Metal-induced B-H activation in Cp*Rh, Cp*Ir, (p-cymene)Ru, and (p-cymene)Os half-sandwich complexes containing the 1,2-dicarba-closo-dodecaborane(12)-1,2-dichalcogenolato ligand

The reactivity of the 16e half-sandwich complexes Cp*Rh[E2C2(B10H10)] (1a.b.), Cp*Ir[E2C2(B10H10)] (2a,b) (E=S (a), Se(b)), (p-cymene)Ru[S2C2(B10H10)] (3). (p-cymene)Os[S2C2(B10H10)] (4) (p-cymene = 1-Me-4-Pr'-beneze) towards various alkynes (acetylene, propyne, 3-methoxypropyne, methyl acetylenemonocarboxylate, dimethyl acetylenedicarboxylate, phenylacetylene, ferrocenylacetylene) was studied. The reactions start with an insertion into one of the M-E bonds, followed (except for MeO2C-Cequivalent toC-CO2Me) by intramolecular, metal-induced B-H activation, formation of an M-B bond, accompanied by simultaneous transfer of a hydrogen atom from boron via the metal atom to the alkyne. This leads to new complexes with a cisoid or transoid geometry (orientation of the E-C=C unit with respect to the C(1)-B bond). This geometry determines the course of further intramolecular reactions which lead selectively to carboranes mon- or disubstituted in B(3.6) positions. Numerous intermediates and final products were characterized by X-ray analysis in the solid state, and by multinuclear magnetic resonance in solution. First catalytic applications of 1a,b became evident by cyclotrimerization reactions.