Structure and C-S bond cleavage in aryl 1-methyl-1-arylethyl sulfide radical cations.
J Org Chem
; 76(2): 573-82, 2011 Jan 21.
Article
em En
| MEDLINE
| ID: mdl-21162540
ABSTRACT
Steady state and laser flash photolysis (LFP) of a series of p-X-cumyl phenyl sulfides (4-X-C(6)H(4)C(CH(3))(2)SC(6)H(5) 1, X = Br; 2, X = H; 3, X = CH(3); 4, X = OCH(3)) and p-X-cumyl p-methoxyphenyl sulfides (4-X-C(6)H(4)C(CH(3))(2)SC(6)H(4)OCH(3) 5, X = H; 6, X = CH(3); 7, X = OCH(3)) has been carried out in the presence of N-methoxy phenanthridinium hexafluorophosphate (MeOP(+)PF(6)(-)) under nitrogen in MeCN. Steady state photolysis showed the formation of products deriving from the C-S bond cleavage in the radical cations 1(+â¢)-7(+â¢) (2-aryl-2-propanols and diaryl disulfides). Formation of 1(+â¢)-7(+â¢) was also demonstrated by LFP experiments evidencing the absorption bands of the radical cations 1(+â¢)-3(+â¢) (λ(max) = 530 nm) and 5(+â¢)-7(+â¢) (λ(max) = 570 nm) mainly localized in the arylsulfenyl group and radical cation 4(+â¢) (λ(max) = 410, 700 nm) probably mainly localized in the cumyl ring. The radical cations decayed by first-order kinetics with a process attributable to the C-S bond cleavage. On the basis of DFT calculations it has been suggested that the conformations most suitable for C-S bond cleavage in 1(+â¢)-4(+â¢) and 7(+â¢) are characterized by having the C-S bond almost collinear with the π system of the cumyl ring and by a significant charge and spin delocalization from the ArS ring to the cumyl ring. Such a delocalization is probably at the origin of the observation that the rates of C-S bond cleavage result in very little sensitivity to changes in the C-S bond dissociation free energy (BDFE). A quite large reorganization energy value (λ = 43.7 kcal mol(-1)) has been calculated for the C-S bond scission reaction in the radical cation. This value is much larger than that (λ = 12 kcal mol(-1)) found for the C-C bond cleavage in bicumyl radical cations, a reaction that also leads to cumyl carbocations.
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Base de dados:
MEDLINE
Assunto principal:
Compostos de Sulfidrila
/
Sulfetos
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Cátions
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Radicais Livres
Idioma:
En
Ano de publicação:
2011
Tipo de documento:
Article