SURFACE ORGANOMETALLIC CHEMISTRY - REDUCTIVE CARBONYLATION OF OSCL3-CENTER-DOT-3H2O SUPPORTED ON SILICA

The reductive carbonylation of silica-supported OsCl3·3H2O was investigated under atmospheric pressure of CO or of a mixture of CO and H2O at relatively mild temperatures. Starting from OsCl3·3H2O a mixture of physisorbed α-[Os(CO)3Cl2]2, cis-[Os(CO)4Cl2] and a species bound to the surface silanol groups, [Os(CO)3Cl2(HOSi)], is formed working at 100°C under CO. At higher temperatures [Os(CO)3Cl2(HOSi)] is the major surface species. Attempts to reduce further on the surface these OsII chlorocarbonyl species failed due to their easy sublimation and to the difficult removal of the chloro ligands. However, when the silica is treated with a weak base such as NaHCO3, α- or β-[Os(CO)3Cl2]2 supported on silica may be reduced with CO to [Os3(CO)12], with CO and H2O to a mixture of [OS3(CO)12] and [H4Os4(CO)12], and finally with H2 to [H4Os4(CO)12]. These reduction processes occur via the anchored [Os(CO)3(OSi)2]n species, as intermediate surface species.