Structure, Conformation, and Thermochemistry of Dimesityl Methanethial S‐oxide (Dimesityl Sulfine)

Abstract

The structure of dimesityl sulfine in solution and in the solid the syn mesityl ring perpendicular to the C=S=O plane. From state was determined by NMR spectroscopy and X-ray cry-the coalescence temperature T, at 303 K, the free energy of stallography, respectively. In the crystal the two mesityl activation for the rotation of the mesityl rings was estimated groups are twisted by approximately 60°, while in solution to be 14 k 0.7 kcal/mol. At higher temperatures (140-185°C) an averaged conformation with C, symmetry is observed, dimesityl sulfine yields up to 95% 5,7-dimethyl-l-mesitylwith the anti mesityl ring located in the C=S=O plane and benzo [c] The therrnal[l61 and photo~hemical['~1['~] decomposition of diphenyl sulfine (la) was investigated by Carlsen and Holm. The primary step in these reactions is the ring closure to diphenyl oxathiirane (2a, Scheme I), which at low temperature could be characterized by UV spectroscopy (h,,, = 390 nm).Li5] Oxathiirane 2a was stable in organic glasses, however, melting of the glass leads to quantitative formation of benzophenone (5a). As a result of the thermal lability of 2a, the photolysis of sulfine l a at room temperature, or thermal decomposition at higher temperatures, yields 5a as the sole product, whereas low temperature photolysis of l a produced, in addition, the two isomeric esters ["] A later theoretical (ab initio CASSCF) study on the H2C=S=0 system suggested that this carbonyl sulfide is a secondary product, formed only in the rigid environment of the organic glass by recombination of a ketone (or aldehyde) and sulfur atoms in their S('D) state. Generally, loss of the sulfur atom and formation of a carbonyl compound is the major route for the sulfine decomposition. The fate of the sulfur atom and the capability of the intermediates of type 2a, 6a, or 7a to transfer sulfur atoms has not yet been systematically investigated. Here we report on the structure, conformation, and thermal rearrangement of the sterically congested dimesityl sulfine lb. Structure of Dimesityl Sulfine (lb) in the Solid State and in SolutionThe sulfine l b was synthesized by oxidation of dimesityl thio~arbonyl[~~I[~~1 with mCPBA and crystallized from pentane. The crystal structure of l b (Figure 1) shows the expected twisting (defined as angle between the planes defined by the C=S=O and the mesityl groups) of both mesityl rings by approximately 60" (58' for ring A and 55" for ring B), similar to dime~itylmethane ['~I and its derivatives. [i91[201 In diphenyl sulfine (la) the syn phenyl ring is twisted by only 25" from the S-C1 -C21 plane, while the anti phenyl ring is twisted by 50".[141 Thus, l a is stabilized by an ap-

Catalytic Transfer of Magnetism Using a Neutral Iridium Phenoxide Complex

“…Lineshape analysis38, 39 of this behavior enabled the activation enthalpy for mesityl group rotation, ΔH ≠ , to be estimated as 65.5 ± 3.1 kJ mol −1 with the corresponding value for ΔS ≠ being +28.0 ± 10.9 J K −1 mol −1 . These ΔH ≠ and ΔS ≠ values are commensurate with those expected for an intramolecular ring rotation40, 41 (see Supplementary Information (SI) for the raw data). We note that similar coalescence effects are also observed when 1 is present in a THF- d 8 solution in accordance with a process where there is little charge separation 40…”

“…These ΔH ≠ and ΔS ≠ values are commensurate with those expected for an intramolecular ring rotation40, 41 (see Supplementary Information (SI) for the raw data). We note that similar coalescence effects are also observed when 1 is present in a THF- d 8 solution in accordance with a process where there is little charge separation 40…”

“…We note that similar coalescence effects are also observed when 1 is present in a THF-d 8 solution in accordance with a process where there is little charge separation. 40 In a separate dynamic process, the two proton resonances of the CH 2 linker are also broadened, in this case into the baseline at 298 K. At 253 K these protons provide two distinct doublets at δ 6.60 and 4.79 that share a common coupling of 13.97 Hz. This behavior is a consequence of the fact that the two CH 2 protons are diastereotopic, due to their differing exo and endo orientations. They become equivalent by inversion of the conformation of the seven-membered ring through ring-flip and alkoxide lone pair inversion.…”

Conformational Studies by Dynamic NMR. 79.1 Dimesityl Sulfine Revisited: Detection of the Helical Antipodes and Determination of Their Enantiomerization Pathways

“…The structure of dimesityl sufine ( 1) (Mes 2 CSO, where Mes = 2,4,6-trimethylphenyl) has been recently obtained by X-ray diffraction . The molecule adopts in the crystal a propeller-like shape with the mesityl rings almost symmetrically twisted with respect to the plane of the bent (119°) CSO moiety, the dihedral angles being 57° and 55° for the rings in the E and Z relationship, respectively.…”

“…This model entails the existence of two possible conformers of different stability (stereolabile diastereoisomers) having the mesityl which is coplanar with the CSO moiety either in a syn or in an anti relationship with respect to the SO group. On steric ground and on the basis of lanthanide-induced shifts (LIS) experiments, the latter situation was considered to be that corresponding to the most stable of the two conformers, thus leading to the proposal that the E -ring was essentially coplanar with and the Z -ring essentially orthogonal to the CSO plane.…”