Selective and efficient platinum(0)-carbene complexes as hydrosilylation catalysts

Science

Volumn 298, Issue 5591, 2002, Pages 204-206

  Markó, István E ^a   Stérin, Sébastien ^a   Buisine, Olivier ^a   Mignani, Gérard ^a   Branlard, Paul ^a   Tinant, Bernard ^a   Declercq, Jean Paul ^a  

^a UNIVERSITÉ CATHOLIQUE DE LOUVAIN   (Belgium)

Author keywords

[No Author keywords available]

Indexed keywords

BYPRODUCTS; CATALYST SELECTIVITY; COLLOIDS; OLEFINS;

HYDROSILYLATION CATALYSTS;

PLATINUM COMPOUNDS;

ALKENE DERIVATIVE; CARBENOID; PLATINUM COMPLEX; POLYMER; SILICON;

CATALYSIS; POLYMER;

ARTICLE; CATALYSIS; CATALYST; CHEMICAL REACTION; COLLOID; CONFORMATION; PRIORITY JOURNAL; REACTION ANALYSIS; STEREOCHEMISTRY;

EID: 0037020203     PISSN: 00368075     EISSN: None     Source Type: Journal    
DOI: 10.1126/science.1073338     Document Type: Article

References (28)

1. Marciniec, J. Gulinski, W. Urbaniak, Z. W. Kornetka, in Comprehensive Handbook on Hydrosilylation, B. Marciniec, Ed. (Pergamon, Oxford, 1992).
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8. P. B. Hitchcock, M. F. Lappert, N. J. W. Warhurst, Angew. Chem. Int. Ed. Engl. 30, 438 (1991).
9. The isomerized olefins 4 are the major by-products, and alkane 6 is usually formed in smaller amounts. Compounds 5 and 7 are typically minor contaminants. It is noteworthy that the internal alkenes 4 and 5 do not undergo hydrosilylation under these conditions. Isomerization of 2 to 4 and/or 5 is believed to be catalyzed by multinuclear platinum species, which are inactive in the hydrosilylation reaction.
10. The presence of colloidal Pt species is easily detected by ultraviolet-visible spectroscopy and is commonly associated with the appearance of a yellow color in the reaction medium.
11. J. Stein, L. N. Lewis, Y. Gao, R. A. Scott, J. Am. Chem. Soc. 121, 3693 (1999).
12. To the best of our knowledge, no monocarbene-Pt(0) complexes have been reported so far in the literature. Two publications describe bis-carbene Pt(0) derivatives: A. J. Arduengo, S. F. Gamper, J. C. Calabrese, F. Davidson, J. Am. Chem. Soc. 116, 4391 (1994); P. L. Arnold, F. G. N. Cloke, T. Geldbach, P. B. Hitchcock, Organometallics 18, 3228 (1999).
13. To the best of our knowledge, no monocarbene-Pt(0) complexes have been reported so far in the literature. Two publications describe bis-carbene Pt(0) derivatives: A. J. Arduengo, S. F. Gamper, J. C. Calabrese, F. Davidson, J. Am. Chem. Soc. 116, 4391 (1994); P. L. Arnold, F. G. N. Cloke, T. Geldbach, P. B. Hitchcock, Organometallics 18, 3228 (1999).
14. G. Chandra, P. B. Hitchcock, M. F. Lappert, P. Y. Lo, Organometallics 6, 191 (1987).
15. G. Beuter, O. Heyke, I. P. Lorenz, Z. Naturforsch. 46, 1694 (1991).
16. These monophosphine complexes are formed rapidly and quantitatively by the exchange reaction between 8 and the corresponding phosphine. However, their high solubility, and sometimes sensitivity, leads to significant losses during the purification step.
17. In all cases, the amount of isomerized alkenes 4 and 5 increases initially, then decreases. The disappearance of 4 and 5 results from their hydrogenation into alkane 6, probably by the in situ-generated colloidal Pt species.
18. The amount of by-products is related to the rate of the reaction and the leaving group ability of the phosphine ligands. The formation of multinuclear Pt species appears to correlate with the weakness of the Pt-P bond.
19. For an excellent review on metal-carbene complexes, see D. Bourissou, O. Gueret, F. P. Gabbai, G. Bertrand, Chem. Rev. 100, 39 (2000).
20. V. P. W. Böhm, W. A. Herrmann, Angew. Chem. Int. Ed. Engl. 39, 4036 (2000).
21. Samples of these Pt-carbene complexes have been stored for several months without noticeable loss of activity. Although they are insensitive toward air and moisture, it is advisable to protect them from light.
22. 3, 300 MHz): δ = -0.27 (s, 6H); 0.31 (s, 6H); 1.0-2.3 (m, 26H); 4.25 (m, 2H); 7.0 (s + d, J = 12 Hz, 2H).
23. Several Pt(II) complexes have been described [D. S. McGuinness, K. J. Cavell, B. F. Yates, J. Chem. Soc. Chem. Commun. 2001, 355 (2001), and references cited therein].
24. Under "normal" conditions, the Pt complexes 14a to 14c are added to a mixture of silane 9 and olefin 10. The "inverse" protocol implies the addition of the silane 9 to a mixture of alkene 10 and Pt catalysts 14a to 14c. No colloidal Pt is formed upon increasing the amount of Pt-carbene catalysts from 30 ppm up to 300 ppm. The rate increases concomitantly with the amount of catalyst, and the reaction can become highly exothermic.
25. The high selectivity observed with this "inverse" procedure stems from the kinetics of the hydrosilylation reaction using our Pt-carbene complexes, which differs significantly from the Karstedt-catalyzed system. To obtain a fair comparison between the two catalysts, both reactions have been performed under identical, nonoptimized conditions.
26. Full experimental and analytical data will be published in a forthcoming full paper. The experimental procedure and comparison data in the case of the industrially interesting polyepoxy silicone oil is described in (26).
27. 3 (450 g, 0.476 mol) over a period of 3 hours. After 5 hours at 70°C, the crude mixture is cooled to 25°C and 22 mg (600 ppm) of thiodiethanol is added. The resulting oil is warmed at 120°C under vacuum (<5 mbar) for 7 hours to eliminate the remaining volatile material. A light oil is obtained, which possesses a viscosity at 25°C of 325 mPa/s, indicating that essentially no epoxide opening/polymerization has occurred during the hydrosilylation reaction.
28. Financial support for this work by Rhodia Silicones and the Université Catholique de Louvain is gratefully acknowledged. I.E.M. is grateful to Rhodia for receiving the 2001 Rhodia Outstanding Award and to J.-P. Delarche for performing some of the reported experiments.