SYNTHESIS, STRUCTURE, AND REACTIVITY OF CLUSTER COMPLEXES CONTAINING THE PT3(MU-3-SN) UNIT AND A POSSIBLE RELATIONSHIP TO HETEROGENEOUS PLATINUM TIN CATALYSTS

The reaction of [Pt3(mu-3-CO)(mu-dppm)3]2+ (1), as the PF6- salt, with Me2SnH2 gave first [Pt3(mu-3-H)(mu-3-SnMe2H)(mu-dppm)3]2+ (2) and then [Pt3{mu-3-SnMe2(O2PF2)}(mu-dppm)3]+ (3) while the reaction of 1 with Ph3SnH gave [Pt(mu-3-CO)(mu-3-SnF3)(mu-dppm)3]+ (4a) and [Pt3(mu-3-Cl)(mu-3-SnF3)(mu-dppm)3] (5). Complexes 4a and [Pt3(mu-3-CO)(mu-3-SnCl3)(mu-3-dppm)3]+ (4b) could also be prepared by reaction of 1 with SnF3- and SnCl3-, respectively. Reaction of 1 with excess SnF3- or SnCl3- gave [Pt3(mu-3-SnF3)2(mu-dppm)3] (6a) or [Pt3(mu-3-SnCl3)2(mu-dppm)3] (6b), respectively. The structure of 6a has been determined by X-ray crystallography. Reaction of 4a with acetylene in CH2Cl2 gave an equimolar mixture of [Pt3Cl(mu-3-HCCH)(mu-dppm)3]+ (8) and 6a, reaction with H2S gave [Pt3H(mu-3-S)(mu-dppm)3]+ (9) and SnS, and reaction with XyNC (Xy = 2,6-Me2C6H3) gave [Pt3(mu-3-SnF3)(XyNC)(mu-dppm)3]+ (7), which contains a terminal XyNC ligand. The stability of the Pt3(mu-3-SnX3) unit, together with the ability of the coordinatively unsaturated Pt3 clusters to mimic properties of a Pt surface, suggests that heterogeneous Pt-Sn-Al2O3 catalysts may contain platinum-tin alloy anchored to the tin(II)-alumina support by similar Pt3(mu-3-Sn) linkages. An ESCA study of the complexes suggests that SnF3- is a stronger sigma-donor than CO but also competes with CO as a pi-acceptor ligand.