Lithium and magnesium complexes of ortho-dimethylarsinoaniline and a novel insertion of dimethylsilanone into an Mg–N bond—molecular structures of [{Li(µ2:η1-NHC6H4AsMe2)(thf)2}2] and the insertion product [{Mg2(µ2:η1-NHC6H4AsMe2)2(µ3:η3-OSiMe2NC6H4AsMe2)(thf)}2]

Treatment of ortho-dimethylarsinoaniline (NASH2) with 1.0 equivalents of LiBut or 0.5 equivalents of MgBu2 in tetrahydrofuran affords the complexes [{Li(NASH)(thf)2}2] (1) and [Mg(NASH)2(thf)1.5] (2) (NASH = NHC6H4AsMe2-2). Both complexes have been characterised spectroscopically. The crystal structure determination of 1 reveals a centrosymmetric dimeric structure with an Li2N2 central unit that does not exhibit arsino–lithium donor interactions. Compound 2 reacts with dimethylsilicone grease to yield the unexpected complex [{Mg2(μ2:η1-NHC6H4AsMe2)2(μ3:η3-OSiMe2NC6H4AsMe2)(thf)}2] (3), via the novel and unprecedented insertion of a dimethylsilanone fragment into an Mg–N bond. Compound 3 is tetranuclear with a 12-membered Mg4N6O2 double stacked cube centre that has Mg atoms residing at alternate corners of each cube. The arsino functionalities of the modified η3-bound ligands co-ordinate to Mg atoms on the vertices.