Vanadyl salen complexes covalently anchored to single-wall carbon nanotubes as heterogeneous catalysts for the cyanosilylation of aldehydes

Single-wall carbon nanotubes (SWNT) have a special structure and morphology consisting of long tubes (μm scale) of less than 2 nm in diameter. We have taken advantage of this geometric feature of SWNT to use them as supports for the preparation of a heterogeneous catalyst. Styryl functionalized vanadyl Schiff base has been covalently anchored on mercapto-modified SWNT through a radical chain mechanism. SWNT is more suitable as support for the complex than high-surface-area activated carbon because the latter exhibits some adventitious activity. The vanadyl-modified SWNT solid was used to effect the catalytic cyanosilylation of aldehydes with trimethysilylcyanide. The system is truly heterogeneous (no leaching observed) and reusable (no decrease in activity) in five consecutive runs. The asymmetric version was also performed using a chiral vanadyl complex obtaining 66% of enantiomeric excess.