Heteroleptic rhodium NHC complexes with pyridine-derived ligands: synthetic accessibility and reactivity towards oxygen

Zenkina, Olena V.; Keske, Eric C.; Kochhar, Gurpaul S.; Wang, Ruiyao; Crudden, Cathleen M.

doi:10.1039/c2dt32095a

Cited by 22 publications

(8 citation statements)

References 81 publications

(154 reference statements)

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“…The observed chemical shifts and coupling constants for the carbene resonance are similar to those that have been reported previously for square planar Rh(I) complexes with NHC ligands. 20,23,24,26,[28][29][30][31] For each complex, the positive electrospray mass spectrum obtained contained the parent ions corresponding to the entire cationic metal complex with one NHC-1,2,3-triazolyl ligand and one COD co-ligand. This suggests that the NHCtriazolyl ligands coordinate to the Rh(I) centre in a bidentate fashion and together with the COD co-ligands form the expected square planar Rh(I) complexes.…”

Section: Dalton Transactionsmentioning

confidence: 99%

Cationic Rh and Ir complexes containing bidentate imidazolylidene–1,2,3-triazole donor ligands: synthesis and preliminary catalytic studies

et al. 2013

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A series of new cationic Rh(I), Rh(III) and Ir(III) complexes containing hybrid bidentate N-heterocyclic carbene–1,2,3-triazolyl donor of general formulae [Rh(CaT)(COD)]BPh4 (2a–d), [Rh(CaT)(CO)2]BPh4 (3a–d) and [M(CaT)(Cp*)Cl]BPh4 (M = Rh, 4a–d; M = Ir, 5a–c), where CaT = bidentate N-heterocyclic carbene–triazolyl ligands, COD = 1,5-cyclooctadiene and Cp* = 1,2,3,4,5-pentamethylcyclopentadienyl, were synthesised. The imidazolium–1,2,3-triazolyl pre-ligands (1a–c and 1e–i) were readily prepared using the Cu(I) catalysed ‘click reaction’ between phenyl azide or benzyl azides with propargyl functionalised imidazolium salts. The single crystal solid state structures of complexes 2a–d; 3a–b; 4a–d and 5a–b confirm the bidentate coordination of the NHC–1,2,3-triazolyl ligand with the NHC coordinating via the ‘normal’ C2-carbon and the 1,2,3-triazolyl donor coordinating via the N3′ atom to form six membered metallocycles. These complexes are the first examples of Rh and Ir complexes containing the hybrid NHC–1,2,3-triazolyl ligands which exhibit a bidentate coordination mode. A number of these complexes showed limited efficiency as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methylpyrroline.

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Section: Dalton Transactionsmentioning

confidence: 99%

Cationic Rh and Ir complexes containing bidentate imidazolylidene–1,2,3-triazole donor ligands: synthesis and preliminary catalytic studies

et al. 2013

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“…On the basis of this fact, our research group has developed in recent years a variety of NHC-based rhodium catalysts active in C–H activation . Particularly, dinuclear compounds with the general formula [Rh(μ-Cl)(NHC)(η 2 - olefin)] 2 proved to be valuable starting materials for the preparation of mononuclear complexes RhCl(NHC)(η 2 - olefin)(L) by simple bridge cleavage with a nucleophilic ligand . These derivatives exhibited excellent activities and selectivities in catalytic alkyne homo- and cross-dimerization, as well as hydroalkenylation of N -vinylpyrazoles, 2-thienylpyridine, and 2-vinylazines , to produce valuable N-bridge heterocycles.…”

