CO Fixation to Stable Acyclic and Cyclic Alkyl Amino Carbenes: Stable Amino Ketenes with a Small HOMO–LUMO Gap

Lavallo, Vincent; Canac, Yves; Donnadieu, Bruno; Schoeller, Wolfgang W.; Bertrand, Guy

doi:10.1002/ange.200600987

Cited by 166 publications

(84 citation statements)

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“…Compared to the optimized structure of the free NHC, the dihedral angles of 2 are significantly diminished in both its d 6 and d 10 metal complexes, the calculated values ranging in between 0  4 and 0  7, respectively. Although a moderate decrease in dihedral angles is observed for 2 in its copper and silver compounds, the optimized geometry obtained for the gold complex stands clearly out from the rest by having a fully planar heterocyclic ring framework.…”

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confidence: 85%

“…The metal-ligand bond strength increases down a group for d 0 complexes while for d 6 Of all the systems studied, the carbenes 3 and 5 form the strongest and weakest bonds with a given metal, respectively. The only exceptions are the d 0 metal complexes of 2 and 1.…”

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confidence: 94%

“…4 In recent years, it has been shown that the carbene backbone can be considerably modified without significant loss of stability by adjusting the ring size and/or introducing heteroatoms into the molecular framework. 5 Among the more striking examples, the two -electron cyclopropenylidene B 6 and the non-planar four-membered carbene C with a pyramidal phosphorus backbone 7 have proven to be stable at room temperature and display typical NHC behaviour. 5i Another interesting type of modification is the replacement of one of the electronegative amino groups in NHCs by a strongly donating alkyl group, thus giving rise to cyclic (alkyl)(amino)carbenes, which display interesting chemical properties as nucleophiles.…”

Section: Introductionmentioning

confidence: 99%

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N-Heterocyclic Carbenes with Inorganic Backbones: Electronic Structures and Ligand Properties

et al. 2008

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The electronic structures of known N-heterocyclic carbenes (NHCs) with boron, nitrogen and phosphorus backbones are examined using quantum chemical methods and compared to the experimental results and to the computational data obtained for a classical carbon analog, imidazol-2-ylidene. The σ-donor and π-acceptor abilities of the studied NHCs in selected transition metal complexes are evaluated using a variety of approaches such as energy and charge decomposition analysis, as well as calculated acidity constants and carbonyl stretching frequencies. The study shows that the introduction of selected heteroatoms into the NHC backbone generally leads to stronger metal-carbene bonds and therefore improves the ligand properties of these systems. The backdonation of -electron density from the metal to the ligand is found to be strong in complexes of the studied NHCs with group 11 metals, where it constitutes up to nearly 35 % of the total orbital interaction energy. The ligand properties of the aluminum analogs of some of the reported NHCs with boron backbones are also assessed.2

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confidence: 85%

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confidence: 94%

Section: Introductionmentioning

confidence: 99%

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N-Heterocyclic Carbenes with Inorganic Backbones: Electronic Structures and Ligand Properties

et al. 2008

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“…Small cyclic unsaturated hydrocarbons such as c-C 3 H, c-C 3 H 2 , c-C 3 H 3 , and c-C 4 H 4 are of great interest for the chemistry of carbon-rich gas-phase environments [1][2][3][4][5][6] and have been the subject of numerous theoretical and experimental investigations. These cyclic molecules are believed to be vital intermediates in the chemical schemes leading to the formation of large carbon-containing molecules such as polycyclic aromatic hydrocarbons in combustion flames, the interstellar environment, and extraterrestrial atmospheres such as on a moon of Saturn, Titan.…”

Section: Introductionmentioning

confidence: 99%

Cyclic Versus Linear Isomers Produced by Reaction of the Methylidyne Radical (CH) with Small Unsaturated Hydrocarbons

