Six- and five-co-ordinate ruthenium(II) complexes with 1,2-bis(dicyclohexylphosphino)ethane. X-Ray crystal structure of the d6 five-co-ordinate [RuCl{(C6H11)2PCH2CH2P(C6H11)2}2]PF6

Abstract

Six- and five-co-ordinate complexes of ruthenium(II) with the bulky dipyhosphine ligand 1,2-bis(dicyclohexylphosphino)ethane (dcpe) have been prepared. In solution, octahedral trans-[RuX₂(dcpe)₂](X = Cl or Br) and trans-[RuH(Cl)(dcpe)₂] can dissociate giving the unsaturated species [RuX(dcpe)₂]⁺ and [RuH(dcpe)₂]⁺, respectively. Phosphorus-31 n.m.r. studies show that the five-co-ordinate d⁶ cations, which are stereochemically non-rigid at room tempreature, possess a trigonal-bipyramidal geometry with the halide or hydride in an equatorial position. The X-ray crystal structure of [RuCl(dcpe)₂]PF₆ has been determined: the crystals are monoclinic, space group P2₁/c, with a= 14.614(3), b= 14.625(3), c= 26.196(3)Å, β= 100.41(1)°, and Z= 4; final R factor 0.052 for 3 219 observed reflections. The ruthenium cation has an approximate trigonalbipyramidal geometry, with the bidentate dcpe ligands bridging axial and equatorial postions. This is the first five-co-ordinate complex of ruthenium(II) structurally characterized as trigonal bipyramidal. According to their co-ordinatively unsaturated nature, the complexes [RuX(dcpe)₂]⁺ react with L(L = CO or MeCN) to form the six-co-ordinate [RuX(L)(dcpe)₂]⁺, whose stereochemistry and dynamic behavious were studied by ³¹P n.m.r. spectroscopy. The influence of the steric properties of the diphosphine on the formation of the [RuX(dcpe)₂]⁺ species is discussed, and a dominant role for steric effects is suggested.