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.

Subazaphenalenephthalocyanine: A Subphthalocyanine Analogue Bearing a Six‐Membered Ring Unit

“…The high-resolution ESI-FT-ICR mass spectrometry experiment revealed an intense peak at m/z = 1187.4768 (calcd for C 74 H 66 BClN 6 O 5 Na [M + +Na]: 1187.4774), and is indicative of chlorination at one of the peripheral or nonperipheral positions, which is often induced during the formation of subphthalocyanines using BCl 3 as a template reagent. [15] The formation of this chlorinated species was also confirmed by 1 H NMR spectroscopy. Signals corresponding to the protons of the axial phenoxy ligand are observed at d = 6.80, 6.66, and 5.74 ppm.…”

Thieno‐Fused Subporphyrazines: A New Class of Light Harvesters

“…For comparison, monochlorination has been observed by Zhu et al . during synthesis of a SubPc analogue with an azaphenalene unit and is likely a result of electrophilic aromatic substitution due to in situ generation of Cl 2 …”

“…For comparison, monochlorination has been observed by Zhu et al [7a] during synthesis of aS ubPc analoguew ith an azaphenalene unit and is likely ar esult of electrophilic aromatic substitution due to in situ generation of Cl 2 . [12] We anticipated that ah igher yield of (TPCl 2 ) could be obtained if the known 2,5-dichloro-3,4-dicyanothiophene( 3)w as used as substrate. [13] Satisfyingly,w ee xperienced a1 6-foldi ncrease in yield when (TPCl 2 ) was now isolated in 8%.M oreover,T LC analysis showedanew spot eluting before (TPCl 2 ) exhibiting an intense dark blue color.T his product was isolated in 0.2 %y ield and wasf ound to be (TPCl 2 ) 2 .I ts yield couldb e increased to 4% (20-foldi ncrease)b yu sing a2 :1 ratio of the thiophene and phthalonitrile.…”

Ring Opening Reactions through C-O Bond Cleavage Uniquely Adding Chemical Functionality to Boron Subphthalocyanine

“…Boron acts as an atomic template to form the subPc macrocycle during the cyclotrimerization of phthalonitrile [12]. Thereafter the boron atom has limited electronic connectivity to the molecular orbitals of the π system, indicated by the retention of most properties of BsubPcs upon varying the nature of the axial substituent [13].…”