6485-83-2Relevant articles and documents
Organocalcium Complex-Catalyzed Selective Redistribution of ArSiH3or Ar(alkyl)SiH2to Ar3SiH or Ar2(alkyl)SiH
Li, Tao,McCabe, Karl N.,Maron, Laurent,Leng, Xuebing,Chen, Yaofeng
, p. 6348 - 6356 (2021/05/29)
Calcium is an abundant, biocompatible, and environmentally friendly element. The use of organocalcium complexes as catalysts in organic synthesis has had some breakthroughs recently, but the reported reaction types remain limited. On the other hand, hydrosilanes are highly important reagents in organic and polymer syntheses, and redistribution of hydrosilanes through C-Si and Si-H bond cleavage and reformation provides a straightforward strategy to diversify the scope of such compounds. Herein, we report the synthesis and structural characterization of two calcium alkyl complexes supported by β-diketiminato-based tetradentate ligands. These two calcium alkyl complexes react with PhSiH3 to generate calcium hydrido complexes, and the stability of the hydrido complexes depends on the supporting ligands. One calcium alkyl complex efficiently catalyzes the selective redistribution of ArSiH3 or Ar(alkyl)SiH2 to Ar3SiH and SiH4 or Ar2(alkyl)SiH and alkylSiH3, respectively. More significantly, this calcium alkyl complex also catalyzes the cross-coupling between the electron-withdrawing substituted Ar(R)SiH2 and the electron-donating substituted Ar′(R)SiH2, producing ArAr′(alkyl)SiH in good yields. The synthesized ArAr′(alkyl)SiH can be readily transferred to other organosilicon compounds such as ArAr′(alkyl)SiX (where X = OH, OEt, NEt2, and CH2SiMe3). DFT investigations are carried out to shed light on the mechanistic aspects of the redistribution of Ph(Me)SiH2 to Ph2(Me)SiH and reveal the low activation barriers (17-19 kcal/mol) in the catalytic reaction.
Linear free-energy relationship and rate study on a silylation-based kinetic resolution: Mechanistic insights
Akhani, Ravish K.,Moore, Maggie I.,Pribyl, Julia G.,Wiskur, Sheryl L.
, p. 2384 - 2396 (2014/04/17)
The substituent effect of different p-substituted triphenylsilyl chlorides on silylation-based kinetic resolutions was explored. Electron-donating groups slow down the reaction rate and improve the selectivity, while electron-withdrawing groups increase the reaction rate and decrease the selectivity. Linear free-energy relationships were found correlating both selectivity factors and initial rates to the σpara Hammett parameters. A weak correlation of selectivity factors to Charton values was also observed when just alkyl substituents were employed but was nonexistent when substituents with more electronic effects were incorporated. The rate data suggest that a significant redistribution of charge occurs in the transition state, with an overall decrease in positive charge. The linear free-energy relationship derived from selectivity factors is best understood by the Hammond postulate. Early and late transition states describe the amount of substrate participation in the transition state and therefore the difference in energy between the diastereomeric transition states of the two enantiomers. This work highlights our efforts toward understanding the mechanism and origin of selectivity in our silylation-based kinetic resolution.
Highly stereoselective synthesis of bicyclo[n.3.0]alkanes by titanium tetrachloride promoted [3 + 2] cycloaddition of allylsilanes and 1-acetylcycloalkenes
Knoelker, Hans-Joachim,Foitzik, Norbert,Goesmann, Helmut,Graf, Regina,Jones, Peter G.,Wanzl, Guenter
, p. 538 - 551 (2007/10/03)
The titanium tetrachloride promoted reaction of allylsilanes 1 with 1-acetylcyclohexene is shown to afford the silylbicyclo[4.3.0]nonanes 9 ([3 + 2] cycloaddition products) along with the 1-acetyl-2-allylcyclohexane 4 (Hosomi-Sakurai product). Here we report that systematic variation of the substituents at the silicon atom of 1 allows suppression of the classical Hosomi Sakurai reaction in favor of the [3+2] cycloaddition. Cycloaddition of the allylsilanes 1d, 1i, and 1k with 1-acetylcycloalkenes 10, containing a 5-, 6-, 7-, 8-, or 12-membered ring, gives rise to the corresponding silylbicyclo[n.3.0]alkanes 11-13. The cycloaddition of allyltriisopropylsilane (1k) and 1-acetyl-2-methylcycloalkenes 15 provides silylbicyclo[n.3.0]alkanes 16 with two contiguous quaternary carbon centers. The stereochemistry of the silylbicyclo[n.3.0]alkanes 11a-c and 14 is unambiguously determined by X-ray analysis and 13C NMR spectroscopy.
