Thermodynamics of metal-ligand bond formation. XXI. Base adducts of nickel(II) glyoximato complexes

Abstract

Bis(glyoximato)nicke1(11) complexes and their BF2-bridged derivatives react with Lewis bases in non-donor solvents forming low-spin 1 : 1 adducts. Thermodynamic data are reported for formation of adducts of glyoximato complexes with PBu3 and of BF2-bridged complexes with pyridine (py), 4-methylpyridine (mpy), piperidine (pip), tributylphosphine, triphenylphosphine, ethane-1,2-diyi- bis(diphenylphosphine) and tetrahydrothiophen. Adduct stability is increased by BF2-bridging; in the Pbu3 adducts this is due to entropy factors. Variation of alkyl groups in the glyoxinie has only a small effect, but replacement of alkyl by Ph or H increases adduct stability while lowering enthalpy of adduct formation. Average values of ΔH� and K (at 30�C) for adducts of BF2-bridged complexes and for PBu3 adducts of H-bridged complexes (last entry) are: PY mpy pip PPh3 PBu3 Pbu3 -ΔH� (kJ mol-l) 29 31 35 23 43 42 K (1.mol-1) 3 5 80 4 800 60