Thioacylsulfanylarsines (RCS2)xAsPh3 − x, x = 1–3: synthesis, structures, natural bond order analyses and reactions with piperidine

Abstract

A series of thioacylsulfanylarsines ((RCS₂)AsPh₂, (RCS₂)₂AsPh, (RCS₂)₃As) were synthesized by treating piperidinium dithiocarboxylates with Ph₂AsCl, PhAsCl₂ or AsCl₃, respectively and characterized. Their molecular structures were determined by X-ray crystallography and compared with those of the corresponding acylsulfanyl derivatives ((RCOS)AsPh₂, (RCOS)₂AsPh, (RCOS)₃As). They exist as monomers, and the environment around the arsenic atoms is distorted tetrahedral with one lone pair at the apex. The structure of the mono(dithiocarboxylate) is different from that of the corresponding thiocarboxylic acid derivative, while the bis and tris derivatives showed similar structure to the corresponding thiocarboxylic acid derivatives ((RCOS)₂AsPh, (RCOS)₃As), respectively. The new compounds showed intramolecular interactions between the thiocarbonyl sulfur and the central arsenic atom. NBO (Natural Bond Orbital) analyses performed on the model compounds (CH₃CS₂)As(CH₃)₂ and (CH₃CS¹₂)(CH₃CS²₂)AsCH₃ at the RHF/LANL2DZ level of theory showed the presence of interactions between the non-bonding orbitals on the thiocarbonyl sulfur (n_S) and the σ*_MS orbitals together with that between the n_S and the σ*_MC orbitals for the former compound; for the latter the presence of both orbital interactions between n_S and σ*_MS1 and between n_s and σ*_MS2 are present. The reaction of the mono(dithiocarboxylate) derivative (R = 4-CH₃C₆H₄) with piperidine in ethanol gave piperidinium diphenyldithioarsinate along with the corresponding N-thioacyl- or N-acyl-piperidine. A similar reaction of the bis(dithiocarboxylate) derivative (R = 4-CH₃C₆H₄) gave the novel di(piperidinium) phenyltrithioarsonate in which two anion charges are delocalized on the AsS₃ moiety and a cyclic phenylarsine sulfide tetramer (PhAsS)₄. The diphenyldithioarsinate and phenyltrithioarsonate salts exist as a dimer and a polymer, respectively, in which 12-membered rings are formed by intermolecular N–H ⋯ S hydrogen bonds.