Cooperative Reactivity of Halomethanes and -silanes at an A-Frame Complex: Transannular Addition versus Bridging Tetrylenes

Abstract

With CH₂X₂ (X = Cl, Br, I) and CCl₄ the diplatinum(0) complex [(μ-dmpm)₂Pt₂(nbe)₂] (dmpm = bis(dimethylphosphino)methane, nbe = norbornene) undergoes facile cooperative addition of one C–X bond at each Pt centre to yield the methylene-bridged diplatinum(II) A-frame complexes [(μ-dmpm)₂Pt₂X₂(μ-CY₂)] (Y = H, Cl). In contrast, reactions with Me_4-nSiX_n (X = Cl, n = 1-3; X = I, n = 1) lead preferentially to transannular oxidative additions of a single Si–X bond over the two metal centres, yielding the complexes [(μ-dmpm)₂{PtX}{Pt(SiMe_4-nX_n-1)}]. In CH₂Cl₂ [(μ-dmpm)₂{PtCl}{Pt(SiCl₃)}] undergoes rearrangement to the silylene-bridged [(μ-dmpm)₂Pt₂Cl₂(μ-SiCl₂)], while in CH₂Br₂ oxidation of the platinum centres to Pt(IV), Cl-Br exchange, and the insertion of a CH₂Br₂-derived methylene unit into the Pt–Si bond are observed. Quantum-chemical calculations provide insights into the differences in reactivity between the halomethanes and -silanes.