Selective stepwise carborane substitution in B(3,6) positions in Cp*Ir half-sandwich complexes containing a chelating 1,2-dicarba-closo-dodecaborane-1,2-dichalcogenolato ligand

Abstract

The 16e complexes IrCp*[E₂C₂(B₁₀H₁₀)] (E = S 1S or Se 1Se) react with methyl acetylenecarboxylate, MeO₂CCCH, at room temperature to give the 18e complexes 2S, 3S and 2Se, 3Se, respectively, as mixtures of isomers, in which the alkyne has been inserted into one of the Ir–chalcogen bonds, Ir-induced B–H activation has taken place, and, after transfer of a carborane hydrogen via the iridium to the alkyne, an Ir–B bond has been formed. Heating of these mixtures at 110 °C in toluene gives again mixtures of isomers as the 16e complexes 4S, 5S and 4Se, 5Se, which differ in the configuration of the olefinic substituent at B(3) and could be separated by chromatography. Treatment of these 16e complexes with MeO₂CCCH again produces 18e complexes 6S–9S and 6Se–9Se, respectively, analogous to 2 and 3, but now with an olefinic substituent at one of the boron atoms (B(3) or B(6)). Heating of these complexes at 110 °C in toluene leads selectively to 16e complexes 10S, 11S and 10Se, 11Se, 12Se, in which the carborane is now substituted both in the B(3) and B(6) positions. In the cases of 9S and 9Se, the major product upon heating in boiling toluene is another type of complex (13S and 13Se), in which the two former alkyne units are linked by a C–C bond and only one Ir–C σ bond is left. The complexes 3Se, 4Se, 7S, 11Se and 13Se were characterized by X-ray structural analysis.