Crystalline Neutral Diboron Analogues of Cyclopropanes

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

MeNHC 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[BArF 4] gives the germaborenium cation 4. Substitution of the bromide atom in 1b against carbon monoxide followed by bromide abstraction using Ag[Al(OtBuF)4] leads to compound 6 exhibiting a B[double bond, length as m-dash]C double bond substituted at the boron atom by a germylium cation. Treating the germaborene [Ge[double bond, length as m-dash]B-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 [Ge[double bond, length as m-dash]B-Br] (1b) with [Cp*Al]4, insertion of a Cp*Al moiety into the B-Br bond was found (13).

Diboriranide σ-Complexes of d- and p-Block Metals

Diboriranides are the smallest conceivable monoanionic aromatic cycles, yet only limited examples have been reported and their reactivity and complexation behavior remain completely unexplored. We report a straightforward synthesis of the first peraryl diboriranide c-(DurB)2 CPh- as its lithium salt in three steps via the corresponding non-classical diborirane from a readily available 1,2-dichlorodiborane(4) (Dur=2,3,5,6-tetramethylphenyl). With the preparation and complete characterization of representative complexes with tin, copper, gold and zinc, we demonstrate the strong preference of the diboriranide for σ-type coordination modes towards main group and transition metal centers under unperturbed retention of the three-membered B2 C-ring's 2e- π-system.