Process for the synthesis of symmetric and unsymmetric oxygen bridged dimers of boron subphthalocyanines (μ-oxo-(BsubPc)2s)

Abstract

A process for the gram scale synthesis of the oxygen bridged dimer of boron subphthalocyanine, μ-oxo-(BsubPc)₂, has been developed. During the development it was found that a wide range of reaction pathways under diverse conditions lead to μ-oxo-(BsubPc)₂ formation. However, obtaining μ-oxo-(BsubPc)₂ as the main reaction product in appreciable yields and its subsequent isolation were extremely challenging. The best balance of purity, yield and conversion was achieved with a time controlled reaction of an equimolar reaction of HO-BsubPc with Br-BsubPc in the presence of K₃PO₄. The purification involved sequentially Soxhlet extraction, Kauffman column chromatography and train sublimation. We have repeated the process and yields ranged from 27 to 30% of pure, doubly-sublimed μ-oxo-(BsubPc)₂. This process also enabled the synthesis of unsymmetric μ-oxo-(BsubPc)₂s by reaction of HO-BsubPc with Br-F₁₂BsubPc, Cl-Cl₆BsubPc and Cl-Cl₁₂BsubPc. After synthesis the solution-state properties of the unsymmetric μ-oxo-(BsubPc)₂s were investigated, and compared to the symmetric μ-oxo-(BsubPc)₂ and more broadly to other BsubPcs. The electronic properties of μ-oxo-(BsubPc)₂ were found to differ from its unsymmetric counterparts, but were found to be similar to halo-BsubPcs. Furthermore, the photophysical properties of μ-oxo-(BsubPc)₂, both symmetric and unsymmetric, differed greatly from all other known BsubPcs.