Noncovalent Interactions Drive the Efficiency of Molybdenum Imido Alkylidene Catalysts for Olefin Metathesis

High-throughput experimentation
and multivariate modeling allow identification of noncovalent interactions
(NCIs) in monoaryloxy-pyrrolide Mo imido alkylidene metathesis catalysts
prepared in situ as a key driver for high activity
in a representative metathesis reaction (homodimerization of 1-nonene).
Statistical univariate and multivariate modeling categorizes catalytic
data from 35 phenolic ligands into two groups, depending on the substitution
in the ortho position of the phenol ligand. The catalytic
activity descriptor TON1h correlates predominantly with
attractive NCIs when phenols bear ortho aryl substituents
and, conversely, with repulsive NCIs when the phenol has no aryl ortho substituents. Energetic span analysis is deployed
to relate the observed NCI and the cycloreversion metathesis step
such that aryloxide ligands with no ortho aryls mainly
impact the energy of metallacyclobutane intermediates (SP/TBP isomers),
whereas aryloxides with pendant ortho aryls influence
the transition state energy for the cycloreversion step. While the
electronic effects from the aryloxide ligands also play a role, our
work outlines how NCIs may be exploited for the design of improved
d0 metathesis catalysts.