A New Protocol to Generate Catalytically Active Species of Group 4-6 Metals by Organosilicon-Based Salt-Free Reductants

Herein, we provide a new protocol to reduce various transition-metal complexes by using organosilicon compounds in a salt-free fashion with the great advantage of generating pure low-valent metal species and metallic(0) nanoparticles, in sharp contrast to reductant-derived salt contaminants obtained by reduction with metal reductants. The organosilicon derivatives 1,4-bis(trimethylsilyl)-2,5-cyclohexadiene (1 a), 1-methyl-3,6-bis(trimethylsilyl)-1,4-cyclohexadiene (1 b), 1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2 a), 2,5-dimethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2 b), 2,3,5,6-tetramethyl-1,4-bis(trimethylsilyl)-1,4-diaza-2,5-cyclohexadiene (2 c), and 1,1'-bis(trimethylsilyl)-1H,1'H-4,4'-bipyridinylidene (3) all served as versatile reductants for early transition-metal complexes and produced only easy-to-remove organic compounds, such as trimethylsilylated compounds and the corresponding aromatics, for example, benzene, toluene, pyrazine, and 4,4'-bipyridyl, as the byproducts. The high solubility of the reductants in organic solvents enabled us to monitor the catalytic reactions directly and to detect any catalytically active species so that we could elucidate the reaction mechanism.