caulton, K. G. Inorg. Chem. 1999, 38, 566.
(7) Perti, P.; Vitulli, G.; Paci, M.; Porri, L. J. Chem. Soc., Dalton Trans.
1980, 1961.
(8) (a) Gru¨nwald, C.; Gevert, O.; Wolf, J.; Gonzalez-Herrero, P.; Werner,
H. Organometallics 1996, 15, 1960. (b) Wolf, J.; Stu¨er, W.; Gru¨nwald, C.;
Werner, H.; Schwab, P.; Schulz, M. Angew. Chem., Int. Ed. 1998, 37, 1124.
(c) Wilhelm, T. E., Belderrain, T. R.; Brown, S. N.; Grubbs, R. Organome-
tallics 1997, 16, 3867. (d) van der Schaaf, P. A.; Hafner, A. Chem. Commun.
2000, 1045.
(14) Franzen, V.; Schmidt, H.-J.; Mertz, C. Ber. 1961, 94, 2942. See also
Supporting Information.
(15) For example: (a) Vigalok, A.; Milstein, D. J. Am. Chem. Soc. 1997,
119, 7873. (b) Ohff, M.; Ohff, A.; van der Boom, M. E.; Milstein, D. J. Am.
Chem. Soc. 1997, 119, 11687. (c) Vigalok, A.; Uzan, O.; Shimon, L. J. W.;
Ben-David, Y.; Martin, J. M. L.; Milstein, D. J. Am. Chem. Soc. 1998, 120,
12539. (d) Vigalok, A.; Rybtchinski, B.; Shimon, L. J. W.; Ben-David, Y.;
Milstein, D. Organometallics 1999, 19, 895. (e) Rybtchinski, B.; Milstein, D.
Angew. Chem., Int. Ed. Engl. 1999, 38, 870. (f) Cohen, R.; van der Boom,
M. E.; Shimon, L. J. W.; Rozenberg, H.; Milstein, D. J. Am. Chem. Soc. 2000,
122, 7723. (g) Ashkenazi, N.; Vigalok, A.; Parthiban, S.; Ben-David, Y.;
Shimon, L. J. W.; Martin, J. M. L.; Milstein, D. J. Am. Chem. Soc. 2000,
122, 8797. (h) Gandelman, M.; Vigalok, A.; Konstantinovski, L., Milstein,
D. J. Am. Chem. Soc. 2000, 122, 9848.
(9) A patent application covering this work has been filed.
(10) Trost, B. M.; Melvin, L. S. In Organic Chemistry, A Series of
Monographs; Sulfur Ylides, Vol. 31; Blomquist, A. T., Wasserman, H. H.,
Eds.; Academic Press: New York, 1975.
(16) The synthesis of compounds 3 will be reported elsewhere.
10.1021/ja0157393 CCC: $20.00 © 2001 American Chemical Society
Published on Web 05/11/2001

Communications to the Editor
J. Am. Chem. Soc., Vol. 123, No. 22, 2001 5373
Scheme 3
Scheme 4
(Scheme 3). Ylide 2 was added to the osmium complex [OsHCl-
(CO)(PiPr3)2]21 in toluene at -30 °C, resulting in an immediate
color change to orange. Stirring for additional 30 min at room
temperature and workup results in quantitative formation of the
benzylidene complex 6. Spectroscopic data for 6 were identical
to the reported literature values.3b
Significantly, the approach described above can be applied also
to the synthesis of carbenes, which could not be prepared by
existing methods. Werner and co-workers have synthesized and
extensively studied the chemistry of novel disubstituted Rh(I)
carbene complexes trans-[RhCl(dCRR′)(PiPr3)2].18 These com-
plexes have been prepared with the aid of SbR3 ligands, which
later were substituted by the bulky triisopropylphosphine ligands.
However, attempts to prepare similar monosubstituted carbene
trans-[RhCl(dCHPh)(PiPr3)2] by use of phenyldiazomethane did
not lead to the desired results.22 Remarkably, this complex can
be synthesized by the new approach and without the aid of stibine
ligands. When bis-(triisopropylphosphine)rhodium chloride dimer
7 reacts with 1 equiv of the sulfur ylide 2 at -30 °C in toluene,
selective formation of the Rh benzylidene complex 8 is observed
(Scheme 4).
