On the mechanism of boron-subphthalocyanine chloride formation

Abstract

A mechanistic study of chloroboron subphthalocyanine (SubPc) formation from phthalonitrile and BCl 3 in aromatic solvents such as p-xylene or toluene suggests that rearrangement of the initial phthalonitrile- BCl 3 adduct produces (1 Z )-3-chloro-N-(dichloroboryl)-1 H -isoindol-1-imine 3, following rearrangement of the initial phthalonitrile- BCl 3 adduct. From three molecules of (1 Z )-3-chloro-N-(dichloroboryl)-1 H -isoindol-1-imine 3, by successive addition, the dichlorosubstituted macrocycle 7 is formed. Quantum-chemical computation shows that the postulated elementary reaction steps leading up to the formation of the SubPc-precursor macrocycle are indeed exothermic, or at least kinetically allowed. The formation of the SubPc is concluded by the elimination of chlorine which is probably catalyzed by BCl 3 in a concerted process which might be represented as: dichlorosubstituted macrocycle 7 + BCl 3 → SubPc · Cl + + BCl 4- → SubPc + Cl 2 + BCl 3. The chlorine formed may be photolytically affected if the reaction is carried out under ordinary laboratory lighting (fluorescent lamps), giving rise to a free-radical chain reaction involving the solvent. Alternatively, molecular chlorine may react with aromatic solvents such as toluene and p-xylene in a Friedel-Crafts-type reaction catalyzed by BCl 3. In this way, such solvents which are reactive in both ways can protect the reactant phthalonitrile, the reaction intermediates, and the product SubPc from degradation by chlorination.