Recycling of Rodium-Based Hydrosilylation Catalysts; A Flourous Approach

The concept of fluorous biphasic separation has been applied in the recycling of rhodium-based catalysts for the hydrosilylation of 1-alkenes and fluorinated 1-alkenes by following two approaches. Hydrosilylation of 1-hexene using various silanes and fluorous versions of Wilkinson's catalyst [RhCl{P(C6H4-4-SiMe2Rf)3}3] (1; Rf = CH2CH2C6F13) or [RhCl{P(C6H4-4-SiMe(Rf)2)3}3] (2; Rf = CH2CH2C8F17) in fluorous biphasic solvent systems afforded the corresponding n-hexylsilanes in high yield. The catalyst activities were similar to those obtained using conventional [RhCl(PPh3)3]. The fluorous phase containing the catalyst was recycled at least twice without noticeable loss of activity, despite the fact that 12 and 1.7% of [Rh] was lost for 1 and 2, respectively, in the first cycle. The fluorous hydride intermediate [Rh(H)(Cl)(SiCl3){P(C6H4-4-SiMe2Rf)3}2] (3; Rf = CH2CH2C6F13) was identified by NMR spectroscopy. In a reverse approach, the original Wilkinson's catalyst was used for the hydrosilylation of 1H,1H,2H-perfluoro-1-alkenes in benzene or toluene as solvent. Fluorous extraction of the products enabled recycling of the nonfluorous catalyst.