Theoretical Elucidation of Manganese(I)–Pincer Catalyzed α-Alkylation of Sulfones with Alcohols

The manganese(I)-pincer catalyzed α-alkylation of sulfones with alcohols offers an efficient and sustainable C-C coupling strategy, though its mechanistic details and selectivity remain poorly understood. In this study, we employ density functional theory (DFT) to elucidate the full catalytic cycle, which comprises four key steps: (i) base-assisted activation of the precatalyst, (ii) alcohol dehydrogenation through a kinetically favorable double hydrogen transfer (barrier: 13.2 kcal/mol), (iii) low-barrier condensation between the resulting aldehyde and sulfone to form an α,β-unsaturated intermediate, and (iv) Mn-H mediated hydrogenation via an intermolecular hydrogen transfer mechanism. The rate-determining step exhibits a barrier of 27.0 kcal/mol, consistent with the requirement for reaction temperatures of 150 °C. Selectivity is governed by both kinetic and thermodynamic factors: the α-alkylation pathway is favored over competing Julia-type olefination and α-alkenylation routes, which are hindered by high endothermicity (43.8 kcal/mol) and substantial kinetic barriers (up to 57.9 kcal/mol). These insights provide a mechanistic foundation for the design of more efficient and selective earth-abundant base-metal catalysts for sustainable synthesis.