Easy abstraction of a hydride anion from an alkyl C–H bond of a coordinated bis(N-heterocyclic carbene)

Cabeza, Javier A.; Damonte, Marina; García‐Álvarez, Pablo; Pérez‐Carreño, Enrique

doi:10.1039/c3cc40619a

Cited by 25 publications

(17 citation statements)

References 34 publications

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“…Due to the ether linker in complex 3e , the OCH 2 signal pattern is simpler and appears as a well-resolved AB doublet (δ H = 4.58 and 4.53, 2 J HH = 14.4 Hz), in agreement with diastereotopic methylene protons. As noted for a ditriazolylidene rhodium complex analogous to 3d , no C–H bond activation of the linker was observed, which differs from the reactivity observed in related diimidazolylidene Rh(III) systems …”

Section: Resultscontrasting

confidence: 55%

Influence of the Linker Length and Coordination Mode of (Di)Triazolylidene Ligands on the Structure and Catalytic Transfer Hydrogenation Activity of Iridium(III) Centers

Vivancos

Albrecht

2017

Organometallics

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A series of ditriazolylidene ligand precursors (2) containing alkyl or ether linkers of different lengths between the triazolium heterocycles (trzH−linker−trzH, with linkers (a) −, (b) CH 2 , (c) (CH 2 ) 2 , (d) (CH 2 ) 3 , and (e) CH 2 OCH 2 ) have been prepared, and synthetic methods have been established to obtain selectively either C trz ,C trz -bidentate chelating complexes (3) or C trz -monodentate coordinating triazolylidene iridium(III) complexes with a pendant triazolium unit (4), as well as bimetallic complexes in which the ditriazolylidene ligand acts as a linker between the two metal centers (5). The linker has a distinct effect on the synthetic accessibility of these complexes, and on their reactivity. The structural properties of the complexes have been identified in solution and in the solid state and have been correlated with catalytic activity of the complexes in transfer hydrogenation catalysis. The best-performing catalysts derived from 3d and 4d achieved rates higher than 200 h −1 . Catalytic activity profiles indicate distinctly different catalytic species for those complexes, while complexes 3a and 4a form the same active species.

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Section: Resultscontrasting

confidence: 55%

Influence of the Linker Length and Coordination Mode of (Di)Triazolylidene Ligands on the Structure and Catalytic Transfer Hydrogenation Activity of Iridium(III) Centers

Vivancos

Albrecht

2017

Organometallics

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“…N -Heterocyclic carbenes (NHCs) are among the most popular ancillary ligands due to a combination of unique features, such as the tunability of electronic and steric properties that influence the metal center. Moreover, the synthesis of NHC ligand precursors and the corresponding complexes is rather simple and very versatile, − allowing the rational design of transition metal catalysts and the improvement of catalytic activity. − Regarding the ruthenium–NHC complexes, most of the literature features ruthenium(II) complexes, while low-valent NHC ruthenium(0) systems are restricted to a few examples based on either [Ru 3 (CO) 12 ] or [Ru(CO) 2 (PPh 3 ) 3 ] as precursors. − …”

Section: Introductionmentioning

confidence: 99%

Hydrogen Transfer Activation via Stabilization of Coordinatively Vacant Sites: Tuning Long-Range π-System Electronic Interaction between Ru(0) and NHC Pendants

et al. 2019

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The insertion of a pyridine substituent on the lateral chain of N-heterocyclic carbene ligands enhances the catalytic activity of [Ru(CO)2(cyclopentadienone)(NHC)] complexes, precursors of Shvo-type catalysts, toward the hydrogenation of 4-fluoroacetophenone in refluxing 2-propanol as hydrogen donor. DFT calculations evidence the role of pyridine in the donor/acceptor properties and complexes reactivity both in the case of imidazolylidene and triazolylidene ligands. Although the NHC-pyridine derived complexes perform somewhat worse than the forerunner Shvo dimer, the slower evolution of the reaction steps is compatible with the FT-ATR spectroscopy time scale and allows to identify in situ intermediates, invisible when using the original Shvo catalyst due to its higher reaction speed. Thus, mechanistic insight has been disclosed by synergic contribution of FT-ATR in situ experiments and DFT calculations performed on the slowest precatalyst (1N) chosen as a model. The proposed reaction mechanism has been based on both energy profile and experimentally identified intermediate.

