The Thermal Sulfenate−Sulfoxide Rearrangement:  A Radical Pair Mechanism

Amaudrut, Jérôme; Wiest, Olaf

doi:10.1021/ja9940928

Cited by 23 publications

(29 citation statements)

References 37 publications

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“…The value of Δ S ≠ obtained from an Eyring plot of k I data for 1 b 2 is positive, but small in magnitude. A somewhat larger value might be anticipated for a dissociation reaction that, owing to its endergonicity, has a relatively late transition state; for example, Δ S ≠ for the homolysis of tert ‐butyl peroxide varies from +27 to +64 J mol −1 K −1 , depending on the solvent,40 and a value of +27 J mol −1 K −1 is found for the dissociation of cinnamyl‐4‐nitrobenzenesulfenate to a radical pair in toluene 41. However, as noted in the Experimental Section, additional complications associated with the use of initial rate data may mean that this values of Δ S ≠ is artificially low.…”

Section: Resultsmentioning

confidence: 99%

n‐Doping of Organic Electronic Materials Using Air‐Stable Organometallics: A Mechanistic Study of Reduction by Dimeric Sandwich Compounds

Guo

Mohapatra

Romanov

et al. 2012

Chemistry A European J

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Several 19-electron sandwich compounds are known to exist as "2×18-electron" dimers. Recently it has been shown that, despite their air stability in the solid state, some of these dimers act as powerful reductants when co-deposited from either the gas phase or from solution and that this behavior can be useful in n-doping materials for organic electronics, including compounds with moderate electron affinities, such as 6,13-bis[tri(isopropyl)silylethynyl]pentacene (3). This paper addresses the mechanisms by which the dimers of 1,2,3,4,5-pentamethylrhodocene (1 b(2)), (pentamethylcyclopentadienyl)(1,3,5-trialkylbenzene)ruthenium (alkyl=Me, 2 a(2); alkyl=Et, 2 b(2)), and (pentamethylcyclopentadienyl)(benzene)iron (2 c(2)) react with 3 in solution. Vis/NIR and NMR spectroscopy, and X-ray crystallography indicate that the products of these solution reactions are 3(·-) salts of the monomeric sandwich cations. Vis/NIR kinetic studies for the Group 8 dimers are consistent with a mechanism whereby an endergonic electron transfer from the dimer to 3 is followed by rapid cleavage of the dimer cation. NMR crossover experiments with partially deuterated derivatives suggest that the C-C bond in the 1 b(2) dimer is much more readily broken than that in 2 a(2); consistent with this observation, Vis/NIR kinetic measurements suggest that the solution reduction of 3 by 1 b(2) can occur by both the mechanism established for the Group 8 species and by a mechanism in which an endergonic dissociation of the dimer is followed by rapid electron transfer from monomeric 1 b to 3.

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Section: Resultsmentioning

confidence: 99%

n‐Doping of Organic Electronic Materials Using Air‐Stable Organometallics: A Mechanistic Study of Reduction by Dimeric Sandwich Compounds

Guo

Mohapatra

Romanov

et al. 2012

Chemistry A European J

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“…Looking first at the MBE rearrangement from allyl sulfenate to sulfoxide [13] for the three model systems, we see moderate barriers (82-104 kJ mol…”

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confidence: 98%

Palladium‐Catalyzed Allylic Sulfinylation and the Mislow–Braverman–Evans Rearrangement

