Reactivity
and Selectivity Differences between Catecholate
and Catechothiolate Ru Complexes. Implications Regarding Design
of Stereoselective Olefin Metathesis Catalysts
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Abstract
The origins of the
unexpected finding that Ru catechothiolate
complexes, in contrast to catecholate derivatives, promote exceptional <i>Z</i>-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 <i>Z</i> selectivity, largely based on steric
differences, should be altered to incorporate electronic factors as
well