Chiral Copper(II) Schiff Base Complexes Derived from Alanine: Structural Insights and Catalytic Performance in Cyclopropanation and C–S Coupling Reactions

Two chiral copper(II) Schiff base complexes (L1Cu and L2Cu) derived from the amino acid L-alanine and two salicylaldehydes (one chlorine-substituted) were synthesized and characterized by SCXRD, spectroscopic techniques (FTIR, UV-Vis, EPR), and thermal analysis. SCXRD revealed distorted square-pyramidal geometries, with axial elongation and strong equatorial Cu–N/O bonds indicative of Jahn-Teller distortion. Spectroscopic data confirmed covalent metal-ligand interactions and a d ₓ²₋ᵧ² ground state. In styrene cyclopropanation, both complexes achieved 99.9 % yield, with trans:cis ratios of 100:0 and 98:2 and RR:SS ratios of 66:34 and 60:40 for L1Cu and L2Cu, respectively. For C–S coupling, L1Cu and L2Cu afforded yields of 93 % and 87 %, respectively, with both generating minor disulfide byproduct (∼6.4 %). Overall, both complexes showed catalytic activity in two distinct transformations, supporting the applicability of these alanine-derived Cu(II) Schiff base systems in cyclopropanation and C–S coupling reactions.