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(SiPh 2 Me) 2 (PMe 2 Ph) 2 ] ( 2a ) and cis -[Pt(SiFMe 2 ) 2 (PEt 3 ) 2 ] ( 2b ), and two cis -bis(stannyl)bis(phosphine)palladium complexes ( 3 ), cis -[Pd(SnMe 3 ) 2 (PMe 3 ) 2 ] ( 3a ) and cis -[Pd(SnMe 3 ) 2 (PMePh 2 ) 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 31 P NMR.