Preparation, crystal structures and spectroscopic properties of novel [MIIICl3 − n(P)3 + n]n+ (M = Co, Rh; n = 0, 1, 2 or 3) series of complexes containing tripodal tridentate phosphine, 1,1,1-tris(dimethylphosphinomethyl)ethane

Cobalt(III) and rhodium(III) complexes of the series of [MIIICl3 − n(P)3 + n]n+ (M = Co or Rh; n = 0, 1, 2 or 3) have been prepared with the use of 1,1,1-tris(dimethylphosphinomethyl)ethane (tdmme) and mono- or didentate phosphines. The single-crystal X-ray analyses of both series of complexes revealed that the M–P and M–Cl bond lengths were dependent primarily on the strong trans influence of the phosphines, and secondarily on the steric congestion around the metal center resulting from the coordination of several phosphine groups. In fact, the M–P(tdmme) bonds became longer in the order of [MCl3(tdmme)] < [MCl2(tdmme)(PMe3)]+ < [MCl(tdmme)(dmpe)]2+ (dmpe = 1,2-bis(dimethylphosphino)ethane) < [M(tdmme)2]3+ for both CoIII and RhIII series of complexes, while the M–Cl bond lengths were shortened in this order (except for [M(tdmme)2]3+). Such a steric congestion around the metal center can also account for the structural and spectroscopic characteristics of the series of complexes, [MCl(tdmme)(dmpm, dmpe or dmpp)]2+ (dmpm = bis(dimethylphosphino)methane, dmpp = 1,3-bis(dimethylphosphino)propane). The X-ray analysis for [CoCl(tdmme)(dmpm or dmpe)](BF4)2 showed that all Co–P bonds in the dmpm complex were shorter by 0.03–0.04 Å than those in the dmpe complex. Furthermore, the first d–d transition energy of the CoIII complexes and the 1JRh–P(tdmme) coupling constants observed for the RhIII complexes indicated an unusual order in the coordination bond strengths of the didentate diphosphines, i.e., dmpm > dmpe > dmpp.