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“…Wang's group 13 has reported that, as a consequence of the high basicity of the NHC ligands, the complexes [Ru(κC-RMeIm)(CO) 4 ] (R = Ph, t Bu) are prone to undergo easy intramolecular C−H bond-activation processes that lead to cyclometalated ruthenium(II) derivatives; 14 Whittlesey's group 7 has shown that [Ru(κC-R 2 Im) 2 (CO) 3 ] (R = i Pr; R 2 Im = Et 2 ImMe 2 , i Pr 2 ImMe 2 ) complexes react easily with oxygen to give the corresponding ruthenium(II) carbonato derivatives [Ru(CO 3 )-(κC-R 2 Im) 2 (CO) 2 ]; Royo's group 12 has reported that [Fe(κC-R 2 Im)(CO) 4 ] (R = Me, Mes, 2,6-C 6 H 3 i Pr 2 ) complexes are useful catalyst precursors for the hydrosilylation of benzaldehyde; and we have recently reported the easy abstraction of a hydride anion from an alkyl C−H bond of the trimethylene- 11 We now report that the reactions of compound 1 with methyl triflate and methyl iodide selectively lead to methyl-and acetylruthenium(II) derivatives, respectively, and we complement these experimental results with theoretical DFT studies that have shed light on the mechanisms of these reactions. We chose complex 1 as a convenient stating material of the type [Ru(κC-R 2 Im) 2 (CO) 3 ] because (a) it can be easily made from [Ru 3 (CO) 12 ] and MeIm(CH 2 ) 3 ImMe (Scheme 1), 11 (b) its strong σ-donating bis(NHC) ligand enhances the nucleophilic character of its ruthenium(0) atom, 11 and (c) its chelating bis(NHC) ligand prevents the formation of mixtures containing cis and trans isomeric products, which have been observed in related ruthenium(0) complexes containing two monodentate NHC ligands. 7 It is noteworthy that no reaction of alkyl halides or pseudohalides with ruthenium(0) complexes of the type [Ru(κ 2 -L 2 )(CO) 3 ] (L 2 = chelating ligand) has been previously described, and although some reactions of methyl iodide with ruthenium(0) derivatives of the types [Ru(κP-PR 3 )(CO) 4 ], 15 trans-[Ru(κP-PR 3 ) 2 (CO) 3 ], 15 and [Ru(κ 3 P 3 -triphos)(CO) 2 ] (triphos = tridentate tripod 16 or pincer 17 P-donor ligand) have been reported, their mechanisms have not been studied by theoretical methods.…”

Section: ■ Introductionmentioning

confidence: 99%

Reactivity of a (Bis-NHC)tricarbonylruthenium(0) Complex with Methyl Triflate and Methyl Iodide. Formation of Methyl- and Acetylruthenium(II) Derivatives: Experimental Results and Mechanistic DFT Calculations

et al. 2013

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The ruthenium(0) complex [Ru{κ2 C 2-MeIm(CH2)3ImMe}(CO)3] (1), MeIm(CH2)3ImMe = 1,3-bis(3-methylimidazol-2-yliden-1-yl)propane, which contains a chelating bis(N-heterocyclic carbene) ligand, reacts with MeOTf at room temperature to give the ionic ruthenium(II) methyl derivative [RuMe{κ2 C 2-MeIm(CH2)3ImMe}(CO)3]OTf ([2]OTf), whereas an analogous reaction of 1 with MeI renders the neutral ruthenium(II) acetyl derivative [RuI{C(O)Me}{κ2 C 2-MeIm(CH2)3ImMe}(CO)2] (3), in which the iodide and acetyl ligands occupy mutually trans coordination sites. The fact that [2]OTf reacts with [Et4N]I to give 3 evidences the participation of the cationic species 2 + in the synthesis of 3. The mechanisms of these reactions in THF solution have been modeled by DFT calculations. They have shown that 2 + can be made from complex 1 and either MeOTf or MeI. In both cases, two plausible reaction pathways have been identified. They start with a rate-determining SN2 substitution process in which the metal atom of 1 attacks the C atom of MeI or MeOTf, displacing the corresponding anion to give, depending on how compound 1 approaches MeI or MeOTf, 2 + or a less stable isomeric species 2′+ that is easily transformed into 2 +. A subsequent CO migratory insertion in 2 + leads to an unsaturated (pentacoordinated) acetyl intermediate that easily adds the iodide anion to end in 3. DFT calculations have also shown that the reaction of 1 with MeOTf to give [2]OTf is thermodynamically more favorable than that of 1 with MeI to give [2]I due to the resonance stabilization and greater solvation energy of the triflate anion. These two effects are also responsible for the fact that the incorporation of the triflate anion with 2 + to give a putative triflate complex analogous to 3 is thermodynamically disfavored, whereas the incorporation of the iodide anion with 2 + to give 3 is thermodynamically favored.

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Easy abstraction of a hydride anion from an alkyl C–H bond of a coordinated bis(N-heterocyclic carbene)

Cited by 25 publications

References 34 publications

Influence of the Linker Length and Coordination Mode of (Di)Triazolylidene Ligands on the Structure and Catalytic Transfer Hydrogenation Activity of Iridium(III) Centers

Influence of the Linker Length and Coordination Mode of (Di)Triazolylidene Ligands on the Structure and Catalytic Transfer Hydrogenation Activity of Iridium(III) Centers

Hydrogen Transfer Activation via Stabilization of Coordinatively Vacant Sites: Tuning Long-Range π-System Electronic Interaction between Ru(0) and NHC Pendants

Reactivity of a (Bis-NHC)tricarbonylruthenium(0) Complex with Methyl Triflate and Methyl Iodide. Formation of Methyl- and Acetylruthenium(II) Derivatives: Experimental Results and Mechanistic DFT Calculations

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