Synthesis and characterization of a four-coordinate nickel carbamato species (MeSiPiPr2)Ni(OC(O)NHMes) generated from the reaction of (MeSiPiPr2)Ni(NHMes) with CO2

Abstract

A tridentate silyl pincer complex of nickel was employed to access a 4-coordinate nickel(II) amide complex possessing a Ni–N bond, in which a bond activation is expected at a position that is trans to the silyl donor. Using 2,4,6-trimethylaniline, a synthetically reliable nickel(II)-NHMes species (2Mes) was prepared and its reactivity toward CO2 was investigated. From an instantaneous reaction with CO2, a four-coordinate nickel(II) carbamato species (MeSiPiPr2)Ni(OC(O)NHMes) (4) was successfully generated and fully characterized by various spectroscopic techniques and X-ray crystallography. A corresponding reaction selectively occurs at a trans position to the silyl donor via a normal insertion process of CO2 into a Ni–N bond. Under aerobic conditions, the CO2 reaction of 2Mes gives a nickel(II) carbonato species {(MeSiOPPO)Ni}2-μ-CO3-κ2O,O (5) isolated as a dark orange crystal (29% yield). Its X-ray structure reveals that a dinuclear nickel complex possessing a Si–O single bond and a PO double bond and two square pyramidal nickel centers are bridged by a carbonate anion. The syntheses of nickel complexes and their characterizations by multi-nuclear NMR spectroscopy and X-ray crystallography are described herein.