Reactivity of an arsanyl-phosphagallene: decarbonylation of CO2 and COS to form phosphaketenes

The synthesis of an arsanyl-phosphagallene [H2CN(Dipp)]2AsP[double bond, length as m-dash]Ga(NacNac) (NacNac = HC[C(Me)N(Dipp)]2; Dipp = diisopropylphenyl) and its reactivity towards heterocumulenes and ketones is described. Reactions with azides, carbodiimides, isocyanates and ketones give rise to heterocycles via cyclization reactions involving the Ga[double bond, length as m-dash]P π-bond (with the Ga–P σ-bond remaining unperturbed in the final products). By contrast, reactions with CO2, CS2 and COS are more intriguing, revealing a reactivity profile in which the phosphorus atom can abstract carbon monoxide from the oxygen-containing heterocumulenes. These reactions result in the formation of gallium phosphaethynolate compounds. Such reactivity is enabled by the presence of a weakly Lewis basic arsanyl moiety which, in contrast to other related compounds featuring phosphanyl groups, is insufficiently nucleophilic to play a role in frustrated Lewis-pair like reactivity.