Synthesis of Molybdenum and Tungsten Alkylidene Complexes That Contain Sterically Demanding Arenethiolate Ligands

Imido alkylidene complexes of Mo
and W and oxo alkylidene complexes
of W that contain thiophenoxide ligands of the type S-2,3,5,6-Ph4C6H (STPP) and S-2,6-(mesityl)2C6H3 (SHMT = S-hexamethylterphenyl) have been prepared
in order to compare their metathesis activity with that of the analogous
phenoxide complexes. All thiolate complexes were significantly slower
(up to ∼10× slower) for the metathesis homocoupling of
1-octene or polymerization of 2,3-dicarbomethoxynorbornene, and none
of them was Z-selective. The slower rates could be
attributed to the greater σ-donating ability of a thiophenoxide
versus the analogous phenoxide and consequently a higher electron
density at the metal in the thiophenoxide complexes.