Reactivity and Selectivity Differences between Catecholate and Catecho­thiolate Ru Complexes. Implications Regarding Design of Stereoselective Olefin Metathesis Catalysts

The origins of the unexpected finding that Ru catecho­thiolate complexes, in contrast to cate­cholate derivatives, promote exceptional Z-selective olefin metathesis reactions are elucidated. We show that species containing a catecho­thiolate ligand, unlike cate­cholates, preserve their structural integrity under commonly used reaction conditions. DFT calculations indicate that, whereas alkene coordination is the stereo­chemistry-determining step with cate­cholate complexes, it is through the metalla­cyclo­butane formation that the identity of the major isomer is determined with catecho­thiolate systems. The present findings suggest that previous models for Z selectivity, largely based on steric differences, should be altered to incorporate electronic factors as well.