Insoluble ligands and their applications: II. Polysiloxane-phosphine ligands, their complexes, and hydrogenation catalysts

Abstract

Solid polysiloxane ligands containing phosphine groups have been prepared by the hydrolytic condensation of (EtO) 3Si(CH 2 n PPh 2 ( n = 2, 3) with Si(OEt) 4. They have been characterised by solid-state NMR spectroscopy and by reaction with cobalt(II) and nickel(II). Both metals formed complexes of the type MCl 2-[Ph 2P(CH 2) n - S] 2 (where S is the polysiloxane matrix), but it was not usually possible to complex all the phosphine groups. The ligands were also treated with [IrCl(cod)] 2 (cod = cyclo-octa-1,5-diene), which gave reproducible complexs having significant activity as hydrogenation catalysts. The system appears to be analogous to the homogeneous complex [Ir(L) 2(cod) (L = tertiary phosphine), since both show first-order dependence on the metal and zero-order for hex-1-ene. During hydrogenation with the polysiloxane catalysts, hex-1-ene undergoes isomerisation, but the isomers are hydrogenated at the same rate as the terminal alkene. The catalysts show slight deterioration on re-use, but are still active after 10 cycles.