(Pyridinylmethylidene)dithioles: Synthesis, Structure, and Reactivity

Article abstract of DOI:10.1021/jo00040a032

Spectral characteristics, an X-ray crystal structure, and molecular orbital calculations indicate that (pyridinylmethylidene)dithioles 3, prepared from butadiynyl precursors 4 and hydrogen sulfide in basic methanol, are analogous in their bonding to the parent 1-aza-6,6λ⁴-dithiapentalenes 1 which, according to ab initio studies at Hartree-Fock level, is best represented as an (iminomethylidene)dithiole.An interaction between the sulfur and the nitrogen atoms is evident from the significant polarization of the S-S bond in those isomers where the nitrogen is proximal to the dithiole moiety.A comparison of the calculated structures of 1 and 3 with experimental data, as well as preliminary calculations on the related system trithiapentalene 2, suggest that ab initio methods using a single determinant are inadequate to describe these hypervalent sulfur systems.For example, an asymmetric structure is calculated to be the minimum energy from for 2 in contradiction to experimental results.Electrophilic substitutions, ring rearrangement, and reaction with electron acceptors are described for 3.