Germaborene reactivity study – addition of carbon nucleophiles, cycloaddition reactions, coordination chemistry

Abstract

^Me NHC substituted germaborenium cation 2 was synthesized directly in reaction of bromo-substituted germaborene 1b with ^MeNHC. The adamantyl isonitrile substituted germaborenium cation 4 was obtained stepwise: substitution of the chloride atom against adamantyl isonitrile at the B–Cl unit in 1a, simultaneous migration of the chloride to the germanium atom followed by chloride abstraction using Na[BAr^F₄] gives the germaborenium cation 4. Substitution of the bromide atom in 1b against carbon monoxide followed by bromide abstraction using Ag[Al(OtBu^F)₄] leads to compound 6 exhibiting a BC double bond substituted at the boron atom by a germylium cation. Treating the germaborene [GeB–Ph] (1c) with selenium, a cycloaddition product 7 was characterised featuring a GeBSe heterocycle. Carbon dioxide reacts with 1b to give a four membered ring molecule 8 as the product of a B–C and Ge–O bond formation. In reaction of 1b with dimethylbutadiene, a product 9 of a [2 + 4] cycloaddition was isolated. Transition metal fragments [Fe(CO)₄ (10), CuBr (11), AuCl (12)] show coordination at the germaborene double bond. Molecular structures of the germaborene coordination compounds 10–12 are presented and the ligand properties are discussed. After treating the germaborene [GeB–Br] (1b) with [Cp*Al]₄, insertion of a Cp*Al moiety into the B–Br bond was found (13).