17114-78-2Relevant articles and documents
Proton-Transfer Reactions between 9-Alkylfluorene and (9-Alkylfluorenyl)lithium in Ether
Murdoch, J. R.,Bryson, J.A.,McMillen, D.F.,Brauman, J.I.
, p. 600 - 610 (1982)
The rates of proton-transfer reactions between 9-substituted fluorenes and 9-substituted fluorenyllithium have been examined in ether at 25 and 71 deg C.A high primary isotope effect (kH/kD = 9.5) and substantial secondary kinetic (1.11 +/- 0.04) and equilibrium (1.19 +/- 0.04) isotope effects are observed for fluorene.Surprisingly, intermolecular steric effects seem to play only a minor role in spite of the fact that the alkyl groups are located directly at the carbon involved in the proton transfer.The barriers for the endergonic cross reactions (i.e., those involving different alkyl groups in the anion and hydrocarbon) are half of the sum of the barriers for the two corresponding identity reactions (i.e., those involving the same alkyl groups in the anion and hydrocarbon).This leads to Broensted slopes which vary from 0.7 for reactions of fluorenyl anion to 1.8 for reactions of 9-(tert-butyl)fluorenyl anion.The rates of the identity and cross reactions give approximate linear correlations with each other and with ΔpK and are dominated by an effect which correlates with ?*.The substituent effect correlated by ?* is inconsistent with a classical field or repulsive steric effect and may originate from solvatation effects.The thermodynamic and kinetic relationships between the identity and cross reactions show that the transition states for the cross reac tions are only responding to half of the substituent effect on the identity reactions and that the substituent effect on the equilibria appears absent from the cross-reaction transition states.The results can be consistent with Marcus' theory only if the substituent effect on the equilibria appears in steps separate from proton transfer.The results suggest that changes in solvation and proton transfer occur as discrete kinetic steps.
The p: K a values of N-aryl imidazolinium salts, their higher homologues, and formamidinium salts in dimethyl sulfoxide
Cole, Marcus L.,Dunn, Michelle H.,Harper, Jason B.,Konstandaras, Nicholas,Luis, Ena T.
supporting information, p. 1910 - 1917 (2020/03/23)
A series of imidazolinium salts, their six-, seven- A nd eight-membered homologues, and the related formamidinium salts were prepared, and their pKa values were determined in DMSO at 25 °C using the bracketing indicator method. The effect of each type of structural variation on the acidity of each salt was considered, particularly noting the importance of ring size and the effect of the steric and electronic nature of the N-aryl substituents. The effect of a cyclic structure was also probed through comparing the cyclic systems with the corresponding formamidinium salts, noting the importance of conformational flexibility in the latter cases. Along with allowing choice of appropriate bases for deprotonation of these species, it is anticipated that the data presented will aid in the understanding of the nucleophilicity, and potentially catalytic efficacy, of the corresponding carbenes.
A zwitterionic carbanion frustrated by boranes - Dihydrogen cleavage with weak lewis acids via an "inverse" frustrated lewis pair approach
Li, Hui,Aquino, Adelia J. A.,Cordes, David B.,Hung-Low, Fernando,Hase, William L.,Krempner, Clemens
, p. 16066 - 16069 (2013/11/19)
The synthesis, structural characterization, and acid-base chemistry of [C(SiMe2OCH2CH2OMe)3]Na (2), a sterically encumbered zwitterionic organosodium compound, is reported. 2 is a strong Bronsted base that forms frustrated Lewis pairs (FLPs) with a number of boron-containing Lewis acids ranging from weakly Lewis acidic aryl and alkyl boranes to various alkyl borates. These intermolecular FLPs readily cleave H2, which confirms that even poor Lewis acids can engage in FLP-mediated H2 cleavage provided that the present bulky base is of sufficiently high Bronsted basicity.
