Aluminum Chloride Activation of Chloro-Boronsubphthalocyanine: a Rapid and Flexible Method for Axial Functionalization with an Expanded Set of Nucleophiles

We have developed a process whereby chloro-boronsubphthalocyanine
(Cl-BsubPc) and other BsubPcs are activated to reaction with oxygen,
sulfur, and nitrogen based nucleophiles by treatment with aluminum
chloride under mild conditions. This allows for the scope of atoms
chemically bound to the boron atom to be expanded beyond those derived
from the traditional oxygen and carbon based nucleophiles. The successful
formation of thiophenoxy and phenylamino derivatives of BsubPc was
confirmed spectroscopically and by X-ray crystallography of single
crystals. We have proposed a detailed mechanism for this process based
on experimental observation and NMR spectroscopy (1H, 11B, and 27Al) which involves formation of a complex
between a halo-BsubPc and AlCl3 (which we denote BsubPc­(Cl)·Al­(Cl′)3). Our observations indicate that the action of phenol on
BsubPc­(Cl)·Al­(Cl′)3 does not involve direct
reaction at the boron atom; rather phenol first reacts at the aluminum
atom along the way to the formation of a new intermediate complex
BsubPc­(OPh)·Al­(O′Ph)3. The consequence is that
the rate of this process is independent of the nature of the starting
BsubPc. Cl-BsubPc and Br-BsubPc as well as BsubPcs with peripheral
substitutents all react to form their respective phenoxy derivatives
at the same rate. Quenching of BsubPc­(OPh)·Al­(O′Ph)3 with a Lewis base ultimately produces a new bond between
the phenol nucleophile and the boron atom of the BsubPc.