A DFT Study of the Hydroacylation Reaction Catalyzed by Rhodium Complexes with Small-Bite-Angle Diphosphine Ligands: The Crucial Role of External Lewis Bases

Hydroacylation catalysts have been previously reported
[Chaplin, A. B. J. Am. Chem. Soc. 2012, 134, 4885] that couple an alkene and a β-thioether
aldehyde using cationic rhodium(I) catalysts with small-bite-angle
diphosphine ligands. The higher catalytic activity was attributed
to the facilitation of reductive elimination of the final product
in the catalytic cycle, while external Lewis bases, including solvent
(acetone and acetonitrile), were found to have a protective effect
against catalyst deactivation. In this contribution, the relative
energetics of these processes are examined computationally, and a
unique role for the external Lewis base is discovered in which the
base intercepts a critical intermediate in a pathway leading to catalyst
deactivation and redirects the reaction to productive hydroacylation.