Olefin Ring Closing Metathesis and Hydrosilylation Reaction in Aqueous Medium by Grubbs Second Generation Ruthenium Catalyst Vivek Polshettiwar and Rajender S. Varma* Sustainable Technology DiVision, National Risk Management Research Laboratory, U.S. EnVironmental Protection Agency, MS 443, Cincinnati, Ohio 45268 Varma.rajender@.epa.goV; polshettiwar.ViVek@epa.goV ReceiVed June 19, 2008 The Grubbs second generation ruthenium catalyst was shown to catalyze various olefin ring closing metathesis and hydrosilylation reactions in aqueous medium. Reactions proceeded in pure water without any additives or cosolvents, in a short period of time. We found that inhomogeneity of the reaction mixture does not prevent high conversion (70-95%) of the products in both reactions. The advent of Grubbs catalyst has fueled the widespread application for various organic transformations, importantly olefin metathesis 1 and very recently hydrosilylation reaction. 2 Olefin metatheses, such as ring-closing metathesis (RCM) and cross-metathesis (CM), are extensively used as a dominant tool for the carbon-carbon bond forming reaction in the synthesis of several small molecules, 3 biomolecules, 4 and macromol- ecules 5 in the drug discovery and polymer industry. Similarly, the hydrosilylation reaction of alkynes to generate vinylsilanes, powerful intermediates in organic synthesis, 6 is a simple and widely used protocol. Both of these reactions are generally carried out in organic solvents and their potential utility in aqueous medium is largely untapped, despite their profound allure for biomolecule syn- thesis 4 and green chemistry. 7 Although there are few protocols for olefin metathesis reactions in aqueous medium, 8-11 surpris- ingly to the best of our knowledge there is no description of the hydrosilylation reaction in aqueous medium. Pioneers in this field, Grubbs et al., prepared water soluble N-heterocyclic- carbene-based olefin metathesis ruthenium catalyst. 9 Although this work led the way to advance the metathesis reaction in aqueous medium, the reaction still needs 12-24 h to complete. Blechert et al. used Grubbs second generation ruthenium catalyst for the RCM reactions; however, they used a mixture of organic solvents and water with extended reaction time. 10 Recently, Raines and co-workers reported olefin metathesis in homoge- neous aqueous medium using second generation Hoveyda- Grubbs catalyst and claimed it as a green protocol. 11 They did not use pure water as a reaction medium; instead they used organic solvents with some percentage of water in it and very often deuterated solvents, which does not justify the protocol to be truly environmentally friendly. Thus, the majority of the reported aqueous RCM methods used a mixture of organic solvent and small amounts of water or expensive and toxic deuterated solvents, e.g., C 6 D 6 , as cosolvents with exotic ruthenium complexes as catalysts. Consequently, we decided to develop simple and environmentally benign RCM and hydrosilylation protocols exclusively in aqueous medium. Engaged in the development of greener synthetic pathways, 12 herein we report an expeditious and benign ring-closing metathesis in pure aqueous medium (without using any organic or deuterated solvent) with conventional Grubbs second genera- tion ruthenium (G-2) catalyst (Figure 1). (1) (a) Grubbs, R. H. Angew. Chem., Int. Ed. 2006, 45, 3760–3765. (b) Trnka, T. M.; Grubbs, R. H. Acc. Chem. Res. 2001, 34, 18–29. (2) (a) Trost, B. M.; Ball, Z.-T. Synthesis 2005, 85, 3–887. (b) Arico, C. S.; Cox, L. R. Org. Biomol. Chem. 2004, 2, 2558–2562. (c) Maifeld, S. V.; Tran, M. N.; Lee, D. Tetrahedron Lett. 2005, 46, 105–108. (3) Grubbs, R. H. Tetrahedron 2004, 60, 7117–7140. (4) (a) Stymiest, J. L.; Mitchell, B. F.; Wong, S.; Vederas, J. C. J. Org. Chem. 2005, 70, 7799–7809. (b) Jenkins, C. L.; Vasbinder, M. M.; Miller, S. J.; Raines, R. T. Org. Lett. 2005, 7, 2619–2622. (5) Frenzel, U.; Nuyken, O. J. J. Polym. Sci. Part A 2002, 40, 2895–2916. (6) Ie, Y.; Chatani, N.; Ogo, T.; Marshall, D. 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