Co-ordination chemistry of higher oxidation states. Part 33. Five-co-ordinate diphosphine complexes of cobalt(III), [Co{Ph2P(CH2)nPPh2}X3] (n = 4 or 5, X = Cl or Br)

Abstract

Oxidation of [Co{Ph₂P(CH₂)_nPPh₂}X₂] (n = 4 or 5, X = Cl or Br) with NOX in CH₂Cl₂ produces intensely coloured [Co{Ph₂P(CH₂)_nPPh₂}X₃], which are rare examples of five-co-ordinate cobalt(III) complexes. The complexes have been characterised by analysis, magnetic measurements (μ_eff. = ca. 3), i.r. and u.v.–visible spectroscopies. First co-ordination sphere bond lengths for the complexes with n = 4 have been obtained from cobalt K-edge extended X-ray absorption fine structure data. The properties of these complexes are compared with those of the monodentate phosphine analogues [Co(PR₃)₂X₃]. Attempts to obtain similar complexes with shorter backbone diphosphines have been unsuccessful.