Molybdenum Benzylidyne Complexes for Olefin Metathesis Reactions

The molybdenum benzylidynes [ArCMo­(OC­(CF3)2CH3)3(1,2-dimethoxyethane)], where Ar = Ph (2a), p-(OCH3)­C6H4 (2b), p-(CF3)­C6H4 (2c), p-(NO2)­C6H4 (2d), or 4-(NO2)-3-(CF3)­C6H3 (2e), and [p-(NO2)­C6H4CMo­(OC­(CF3)2CH3)3] (2f) catalyze the ring-closing metathesis (RCM) reaction of diallyl N-tosylamide (3) to produce 1-tosyl-2,5-dihydro-1H-pyrrole (4) and ethylene. The scope of RCM catalytic activity of 2e, cross-metathesis of 1-hexene, and ring-opening metathesis polymerization of cyclooctene were explored. The X-ray crystal structure of 2e was determined. Variable-temperature 1H NMR spectra revealed the formation of intermediates during the reaction of 3 with 2f and the reforming of 2f after completion of the reaction. The use of 13C-labeled Mo benzylidyne did not show transfer of the carbon atom next to Mo to any of the products.