A comparison of binuclear dimethylplatinum(ii) complexes with the bridging ligands X(PPh2)2, X = CH2 or NH

Abstract

The reaction of [Pt₂Me₄(μ-SMe₂)₂], 1, with dppa = Ph₂PNHPPh₂ gave the complex [Pt₂Me₄(μ-SMe₂)(μ-dppa)] and, with more dppa, a mixture of the binuclear complex [Pt₂Me₄(μ-dppa)₂] and the mononuclear complex [PtMe₂(dppa)]. In contrast, reaction of [Pt₂Me₄(μ-SMe₂)(μ-dppa)] with dppm = Ph₂CH₂PPh₂ or of [Pt₂Me₄(μ-SMe₂)(μ-dppm)] with dppa gave only the binuclear complex [Pt₂Me₄(μ-dppm)(μ-dppa)]. This unusual complex, which has both bridging dppm and dppa ligands in equivalent positions in an organometallic complex, is more inert to rearrangement to mononuclear complexes, [PtMe₂(dppm)] and [PtMe₂(dppa)], than either symmetrical complex [Pt₂Me₄(μ-dppm)₂] or [Pt₂Me₄(μ-dppa)₂]. A combination of structural and NMR evidence indicates that all binuclear dimethylplatinum(II) complexes adopt a twist boat conformation, and the activation energy for fluxionality via a boat intermediate follows the series [Pt₂Me₄(μ-dppm)₂] >> [Pt₂Me₄(μ-dppm)(μ-dppa)] > [Pt₂Me₄(μ-dppa)₂].