Carbon Monoxide Activation by a Molecular Aluminium Imide : C‐O Bond Cleavage and C‐C Bond Formation

Abstract

Anionic molecular imide complexes of aluminium are accessible via a rational synthetic approach involving the reactions of organo azides with a potassium aluminyl reagent. In the case of K 2 [( NON )Al(NDipp)] 2 ( NON = 4,5‐bis(2,6‐di iso propylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethyl‐xanthene; Dipp = 2,6‐di iso propylphenyl) structural characterization by X‐ray crystallography reveals a short Al‐N distance, which is thought to be due primarily to the low coordinate nature of the nitrogen centre. The Al‐N unit is highly polar, and capable of the activation of relatively inert chemical bonds, such as those found in dihydrogen and carbon monoxide. In the case of CO, uptake of two molecules of the substrate leads to C‐C coupling and C º O bond cleavage. Thermodynamically, this is driven – at least in part – by Al‐O bond formation. Mechanist‐ically, a combination of quantum chemical and experimental observations suggest that the reaction proceeds via exchange of the NR and O substituents through intermediates featuring an aluminium‐bound isocyanate fragment.