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

The reaction of Ph 2 PCH 2 OH with PhPCl 2 and PCl 3 in the presence of Et 3 N afforded new phosphonite compounds PhP(OCH 2 PPh 2 ) 2 1 and P(OCH 2 PPh 2 ) 3 2, respectively. The reaction between 1 and [NiCl 2 (DME)] in dichloromethane gave the five-coordinate complex [NiCl 2 (1-κ 3 P , P , P )] 3. Conversely, 1 reacts with [NiCl 2 (DME)] in the presence of NH 4 PF 6 in dichloromethane to yield the four coordinate ionic complex [NiCl(1-κ 3 P , P , P )][PF 6 ] 4. The reactions between 1, [NiCl 2 (DME)] and KPF 6 in the presence of RNC (R = Xylyl, t Bu and i Pr) in dichloromethane yielded the five coordinate monocationic [NiCl(1-κ 3 P , P , P )(RNC)][PF 6 ] (R = Xylyl) and dicationic [Ni(1-κ 3 P , P , P )(RNC) 2 ][PF 6 ] 2 (R = t Bu and i Pr) complexes, respectively. The analogous reaction of 2 with [NiCl 2 (DME)] in the presence of KPF 6 gave complex [NiCl(2-κ 4 P , P , P , P )][PF 6 ], 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, N -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 t 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.