The Mechanism of Addition of Phenols to Tetramesityldisilene. Evidence for Both Nucleophilic and Electrophilic Rate-Determining Steps

Importance of frontier orbital interactions in addition reaction of water to disilene

“…The large k H / k D value of 5.27 for the addition of p ‐CF 3 –C 6 H 4 –OH(D) to tetramesityldisilene was observed by Apeloig and Nakash 2b. The results suggest the existence of the third pathway involving a similar transition state to TS L at the rate‐determining step (C E –TS L –P F ) 2a. We obtained a similar pathway in the addition of hydrogen fluoride to disilene.…”

“…We have found the search for transition states by ab initio MO calculations combined with the FMO theory provides a good perspective view of the reaction mechanisms of disilenes with water. The results are applicable to explain the stereoselective ambiguity of the alcohol addition to disilenes found experimentally 2.…”

“…Sekiguchi et al 11 found, however, that transient disilenes ( E )‐ and ( Z )‐PhMeSiSiMePh reacted with alcohols in a syn fashion with high diastereoselectivity at the low concentration of alcohols, but the anti ‐products were found at the high concentration of alcohols; the stereoselectivity was modified also by the kinds of alcohols. Apeloig and Nakash 2a showed that the addition of p ‐methoxyphenol to ( E )‐1,2‐di‐ tert ‐butyl‐1,2‐dimesityldisilene was syn ‐selective in benzene but anti ‐selective in a polar tetrahydrofuran 2a; the selectivity was independent of the concentration of the alcohol. A number of explanations have been proposed for the stereochemical ambiguity.…”

“…(1) Sekiguchi et al 11 proposed that at the low concentration of alcohol, the intramolecular syn ‐addition of hydrogen from the Lewis adduct is favored, while at the high concentration of the alcohol, the anti ‐addition of a proton of the extra alcohol competes to the intramolecular syn ‐addition. (2) Apeloig and Nakash 2a suggested that rotation around the SiSi bond in the intermediate Lewis adduct may explain the formation of the anti ‐adduct. Our theoretical results suggest that the stereochemical ambiguity found experimentally is explained by the competition of the antarafacial and suprafacial pathways, which lead to the anti ‐ and the syn ‐adducts, respectively, at least in the concentration‐independent cases.…”

Cycloaddition Reactions of Aldehydes to Tetramesityldisilene and Tetramesitylgermasilene: Evidence for a Biradical Intermediate

“…1 However, despite the obvious synthetic potential of these compounds, relatively few mechanistic investigations of the reactions of dimetallenes have been carried out. There have been a few reports concerning the mechanism of the addition of alcohols, [2][3][4][5][6] and alkynes 2,7 to disilenes, and recently, we reported our preliminary results on the mechanism of alkene additions to tetramesitylgermasilene and tetramesityldisilene. 8 In contrast, the mechanism for the addition of carbonyl compounds such as aldehydes and ketones to dimetallenes has not been examined, despite being one of the most extensively investigated synthetic reactions of dimetallenes.…”