Affiliation: Princeton University
Title: Leveraging Polarizability and Electrophilicity in Catalysts for Challenging Coupling Reactions
A general approach by our group for the development of new catalytic synthetic methods that occur with higher efficiency and selectivity, use simpler reagents, and proceed with lower energy demand involves new ancillary ligand design coupled with fundamental studies of how metal-ligand bonding dictates catalytic reactivity. In this context, the presentation will focus on our recent efforts to discover new phosphorus- and sulfur-based ligands and associated metal catalysts that manifest special properties from seemingly "weak" interactions, for instance London dispersion. Two case studies will be discussed that exemplify such effects and emphasize many lessons yet to be learned about how structure controls reactivity in synthetic catalysts. In one case, a new transmetalation mechanism can be triggered in reactions of low-coordinate Pd complexes possessing polarizable diamondoid substituents, which enables smooth coupling catalysis even with historically unstable organoboron reagents. Studies of oxidative dehydrogenative coupling reactions will also showcase evidence for a C−H bond activation mechanism, termed electrophilic CMD or "eCMD", which has characteristics distinct from established SEAr and concerted metalation-deprotonation (CMD) pathways for C−H functionalization. Transition state analyses suggest this reaction pathway could be a general class of C−H activation manifested by many other transition metal catalysts, and selection rules have been identified for predicting what catalyst structures manifest either classic CMD or eCMD, which occur with unique substrate preferences and selectivity.