Easy activation of two C–H bonds of an N-heterocyclic carbene N-methyl group

Cabeza, Javier A.; Rı́o, Ignacio del; Miguel, Daniel; Sánchez-Vega, M. Gabriela

doi:10.1039/b506287j

Cited by 87 publications

(93 citation statements)

References 49 publications

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“…13 This fact indicates that the reaction proceeds through an associative mechanism. The lower tendency of [Os 3 (CO) 12 ] to undergo CO substitution reactions under mild conditions, as compared with that of [Ru 3 (CO) 12 ], is well documented in the chemical literature. 21 The very bulky but very basic NHCs t Bu 2 Im and Ad 2 Im react with [Os 3 (CO) 12 ] upon heating (70 1C, 3 h) to give substituted derivatives with abnormally-coordinated NHCs, i.e., [Os 3 (a-R 2 Im)(CO) 11 ] (R = t Bu (7), Ad (8); Scheme 3).…”

Section: Ruthenium Andmentioning

confidence: 93%

“…The first one is devoted to the NHC chemistry of ruthenium and osmium carbonyl clusters, while the NHC chemistry of other transition metal clusters is collected in the second section. 12,13 Under analogous conditions, the large 1,3-dimesitylimidazol-2-ylidene (Mes 2 Im) reacts more slowly to give a similar monosubstituted derivative (2 in Scheme 2), but the bulkier 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene (Dipph 2 Im) fails to give an analogous reaction product. 12 ] at room temperature to give the air-stable orange trinuclear cluster [Ru 3 (Me 2 Im)(CO) 11 ] (1 in Scheme 2).…”

Section: Pablo Garcı´a-á Lvarezmentioning

confidence: 99%

“…As the NHC chemistry of ruthenium and osmium clusters has been investigated to a much greater extent than that of the remaining transition metal clusters, the first section is split into three subsections, namely, (a) clusters with simple five-membered-ring NHCs, (b) clusters with functionalised five-membered-ring NHCs and (c) ruthenium clusters containing six-membered-ring NHCs. 13 Since these NHCs have rather similar electronic properties, 8 12 ] also reacts with the oxazole-derived NHC 3-methyloxazol-2-ylidene (MeOx), which is less basic but also smaller than Me 2 Im, to give [Ru 3 (MeOx)(CO) 11 ] (3 in Scheme 2). 12,13 Under analogous conditions, the large 1,3-dimesitylimidazol-2-ylidene (Mes 2 Im) reacts more slowly to give a similar monosubstituted derivative (2 in Scheme 2), but the bulkier 1,3-bis(2,6-diisopropylphenyl)imidazole-2-ylidene (Dipph 2 Im) fails to give an analogous reaction product.…”

Section: Pablo Garcı´a-á Lvarezmentioning

confidence: 99%

“…The very bulky but also very basic NHCs 1,3-di-tertbutylimidazol-2-ylidene ( t Bu 2 Im) and 1,3-diadamantylimidazol-2-ylidene (Ad 2 Im) also reacts with one equivalent of [Ru 3 (CO) 12 ] at room temperature to give monosubstituted products (4 and 5 in Scheme 2), 17,18 but, in this case, the NHCs are abnormally coordinated 19 (through their C-4 atom) to the metal atom. It seems that the bulk of their N-R substituents prevents these carbenes from approaching the metal centre through the lone pair on the C-2 atom and that the stronger s-donating character of the abnormal NHCs (in comparison with that of the corresponding normal NHCs) 19,20 may also contribute to the driving force of these reactions.…”

Section: Ruthenium Andmentioning

confidence: 99%

“…In the case of osmium clusters, it has been shown that Me 2 Im is the only NHC that has the appropriate combination of volume (small) and basicity (high) to react with [Os 3 (CO) 12 ] at room temperature, giving [Os 3 (Me 2 Im)(CO) 11 ] (6, Scheme 3). 13 This fact indicates that the reaction proceeds through an associative mechanism.…”

Section: Ruthenium Andmentioning

confidence: 99%

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The N-heterocyclic carbene chemistry of transition-metal carbonyl clusters

Cabeza

García‐Álvarez

2011

Chem. Soc. Rev.