et al. 2009

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The reactions of the methylidyne radical (CH) with ethylene, acetylene, allene, and methylacetylene are studied at room temperature using tunable vacuum ultraviolet (VUV) photoionization and time-resolved mass spectrometry. The CH radicals are prepared by 248 nm multiphoton photolysis of CHBr 3 at 298 K and react with the selected hydrocarbon in a helium gas flow. Analysis of photoionization efficiency versus VUV photon wavelength permits isomer-specific detection of the reaction products and allows estimation of the reaction product branching ratios. The reactions proceed by either CH insertion or addition followed by H atom elimination from the intermediate adduct. In the CH + C 2 H 4 reaction the C 3 H 5 intermediate decays by H atom loss to yield 70(±8)% allene, 30(±8)% methylacetylene and less than 10% cyclopropene, in agreement with previous RRKM results. In the CH + acetylene reaction, detection of mainly the cyclic C 3 H 2 isomer is contrary to a previous RRKM calculation that predicted linear triplet propargylene to be 90% of the total H-atom co-products. High-level CBS-APNO quantum calculations and RRKM calculation for the CH + C 2 H 2 reaction presented in this manuscript predict a higher contribution of the cyclic C 3 H 2 (27.0%) versus triplet propargylene (63.5%) than these earlier predictions.Extensive calculations on the C 3 H 3 and C 3 H 2 D system combined with experimental isotope ratios for the CD + C 2 H 2 reaction indicate that H-atom assisted isomerization in the present experiments is responsible for the discrepancy between the RRKM calculations and the experimental results. Cyclic isomers are also found to represent 30(±6)% of the detected products in the case of CH + methylacetylene, together with 33(±6)% 1,2,3-butatriene and 37(±6)% vinylacetylene. The CH + allene reaction gives 23(±5)% 1,2,3-butatriene and 77(±5)% vinylacetylene, whereas cyclic isomers are produced below the detection limit in this reaction. The reaction exit channels deduced by comparing the product distributions for the aforementioned reactions are discussed in detail.3

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“…2 In recent years, it has been shown that the backbones of NHCs can be significantly modified without diminishing their stability and examples of saturated 7 and acyclic 8 carbenes, and NHCs with four-, six-, and seven-membered rings have been reported; 9 the first example of a stable carbene which remarkably lacks π-donor heteroatoms has also been published. 10 In addition, there have been extensive efforts to isolate and characterize the isovalent p-block analogues of imidazol-2-ylidene, collectively known as the main group carbene analogues. These compounds have been successfully synthesized for many elements from Groups 13 to 16: 11 in each case, the main group centre is dicoordinate, electron rich (bears a lone pair of electrons), and formally anionic (Group 13), neutral (Group 14), cationic (Group 15), or dicationic (Group 16).…”

Section: Introductionmentioning

confidence: 99%

Electronic Structures of Main-Group Carbene Analogues

et al. 2007

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The electronic structures of fifteen Group 13-16 carbene analogues are analyzed using various quantum chemical methods and compared to the data obtained for the parent N-heterocylic carbene (NHC), imidazol-2-ylidene. The results of this study present a uniform analysis of the similarities and differences in the electronic structures of p-block main group carbene analogues. Though all systems are formally isovalent, the theoretical analyses unambiguously indicate that their electronic structures run the gamut from C=C localized (Group 13) to C=N localized (Group 16) via intermediate, more delocalized, systems. In particular, neither the stibenium ion nor any of the chalcogenium dications is a direct analogue of imidazol-2-ylidene as they all contain two lone pairs of electrons around the divalent main group center, instead of the expected one. The reason behind the gradual change in the electronic structure of main group analogues of imidazol-2-ylidene was traced to the total charge of the systems, which changes from anionic to dicationic when moving from left to right in the periodic table. Results from theoretical analyses of aromaticity show that all Group 13-16 analogues of imidazol-2-ylidene display some degree of aromatic character. The heavier Group 13 anions benefit the least from π-electron delocalization, whereas the cationic Group 15 systems are on par with the parent carbon system and display only slightly less aromatic character than cyclopentadienide, a true 6π-electron aromatic species. The σ-donor and π-acceptor ability of the different main group carbene analogues is also evaluated.

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CO Fixation to Stable Acyclic and Cyclic Alkyl Amino Carbenes: Stable Amino Ketenes with a Small HOMO–LUMO Gap

Cited by 166 publications

References 53 publications

N-Heterocyclic Carbenes with Inorganic Backbones: Electronic Structures and Ligand Properties

N-Heterocyclic Carbenes with Inorganic Backbones: Electronic Structures and Ligand Properties

Cyclic Versus Linear Isomers Produced by Reaction of the Methylidyne Radical (CH) with Small Unsaturated Hydrocarbons

Electronic Structures of Main-Group Carbene Analogues

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