Metal-Organic Self-Assembled Trefoil Knots for C - Br Bond Activation

Synthesizing molecular knots that mimic the catalytic functionality of stereospecific or stereoselective enzymes are an intriguing task in chemistry. Synthetic anion receptors even with moderate halide binding affinities may catalyze chemical reactions involving carbon-halogen bond cleavage. Herein we report isostructural self-assembled trefoil molecular knots (Cu-TK, Cd-TK, Zn-TK) based on Cu(II), Cd(II), and Zn(II) that are capable of binding and stabilizing bromide within their central cavity and are capable of catalyzing C-Br bond cleavage. We also describe the role of noncovalent interactions between the knots and bromide as well as the size and shape of the knots on their catalytic efficiency. Among the studied three knots, Cu-TK was found to be more effective than Zn-TK and Cd-TK in catalyzing C-Br bond cleavage. The catalytic efficiency of the knots toward C-Br bond cleavage was found to be related to a balance between their attractive electrostatic interactions with bromide as well as cavity size and shape of the knots.