Dynamic Behavior of Acetylacetonato, Triphenylphosphine and Alkyl Ligands in NiR(acac)(PPh3)n (R=C2H5, CH3) in Solution and Disproportionation of the Alkylnickel Complexes in Pyridine

Dynamic behavior of acetylacetonato (acac), triphenylphosphine (PPh3) and ethyl (in the case of 1) ligands of NiR(acac)(PPh3)n (R=C2H5, n=1 (1); R=CH3, n=2 (2)) in solution has been studied. PPh3 ligand(s) in 1 and 2 exchange rapidly on NMR time scale with free PPh3 in solution. Addition of excess PPh3 makes the exchange rate much faster and an SN2 mechanism is proposed to explain the acceleration effect. 31P-NMR spectrum of 1 in pyridine shows that the PPh3 ligand is replaced by the solvent molecule. Acac ligands in 1 and 2 also undergo rapid interchange on NMR time scale. The activation energy for the acac interchange is about 10 kcal/ mol. On standing a specifically deuterated ethylnickel complex, Ni(CH2CD3)(acac)(PPh3) 1-d3 in solution, the hydrogens and deuteriums in the ethyl group were scrambled. Appearance of the methyl proton signals in the 1H-NMR spectrum of the deuterated ethylnickel complex after the treatment in solution demonstrates the occurrence of the H–D scrambling in solution. Both 1 and 2 undergo disproportionation reactions in pyridine. The rate of the disproportionation is second-order with respect to the concentration of 2.