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36 pages, 9272 KiB

Open AccessEditor’s ChoiceReview

Heterobimetallic Complexes of Bi- or Polydentate N-Heterocyclic Carbene Ligands and Their Catalytic Properties

by Csilla Enikő Czégéni, Ferenc Joó, Ágnes Kathó and Gábor Papp

Catalysts 2023, 13(11), 1417; https://doi.org/10.3390/catal13111417 - 5 Nov 2023

Viewed by 3306

This review summarizes developments in the synthesis and catalytic applications of those heterobimetallic carbene complexes in which at least two different metals are bound to the same ligand by at least one M-C(carbene) bond each. Several new synthetic methods for such complexes yielding [...] Read more.

This review summarizes developments in the synthesis and catalytic applications of those heterobimetallic carbene complexes in which at least two different metals are bound to the same ligand by at least one M-C(carbene) bond each. Several new synthetic methods for such complexes yielding well-defined and thoroughly characterized compounds are presented. The new complexes were found to be catalytically active in several (most often tandem) reactions. In certain cases, the incorporation of two different metals into the same imidazole- or triazol-based NHC-carbene complex resulted in the substantially higher catalytic activity of the heterobimetallic complex compared either to its homobimetallic analogs or to mixtures of comparable mononuclear complex fragments containing the two metals independently. This is a clear demonstration of advantageous metal–metal cooperation within the catalyst. Opposite examples are also discussed, where the heterobimetallic carbene complex proved inferior in relation to its homobimetallic analogs or to mixtures of homonuclear fragments. Full article

(This article belongs to the Special Issue Organometallic Homogeneous Catalysis)

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29 pages, 7216 KiB

Open AccessReview

Added Complexity!—Mechanistic Aspects of Heterobimetallic Complexes for Application in Homogeneous Catalysis

by Zeno Fickenscher and Evamarie Hey-Hawkins

Molecules 2023, 28(10), 4233; https://doi.org/10.3390/molecules28104233 - 22 May 2023

Cited by 9 | Viewed by 3424

Abstract

Inspired by multimetallic assemblies and their role in enzyme catalysis, chemists have developed a plethora of heterobimetallic complexes for application in homogeneous catalysis. Starting with small heterobimetallic complexes with σ-donating and π-accepting ligands, such as N-heterocyclic carbene and carbonyl ligands, more and more [...] Read more.

Inspired by multimetallic assemblies and their role in enzyme catalysis, chemists have developed a plethora of heterobimetallic complexes for application in homogeneous catalysis. Starting with small heterobimetallic complexes with σ-donating and π-accepting ligands, such as N-heterocyclic carbene and carbonyl ligands, more and more complex systems have been developed over the past two decades. These systems can show a significant increase in catalytic activity compared with their monometallic counterparts. This increase can be attributed to new reaction pathways enabled by the presence of a second metal center in the active catalyst. This review focuses on mechanistic aspects of heterobimetallic complexes in homogeneous catalysis. Depending on the type of interaction of the second metal with the substrates, heterobimetallic complexes can be subdivided into four classes. Each of these classes is illustrated with multiple examples, showcasing the versatility of both, the types of interactions possible, and the reactions accessible. Full article

(This article belongs to the Topic Catalytic Applications of Transition Metals)

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14 pages, 3578 KiB

Open AccessArticle

Synergistic Catalysis in Heterobimetallic Complexes for Homogeneous Carbon Dioxide Hydrogenation

by Zeno B. G. Fickenscher, Peter Lönnecke, Anna K. Müller, Oldamur Hollóczki, Barbara Kirchner and Evamarie Hey-Hawkins

Molecules 2023, 28(6), 2574; https://doi.org/10.3390/molecules28062574 - 12 Mar 2023

Cited by 9 | Viewed by 2939

Abstract

Two heterobimetallic Mo,M’ complexes (M’ = Ir^III, Rh^III) were synthesized and fully characterized. Their catalytic activity in homogeneous carbon dioxide hydrogenation to formate was studied. A pronounced synergistic effect between the two metals was found, most notably between Mo [...] Read more.

