Phosphine-Free NNN Bis-Iminopyridine Supported Zinc(II) Catalysts: A Sustainable Platform for C─C Bond Formation Reactions via Borrowing Hydrogen Approach of Primary Alcohols.

In this study, we present a methodology for direct C─C bond formation using renewable primary alcohols as alkylating agents, catalyzed by base metal-derived Zn(II) complexes. We utilized two well-defined phosphine-free NNN bis-iminopyridine pincer ligands (L1 and L2) for the synthesis of zinc(II) catalysts C1 and C2, which were thoroughly characterized using UV-vis, IR, HRMS, and single-crystal x-ray diffraction techniques. Both complexes C1 and C2 effectively promoted the selective mono-alkylation of a variety of carbo-nucleophile, including aromatic ketones, α-tetralone, fluorene, and oxindole, by employing both aromatic and aliphatic primary alcohols as alkyl sources. A wide range of substrates, encompassing 42 derivatives, were investigated, resulting in isolated yields as high as 92%. The developed method was successfully applied at the gram scale, demonstrating its practical applicability and potential for scalability. Additionally, control experiments were performed to elucidate the reaction mechanism, and HRMS analysis verified the presence of significant Zn(II) intermediates involved in the catalytic process.