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.
Interaction of a bulky N-heterocyclic carbene ligand with Rh(I) and Ir(I). Double C-H activation and isolation of bare 14-electron Rh(III) and Ir(III) complexes
Scott, Natalie M.,Dorta, Reto,Stevens, Edwin D.,Correa, Andrea,Cavallo, Luigi,Nolan, Steven P.
, p. 3516 - 3526 (2005)
Reactivity and structural studies of unusual rhodium and iridium systems bearing two N-heterocyclic carbene (NHC) ligands are presented. These systems are capable of intramolecular C-H bond activation and lead to coordinatively unsaturated 16-electron complexes. The resulting complexes can be further unsaturated by simple halide abstraction, leading to 14-electron species bearing an all-carbon environment. Saturation of the vacant sites in the 16- and 14-electron complexes with carbon monoxide permits a structural comparison. DFT calculations show that these electrophilic metal centers are stabilized by π-donation of the NHC ligands.
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).
Photoelectron spectroscopy of a carbene/silylene/germylene series
Arduengo III, Anthony J.,Bock, Hans,Chen, Han,Denk, Michael,Dixon, David A.,Green, Jennifer C.,Hermann, Wolfgang A.,Jones, Nancy L.,Wagner, Matthias,West, Robert
, p. 6641 - 6649 (1994)
The photoelectron spectra [HeI and He II] are reported for a carbene, a silylene, and a germylene (1,3-di-tert-butylimidazol-2-ylidene, 1,3-di-tert-butyl-1,3,2-diazasilol-2-ylidene, and 1,3-di-tert-butyl-1,3,2-diazagermol-2-ylidene). The experimental photoelectron spectra are assigned on the basis of predictions from density functional theory (DFT) calculations and first-order time-dependent perturbation theory. The predicted spectra agree well with the experimental ones both in ionization energy and band intensity. The carbene 1,3-di-tert-butylimidazol-2-ylidene is found to have a highest occupied molecular orbital (HOMO) that is essentially the in-plane lone pair of electrons at the carbene center (C σ-1p). The second ionization from the carbene occurs from a π-molecular orbital (π-3) that is largely the C=C double bond in the imidazole ring with some contributions from the nitrogens and the carbene center. The HOMOs of the silylene and germylene are derived from the π-3, orbital which changes character to become more concentrated on the two-coordinate main group IV center (Si or Ge) and less involved with the C=C double bond. The Si σ-1p and Ge σ-1p orbitals are subjacent and responsible for the second ionization bands. The molecular orbital structure and total electron distribution predicted from the DFT calculations are used to illustrate the differences in structure and chemistry in the carbene, silylene, and germylene compounds. The X-ray structure of 1,3-di-tert-butylimidazol-2-ylidene is also reported.
Steric Properties of N-Heterocyclic Carbenes affect the Performance of Electronic Probes
Barnett, Christopher,Cole, Marcus L.,Harper, Jason B.
supporting information, p. 4954 - 4958 (2021/12/02)
Electronic probes of ligands, particularly carbenes, are widely used in assessing electronic properties; the results inform the selection of a ligand for a given application. As such, it is important to ensure the data obtained is reliable and unaffected by other factors, such as the steric bulk of the ligand. The effects of such steric factors on two commonly used electronic probes (based on palladium and selenium) are investigated here, with the selenium adduct found to be particularly sensitive. It is hoped that this serves as a cautionary tale to always critically evaluate what a probe is measuring.
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.
Synthesis of Stable Pentacoordinate Silicon(IV)-NHC Adducts: An Entry to Anionic N-Heterocyclic Carbene Ligands
Medici, Fabrizio,Gontard, Geoffrey,Derat, Etienne,Lemière, Gilles,Fensterbank, Louis
supporting information, p. 517 - 520 (2018/03/08)
This work features the previously undescribed interactions of Martin's spirosilane with different types of N-heterocyclic carbenes (NHCs). The level of interaction proved to be strongly dependent on the size of the Lewis base and could vary from the formation of isolable classical Lewis adducts to abnormal Lewis adducts, as evidenced by X-ray diffraction structure analyses and NMR studies. It has been found that abnormal adducts could be used as precursors for the synthesis of anionic NHCs bearing a weakly coordinating siliconate component. Complexation of these new types of carbenes with gold(I) and copper(I) has been efficiently accomplished. DFT calculations performed on the siliconate-based anionic NHC ligands revealed a high-lying HOMO and therefore a strong σ-donor character.
METHOD FOR PREPARING CARBENE IN SOLUTION, NOVEL STABLE FORM OF CARBENE OBTAINED IN PARTICULAR BY MEANS OF SAID METHOD, AND USES THEREOF IN CATALYSIS
-
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
Construction of tetrasubstituted carbon by an organocatalyst: Cyanation reaction of ketones and ketimines catalyzed by a nucleophilic N-heterocyclic carbene
Fukuda, Yoshimasa,Kondo, Kazuhiro,Aoyama, Toyohiko
, p. 2649 - 2652 (2008/02/04)
A method for cyanation reaction of ketones and ketimines having lower reactivity than aldehydes and aldimines with TMSCN in the presence of N-heterocyclic carbene prepared from 1,3-bis(2,4,6-trimethylphenyl)imidazolium chloride and potassium tert-butoxide
