ChemInform Abstract: Transition-Metal-Promoted Reactions of Boron Hydrides. Part 11. Catalytic and Stoichiometric Alkyne Insertion Reactions. Synthesis and Structural Characterization of a (Metallovinyl)carborane Containing a Boron-Boron Bridging Carbon Atom: nido-4,5-μ-(CpFe(CO)(PPh3)(η1:μ-trans-MeC=CMe))-2,3-Et2C2B4H5.

ChemInform Abstract

The use of transition metal complexes to promote or catalyze the two-carbon insertion of an acetylene into the small carborane (II) is reported. Two new methods, one stoichiometric and one catalytic, are employed. It is found that the reaction of the Na salt of (II) with the acetylene complex (I) results in the formation of the first (metallovinyl)carborane complex (III). Thermolysis of (III) produces the two-carbon insertion product (IV), presumably via a β-hydride-abstraction alkene-elimination mechanism. The structure of (III) is confirmed by a single-crystal X-ray analysis (space group Pca21, Z=4), which shows that the carborane is bound to the olefin via a B-C-B three-center, two-electron bond. The formation of the nido-tetracarbon carborane (IV) results also in the catalytic dehydro alkyne insertion reaction of (II) with (V) when either tri- or mononuclear Ru complexes are used as catalysts.