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.