Distinct Reactivity of Mono- and Bis-NHC Silver Complexes: Carbene Donors versus Carbene–Halide Exchange Reagents

Hintermair, Ulrich; Englert, Ulli; Leitner, Walter

doi:10.1021/om101056y

Cited by 61 publications

(52 citation statements)

References 47 publications

(80 reference statements)

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“…Silver imidazol‐2‐ylidene complexes like 1 homo and 1 hetero are remarkably stable and straightforward prepared by deprotonation of the imidazolium precursor by basic silver(I) salts such as Ag 2 O . While imidazolium salts with non‐coordinating anions lead to clean formation of homoleptic bis‐NHC complexes, imidazolium halides as precursors typically yield, depending on the solvent polarity, a mixture of the cationic homoleptic and neutral heteroleptic NHC complex . In our case, 1,3‐bis(2,4,6‐trimethylphenyl)imidazo‐lium chloride was treated with excess Ag 2 O in acetonitrile.…”

Section: Resultsmentioning

confidence: 76%

H(C)Ag: a triple resonance NMR experiment for ¹⁰⁹Ag detection in labile silver‐carbene complexes

Weske

Wiegmann

et al. 2015

Magnetic Reson in Chemistry

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In silver complexes, indirect detection of (109) Ag resonances via (1) H,(109) Ag-HMQC frequently suffers from small or absent JHAg couplings or rapid ligand dissociation. In these cases, it would be favourable to employ H(X)Ag triple resonance spectroscopy that uses the large one-bond JXAg coupling (where the donor atom of the ligand X is the relay nucleus). We have applied an HMQC-based version of the H(C)Ag experiment to a labile silver-NHC complex (NHC=N-heterocyclic carbene) at natural (13) C isotopic abundance and variable temperature. In agreement with simulations, H(C)Ag detection became superior to (1) H,(109) Ag-HMQC detection above -20 °C.

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Section: Resultsmentioning

confidence: 76%

H(C)Ag: a triple resonance NMR experiment for ¹⁰⁹Ag detection in labile silver‐carbene complexes

Weske

Wiegmann

et al. 2015

Magnetic Reson in Chemistry

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“…13 CNMR spectra showedt he characteristic carbene signals at 180.7 and 180.9 ppm for 2a and 2b,r espectively. [46][47][48][49][50] The use of silver intermediates precluded any radical polymerization of the vinyl moiety at an earlier stage;s ome other protocols use harsh reactionc onditions under which such unwanteds ide reactions could occur. [51] Transmetallation with PdCl 2 (PhCN) 2 gave NHC-Pd II dimers 3a and 3b (Ref.…”

Section: Resultsmentioning

confidence: 99%

Polymer‐Supported Palladium(II) Carbene Complexes: Catalytic Activity, Recyclability, and Selectivity in C−H Acetoxylation of Arenes

Majeed

Shayesteh

Wallenberg

et al. 2017

Chemistry A European J

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Heterogeneous catalysts for selective oxidation of C-H bonds were synthesized by co-polymerization of new N-heterocyclic carbene-palladium(II) (NHC-Pd ) monomers with divinylbenzene. The polymer-supported NHC-Pd -catalysed undirected C-H acetoxylation of simple and methylated arenes as well as polyarenes, with similar or superior efficiency compared to their homogeneous analogues. In particular, the regioselectivity has been improved in the acetoxylation of biphenyl and naphthalene compared to the best homogeneous catalysts. The new polymer-supported catalysts maintain the original oxidation state of Pd after repeated catalytic reactions, and exhibit no significant leaching of palladium. In addition, the new catalysts have been successfully recovered and reused without loss of activity over several cycles of reactions.

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“…With these ditopic NHC precursors 5a−d in hand, coordination polymerization with selected iridium(I) salts were then carried out via a solution phase self-assembly process. However, attempts to prepare polymer 6a via silver carbene route 51 were unsuccessful, as the precipitated Ag-NHCs species can hardly react further with the Ir precursors. After a comprehensive survey of reaction conditions (see Supporting Information), lithium bis(trimethylsilyl)amid (LiHMDS) was eventually found to be adequate for this purpose, and the in situ-generated bis-NHC reacted smoothly with different iridium(I) precursors in DMF, respectively, to give NHC-Ir coordination polymers 6a−e in very good yields (93−99%).…”

Section: ■ Results and Disscusionmentioning

confidence: 99%

Robust Iridium Coordination Polymers: Highly Selective, Efficient, and Recyclable Catalysts for Oxidative Conversion of Glycerol to Potassium Lactate with Dihydrogen Liberation

et al. 2015

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Along with the rapid expansion of the biodiesel industry to deal with the world energy crisis, inexpensive glycerol is also produced in large scale as the main byproduct in biodiesel production via transesterification. Much attention has been paid to the development of environmentally benign technologies for the transformation of glycerol to valuable DL-lactic acid and its derivatives. Herein, a series of NHC-Ir coordination polymers were readily synthesized via reaction of some structurally rigid bisbenzimidazolium salts with iridium precursors under alkaline conditions and were successfully applied as robust self-supported catalysts in the oxidative dehydrogenation of glycerol to potassium lactate with dihydrogen liberation. Extremely high activity and selectivity were attained in open air under the mild reaction conditions even with ppm-level loadings of the catalysts, which were readily recovered after reaction by simple filtration and reused for up to 31 runs without obvious loss of activity or selectivity. Probably owing to the effective suppression of inactive binuclear iridium species in a homogeneously catalyzed reaction, the catalysts assembled via self-supported strategy exhibited high selectivity and productivity for potassium lactate, with up to 1.24 × 10 5 turnover numbers (TON) being attained even in large-scale reactions of neat glycerol at an elevated temperature. The high catalytic activity, recyclability, and scalability of the robust self-supported catalysts highlight their potential toward the development of practical technologies for transformation of glycerol to value-added chemicals.

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Distinct Reactivity of Mono- and Bis-NHC Silver Complexes: Carbene Donors versus Carbene–Halide Exchange Reagents

Cited by 61 publications

References 47 publications

H(C)Ag: a triple resonance NMR experiment for ¹⁰⁹Ag detection in labile silver‐carbene complexes

H(C)Ag: a triple resonance NMR experiment for ¹⁰⁹Ag detection in labile silver‐carbene complexes

Polymer‐Supported Palladium(II) Carbene Complexes: Catalytic Activity, Recyclability, and Selectivity in C−H Acetoxylation of Arenes

Robust Iridium Coordination Polymers: Highly Selective, Efficient, and Recyclable Catalysts for Oxidative Conversion of Glycerol to Potassium Lactate with Dihydrogen Liberation

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Distinct Reactivity of Mono- and Bis-NHC Silver Complexes: Carbene Donors versus Carbene–Halide Exchange Reagents

Cited by 61 publications

References 47 publications

H(C)Ag: a triple resonance NMR experiment for 109Ag detection in labile silver‐carbene complexes

H(C)Ag: a triple resonance NMR experiment for 109Ag detection in labile silver‐carbene complexes

Polymer‐Supported Palladium(II) Carbene Complexes: Catalytic Activity, Recyclability, and Selectivity in C−H Acetoxylation of Arenes

Robust Iridium Coordination Polymers: Highly Selective, Efficient, and Recyclable Catalysts for Oxidative Conversion of Glycerol to Potassium Lactate with Dihydrogen Liberation

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H(C)Ag: a triple resonance NMR experiment for ¹⁰⁹Ag detection in labile silver‐carbene complexes

H(C)Ag: a triple resonance NMR experiment for ¹⁰⁹Ag detection in labile silver‐carbene complexes