SURFACE ORGANOMETALLIC CHEMISTRY OF ZIRCONIUM - APPLICATION TO THE STOICHIOMETRIC ACTIVATION OF THE C-H BONDS OF ALKANES AND TO THE LOW-TEMPERATURE CATALYTIC HYDROGENOLYSIS OF ALKANES

Tetrakis(neopentyl)zirconium reacts With the surface of silica, dehydroxylated at 773 K, to give the surface tris(neopentyl)zirconium complex, Si-O-ZrNp3 (1). Under molecular hydrogen (423 K, 400 torr), 1 is transformed into surface zirconium hydrides (2) and silicon hydrides. Complex 2 activates the C-H bonds of cyclooctane and methane via a sigma-bond metathesis reaction, and selectively at low temperatures hydrogenolyzes alkanes such as neopentane, isobutane and propane, but not ethane. The mechanism proposed involves, inter alia, the activation of C-H bonds of the alkanes and the on of the C-C bond of the alkyl groups via beta-methyl migration steps.