Co-ordination and catalytic chemistry of 1,1′-bis(diphenylphosphino)-ruthenocene (dppr). Synthesis of [MCl2(dppr)] (M = Ni, Pd or Pt) and molecular structures of dppr and [PtCl2(dppr)]·0.5CH2Cl2

Abstract

Three complexes of 1,1′-bis(diphenylphosphino)ruthenocene (dppr) viz. [MCl2(dppr)] (M =Ni, Pd or Pt) were synthesized and characterized. An improved synthesis of dppr was elaborated. The crystal structures of dppr and [PtCl2(dppr)]·0.5CH2Cl2 were determined by X-ray crystallography. That of dppr shows a ruthenocene derivatized by a PPh2 group on each C5 ring. It is centrosymmetric with two PPh2 groups trans disposed and the C5 rings staggered and anti. The C5 (centroid) ⋯ C5 (centroid) separation is 3.66 Å. In [PtCl2(dppr)] the planar platinum(II) centre is angularly distorted by the large bite size of dppr to give a large bite angle (P-Pt-P) of 101.0(1)° with a compressed Cl-Pt-Cl angle of 85.6(1)° and other C5 ring deformations. The C5 rings in dppr are parallel (θ = 0°) but subtended at 8.8° in the platinum(II) complex. The catalytic efficiency of [PdCl2(dppr)] in the Grignard coupling of MgPhBr with 1,2-dibromobenzene, which results in 93% conversion of the latter and gives 2-bromobiphenyl (79%) and o-terphenyl (15%) under reflux conditions, is superior to that shown by [PdCl2(dppf)] and [Pd(dppf)2] [dppf =1,1′-bis(diphenylphosphino)ferrocene]. This catalytic enhancement by dppr is consistent ,_ with a greater C5 ring separation and larger bite angle subtended by dppr compared to that of dppf.