Chemistry’s First Definitive Silylidyne

Transition-metal complexes containing a metal-carbon triple bond, known as metal alkylidynes, are among the most important organometallic compounds—they are in part the basis of Nobel-Prize-winning research on olefin metathesis. Alexander C. Filippou and coworkers at the University of Bonn, in Germany, have broadened the scope of this chemistry by preparing the first silicon analog, a molybdenum silylidyne (Angew. Chem. Int. Ed. 2010, 49, 3296). Filippou’s group and others have previously synthesized germanium, tin, and lead congeners of alkylidyne complexes. But isolating the silicon analog has remained one of silicon chemistry’s most challenging targets. The problem has been finding a suitable organosilicon(II) precursor, Filippou says. His team recently came up with one in the form of a bulky arylsilicon chloride stabilized by an imidazole N-heterocyclic carbene (Chem. Eur. J. 2010, 16, 2866). Treating this carbene-chlorosilylene adduct with a molybdenum complex and subsequently heating the stable Mo=Si intermediate product with a carbene-trapping triarylborane led to the molybdenum silylidyne complex shown, C₅H₅(CO)₂Mo≤SiR, where R is a bulky substituted phenyl. Isolating the metal silylidyne shows the potential of carbene-chlorosilylene adducts for generating novel compounds with silicon multiple bonds and opens the door to potential new chemistry of silylidyne complexes, the researchers note.