Coordination Chemistry of Boron Subphthalocyanine With BINOL Derivatives: Unexpected Oxidation to Oxa[4]Helicene and Properties of the Resulting Axially Coordinated Complexes Containing Oxa[4]Helicene and/or BINOL Derivatives

In the course of our research on axially coordinated metalloporphyrinoids with stable bonding based on the hard and soft acid-base (HSAB) theory, we focused on boron subphthalocyanine because of the hard acid character of the boron(III) center. 1,1'-Bi-2-naphthol (BINOL) was selected as an axial ligand to introduce chirality into the otherwise achiral subphthalocyanine. Surprisingly, treatment of unsubstituted BINOL with boron subphthalocyanine resulted in the formation of a complex coordinated to an oxa[4]helicene derivative formed via a ring-closure reaction of BINOL. In contrast, treatment of the monomethyl ether of BINOL with boron subphthalocyanine afforded the expected axially coordinated complex. Based on several control experiments, we propose a reaction mechanism for the formation of the oxa[4]helicene involving coordination of BINOL, followed by deprotonation and racemization, and subsequent intramolecular ring-closure via an ionic process. To characterize and elucidate the fundamental properties of the resulting complexes, single-crystal x-ray diffraction, NMR spectroscopy, UV-vis absorption spectroscopy, and electrochemical studies were carried out. Furthermore, we investigated the chirality-derived properties of the complexes, and the chirality-induced spin selectivity (CISS) effect was evaluated using magnetic conductive atomic force microscopy (mc-AFM), revealing a large spin polarization.