Nickel(II) complexes of the type [RM(oxam)MR] (oxam: oxalamidinate, R=n-butyl, n-hexyl): the first binuclear n-alkyl nickel complexes

The reaction between one equivalent of [(acac)Ni(A)Ni(acac)] (A: N1,N2-bis(2-pyridylmethyl)-N3,N4-bis-(2,4,6-trimethylphenyl)oxalamidinate) and two equivalents of R-Li (R=n-butyl; n-hexyl) results in the formation of the binuclear complexes [(R–Ni)(A)(Ni–R)] (1: R=n-butyl: 2=n-hexyl). Both compounds were characterized by 1H- and 13C-NMR spectroscopy, elemental analysis, and mass spectroscopy. X-ray single diffraction studies of single crystals of 1 and 2 show that symmetrical binuclear complexes are formed in which the two Ni(II) centers are connected by the oxalamidinato bridging ligand A in a planar-square environment. No agostic interactions between the β-hydrogens of the n-alkyl groups and the metal centers were observed. DTA- and DTG-investigations show, that 1 and 2 are surprisingly thermally stable (decomposition temperature of 1: 188 °C under formation of butenes). Heating up a 1:1 mixture of 1 and 2 in toluene results in the formation of octane, decane and dodecane indicating an intermolecular transfer reaction of the n-alkyl-groups in solution. CV measurements display that the oxam complexes [(R–M)(A)(M–R)] (M=Ni, R=CH3 (3), Ph (4), CCH (6), CCPh (7); M=Pd, R=CH3 (5) are reversibly reduced in two steps indicating electronic interactions between the two metal centers.