Reaction of GaIIIClPc, SnIVCl2TPP and BIIIClSubPc with cyanide anions: reduction of macrocycles vs. formation of cyano-containing macrocyclic anions

Abstract

The reaction of Ga^IIIClPc, Sn^IVCl₂TPP and B^IIIClSubPc containing phthalocyanine (Pc), tetraphenylporphyrin (TPP) and subphthalocyanine (SubPc) macrocycles with cyanide in the presence of cryptand[2.2.2] under anaerobic conditions yields crystalline salts in which cyano anions substitute chloride anions at Ga^III, Sn^IV or B^III, as well as reducing the macrocycles or adding one or two CN⁻ to them. The reaction of Ga^IIICl(Pc²⁻) with CN⁻ yields {crypt(K⁺)}{Ga^IIICN(Pc˙³⁻)}˙⁻·0.5C₆H₄Cl₂ (1) in which the Pc²⁻ macrocycle is reduced to Pc˙³⁻. Such reduction could probably occur through the addition of CN⁻ to Pc²⁻ forming {Ga^III(CN)[Pc(CN)]³⁻}⁻ which can decompose further interacting with an excess of CN⁻. As a result, Pc˙³⁻ and cyanogene anions are formed. The interaction of Sn^IVCl₂(TPP²⁻) with CN⁻ is accompanied by the addition of CN⁻ to the meso-carbon atom of porphyrin forming diamagnetic TPP(CN)³⁻ macrocycles in {crypt(K⁺)}{Sn^IV(CN)₂[TPP(CN)]³⁻}⁻ (2). Salt 2 shows a strong NIR absorption band with the maximum at 854 nm whose intensity is comparable with that of the Soret band. The interaction of B^IIICl(SubPc²⁻) with three equivalents of CN⁻ is accompanied by the addition of two CN⁻ to carbon atoms of SubPc²⁻ closest to meso-nitrogen atoms forming {B^III(CN)[SubPc(CN)₂]⁴⁻}²⁻. Most probably these dianions transfer electrons to C₆H₄Cl₂ producing the {B^III(CN)[SubPc(CN)₂]˙³⁻}˙⁻ radical anions which form σ-bonded diamagnetic dianions in {crypt(K⁺)}₂{B^III(CN)[SubPc(CN)₂]}₂²⁻·3C₆H₄Cl₂ (3). The remaining carbon atom closest to the meso-nitrogen atom is involved in this dimerization. According to the calculations, the energy of the C–CN bond is minimal for {Ga^III(CN)[Pc(CN)]³⁻}⁻ enabling further transformation of these anions to {Ga^IIICN(Pc˙³⁻)}˙⁻ in 1, whereas cyano-containing anions in 2 and 3 with higher energy of this bond are stable towards the elimination of CN. Optical and magnetic properties of 1–3 together with their crystal and molecular structures are presented. The possible ways of the formation of 1–3 are discussed based on DFT calculations.