Pendant Alkyl and Aryl Groups on Tin Control Complex Geometry and Reactivity with H₂/D₂ in Pt(SnR₃)₂(CNBu^t)₂ (R = Bu^t, Prⁱ, Ph, Mesityl)

Abstract

The complex Pt­(SnBut3)2­(CNBut)2­(H)2, 1, was obtained from the reaction of Pt­(COD)2 and But3SnH, followed by addition of CNBut. The two hydride ligands in 1 can be eliminated, both in solution and in the solid state, to yield Pt­(SnBut3)2­(CNBut)2, 2. Addition of hydrogen to 2 at room temperature in solution and in the solid state regenerates 1. Complex 2 catalyzes H2−D2 exchange in solution to give HD. The proposed mechanism of exchange involves reductive elimination of But3SnH from 1 to afford vacant sites on the Pt center, thus facilitating the exchange process. This is supported by isolation and characterization of Pt­(SnMes3)­(SnBut3)­(CNBut)2, 3, when the addition of H2 to 2 was carried out in the presence of free ligand Mes3SnH (Mes = 2,4,6-Me3C6H2). Complex Pt­(SnMes3)2­(CNBut)2, 5, can be prepared from the reaction of Pt­(COD)2 with Mes3SnH and CNBut. The exchange reaction of 2 with Ph3SnH gave Pt­(SnPh3)3(CNBut)2­(H), 6, wherein both SnBut3 ligands are replaced by SnPh3. Complex 6 decomposes in air to form square planar Pt­(SnPh3)2­(CNBut)2, 7. The complex Pt­(SnPri3)2­(CNBut)2, 8, was also prepared. Out of the four analogous complexes Pt­(SnR3)2­(CNBut)2 (R = But, Mes, Ph, or Pri), only the But analogue does both H2 activation and H2−D2 exchange. This is due to steric effects imparted by the bulky But groups that distort the geometry of the complex considerably from planarity. The reaction of Pt­(COD)2 with But3SnH and CO gas afforded trans-Pt­(SnBut3)2­(CO)2, 9. Compound 9 can be converted to 2 by replacement of the CO ligands with CNBut via the intermediate Pt­(SnBut3)2­(CNBut)2­(CO), 10