Activation of Water at the Active-Site Cavity of Zinc Phthalocyanine with Tris(pentafluorophenyl)borane

Activation of water bound with Zn2+ has attracted much attention as an artificial model of natural enzymes. Despite many attempts, water activation accompanied with a change in the coordination geometry of Zn2+ in complexes remains a challenge. In this study, we discover a new structure that is composed of partially protonated zinc phthalocyanine (ZnPc), hydroxide ion, and tris(pentafluorophenyl)borane (TPFB). The coordination of TPFB with water bounded with ZnPc results in the dissociation of water, and the dissociated proton from water moves to one nitrogen atom of the phthalocyanine ring through the intramolecular proton transfer. On the basis of this reaction, the coordination geometry transforms from a five-coordinated to a distorted tetrahedral species. The Zn2+-bound hydroxide nucleophile in the ZnPc-TPFB complex attacks amide of epsilon-caprolactam to produce hydrolyzed 6-aminohexanoic acid in toluene.