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In the last decade, chemists have dedicated many efforts to investigate the coordination chemistry of N-heterocyclic carbenes (NHCs). Although most of that research activity has been devoted to mononuclear complexes, transition-metal carbonyl clusters have not escaped from these investigations. This critical review, which is focussed on the reactivity of NHCs (or their precursors) with transition-metal carbonyl clusters (mostly are of ruthenium and osmium) and on the transformations underwent by the NHC-containing species initially formed in those reactions, shows that the polynuclear character of these metallic compounds or, more precisely, the close proximity of one or more metal atoms to that which is or can be attached to the NHC ligand, is responsible for reactivity patterns that have no parallel in the NHC chemistry of mononuclear complexes (74 references).

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Section: Ruthenium Andmentioning

confidence: 93%

Section: Pablo Garcı´a-á Lvarezmentioning

confidence: 99%

Section: Pablo Garcı´a-á Lvarezmentioning

confidence: 99%

Section: Ruthenium Andmentioning

confidence: 99%

Section: Ruthenium Andmentioning

confidence: 99%

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The N-heterocyclic carbene chemistry of transition-metal carbonyl clusters

Cabeza

García‐Álvarez

2011

Chem. Soc. Rev.

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An Air/Water‐Stable Tridentate N‐Heterocyclic Carbene‐ Palladium(II) Complex: Catalytic CH Activation of Hydrocarbons via Hydrogen/Deuterium Exchange Process in Deuterium Oxide

et al. 2009

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While developing novel catalysts for carbon-carbon or carbon-heteroatom coupling (N, O, or F), we were able to introduce tridentate NHC-amidate-alkoxide palladium(II) complexes. In aqueous solution, these NHC-Pd(II) complexes showed high ability for C-H activation of various hydrocarbons (cyclohexane, cyclopentane, dimethyl ether, THF, acetone, and toluene) under mild conditions. Keywords NHC ligand; C-H activation; H/D exchange; Palladium complex; Intermolecular reactionCarbon-carbon or carbon-heteroatom cross-coupling reactions catalyzed by transition metal catalysts have been widely investigated and established because of their significance in organic synthesis. In particular, homogeneous Pd catalysis has been well studied in the most powerful and versatile synthetic process such as Heck [1] , Suzuki [2] , Stille [3] , Sonogashira [4] , Negishi [5] , and Buchwald-Hartwig reactions [6] . However, these reactions have required alkenyl/aryl halide substrates. Alternatively, the more desirable direct functionalization of hydrocarbons via C-H bond activation has still remained a challenge in cross-coupling reactions.In recent years, a substantial number of metal complexes that are able to selectively activate C-H bonds under mild conditions have been discovered. [7] In spite of these advances, practical catalysts for the C-H bond functionalization remain elusive, due to the requirement of high energy to break C-H bond and subsequent vulnerability of the metal-carbon bond. Additionally, the C-H bond activation is often inhibited by water or by the product eliminated from the metal complex during the reaction. [8] Recently, N-Heterocyclic carbene (NHC) ligands, which are known to enhance σ-donor coordination, have shown improved behaviour toward C-H bond activation during the past several years. [9] A number of organometallic species at various oxidation states (Pd, Pt, Ru, and Ir) are stabilized by the use of NHC ligands, increasing the capability to obtain efficient catalysts for C-H activation. [10] However, most examples refer to intramolecular processes, while intermolecular or catalytic examples being rare. With these challenges in mind, we report herein the efficient C-H bond activation of hydrocarbons in aqueous solution (1)Recently, we have succeeded in preparing air-stable tridentate NHC-amidate-alkoxide ligand/palladium complex 1 from an amino alcohol. [12] We found that H/D exchange on benzene using D 2 O as both the solvent and deuterium source, occurred via C-H bond activation in the presence of Pd complex 1 and silver tetrafluoroborate. As shown in equation (1), the H/D exchange reaction was demonstrated with benzene (20 μL), palladium complex 1 (5 mol %) and AgBF 4 in deuterium oxide (700 μL) for 22 hours at 55 °C and 100°C . The efficiency of the H/D exchange giving deuterated isotopomers showed significant enhancement, when temperature was increased from 55 °C to 100 °C. While evaluating H/D exchange with palladium complex 1 and AgBF 4 , we found that a dimeric structure 2 was present ...

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