Heteroleptic Nickel Complexes of a Bulky Bis(carbene)borate Ligand

Abstract

Bis(carbene)borate ligand transfer to the nickel nitrosyl synthon Ni(NO)(PPh$_3$)$_2$Br provides the new nickel nitrosyl complex Ph$_2$B($^{\rm{t}}$BuIm)$_2$Ni(NO)(PPh$_3$). The solid state structure reveals a trigonal pyramidal nickel ion with a very long bond to the apical PPh$_3$ ligand. The complex reversibly dissociates PPh$_3$ in solution to afford three-coordinate Ph$_2$B($^{\rm{t}}$BuIm)$_2$Ni(NO), with NMR data providing evidence for PPh$_3$ binding at low temperatures. Ligand transfer to Ni(PMe$_3$)$_2$Cl$_2$ provides the square planar complex, Ph$_2$B($^{\rm{t}}$BuIm)$_2$Ni(PMe$_3$)Cl, which shows no evidence for rearranging to the form a homoleptic complex with two bis(carbene)borate ligands. This complex is a suitable synthon for the [Ph$_2$B($^{\rm{t}}$BuIm)$_2$Ni]$^+$ fragment, as demonstrated by the synthesis of the $\pi$-allyl complex Ph2B(tBuIm)$_2$Ni($\eta ^3$-C7H7). The $\pi$-allyl complex reacts with O$_2$ to provide benzaldehyde and an unstable complex that is tentatively identified as the nickel(II) hydroxide [Ph$_2$B(tBuIm)$_2$Ni($\mu$-OH)]$_2$.