Intercepting a Transient Phosphino-Arsinidene.

A phosphino-arsinidene derived from a diazaphospholidine scaffold (Ar**NCH2 )2 PAs (where Ar**=2,6-bis[(4-tert-butylphenyl)methyl]-4-methylphenyl) was generated in situ and trapped with a range of reagents. Metathesis reactions between (Ar**NCH2 )2 PCl and either [Na(18-crown-6)][AsCO] or [Na(dioxane)x ][AsCO] are believed to afford an arsaketene, (Ar**NCH2 )2 PAsCO, which readily loses carbon monoxide under ambient conditions. The resulting transient arsinidene was shown to undergo cycloaddition reactions with excess AsCO- , but can be stabilised in the presence of Lewis bases. It displays contrasting reactivity from a previously reported phosphino-phosphinidene. With isonitriles, rearrangements occur, however with PPh3 a phosphine-stabilised arsinidene could be isolated and used for subsequent reactivity studies. This species was found to be a suitable starting material for a transition metal complex of the phosphino-arsinidene, in which the P-As moiety coordinates side-on to the metal centre.