PNNL

Abstract

The synthesis of heteroleptic [Ni(P2N2)(diphosphine)][BF4]2 complexes and the cleavage of P-C and C-H bonds of the P2N2 ligand in those complexes are reported. The products are 5-coordinate iminium formyl complexes in which Ni-C and P-H bonds have formed. The reactivity of [Ni(P2N2)(diphosphine)][BF4]2 complexes is influenced by the rigidity of the diphosphine, the steric effect of the substituents, and length of the carbon linker of the diphosphine ligands. Diphosphine ligands bearing rigid backbone (e.g., dmpbz) or aromatic substituents (e.g., dppe) react with [Ni(PtBu2NBn2)(CH3CN)2][BF4]2 to give P-C/C-H bond cleavage products. Both [Ni(PtBu2NBn2)(dmpe)(MeCN)][BF4]2 and [Ni(PtBu2NBn2)(dmpm)(MeCN)][BF4]2 were prepared by the reaction of [Ni(PtBu2NBn2)(CH3CN)2][BF4]2 with the corresponding diphosphine ligands. [Ni(PtBu2NBn2)(dmpe)(MeCN)][BF4]2 readily undergoes P-C/C-H bond cleavage in nitromethane. In sharp contrast, [Ni(PtBu2NBn2)(dmpm)][BF4]2 is stabilized by dmpm, a diphosphine with small bite angle, and does not show P-C/C-H bond cleavage reactivity. Computational results show that for complexes bearing less bulky diphosphine ligands, the barriers for the rate-determining transition-states are higher than those for complexes bearing more rigid or more bulky ligands, a result consistent with experimental studies. The calculated barriers for the first transition state are correlated to increased values of the dihedral angle formed by the two NiP2 planes. The research at PNNL was supported by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences, Division of Chemical Sciences, Geosciences & Biosciences. Pacific Northwest National Laboratory is operated by Battelle for the US Department of Energy. H. Li and M. B. Hall thank the National Science Foundation (CHE-1300787 and 1664866) and the Welch Foundation (A-0648) for financial support and the Texas A&M High Performance Research Computing Center and the Laboratory for Molecular Simulation for providing computing resources.