Synthesis and evaluation of new mono- and binuclear salen complexes for the Cα-alkylation reaction of amino acid substrates as chiral phase transfer catalysts.

• Synthesis and Evaluation: Zn(II) mono- and Cu(II) binuclear salen complexes were synthesized and assessed for their catalytic performance in Cα-alkylation reactions. • Substituent Effects: Introducing a methoxy group at position 3 of the phenyl group in the salicylidene ligand significantly enhanced the asymmetric yield, while an allyl group reduced the yield. • Computational Insights: DFT calculations revealed that the improved performance with the methoxy substituent is likely due to increased stability of the binuclear complex during the transition state. • Dimeric Complex Advantage: A covalently cross-linked binuclear salen complex exhibited higher catalytic activity compared to mononuclear complexes, potentially due to enhanced intramolecular rigidity. • Future Directions: Further optimization of reaction conditions and exploration of different substrates and alkylating agents are suggested to enhance catalytic efficiency and versatility. Detailed mechanistic studies could aid in the rational design of more efficient chiral salen complexes for asymmetric catalysis. In this study, we present a series of Zn(II) mono- and Cu(II) binuclear salen complexes synthesized and assessed for their effectiveness in the Cα-alkylation reaction. Through systematic experimentation, it was observed that the introduction of a methoxy group at position 3 of the phenyl group in the salicylidene ligand led to a notable enhancement in asymmetric yield, while an allyl group reduced yield. Computational DFT calculations supported the involvement of the binuclear complex in the transition state of the reaction, elucidating the underlying mechanisms governing the observed catalytic behavior. A newly synthesized binuclear complex exhibited significantly higher catalytic activity compared to its mononuclear counterpart which could potentially be explained by increased intramolecular rigidity. This comprehensive investigation not only advances our understanding of structure-activity relationships in chiral salen complexes but also provides valuable insights for the rational design and optimization of catalysts for the asymmetric Cα-alkylation reaction. [Display omitted] [ABSTRACT FROM AUTHOR]