Preparation of Tungsten-Based Olefin Metathesis Catalysts Supported on Alumina

A new tungsten alkylidene complex, W(NAr)(CHCMe2Ph)(OHIPT-NMe2)(pyrrolide) {Ar = 2,6-(i-Pr)(2)C6H3; HIPT-NMe2 = 2,6-[2,4,6-(i-Pr)(3)C6H2](2)-4-NMe2-C6H2}, has been synthesized and shown to be highly selective for Z homocoupling metathesis of selected terminal olefins in pentane, as is W(NAr)(CH2CH2CH2)(OHIPT)(pyrrolide) (5). Both 5 and W(NAr)(CHCMe2Ph)(OHIPT-NMe2)(pyrrolide) (6) are adsorbed onto calcined alumina. Control experiments and metathesis homocoupling of four substrates lead to the conclusions that 5 is largely adsorbed in a reaction that liberates HIPTOH, while 6 is adsorbed largely through an interaction between the dimethylamino group and an acidic site on the surface. There is no evidence that any adsorbed catalyst can give rise to Z selectivity of a magnitude equal to that found in a homogeneous reaction involving 5 or 6.