A Dicyanomethyl Radical Conjugated with a Pyridylamino Group: Combining Radical‐based Dynamic Covalent Chemistry and Coordination Chemistry
Hiroki Hasegawa, Daisuke Sakamaki, Hideki Fujiwara
Abstract
Abstract In 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 ( 1 2 ). 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 ( 2 2 ) in solution and has suitable thermodynamic parameters for application in DCC. 2 2 coordinates to PdCl 2 in a 2 : 2 ratio to selectively form a metallamacrocycle ( 2 2 ) 2 (PdCl 2 ) 2 , and its structure was clarified by single crystal X‐ray analysis. Variable‐temperature NMR, ESR, and electronic absorption measurements revealed that ( 2 2 ) 2 (PdCl 2 ) 2 also undergoes the reversible C−C bond formation/dissociation reaction. Ligand‐exchange experiment showed that 2 2 was liberated from ( 2 2 ) 2 (PdCl 2 ) 2 by the addition of another ligand with a higher affinity for Pd II . This work demonstrated that DCC based on dicyanomethyl radicals works orthogonally to metal‐ligand coordination reactions.