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Rhodium(I) polysiloxyphosphine complexes as hydrogenation catalysts

University of British Columbia

A new synthetic route to insoluble catalytic chloro(polysiloxy-phosphine)rhodium complexes has been developed. This was achieved by synthesizing the characterizable monomeric complexes [formulae not included], which were subsequently homopolymerized and copolymerized with Cl₃Si-CH₃ or an excess of a ligand by hydrolysis in water/dioxane mixture. The idealized formulae of the products obtained are the following [formulae not included]. The nature of the metal centres in the polymers was probed by studying reactions of the polymers with hydrogen and carbon monoxide. All the polymers, with the exception of the carbonyl complex, are active catalysts for the hydrogenation of olefins. Their catalytic activity towards styrene and cyclohexene decreases upon recycling. Copolymerization of the trisphosphine species with Cl₃Si-CH₃ allows higher activity to be maintained over a larger number of cycles. Copolymerization with an excess of a phosphine (P/Rh>3) results in initially lower activity but prevents its further decrease. An increase of the length of the spacer "arm" between the matrix and the metal centre causes an increase of the overall life-time of the trisphosphine catalytic complexes. Deactivation of the trisphosphine complexes is postulated to be partly due to dimerization of the starting complexes to di-μ-chloro-tetraphosphine species and the phenomena described above are thought to be the result of improved metallic site isolation which in turn prevents the dimerization. Soluble siloxyphosphinerhodium(I) complexes were also synthesized to serve as study models for the polymeric analogues. They are also effective hydrogenation catalysts but their activity is considerably higher than that of the polymers.

Text

2010-03-04

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http://hdl.handle.net/2429/21498

Chemistry

University of British Columbia

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