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

Abstract

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-Pri-benzene) 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—C≡C—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 cisoidor 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 mono- 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.