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

Dipankar Panigrahi,Ganesan Mani,Rohit Gupta,Munmun Mondal

doi:10.1039/d1ra08961g

Abstract

The reaction of Ph2PCH2OH with PhPCl2 and PCl3 in the presence of Et3N afforded new phosphonite compounds PhP(OCH2PPh2)21 and P(OCH2PPh2)32, respectively. The reaction between 1 and [NiCl2(DME)] in dichloromethane gave the five-coordinate complex [NiCl2(1-κ3P,P,P)] 3. Conversely, 1 reacts with [NiCl2(DME)] in the presence of NH4PF6 in dichloromethane to yield the four coordinate ionic complex [NiCl(1-κ3P,P,P)][PF6] 4. The reactions between 1, [NiCl2(DME)] and KPF6 in the presence of RNC (R = Xylyl, tBu and iPr) in dichloromethane yielded the five coordinate monocationic [NiCl(1-κ3P,P,P)(RNC)][PF6] (R = Xylyl) and dicationic [Ni(1-κ3P,P,P)(RNC)2][PF6]2 (R = tBu and iPr) complexes, respectively. The analogous reaction of 2 with [NiCl2(DME)] in the presence of KPF6 gave complex [NiCl(2-κ4P,P,P,P)][PF6], 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 KOBut 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.

Highlights

Monophosphine and diphosphine ligands have found profound applications in homogeneous catalysis reactions.[1]
The 31P{1H} NMR spectrum of 1 and 2 in CDCl3 showed two singlets for the two different phosphorus atoms [À13.4 (PPh2) and 162.9 ppm (PPh) for 1 and À13.8 (PPh2) and 140.1 ppm (P) for 2]. These chemical shi values appear in the deshielded region except the peak at 140.1 ppm of 2 relative to the values of reported compounds: PhP{O(CH2)3PPh2}2 [À15.96 (PPh2) and 156.24 (PPh)] and PhP{O(CH2)10PPh2}2 [À16.02 (PPh2) and 155.36 (PPh)]
New tridentate diphosphine-phosphonite and tetradentate tripodal triphosphine–phosphite ligands were conveniently synthesized in high yields

Summary

Introduction

Monophosphine and diphosphine ligands have found profound applications in homogeneous catalysis reactions.[1]. The equimolar reaction between 1 and [NiCl2(DME)] in dichloromethane at room temperature followed by crystallization afforded the neutral ve-coordinate nickel(II) complex 3 as a green crystalline compound.

Results

Conclusion