Surface-mediated organometallic synthesis: the role of the oxidation state and of ancillary ligands in the high-yield and selective syntheses of platinum carbonyl dianions [Pt3(CO)6]n 2- (n = 6, 5, 4, 3) by reductive carbonylation under mild conditions and in the presence of surface basicity of various silica-supported Pt(IV) or Pt(II) compounds.

The reductive carbonylation under 1 atm of CO and in the presence of surface basicity of silica-supported Na-2[PtCl6], K-2[PtCl4], [Pt(CH3CN)(2)Cl-2], or [Pt(COD)Cl-2] (COD = cis,cis-1,5-cyclooctadiene) leads to the formation in high yields of platinum carbonyl dianionic clusters [Pt-3(CO)(6)](n)(2-) (n = 6, 5, 4, 3). Remarkably the silica surface plays a key role in these reductive carbonylations since no carbonyl cluster is obtained by reductive carbonylation of solid Na-2[PtCl6] in the absence of silica. The selectivity of the reaction can be easily tuned by controlling the surface metal loading, the basicity of the surface, and the nature of the platinum precursor (platinum oxidation state and nature of the coordination sphere). In particular, the one-step silica-mediated synthesis of [Pt-18(CO)(36)](2-) from K-2[PtCl4] (90% yield) is very convenient when compared to the traditional synthesis in methanol solution (67% yield), which requires two steps: (i) formation of [Pt-12(CO)(24)](2-) and (ii) addition of Na-2[PtCl6] drop by drop (molar ratio [Pt-12(CO)(24)](2-):Na-2[PtCl6] = 1:1) under a flow of CO.