17114-78-2Relevant academic research and scientific papers
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.
Development of a Robust Protocol for the Determination of Weak Acids' p KaValues in DMSO
Jung, Sebastian T.,Podlech, Joachim
, p. 10951 - 10957 (2020/09/23)
Two methods for the determination of pKa values of weak acids are described, a direct titration with dimsyl potassium in the presence of an indicator and a back-titration in which an analyte/indicator mixture is deprotonated and then titrated with ammonium chloride. Both methods have been validated by measuring pKa values of compounds, for which values had been determined previously. The back-titration method was applied to measure pKa values of two 1,3-dithiane-derived bissulfoxides and a monosulfone.
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.
Experimental Evidence for p Ka-Driven Asynchronicity in C-H Activation by a Terminal Co(III)-Oxo Complex
Goetz, McKenna K.,Anderson, John S.
, p. 4051 - 4062 (2019/03/07)
C-H activation by transition metal oxo complexes is a fundamental reaction in oxidative chemistry carried out by both biological and synthetic systems. This centrality has motivated efforts to understand the patterns and mechanisms of such reactivity. We have therefore thoroughly examined the C-H activation reactivity of the recently synthesized and characterized late transition metal oxo complex PhB (tBuIm)3CoIIIO. Precise values for the pKa and BDFEO-H of the conjugates of this complex have been experimentally determined and provide insight into the observed reactivity. The activation parameters for the reaction between this complex and 9,10-dihydroanthracene have also been measured and compared to previous literature examples. Evaluation of the rates of reaction of PhB(tBuIm)3CoIIIO with a variety of hydrogen atom donors demonstrates that the reactivity of this complex is dependent on the pKa of the substrate of interest rather than the BDEC-H. This observation runs counter to the commonly cited reactivity paradigm for many other transition metal oxo complexes. Experimental and computational analysis of C-H activation reactions by PhB(tBuIm)3CoIIIO reveals that the transition state for these processes contains significant proton transfer character. Nevertheless, additional experiments strongly suggest that the reaction does not occur via a stepwise process, leading to the conclusion that C-H activation by this CoIII-oxo complex proceeds by a pKa-driven "asynchronous" concerted mechanism. This result supports a new pattern of reactivity that may be applicable to other systems and could result in alternative selectivity for C-H activation reactions mediated by transition metal oxo complexes.
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
supporting information, 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.
Nickel-catalyzed cross-coupling of aryl bromides with tertiary grignard reagents utilizing donor-functionalized N-heterocyclic carbenes (NHCs)
Lohre, Claudia,Droege, Thomas,Wang, Congyang,Glorius, Frank
supporting information; experimental part, p. 6052 - 6055 (2011/06/25)
Metal-catalyzed cross-coupling reactions are among the most important transformations in organic synthesis, allowing the efficient construction of complex structures from simpler, readily available building blocks.Many applications in large and small-scale synthesis can be found in different areas such as agrochemicals, pharmaceuticals and supramolecular chemistry. Whereas the coupling of sp2-hybridized carbon atoms in either reaction partner is well established, the use of CACHTUNGTRENUNG(sp3)-hybridized substrates presents some challenges. Catalytic cross-coupling of sterically hindered tertiary alkyl substrates is especially difficult, generally resulting in low yields, and thus, only few reports exist.[27] A big challenge in this field is not only to get the required level of reactivity, but also to overcome competing pathways like β-hydride elimination, hydrodehalogenation or isomerization
4,5-disubstituted N,N′-Di-tert-alkyl imidazolium salts: New synthesis and structural features
Grishina, Anastasia A.,Polyakova, Svetlana M.,Kunetskiy, Roman A.,Cisarova, Ivana,Lyapkalo, Ilya M.
supporting information; experimental part, p. 96 - 100 (2011/03/21)
It's getting crowded! The synthesis of a new subfamily of imidazolium cations with exceptionally spatially demanding substitution patterns (see scheme) paved the way to reconcile two antagonising effects: steric hindrance and innately high donating ability/basicity in the peralkylated imidazol-2-ylidene ligands/uncharged bases.
Equilibrium acidities of some sulfones and sulfoxides in tetrahydrofuran
Streitwieser, Andrew,Wang, George Peng,Bors, Daniel A.
, p. 10103 - 10112 (2007/10/03)
Ion pair acidities are reported in tetrahydrofuran (THF) solution for the lithium and cesium salts of several sulfones and one sulfoxide. These salts are shown to be monomeric in the THF solutions studied. Thermodynamic constants are reported for several salts. The results and some conductivity studies show that both the lithium and cesium salts are contact ion pairs in THF. Because of ion association the relative pKs are slightly lower for cesium salts and much lower for lithium salts than for the free ions in DMSO solution.
Unverbrueckte fluorenylkomplexe des typs (C5H5)(9-R-C13H8)ZrCl2 (R = Me3Si, Alkyl, Aryl): Synthese, charakterisierung und anwendung als katalysatoren bei der homogenen olefinpolymerisation
Schmid, Michael A.,Alt, Helmut G.,Milius, Wolfgang
, p. 15 - 22 (2007/10/03)
The reaction of various 9-substituted fluorene compounds (9-R-C13H9) (R = Me3Si, alkyl, aryl) (1a-i) with butyllithium followed by treatment with (C5H5)ZrCl3 leads to unbridged fluorenyl complexes of the type (C5H5)(9-R-C13H8)ZrCl2 (2a-i). In combination with methylaluminoxane, complexes 2a-i show a high catalytic activity as homogeneous ethylene polymerization catalysts. Compounds 2c (R = iPr), 2d (R = cyclohexyl), and 2e (R = tBu) were characterized by X-ray structure analyses.
Carbanions 27. Rearrangements of (9-alkyl-9-fluorenyl)-methyllithium (or cesium) and 2,2-diphenyl-3,3-dimethyl-butyllithium
Grovenstein Jr., Erling,Singh, Jagvir,Patil, Bhalchandra B.,VanDerveer, Don
, p. 5971 - 5998 (2007/10/02)
A study has been made upon the products from warming various (9-alkyl-9-fluorenyl)methyllithium (or cesium) compounds in THF to near 0°C followed by carbonation. When the 9-alkyl group is ethyl, the result is chiefly the protonated product (9-alkyl-9- fluorenyl)methane; a similar product evidently is formed when the 9-alkyl group is 1-norbornyl. When the 9-alkyl group is tert-butyl, the minor product is 9-neopentylfluorene-9-carboxylic acid from a [1,2]-migration of the tert-butyl group while the major product is 9-methylfluorene-9-carboxylic acid from an intramolecular elimination as shown by deuterium labeling. When the 9-alkyl is neopentyl, the major product is 9-neopentyl-9,10-dihydro-phenanthrene-9-carboxylic acid along with some 9-neopentylphenanthrene which becomes the major product in diethyl ether solution at 35°C. 2,2-Diphenyl-3,3-dimethylbutyllithium undergoes predominantly [1,2]-phenyl migration in THF at 0°C. From an x-ray crystal study upon 9-tert-butyl-9-(chloromethyl)fluorene and 9-neopentyl-9-(chloromethyl) fluorene, it is concluded that steric acceleration is responsible for the unusual reactions of (9-alkyl-9-fluorenyl)methyllithiums when the 9-alkyl groups are tert-butyl and neopentyl.
