A Dicyanomethyl Radical Conjugated with a Pyridylamino Group: Combining Radical‐based Dynamic Covalent Chemistry and Coordination Chemistry

Abstract

AbstractIn this work, we aimed to develop a dicyanomethyl radical that undergoes both reversible C−C bond formation/dissociation and metal‐ligand coordination reactions to combine dynamic covalent chemistry (DCC) based on organic radicals with coordination chemistry. We have previously reported a dicyanomethyl radical conjugated with a triphenylamine (1⋅) that exhibits a monomer/dimer equilibrium between the σ‐bonded dimer (12). We designed and synthesized a novel dicyanomethyl radical with a pyridyl group as a coordination point (2⋅) by replacing the phenyl group of 1⋅ with a 3‐pyridyl group. We showed that 2⋅ is also in an equilibrium with the σ‐bonded dimer (22) in solution and has suitable thermodynamic parameters for application in DCC. 22 coordinates to PdCl2 in a 2 : 2 ratio to selectively form a metallamacrocycle (22)2(PdCl2)2, and its structure was clarified by single crystal X‐ray analysis. Variable‐temperature NMR, ESR, and electronic absorption measurements revealed that (22)2(PdCl2)2 also undergoes the reversible C−C bond formation/dissociation reaction. Ligand‐exchange experiment showed that 22 was liberated from (22)2(PdCl2)2 by the addition of another ligand with a higher affinity for PdII. This work demonstrated that DCC based on dicyanomethyl radicals works orthogonally to metal‐ligand coordination reactions.