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)]·0.5CH2 Cl2

Abstract

Three complexes of 1,1′-bis(diphenylphosphino)ruthenocene (dppr) viz. [MCl 2 (dppr)] (M = Ni, Pd or Pt) were synthesized and characterized. An improved synthesis of dppr was elaborated. The crystal structures of dppr and [PtCl 2 (dppr)]·0.5CH 2 Cl 2 were determined by X-ray crystallography. That of dppr shows a ruthenocene derivatized by a PPh 2 group on each C 5 ring. It is centrosymmetric with two PPh 2 groups trans disposed and the C 5 rings staggered and anti. The C 5 (centroid) · · · C 5 (centroid) separation is 3.606 A. In [PtCl 2 (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 C 5 ring deformations. The C 5 rings in dppr are parallel (θ = 0°) but subtended at 8.8° in the platinum(II) complex. The catalytic efficiency of [PdCl 2 (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 [PdCl 2 (dppf)] and [Pd(dppf) 2 ] [dppf = 1,1′-bis(diphenylphosphino)ferrocene]. This catalytic enhancement by dppr is consistent with a greater C 5 ring separation and larger bite angle subtended by dppr compared to that of dppf.