Unprecedented observation and characterization of sulfur-centred bifurcated hydrogen bonds

Abstract

It is observed that the sulfur atom can unprecedentedly serve as a good acceptor to form the O–H⋯S⋯H–O bifurcated H-bond.

Water oxidation by Brønsted acid-catalyzed in situ generated thiol cation: dual function of the acid catalyst leading to transition metal-free substitution and addition reactions of S–S bonds

“…The following configuration adjustment of 14a or 14a′ to 15a or 15a′ may then take place to afford thiol cation 10a , meanwhile releasing free 4a′ and 4a (steps ii–v). Next, the reaction of 2-PyS + ( 10a ) with water is more likely promoted by the basic pyridyl group or one of the S atoms of 1a to firstly give complex 16a or 16a′ (complex of 10a , H 2 O, and 1a , possibly formed via an S + ⋯O coordination bond and an OH⋯N or OH⋯S hydrogen bond) 22 and then by forming new S–O and new H–N or H–S bonds to give complex 17a or 17a′ bearing new O⋯HN or O⋯HS hydrogen bond (steps vi–vii). The DFT study also revealed that 17a is more stable and more easily formed than 17a′ as N is known to be basic than S. Then, by releasing 1a-H + or 1a-H + ′ , sulfenic acid 11a was generated from 17a or 17a′ (step viii).…”

“…The S–S bond of 1a-H + or 1a-H + ′ may then heterolytically cleave to give thiol cation PyS + 10a and thiopyridone 4a′ (which then tautomerizes to thiol 4a ) or directly thiol 4a . Then, promoted by the basic pyridyl group or one of the S atoms of disulfide 1a via S + ⋯O coordination and the formation of the OH⋯N or OH⋯S hydrogen bond 22 (complex 16a and 16a′ of Fig. 1), 10a may react with water to give complex 17a or 17a′ .…”