Polarization and Polarizability as Design Elements in Catalysis
The research in our group is founded on a mechanism-driven approach to design transition metal complexes that promote unique elementary catalytic steps, control speciation between active and inactive catalyst states, and provide testable cases to challenge assumptions about the limits of transition metal reactivity in order to address long-standing sustainability challenges in catalytic chemical synthesis and contemporary problems of plastics pollution and recycling. This presentation will focus on our recent efforts to discover new ancillary ligands and associated catalysts that manifest special properties from seemingly "weak" interactions, for instance dispersion, which have long been overlooked as catalyst design elements. We have discovered aliphatic phosphines that leverage large polarizability, which can trigger unprecedented transmetalation steps in coupling chemistry, facilitate the first ever characterization and reactivity studies of a central catalyst intermediate in contemporary cross-coupling methods, and enable direct visible light-induced bond weakening. In another area, charge transfer effects are realized as an important strategy to overcome a general limitation in the catalytic synthesis of functional polymers relevant to plastics upcycling. Ionic thioether ligands that we have developed have also been shown to strongly polarize base-assisted C–H cleavage transition states, which correlates to unusual non-directed site selectivity during C–H functionalization. Based on extensive mechanistic studies, we have generalized a model for a polarized, concerted mechanistic continuum in C–H heterolysis that reconciles a wide array of reactivity patterns in the literature and can potentially be leveraged for a priori prediction of catalyst-controlled selectivity – a major standing challenge in this field.