Section: Introductionmentioning

confidence: 99%

Hydride–Rhodium(III)-N-Heterocyclic Carbene Catalyst for Tandem Alkylation/Alkenylation via C–H Activation

et al. 2019

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The unsaturated hydride complex RhClH{κ 2 -N,C-(C 11 H 8 N)}(IPr) {IPr = 1,3-bis-(2,6-diisopropylphenyl)imidazolin-2-carbene} (2) has been prepared via C− H activation of 2-phenylpyridine and fully characterized by spectroscopic methods and X-ray diffraction analysis. Complex 2 efficiently catalyzes the isomerization of terminal and internal olefins under mild conditions to give preferentially the E regioisomers. Complex 2 also catalyzes the hydroarylation of terminal olefins with 2-phenylpyridine to yield selectively mono-ortho-alkylated derivatives. Tandem isomerization−alkylation processes were observed for internal olefins. In contrast to olefins, double alkenylation is operative for internal alkynes. The marked complementary reactivity of olefins and alkynes allows for a tandem alkylation/alkenylation of 2-phenylpyridine to yield substituted styrenes. These heterobiaryl compounds exhibit axial chirality. The rotational barrier has been experimentally calculated and corroborated by density functional theory (DFT) calculations. A catalytic cycle for hydroarylation reactions has been proposed based on the identification of key reaction intermediates and H/D exchange experiments. The reaction seems to proceed by initial C−H activation of 2-phenylpyridine, subsequent insertion of alkene or alkyne, and reductive elimination steps. According to experimental results, DFT calculations have shown a higher energy barrier for bis-alkylation processes than for bis-alkenylation ones that display a feasible activation energy. Moreover, it has been found that reductive elimination is the rate-limiting step for alkene hydroarylation, whereas migratory insertion is the rate-limiting step for alkyne hydroarylation processes.

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“…23 In particular, NHC complexes of Rh and other transition metals can undergo cleavage of the metal-carbon bond of the NHC under remarkably mild conditions. 16,[24][25][26][27][28][29] In addition, we have also demonstrated that Rh-NHC complexes can react rapidly with oxygen, in some cases providing Rh-O 2 complexes with highly unusual bonding modes (Fig. 1).…”

Section: Introductionmentioning

confidence: 60%

“…As expected, complexes 5 and 6, which instead contain saturated NHCs, display resonances that are even further downshifted at >200 ppm. 35,69 In contrast to this, Rh III NHC complexes generally exhibit a significant upfield shift of the carbene resonance (Δ ∼ 20 ppm) seemingly regardless of the nature of the ancillary ligands, 29,[70][71][72] or the nature of the carbene itself. 73 We observed this upfield shift in cationic complexes 7 and octahedral P-N chelate complexes 9 and 10 (Table 2).…”

Section: Nmr Spectroscopymentioning

confidence: 91%

“…1). [29][30][31][32][33][34][35] Interestingly, in some cases, oxidation of the complex can lead to cleavage of the metalcarbon bond of the carbene, 29 while in others, 16,31,32,35 the complexes are stable for extended periods of time under ambient conditions. For example, in powder form, complex 4 is stable for more than two years in a closed vial on the benchtop as long as it is protected from exposure to atmospheric CO.…”

Section: Introductionmentioning

confidence: 99%

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Dioxygen adducts of rhodium N-heterocyclic carbene complexes

et al. 2013

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Rhodium complexes functionalized by N-heterocyclic carbene ligands react with dioxygen to form adducts. Depending on the specifics of the ancillary ligands, oxygen binds to Rh either as a peroxide to form a fully oxidized Rh(III) complex, or as singlet dioxygen in a Rh(I) square planar complex. We have shown through analysis of a series of compounds, some previously published and some novel, that the presence of additional ligands that would support the formation of an octahedral geometry, as typically found with Rh(III) complexes, is critical for formation of the peroxide. In addition, we have demonstrated through DFT studies, that the potential energy surface with regard to the O-O bond length is relatively shallow, which provides a rationale for the distribution of bond lengths observed for apparently similar complexes analyzed by crystallography.

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Heteroleptic rhodium NHC complexes with pyridine-derived ligands: synthetic accessibility and reactivity towards oxygen

Cited by 22 publications

References 81 publications

Cationic Rh and Ir complexes containing bidentate imidazolylidene–1,2,3-triazole donor ligands: synthesis and preliminary catalytic studies

Cationic Rh and Ir complexes containing bidentate imidazolylidene–1,2,3-triazole donor ligands: synthesis and preliminary catalytic studies

Hydride–Rhodium(III)-N-Heterocyclic Carbene Catalyst for Tandem Alkylation/Alkenylation via C–H Activation

Dioxygen adducts of rhodium N-heterocyclic carbene complexes

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