Intramolecular sulphur(IV)-oxygen interaction in sulphoxides and sulphilimines with 2-methoxycarbonyl-phenyl and 2-nitrophenyl groups: an X-ray study

Abstract

The molecular structures of methyl 2-(methylsulphinyl)benzoate, S-(2-methoxy-carbonylphenyl)- S-methyl- N-(4-methoxyphenylsulphonyl)- sulphilimine, dimethyl 2,2′-sulphinyldibenzoate, methyl 2-(2-nitrophenylsulphinyl) benzoate, 2,2′-dinitrodiphenyl sulphoxide and methyl 2-(2-nitrophenylsulphinyl)phenylacetate exhibiting S(IV)⋯O-(carbonyl) or S(IV)⋯O(nitro) close contact have been investigated by X-ray diffraction. The observed axial (ArMeSO, ArMeSNSO 2Ar) and axial-twist (Ar 2SO) conformations are interpreted by taking into account steric effects, conjugation and sulphur(IV)—oxygen interaction. Linear and non-linear X=S(IV)⋯O close contacts (2.664–2.778 and 2.847–3.618 A, respectively) related to favourable “bond direction” and unfavourable “lonepair direction” approaches are discussed and compared with corresponding (shorter) XS(II)⋯O close contacts. The relative positions of aryl rings, the geometry of rings with S⋯O contacts and the nature of the counter-atom (X = O, N) mainly determine sulphur(IV)—oxygen interaction. The data are in good agreement with the nearly equal anchimeric assistance of the o-CO 2Me and o-CO 2H groups, and with the lack of neighbouring-group activity in cases where six-membered rings with S⋯O contacts should be formed. Sulphur—oxygen bond lengths in OS⋯O and OSO systems with close contacts or hypervalent bonds are compared. Changes in CO, NO and S(IV)C ar bond lengths caused by sulphur(IV)—oxygen interaction are negligible.