Kleimark

Prestat

Poli

et al. 2011

Chemistry A European J

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Sulfoxides play important roles in organic and medicinal chemistry, as chiral handles, [1] ligands, [2] or bioisosteres.[3]The most common method for sulfoxide preparation is controlled sulfide oxidation, [4] but a more convergent approach would be to make them by formation of the C À S bond. Poli, Madec and co-workers recently disclosed a method for direct sulfoxide formation involving a Pd-catalyzed allylation or arylation of an intermediate sulfenate anion. [5] This strategy is illustrated by the reaction between tertbutyl 3-p-tolylsulfinylpropionate and cinnamyl acetate, which gave the cinnamyl p-tolyl sulfoxide. In this reaction, the sulfenate anion and h 3 -allyl complex are generated in situ and react with each other to afford the final product. Herein, we disclose our theoretical results for the formation of the allyl sulfoxides (Scheme 1).A simplified mechanistic scheme for the formation of phenyl allyl sulfoxide is shown in Scheme 2. Sulfenate anion and h 3 -allyl Pd complexes are formed in situ and react by nucleophilic displacement. However, it is not a priori clear whether initial attack occurs from the formally anionic oxygen atom or the formally neutral sulfur atom. The observed product is the allyl sulfoxide, but this would be expected to be formed also from a rapid Mislow-BravermanEvans (MBE) rearrangement [6] even if the allyl sulfenate would be the initially formed product. Since the two mechanisms are closely linked, we initiated our investigation by a detailed computational study of the MBE rearrangement. Our standard workhorse for computational investigations of reaction mechanisms is DFT at the B3LYP level [7] with a polarized double-z basis set (6-31G*), augmented by vibrational corrections, ECP basis sets for heavy elements, [8] continuum solvation, [9] and dispersion corrections.[10] However, Jorgensen and co-workers showed that even though trends in the MBE rearrangement kinetics could be well reproduced by similar methods, the equilibrium was erroneously calculated to favor the sulfenate product, not the sulfoxide.[11] We could verify that the same problem exists also when applying our standard methods to methyl allyl sulfoxide. The correct preference for the sulfoxide could only be reproduced by using large basis sets. The results seemed reasonably well converged at the cc-PVDZ level, but due to a slight shift in energy when going to the cc-PVTZ basis [12] we selected the latter basis set for further studies. Geometries were well converged already at the 6-31G* level, as evidenced by small differences in energy between cc-PVTZ and cc-PVTZ//6-31G* calculations. Single-point cc-PVTZ calculations at 6-31G*-derived IRC points also revealed that the transition state of the rearrangement shifted by less than 0.1 with the larger basis set. Details of these investigations can be found in the Supporting Information. In conclusion, to ensure proper energetics in our studies of the Pd-catalyzed process, we performed geometry optimizations at the B3LYP level with the lacvp* basis set, [8] val...

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“…The biradical mechanism was predicted to be the lowest energy pathway. This mechanism was confirmed later in an experimental study of the thermolysis of the cinnamyl-4-nitrobenzenesulfenate [9]. Freeman et al [8] studied the [2,3]-sigmatropic rearrangement in hydrogen and alkyl 3-propenyl sulfoxides.…”

Section: Introductionmentioning

confidence: 78%

A theoretical study of the sulfenate–sulfoxide rearrangement. Effect of the hydrogen bond complexation

Zborowski

Alkorta

Elguero

2010

Int J of Quantum Chemistry

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A DFT study of the thermal and radical sulfenate-sulfoxide rearrangement of derivatives of 3-propenyl sulfoxide has been carried out. The effect of the substitution and hydrogen bond complexation has been analyzed. The results show that without external factors the radical breakdown path is the one preferred by the alkyl and aromatic derivatives while the unsubstituted system proceeds preferentially through a two-step series of [1,3]-and [2,3]-sigmatropic shifts. The inclusion of a hydrogen bond donor interacting with the oxygen atom increases the stability of all the species except the radical and the final products. Thus, in the dimethyl derivative the radical and two-step processes present similar limiting steps. The analysis of the electron density of the systems provides some relationships between the properties at the bond critical point and the interatomic distances for the SÁÁÁC and HÁÁÁO cases.

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The Thermal Sulfenate−Sulfoxide Rearrangement: A Radical Pair Mechanism

Cited by 23 publications

References 37 publications

n‐Doping of Organic Electronic Materials Using Air‐Stable Organometallics: A Mechanistic Study of Reduction by Dimeric Sandwich Compounds

n‐Doping of Organic Electronic Materials Using Air‐Stable Organometallics: A Mechanistic Study of Reduction by Dimeric Sandwich Compounds

Palladium‐Catalyzed Allylic Sulfinylation and the Mislow–Braverman–Evans Rearrangement

A theoretical study of the sulfenate–sulfoxide rearrangement. Effect of the hydrogen bond complexation

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