Ab initio MO calculations on 1,2-dithietes and valence isomers

Abstract

mThe valence isomerization of the 1,2-dithiete parent compound to the open-chain dithial was studied by CASSCF multiconfiguration methods including the CASPT2 perturbational treatment. The isomerization energy remains small at the highest level of theory. In agreement with Jonas and Frenking, the cyclic structure is only then preferred over the acyclic ones if f-functions on the sulfur atoms are considered. If they are included, the 1,2-dithiete is more stable by 3.8 kcal/mol and the barrier amounts to 24.9 kcal/mol at the CASPT2(8,8)/6-31G(2 df)//MP2/6-31G* level of theory. According to MP2/6-31G* geometry optimizations, substitution of H by NH, and CH, reduces the stability of the 1,2-dithiete ring structures relative to the open-chain dithiocarbonyl structures, whereas the inverse holds for acceptor substitution by CN and CF,. A higher stability of benzodithiete relative to orfho-dithiobenzoquinone is predicted at all employed levels of theory. This is in good agreement with conclusions drawn from experimental results. Whereas the experimental microwave geometry of 1,2-dithiete is well reproduced theoretically, the experimental electron diffraction geometry of 3,4-bis-(trifluoromethyl)-1,2-dithiete differs from the calculated one. 0 1996 John Wiley & Sons, Inc.

A η4‐Dithio‐para‐benzoquinone Metal Complex

“…Mulliken population analysis reveals a net increase in the electron count of the ligand by 0.2, while according to NPA this value is about 0.8. This situation results in lengthening of the C2C3 and C3′C2′ bonds in 4, and of the corresponding bonds C2C3 and C5C6 in 1 , by about 0.1 Å relative to calculated dithiobenzoquinone bond lengths 15b. The atomic orbital analysis phase of the NPA reveals an occupancy for the degenerate iridium d xy and d yz orbitals of 1.368 and 1.216, respectively.…”

Sterically Hindered o‐Quinone Annulated with Dithiete: A Molecule Comprising Diolate and Dithiolate Coordination Sites

“…has reported the synthesis of complex in which o ‐dithioquinone is coordinated as diene η 4 ‐ligand on iridium. 1,2‐Benzodithietes are regarded as valent isomers of dithioquinones, moreover, DFT calculations performed by Fabian and Mann2 indicate a higher stability for the dithiete structure compared with dithioquinone. Spectroscopic investigations made for some reaction intermediates [3, 4 ] at low temperatures also confirm this theoretical prediction.…”

First Detection of a Selenenyl Fluoride ArSeF by NMR Spectroscopy: The Nature of Ar2Se2/XeF2 and ArSeSiMe3/XeF2 Reagents

“…The importance of f-type polarization functions for correct ab initio and DFT calculations of sulfur compunds has been established. [50][51][52] Therefore calculations with the large basis set 6-311 + G(3df,3pd) are included here. This results in a more strongly exothermic disproportionation energy, mainly for CF 3 SÀF, less so for MeSeÀF; in the case of MeTeÀF the energies remain largely unchanged.…”