Using IR vibrations to quantitatively describe and predict site-selectivity in multivariate Rh-catalyzed C-H functionalization

Achieving selective C-H functionalization is a significant challenge that requires discrimination between many similar C-H bonds. Yet, reaction systems employing Rh₂(DOSP)₄ and Rh₂(BPCP)₄ were recently demonstrated to afford high levels of selectivity in the C-H insertion of carbenes into toluene-derived substrates. Herein, we explore the origin of this selectivity through a systematic analysis of substrate and reagent features that alter levels of selectivity from 20:1 to 1:610 for secondary (or tertiary)-to-primary benzylic C-H functionalization of toluene derivatives. Describing this variation using infrared vibrations and point charges, we have developed a mathematical model from which are identified features of the systems that determine levels of site-selectivity and are applied as predictive factors to describe the selectivity behavior of new substrate/reagent combinations.