Synthesis and characterisation of anionic and neutral gallium(i) N-heterocyclic carbene analogues

Abstract

A high yield synthesis of a new, extremely bulky anionic gallium(I) N-heterocyclic carbene analogue, [(DAB*)Ga:]⁻ (DAB* = {N(Ar*)C(H)}₂, Ar* = C₆H₂{C(H)Ph₂}₂Me-2,6,4) has been developed and four monomeric sodium complexes of the heterocycle have been crystallographically characterised. The gallium(I) heterocycle has been utilised in the preparations of the heteroleptic zinc and cadmium gallyl complexes, [(DAB*)GaMX(tmeda)] (M = Zn or Cd, X = Br or I), which were crystallographically characterised. In addition, [(DAB*)Ga:]⁻ was oxidatively coupled to give the diamagnetic digallane(4), [(DAB*)GaGa(DAB*)]. The moderate yield synthesis of the six-membered gallium(I) heterocycle, [(^ButMesNacnac)Ga:] (^ButMesNacnac = [(MesNCBu^t)₂CH]⁻, Mes = mesityl), is described, and the compound found to be a monomer in the solid state by an X-ray crystallographic analysis. A low yield by-product from this synthesis, [Ga₅I₄(^ButMesNacnac)₃], was also isolated and shown by X-ray crystallography to be a rare example of a compound bearing a group 13 metal–metal bonded chain stabilised by β-diketiminate ligands. A preliminary analysis of the bonding in the compound was carried out using DFT calculations.