- Synthesis of tridentate 2,6-bis(imino)pyridyl ruthenium(II) complexes with n-heterocyclic carbene ligands: Activation of imidazolium salts
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Low-valent Ru(0) complexes, [η2-N3]Ru(η6-Ar) (1) or {[N3]Ru}2(μ-N2) (2), where Ar = C6H6 or C6H5Me, and [N3] = 2,6-(2,4,6-(CH3/s
- Yoo, Hyojong,Berry, Donald H.
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- Ring expansion of heterocyclic ketene N,X-acetals and 2-alkylidenedihydroindoles with methanesulphonyl azide by [3 + 2] cycloaddition and subsequent extrusion of molecular nitrogen
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Methanesulphonyl azide (2) reacts readily with isolated cyclic ketene N,X-acetals of type 1, viz. 10a, d, 15b, d, and 22a-c, or those that are generated in situ by deprotonation of the corresponding 2-alkylbenzazolium tetrafluoroborates, i.e. 14a → 15a, 14b → 15b, and 18 → 19. Ring-expanded products are formed by extrusion of molecular nitrogen from intermediate labile [3 + 2] cycloadducts 3 with concomitant 1,2-shift of N (route A1 → 12, 24) or X (route A2 → 16, 20, 21). In addition, 3 may undergo [3 + 2] cycloreversion into N-sulphonylimine 5 and diazoalkane 6 (route B → 13, 17, 25). The configurations of the cyclic N-sulphonylamidines 16b and 21b, the N-sulphonylimine 24 and the N-sulphonylamine 27 are elucidated by means of X-ray diffraction analyses. The ratio of the (useful) ring-expansion reactions vs. the unwanted formation of 5 + 6 is hardly influenced by the solvent employed and temperature of the experiment but strongly by the nature of the potential migrating atom and the substituents at the α-carbon atom. VCH Verlagsgesellschaft mbH, 1996.
- Quast, Helmut,Ivanova, Svetlana,Peters, Eva-Maria,Peters, Karl,Von Schnering, Hans Georg
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- Br?nsted Basicities and Nucleophilicities of N-Heterocyclic Olefins in Solution: N-Heterocyclic Carbene versus N-Heterocyclic Olefin. Which Is More Basic, and Which Is More Nucleophilic?
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A Br?nsted basicity scale comprising nine representative N-heterocyclic olefins (NHOs) was established by measuring the equilibrium acidities of their corresponding precursors in DMSO using an ultraviolet-visible spectroscopic method. The basicities (pKaHs) of the investigated NHOs cover a range from 14.7 to 24.1. The basicities of unsaturated NHOs are stronger than those of their N-heterocyclic carbene (NHC) analogues; however, the basicities for the saturated ones are much weaker than those of their NHC analogues, which is largely due to the aromatization effect that intrinsically influences the acidic dissociations of NHC and NHO precursors. The nucleophilicities of four NHOs were measured photometrically by monitoring the kinetics of reactions of these NHOs with common reference electrophiles for quantifying nucleophilic reactivities. In general, the nucleophilicity of the NHOs is much stronger than that of commonly used Lewis bases such as Ph3P or DMAP [4-(dimethylamino)pyridine] but weaker than that of their NHC analogues; however, caution should be taken when generalizing this conclusion to a wide range of electrophiles with distinctively electronic and structural properties.
- Li, Zhen,Ji, Pengju,Cheng, Jin-Pei
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p. 2974 - 2985
(2021/02/06)
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- Expanding the Ligand Framework Diversity of Carbodicarbenes and Direct Detection of Boron Activation in the Methylation of Amines with CO2
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A simple and convergent synthetic strategy used to increase the diversity of the carbodicarbene ligand framework through incorporation of unsymmetrical pendant groups is reported. Structural analysis and spectroscopic studies of ligands and their Rh complexes are reported. Reactivity studies reveal carbodicarbenes as competent organocatalysts for amine methylation using CO2 as a synthon. A unique B-H-activated boron-carbodicarbene complex was isolated as a reaction intermediate, providing mechanistic insight into the CO2 functionalization process.
- Chen, Wen-Ching,Shen, Jiun-Shian,Jurca, Titel,Peng, Chun-Jung,Lin, Yen-Hsu,Wang, Yi-Ping,Shih, Wei-Chih,Yap, Glenn P. A.,Ong, Tiow-Gan
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p. 15207 - 15212
(2016/01/25)
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- Synthesis, NMR Spectra, and Photoelectron Spectra of Cyclic Ketene N,X-Acetals (2-Alkylidene-N-heterocycles)
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Deprotonation by sodium hydride of the N-methyl-2-alkylazolium salts 10c, 14-16, and 18 and of the perimidinium salt 20 as well affords the corresponding ketene N,X-acetals 1c, 3-5, 7 and 8 as air-sensitive distillable oils or low-melting crystals.The α-c
- Quast, Helmut,Ach, Manfred,Kindermann, Markus K.,Rademacher, Paul,Schindler, Michael
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p. 503 - 516
(2007/10/02)
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- An Improved Method for the Synthesis of 1,3-Dimethyl- and 1,3-Diethyl-2-methylenebenzimidazoline
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1,3-Dialkyl-2-methylbenzmidazolium tetrafluoroborates (2a, b) have been directly synthesized in 70-90percent yield by alkylation of 2-methylbenzimidazole (1) with trialkyloxonium tetrafluoroborate in 1,2-dichloroethane in the presence of N,N-dicyclohexylethylamine.Deprotonation of 2 with sodium hydride in benzene in the presence of N,N,N',N'-tetramethylguanidine gives the corresponding methylene bases 3a, b with 70-80percent yield.
- Reichardt, Christian,Kaufmann, Norbert
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p. 3424 - 3427
(2007/10/02)
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