Controlling Reductive Elimination Pathways in Ti(IV) Pincer Complexes: Concerted versus Radical Mechanisms via Ligand Design.

Oxidatively induced reductive elimination (OIRE) is a powerful strategy for the formation of carbon-carbon bonds and has been widely employed in late transition metal catalysis. In contrast, early transition metals, especially titanium, have remained largely unexplored in this context. Here, we report two classes of pyridine-based titanium complexes that are structurally similar yet electronically distinct and investigate their oxidation chemistry. Depending on the ligand, the organyl bound to titanium, and the oxidant, selective alkyl radical expulsion is demonstrated, and most notably, a rare, highly selective, and quantitative concerted reductive elimination from a titanium(IV) complex was established. A combination of quantum chemical calculations, electrochemical measurements, and crossover experiments provided valuable insights into the reaction mechanism. These results demonstrate that appropriate ligand design, particularly the use of tridentate, redox-active ligands, can effectively suppress competing one-electron pathways and allow for selective concerted reactivity. In this way, control over this traditionally elusive elementary step in titanium chemistry was achieved, marking an advance in the development of OIRE processes for early transition metals.