2 research outputs found
Rollover Cyclometalation Pathway in Rhodium Catalysis: Dramatic NHC Effects in the C–H Bond Functionalization
Organometallic chelates are readily obtained upon coordination
of metal species to multidentate ligands. Because of the robust structural
nature, chelation frequently serves as a driving force in the molecular
assembly and chemical architecture, and they are used also as an efficient
catalyst in numerous reactions. Described herein is the development
of a Rh(NHC) catalytic system for the hydroarylation of alkenes and
alkynes with 2,2′-bipyridines (bipy) and 2,2′-biquinolines;
the most representative chelating molecules. Initially generated (bipy)Rh(NHC)
chelates become labile because of the strong <i>trans</i>-effect of <i>N</i>-heterocyclic carbenes, thus weakening
a rhodium–pyridyl bond, which is <i>trans</i> to
the bound NHC. Subsequent rollover cyclometalation leads to the C–H
bond activation, eventually giving rise to double functionalization
of chelate molecules. Density functional calculations are in good
agreement with our mechanistic proposal based on the experimental
data. The present study elucidated for the first time the dramatic
NHC effects on the rollover cyclometalation pathway enabling highly
efficient and selective bisfunctionalization of 2,2′-bipyridines
and 2,2′-biquinolines