(Benzimidazolylmethyl)amine Zn II and Cu II Carboxylate Complexes: Structural, Mechanistic and Kinetic Studies of Polymerisation Reactions of ϵ‐Caprolactone

Compounds N ‐(1 H ‐benzimidazol‐2‐ylmethyl)aniline ( L1 ), N ‐(1 H ‐benzimidazol‐2‐ylmethyl)‐2‐bromoaniline ( L2 ), and N ‐(1 H ‐benzimidazol‐2‐ylmethyl)‐2‐aminothiophenol ( L3 ) react with Zn II and Cu II carboxylates to form complexes [Zn 2 ( L1 ) 2 (OBn) 4 ] ( 1 ), [Zn 2 ( L2 ) 2 (OBn) 4 ] ( 2 ), [Zn 2 ( L3 ) 2 (OBn) 4 ] ( 3 ), [Cu 2 ( L2 ) 2 (OBn) 4 ] ( 4 ), [Zn( L1 ) 2 (OAc) 2 ] ( 5 ), [Zn( L2 ) 2 (OAc) 2 ] ( 6 ) and [Cu 2 ( L1 ) 2 (OAc) 4 ] ( 7 ). Structures of 2 , 4 and 6 revealed that L1 – L3 are monodentate, binding through the imidazolyl N‐atom. The X‐band EPR spectrum of 4 in the solid state is consistent with an antiferromagnetically‐coupled (singlet) ground state and a low‐lying EPR‐active triplet excited state characterised by two main transitions. In dimethyl sulfoxide (DMSO) solution, a single resonance confirmed the retention of the dinuclear paddlewheel core. Complexes 1 – 7 formed active catalysts towards ring‐opening polymerisation of ϵ‐caprolactone. The polymerisation reactions follow first‐order kinetics with respect to the monomer and occur through a coordination–insertion pathway.