Evaluating Coordinative Binding Mechanisms through Experimental and Computational Studies of Methoxy-Substituted Arylazothioformamide Copper(I) Complexes

Abstract

Redox-active arylazothioformamide (ATF) ligands, when reacted with CuI salts, coordinate to form a variety of 1 : 1 dimers and 2 : 1 ligand-metal complexes through a N=N−C=S chelation motif. In this study, monosubstituted (ortho/meta/para) methoxy regioisomers of ATF were synthesized and evaluated with CuI halide and BF4 salts. UV-Vis binding association studies revealed a 2 : 1 binding association model against all species producing a para ≫ ortho > meta pattern across the methoxy substitution range. To understand why the 2 : 1 non-linear binding model was preferred over a 1 : 1 model for CuI halide salt dimers (i. e., A2B2), a series of mechanisms were computed indicating that metal salt dimers (i. e., B+B→B2) or ligand-metal salt-metal salt- (i. e., AB+B→AB2) interactions provide favorable pathways. Combined, the data substantiate the 2 : 1 binding association mechanistically even as the substitution pattern, steric bulk, and electronics alter the coordination strength of the ligands to the CuI center.