Direct access to a neutral alumene via CO reduction by a dialane and further CO homologation

Multiple bonds between heavy elements have been shown to be not only stable but also offer divergent reactivity. Accordingly, there has been a drive in research to isolate such species. Here we report on the synthesis of a compound containing an aluminium–carbon double bond (alumene). The alumene was formed by exposing a dialane to a CO atmosphere. Experimental data and quantum chemical calculations confirm the existence of a π-bond between the aluminium and carbon centre. The mechanism for the formation of the alumene was calculated and indicated a heterocyclic intermediate, which we were able to observe spectroscopically. Treating the alumene with excess CO leads to CO homologation, forming a C₃O₂ chain initiated by interaction of a CO molecule with the π-bond of Al=C.