Preparation and characterisation of (SeNSNS)n(AsF6)2 containing the ‘electron-rich aromatic’ 6π SeNSNS2+(n= 1) and 7π SeNSNS˙+(n= 2)

Abstract

Attempted syntheses of SeNSAsF₆ from the reactions of SNAsF₆ with Se₈(AsF₆)₂(4 : 1) or Se (1 : 1) gave ([graphic omitted])_n(AsF₆)₂(n= 1 and 2), Se₄(AsF₆)₂ and trace amounts of [graphic omitted]e(AsF₆)₂ and (Se/[graphic omitted]e)₂(AsF₆)₂. The formation of ([graphic omitted])_n(AsF₆)₂(n= 1 and 2) as the major product is consistent with generation of a SeNS⁺ intermediate which undergoes a concerted symmetry-allowed cycloaddition reaction with SN⁺ to give [graphic omitted]²⁺. The crystal structure of [graphic omitted](AsF₆)₂ consists of disordered [graphic omitted]²⁺ cations and AsF₆^– anions, that of ([graphic omitted])₂(AsF₆)₂ consists of AsF₆^– anions and two independent disordered [graphic omitted]˙⁺ radical cations weakly linked into a non-centrosymmetric dimer by two long Se ⋯ S bonds [3.12(4), 3.09(2); 3.32(5), 3.16(6)Å]. The structure of (Se/[graphic omitted]e)₂(AsF₆)₂ contains a 50:50 mixture of disordered [graphic omitted]e˙⁺ and [graphic omitted]˙⁺ radical cations joined by two long Se/S ⋯ Se bonds [3.077(3), 3.138(3)Å]. There are significant interionic interactions in all the salts. The ⁷⁷Se [–60 °C, δ(Me₂Se)= 2422.4, ν_½, = 10.4 Hz] and ¹⁴N NMR [room temperature (r.t.), δ(MeNO₂)= 68.9, ν_½, = 446 Hz] spectra of [graphic omitted]²⁺ are consistent with a delocalised 6π ring structure. The [graphic omitted]²⁺ cation readily reacts with CCl₃F to give Cl[graphic omitted]AsF₆ the identity of which was confirmed by the determination of its crystal structure. The ESR spectrum of [graphic omitted]˙⁺ in SO₂ solution at r.t. (g= 2.026, broad) and the spectrum of powdered [graphic omitted]˙⁺ in frozen SO₂ at –160 °C were similar to but not identical with those of [graphic omitted]e˙⁺, [graphic omitted]e˙⁺ and [graphic omitted]˙⁺ indicative of a planar 7π system.