157197-53-0Relevant articles and documents
Basicity of a stable carbene, 1,3-di-tert-butylimidazol-2-ylidene, in THF
Kim, Yeong-Joon,Streitwieser, Andrew
, p. 5757 - 5761 (2002)
The basicity of 1,3-di-tert-butylimidazol-2-ylidene (1) was measured in THF against three hydrocarbon indicators. Both ion pairs and free ions were found and the corresponding equilibrium constants were measured. Homoconjugation was not found in either THF or DMSO. The carbene is effectively more basic in DMSO by several pK units, probably because of hydrogen bonding of 1-H+ to DMSO. Model ab initio computations are consistent with these results.
N-Heterocyclic carbene-organocatalyzed ring-opening polymerization of ethylene oxide in the presence of alcohols or trimethylsilyl nucleophiles as chain moderators for the synthesis of α,ω-heterodifunctionalized poly(ethylene oxide)s
Raynaud, Jean,Absalon, Christelle,Gnanou, Yves,Taton, Daniel
, p. 2814 - 2823 (2010)
The present study describes innovations in the ring-opening polymerization (ROP) of ethylene oxide (EO) using N-heterocyclic carbenes (NHCs) as organocatalysts, which enables the synthesis of α,ω- heterodifunctionalized poly(ethylene oxide)s (PEOs). Two representative NHC catalysts, namely, 1,3-bis(diisopropyl)imidazol-2-ylidene (1) and 1,3-bis(di-tert-butyl)imidazol-2-ylidene (2), were efficiently employed in conjunction with a variety of chain regulators of general structure NuE, where Nu and E are the nucleophilic and the electrophilic part, respectively, with E = H or SiMe3 (e.g., PhCH2OH, HCCCH2OH, N 3SiMe3, and PhCH2OSiMe3). Catalytic amounts of the NHC (typically [NHC]/[NuE]/[EO] = 0.1/1/100 in moles) were indeed utilized to trigger the metal-free ROP of EO at 50°C in dimethyl sulfoxide, allowing the polymerization to proceed to completion. In this way, PEOs of dispersities lower than 1.2 and molar masses perfectly matching the [EO]/[NuE] ratio were obtained, attesting to the controlled/living character of these NHC-catalyzed polymerizations. Characterization of α,ω- difunctionalized PEOs by combined techniques such as 1H NMR spectroscopy, MALDI-TOF mass spectrometry, and size exclusion chromatography confirmed the quantitative introduction of the nucleophilic moiety (Nu) and its electrophilic component (E = H or SiMe3) in the α- and ω-position of the PEO chains, respectively, and the formation of polymers with narrowly distributed molar masses. These results are discussed in the light of the existence of two possible mechanisms. The first one involves a direct attack of the NHC catalyst onto EO and the formation of a zwitterionic intermediate (activated monomer mechanism). The second possibility is the activation by the NHC of the E moiety of the NuE chain regulator first and then of the α-Nu,ω-OE PEO chain (activated chain end mechanism).
Progressing the Frustrated Lewis Pair Abilities of N-Heterocyclic Carbene/GaR3Combinations for Catalytic Hydroboration of Aldehydes and Ketones
Bole, Leonie J.,Uzelac, Marina,Hernán-Gómez, Alberto,Kennedy, Alan R.,O'Hara, Charles T.,Hevia, Eva
supporting information, p. 13784 - 13796 (2021/07/26)
Exploiting the steric incompatibility of the tris(alkyl)gallium GaR3 (R = CH2SiMe3) and the bulky N-heterocyclic carbene (NHC) 1,3-bis(tert-butyl)imidazol-2-ylidene (ItBu), here we report the B-H bond activation of pinacolborane (HBPin), which has led to
Syntheses, Structures, and Reactivity of NHC Copper(I) Boryl Complexes: A Systematic Study
Kleeberg, Christian,Borner, Corinna
, p. 4136 - 4146 (2018/11/23)
Five novel NHC copper(I) boryl complexes were synthesized by B-B activation via σ-bond metathesis of symmetrical tetraalkoxy and unsymmetrical dialkoxy diamino diborane(4) derivatives. Despite their low stability, the NHC copper boryl complexes were thoroughly characterized spectroscopically and structurally. Variation of the NHC ligand (ItBu or Me2IiPr) as well as of the boryl ligand (Bpin, Bdmab, or BiPrEn) allowed, for the first time systematically, a study in such complexes of the dependence on steric encumbrance. For sterically more demanding ligand combinations, mononuclear linear complexes were obtained, while with less demanding ligand combinations, dimeric dinuclear complexes with two bridging μ-boryl ligands were obtained, exhibiting extremely short Cu···Cu distances (?). The decomposition of all these complexes was found to proceed via a common pathway, leading ultimately to elemental copper, the free NHC ligand, and the respective symmetrical diborane(4) derivative. The rate of decomposition depended strongly on the steric encumbrance of the individual complex. Two apparently low-valent copper clusters were observed and suggested to be relevant species with respect to the reductive decomposition of the copper(I) boryl complexes.
METHOD FOR PREPARING CARBENE IN SOLUTION, NOVEL STABLE FORM OF CARBENE OBTAINED IN PARTICULAR BY MEANS OF SAID METHOD, AND USES THEREOF IN CATALYSIS
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Paragraph 0196; 0202-0205, (2017/01/02)
The invention relates to a method for preparing carbene by means of deprotonation of a precursor salt using a strong base. A purpose of the invention is to enhance the synthesis of carbenes, i.e. to simplify same, to make said synthesis more economical an