Stable platinum(0) catalysts for catalytic hydrosilylation of styrene and synthesis of [Pt(Ar-bian)(η2-alkene)] complexes

The use of alkenes and bidentate N-ligands in the platinum(O) -catalyzed hydrosilylation of styrene with triethylsilane has been evaluated, A number of bidentate N-ligands, phen, bpy, dafo, and phenyl-bian, were tested at various reaction temperatures using in situ formed catalysts with [Pt(nbe)(3)] as a precursor. The main conclusions are: (i) ligands, such as phen, which form stable platinum(O) complexes, give lower catalytic activities compared to the ligands which form less stable complexes; (ii) a small ligand effect is observed with dafo and phenyl-bian compared to [Pt(nbe)(3)], the precursor complex, displaying the lability of these ligands. The complex [Pt(nbe)(3)], that only has labile alkene ligands, is an active catalyst at low temperatures. At higher temperatures, the catalyst is no longer stable and a decrease in yield is observed. Several novel complexes have been synthesized: [Pt(m,m-(CF3)(2)-C6H3-bian)(tcne)], [Pt(m,m-(CF3)(2)C6H3-bian)(ma)], [Pt(p-MeC-C6H4-bian)(ma)], [Pt(p-MeOC6H4-bian)(dmfu)] and [Pt(phenyl-bian)(dmfu)]. Whereas the two [Pt(Ar-bian)(ma)] complexes are intrinsically more active than the two [Pt(Ar-bian)(dmfu)] complexes, the latter are much more stable, i.e. the nature of the alkene in these complexes is an important factor in determining their catalytic behavior. Compared to [Pt(Me-nq)(nbe)(2)], the two [Pt(Ar-bian)(dmfu)] complexes are much more stable resulting in significantly higher overall yields. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003.