Structure and Facile Unimolecular Twist-Rotation of<i>cis</i>-Bis(silyl)bis(phosphine)platinum and<i>cis</i>-Bis(stannyl)bis(phosphine)palladium Complexes

Abstract

The structures and fluxional behavior of two cis-bis(silyl)bis(phosphine)platinum complexes (2), cis-[Pt(SiPh2Me)2(PMe2Ph)2] (2a) and cis-[Pt(SiFMe2)2(PEt3)2] (2b), and two cis-bis(stannyl)bis(phosphine)palladium complexes (3), cis-[Pd(SnMe3)2(PMe3)2] (3a) and cis-[Pd(SnMe3)2(PMePh2)2] (3b), were examined. The molecular structures of 2a and 3a were determined by X-ray crystallographic analysis. The complexes have twisted square-planar structures with cis-orientation of the ligands. The bis(silyl)platinum complexes, 2a and 2b, show fluxional behavior on the NMR time scale. In the fluxional process, the spin−spin coupling between P, Si, and Pt is retained; namely these nuclear spin states are intramolecularly conserved. The fluxionality of 2a and 2b is attributed to unimolecular twist-rotation via a pseudotetrahedral transition state. Similar fluxionality of the bis(stannyl)palladium complex, 3b, is evident by utilizing both solution- and solid-state 31P NMR.