Four- and five-coordinate nickel(ii) complexes bearing new diphosphine-phosphonite and triphosphine-phosphite ligands: catalysts for -alkylation of amines.

The reaction of PhPCHOH with PhPCl and PCl in the presence of EtN afforded new phosphonite compounds PhP(OCHPPh)1 and P(OCHPPh)2, respectively. The reaction between 1 and [NiCl(DME)] in dichloromethane gave the five-coordinate complex [NiCl(1-κ ,,)] 3. Conversely, 1 reacts with [NiCl(DME)] in the presence of NHPF in dichloromethane to yield the four coordinate ionic complex [NiCl(1-κ ,,)][PF] 4. The reactions between 1, [NiCl(DME)] and KPF in the presence of RNC (R = Xylyl, Bu and Pr) in dichloromethane yielded the five coordinate monocationic [NiCl(1-κ ,,)(RNC)][PF] (R = Xylyl) and dicationic [Ni(1-κ ,,)(RNC)][PF] (R = Bu and Pr) complexes, respectively. The analogous reaction of 2 with [NiCl(DME)] in the presence of KPF gave complex [NiCl(2-κ ,,,)][PF], 8. The structures of all complexes were determined by single crystal X-ray diffraction studies and supported by spectroscopic methods. To demonstrate their catalytic application, -alkylation reactions between primary aryl amines, benzyl and 4-methoxy benzyl alcohols were found to proceed smoothly in the presence of 2.5 mol% of complexes bearing ligand 1 and <0.5 mmol of KOBu in toluene at 140 °C. The C-N coupled products were formed in very good yields. Its substrate scope includes sterically encumbered, heterocyclic amines and aliphatic alcohol.