Preparation of Tungsten‐Based Olefin Metathesis Catalysts Supported on Alumina

A new tungsten alkylidene complex, W(NAr)(CHCMe 2 Ph)(OHIPT‐NMe 2 )(pyrrolide) {Ar=2,6‐( i‐ Pr) 2 C 6 H 3 ; HIPT‐NMe 2 =2,6‐[2,4,6‐( i‐ Pr) 3 C 6 H 2 ] 2 ‐4‐NMe 2 ‐C 6 H 2 }, has been synthesized and shown to be highly selective for Z homocoupling metathesis of selected terminal olefins in pentane, as is W(NAr)(CH 2 CH 2 CH 2 )(OHIPT)(pyrrolide) ( 5 ). Both 5 and W(NAr)(CHCMe 2 Ph)(OHIPT‐NMe 2 )(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 .