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• W2949272946 abstract "This contribution describes a study of scope, regioselection, enantioselection, metal and ancillary ligand effects, and kinetics in the catalytic PhSiH3 hydrosilylation of olefins using the organolanthanide precatalysts Cp’2LnCH(SiMe3)2, Me2SiCp”2LnCH(SiMe3)2, and Me2SiCp”(R*Csh)LnCH(SiMe3)2 (Cp’ = v5 Me5C5; Cp” = vSMe& Ln = lanthanide; R* = chiral auxillary). Sluggish catalyst initiation processes were first circumvented by hydrogenolysis of the Ln-CH(SiMe3)p functionality. For a-olefins, hydrosilylation turnover frequency and selectivity for 2,l addition regiochemistry are enhanced by openness of the metal ligation sphere (Cp’2Ln MezSiCp”2, Me2SiCp”(R*C5&)) and increasing Ln3+ ion radius. For styrenic olefins, complete 2,l regioselectivity (Si delivery to the benzylic position), rate enhancement by para electron-releasing substituents, and tumover frequencies as high as 400 h-’ (60 “C) are observed. For 1-hexene, 2,l addition regioselectivities as high as 76% and tumover frequencies > 1000 h-’ (90 “C) are observed. For 2-phenyl-l-butene, (R)-MezSiCp”[(-)-menthyl Cp]SmCH(SiMe& and (5‘)Me2SiCp”[(-)-menthylCp]SmCH(SiMe3)2 effect asymmetric hydrosilylation with ee values of 68% and 65%, respectively (25 “C). The former reaction obeys the rate law v = k[Sm]’[olefin]O[PhSiH3]’. D20 quenching of the reaction yields PhCD(CH3)(CH2CH3) and PhSiH2D as mechanistically informative products. The hydrosilylation of 1,5-hexadiene effected by Cp’2SmCH(SiMe3)2 affords predominantly cyclopentylCH2SiH2Ph, while Me2SiCp”zSmCH(SiMe3)2 and (R)-MezSiCp”[( -)-menthylCp]SmCH(SiMe3)2 also yield hydrosilylation products derived from 1,5hexadiene skeletal rearrangement. The hydrosilylation mechanism is discussed in terms of a hydride/alkyl cycle involving rapid, exothermic olefin insertion into an Ln-H bond followed by turnover-limiting Si-WLn-alkyl transposition (delivery of the alkyl group to Si). Olefin hydrosilylation processes form the basis for a large class of silicon-carbon bond-forming transformations of great importance in the production of organosilanes.’ Of the effective homogeneous catalysts for olefin hydrosilylation, organolanthanides2 offer a number of distinctive as well as potentially informative and useful characteristic^.^-^ These derive from the high electrophilicity of the metal centers, inaccessibility of conventional oxidative additiodreductive elimination sequences, relatively constrainedimmobile yet tunable (e.g., coordinative unsaturation; asymmetry) ancillary ligation, and the possibility of coupling hydrosilylation to other organolanthanide-catalyzed transformations. In regard to the mechanism of organolanthanide-catalyzed hydrosilylation, two pathways seem most reasonable on the basis of precedent and metal-ligand bond enthalpy considerations (Scheme l).5.6 Pathway A invokes exothermic (enthalpy data @ Abstract published in Advance ACS Abstracts, June 15, 1995. (1) (a) Ojima, I. In The Chemistry of Organic Silicon Compounds; Patai, S . , Rappoport, Z., Eds.; John Wiley: Chichester, 1989; Chapter 25 and references therein. (b) Marciniec, B.; Gulinski, J. J. Organomet. Chem. 1993, 446, 15-23. (c) Hiyama, T.; Kusumoto, T. In Comprehensive Organic Synthesis; Trost, B. M., Ed.; Pergamon Press: Oxford, 1991; Vol. 8, Chapter 3.12. (d) Collman, J. P.; Hegedus, L. S.; N$rton, J. R.; Finke, R. G. Principles and Applications of Organotransition Metal Chemistry; University Science Books: Mill Valley, CA, 1987; pp 564-567 and references therein. (e) Coniu, R. J. P.; GuCrin, G.; Moreau, J . J . E. Top. Stereochem. 