-30 °C resulting in clean conversion to the Rh-benzylidene
complexes 4. The Rh(I)-benzylidene complexes are not stable
at room temperature and were characterized by multinuclear NMR
spectroscopy at -40 °C. The carbene protons exhibit very
characteristic low-field doublets at 19.8 and 17.2 ppm for 4a and
4b, respectively, in the 1H NMR spectrum, due to coupling with
the Rh center. For comparison, the sole isolated alkylidene
complex of the type RhdCHR shows a resonance of the carbene
proton at 20.41 ppm.17 The carbenoid carbon gives rise to an
extremely low-field signal in 13C NMR at 340.8 and 283.6 ppm
for 4a and 4b, respectively, that provides unequivocal proof of
the M)CHR structure. Indeed, both Ru and Rh carbenes show
extremely low-field signals for the carbenoid carbon atom.1,17,18
Carbenes 4 can alternatively be prepared by reaction of the PCX
based Rh(I) complexes 3 with phenyldiazomethane.19
Stable, well-known metal carbenes can also easily and cleanly
be prepared by the sulfur ylide approach. An example is the
preparation of the synthetically very useful Grubbs’ catalyst,
(PCy3)2Cl2RudCHPh (5).1 The reaction of (PPh3)3RuCl2 in CH2-
Cl2 with the freshly prepared sulfur ylide 2 in THF at -30 °C
and concomitant substitution of the PPh3 ligands by tricyclo-
hexylphosphine at room-temperature results, after the workup,
in the Ru-benzylidene complex 5 in 96% yield20 (Scheme 3).
The NMR spectra of this complex are identical to the reported
ones.1
The 31P NMR spectrum of 8 shows a doublet at 32.1 ppm, due
to coupling with the Rh center (d, JRhP ) 167.4 Hz). The carbene
proton exhibits a low-field doublet of triplets at 20.17 ppm in 1H
NMR, due to coupling with Rh and P atoms. The carbenoid
carbon resonates at 317.86 ppm, which is in excellent agreement
with the signal at 316.11 ppm observed for the analogous carbon
of Werner’s diphenylcarbene trans-[RhCl(dCPh2)(PiPr3)2].18a
Compound 8 is moderately stable and decomposes at room
temperature within 3-4 days.
In summary, a new, general, synthetically simple and safe
method for the synthesis of metal carbene complexes is described.
The method involves the reaction of a metal precursor with a
sulfur ylide as the carbene donor. The reaction is selective and
can be applied to different metals: alkylidenes of ruthenium,
osmium, and rhodium were synthesized. Moreover, this approach
allows the direct synthesis of new metal carbene complexes, which
are difficult to prepare by known methods.
The scope of this method is not limited to rhodium and
ruthenium carbenes. For instance, Werner’s hydrido-osmium
carbene 63 was also successfully prepared by this approach
(17) Vigalok, A.; Milstein, D. Organometallics 2000, 19, 2061.
(18) (a) Schwab, P.; Mahr, N.; Wolf, J.; Werner, H. Angew. Chem., Int.
Ed. Engl. 1993, 32, 1480. (b) Werner, H. J. Organomet. Chem. 1995, 500,
331. (c) Werner, H.; Schwab, P.; Bleuel, E.; Mahr, N.; Steinert, P.; Wolf, J.
Chem. Eur. J. 1997, 3, 1375. (d) Bleuel, E.; Weberndo¨rfer, B.; Werner, H. J.
Organomet. Chem. 2001, 617-618, 502.
Acknowledgment. This work was supported by the Israel Science
Foundation, Jerusalem, Israel, and by the Tashtiot program of the Israeli
Ministry of Science. D.M. is the holder of the Israel Matz Professorial
Chair of Organic Chemistry. We thank Yehoshua Ben-David for technical
assistance.
(19) Gandelman, M.; Rybtchinski, B.; Cohen, R.; Milstein, D. Unpublished
results.
(20) This procedure was performed under
a nitrogen atmosphere.
[Ph2SCH2Ph]BF4 1 (212 mg, 0.584 mmol) was dissolved in THF (5 mL) and
cooled to -30 °C. A solution of KN(SiMe3)2 (140 mg, 0.584 mmol) in THF
(2 mL) was added, resulting in a rapid change of color to yellow. The yellow
solution was added, at -30 °C, to a solution of Ru(PPh3)3Cl2 (552 mg, 0.576
mmol) in CH2Cl2 (10 mL). The mixture was kept at -30 °C for an additional
30 min. A solution of tricyclohexylphosphine (352 mg, 1.240 mmol) in CH2-
Cl2 (7 mL) was then added, and the mixture was warmed to room temperature
and stirred for 2 h. The solvent was removed under vacuum, and the residue
was washed with ethanol (3 × 25 mL) to remove the residual phosphine,
sulfide, and silyl byproducts. The remaining solid was dried under high vacuum
to give the clean Grubbs’ carbene 5 (510 mg, 0.553 mmol) in 96% yield.
Supporting Information Available: Text describing the synthesis
of compounds 1, 4-6, 8 and the characterization of compounds 1, 4,
and 8 (PDF). This material is available free of charge via the Internet at
http://pubs.acs.org.
JA0157393
(21) Esteruelas, M. A.; Werner, H. J. Organomet. Chem. 1986, 303, 221.
(22) Werner, H.; Mahr, N.; Frenking, G.; Jonas, V. Organometallics 1995,
14, 619.