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 (μeff. = 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.