1984, 15, 121-151. (2) (a) Schaverien, C. J . Adv. Organomet. Chem. 1994, 36, 283-362. (b) Schumann, H. In Fundamental and Technological Aspects of Organof-Element Chemistry, Marks, T. J., Fragali, I., Eds.; D. Reidel: Dordrecht, Holland, 1985; Chapter 1. (c) Evans, W. J. Adv. Organomet. Chem. 1985, 24, 131-177. (d) Kagan, H. B.; Namy, J. L. In Handbook on the Physics and Chemistry of Rare Earths; Gschneider, K. A,, Eyring, L., Eds.; Elsevier: Amsterdam, 1984; Chapter 50. (e) Marks, T. J.; Ernst, R. D. In Comprehensive Organometallic Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982; Chapter 21. 0002-786319511517-7157$09.0010 shown are for L,M = Cp’zSm, Cp’ = v5-Me5C# olefin insertion into a metal-silyl bond, for which there is precedent in both early and late transition metal ~hemistry,’~-~*’ followed by what is essentially a (less exothermic) protonolysis (0 bond metathesis) step, for which there is formal precedent2 Although pathway A is formally analogous to organolanthanide-catalyzed group 15 transformations such as hydroaminations and hydropho~phination,~ the polarity of an Si-H bond is of course expected to be quite different from that of an N-H or P-H bond.’O Pathway B invokes exothermic insertion of olefin into (3) For leading references in organolanthanide-catalyzed hydrosilylation, see: (a) Beletskaya, I. P.; Voakoboinikov, A. Z.; Parshina, I. N.; Magomedov, G. K.-I. Izv. Akad. Nank. USSR 1990, 693-694. (b) Marks, T. J., Plenary Lecture, First International Conference on f-Elements, Leuven, Sept. 4-7, 1990. (c) Watson, P. L., Section Lecture, First International Conference on f-Elements, Leuven, Sept. 4-7, 1990. (d) Sakakura, T.; Lautenschlager, H.-J.; Tanaka, M. J. Chem. SOC., Chem. Commun. 1991, 40-41. (e) Molander, G. A.; Julius, M. J. Org. Chem. 1992,57,6347-6351. (f) Brard, L. Ph.D. Thesis, Northwestern University, 1992. (g) Fu, P.-F.; Brard, L.; Marks, T. J. Abstracts of Papers; 207th National Meeting of the American Chemical Society, San Diego, CA; American Chemical Society: Washington, DC, 1994; INOR 40. (h) Fu, P.-F.; Marks, T. J. Abstracts of Papers; XXVII Organosilicon Symposium, March 18-19, 1994, Troy, NY, P15. (4) For complementary studies of group 4 metallocene-catalyzed hydrosilylation, see: (a) Takahashi, T.; Hasegawa, M.; Suzuki, N.; Saburi, M.; Rousset, C. J.; Fanwick, P. E.; Negishi, E. J. Am. Chem. Sac. 1991, 113,8564-8566. (b) Kesti, M. R.; Waymouth, R. M. Organometallics 1992, ( 5 ) Nolan, S . P.; Porchia, M.; Marks, T. J. Organometallics 1991, 10, (6) (a) King, W. A,; Marks, T. J. Inorg. Chim. Acta 1995, 229, 343354. (b) Nolan, S. P.; Stern, D.; Marks, T. J. J. Am. Chem. SOC. 1989, 1 1 1 , 7844-7853. (c) Schock, L. E.; Marks, T. J. J. Am. Chem. SOC. 1988, 110, 7701 -77 15. (7) (a) Tilley, T. D. in ref la, Chapter 24. (b) Brookhart, M.; Grant, B. E. J. Am. Chem. SOC. 1993, 115, 2151-2156 and references therein. (c) Bergens, S . H.; Noheda, P.; Whelan, J.; Bosnich, B. J , Am. Chem. SOC. 1992, 114, 2128-2135. 11, 1095-1103." @default.
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• W2949272946 title "ChemInform Abstract: Regioselection and Enantioselection in Organolanthanide-Catalyzed Olefin Hydrosilylation. A Kinetic and Mechanistic Study." @default.
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