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

Article abstract of DOI:10.1016/j.jorganchem.2003.07.021

The reaction between one equivalent of [(acac)Ni(A)Ni(acac)] (A: N ¹, N ²-bis(2-pyridylmethyl)- N ³, N ⁴-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.