Two heterobimetallic Mo,M’ complexes (M’ = Ir^III, Rh^III) were synthesized and fully characterized. Their catalytic activity in homogeneous carbon dioxide hydrogenation to formate was studied. A pronounced synergistic effect between the two metals was found, most notably between Mo and Ir, leading to a fourfold increase in activity compared with a binary mixture of the two monometallic counterparts. This synergism can be attributed to spatial proximity of the two metals rather than electronic interactions. To further understand the nature of this interaction, the mechanism of the CO₂ hydrogenation to formate by a monometallic Ir^III catalyst was studied using computational and spectroscopic methods. The resting state of the reaction was found to be the metal-base adduct, whereas the rate-determining step is the inner-sphere hydride transfer to CO₂. Based on these findings, the synergism in the heterobimetallic complex is beneficial in this key step, most likely by further activating the CO₂. Full article

(This article belongs to the Special Issue Progress in Metal Catalysis)

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62 pages, 20590 KiB

Open AccessReview

Transition Metal–(μ-Cl)–Aluminum Bonding in α-Olefin and Diene Chemistry

by Ilya E. Nifant’ev, Ildar I. Salakhov and Pavel V. Ivchenko

Molecules 2022, 27(21), 7164; https://doi.org/10.3390/molecules27217164 - 23 Oct 2022

Cited by 5 | Viewed by 3984

Abstract

Olefin and diene transformations, catalyzed by organoaluminum-activated metal complexes, are widely used in synthetic organic chemistry and form the basis of major petrochemical processes. However, the role of M–(μ-Cl)–Al bonding, being proven for certain >C=C< functionalization reactions, remains unclear and debated for essentially [...] Read more.

Olefin and diene transformations, catalyzed by organoaluminum-activated metal complexes, are widely used in synthetic organic chemistry and form the basis of major petrochemical processes. However, the role of M–(μ-Cl)–Al bonding, being proven for certain >C=C< functionalization reactions, remains unclear and debated for essentially more important industrial processes such as oligomerization and polymerization of α-olefins and conjugated dienes. Numerous publications indirectly point at the significance of M–(μ-Cl)–Al bonding in Ziegler–Natta and related transformations, but only a few studies contain experimental or at least theoretical evidence of the involvement of M–(μ-Cl)–Al species into catalytic cycles. In the present review, we have compiled data on the formation of M–(μ-Cl)–Al complexes (M = Ti, Zr, V, Cr, Ni), their molecular structure, and reactivity towards olefins and dienes. The possible role of similar complexes in the functionalization, oligomerization and polymerization of α-olefins and dienes is discussed in the present review through the prism of the further development of Ziegler–Natta processes and beyond. Full article

(This article belongs to the Special Issue Frontiers in Metal Complexes)

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16 pages, 8764 KiB

Open AccessArticle

Ru/Pd Complex and Its Monometallic Fragments as Catalysts for Norbornene Polymerization via ROMP and Addition

by Thaís R. Cruz, Gustavo H. C. Masson, Kelly A. E. Amorim, Antonio E. H. Machado, Beatriz E. Goi and Valdemiro P. Carvalho-Jr.

Catalysts 2022, 12(10), 1111; https://doi.org/10.3390/catal12101111 - 26 Sep 2022

Cited by 3 | Viewed by 2452

Abstract

The [Ru(PPh₃)₂Cl-piperidine(4-aminomethyl)] complex (mono-Ru) was synthesized from [Ru(PPh₃)₃Cl₂] and 4-(aminomethyl)piperidine, whereas the [(PPh₃)PdCl(Shiff-pip)] complex (mono-Pd) was obtained by reacting [Pd(PPh₃)₂Cl₂] with its respective Schiff base [...] Read more.

The [Ru(PPh₃)₂Cl-piperidine(4-aminomethyl)] complex (mono-Ru) was synthesized from [Ru(PPh₃)₃Cl₂] and 4-(aminomethyl)piperidine, whereas the [(PPh₃)PdCl(Shiff-pip)] complex (mono-Pd) was obtained by reacting [Pd(PPh₃)₂Cl₂] with its respective Schiff base ligand, both at a 1:1 molar ratio. The heterobimetallic [RuCl₂(PPh₃)₂](μ-Schiff)Pd(PPh₃)Cl] complex (Ru/Pd) was synthesized via a one-pot, three-component reaction of mono-Ru, [(Pd(PPh₃)₂Cl₂] and salicylaldehyde. All complexes were fully characterized by FTIR, UV-Vis, and NMR spectroscopy, as well as elemental analysis, MALDI-TOF mass spectrometry, cyclic voltammetry, and computational studies. Ru/Pd was able to polymerize norbornene (NBE) by two different mechanisms: ROMP and vinyl polymerization. The Ru fragment was active for ROMP of NBE, reaching yields of 68 and 31% for mono-Ru and Ru/Pd, respectively, when the [NBE]/[Ru] = 3000 molar ratio and 5 μL EDA addition were employed at 50 °C. The poly(norbornene) (polyNBE) obtained presented an order of magnitude of 10⁴ g mol⁻¹ and Ð values between 1.48 and 1.79. For the vinyl polymerization of NBE, the Pd fragment was active using MAO as a cocatalyst, reaching a yield of 47.0% for Ru/Pd and quantitative yields for mono-Pd when [Al]/[Pd] = 2500 and [NBE]/[Pd] = 20,000 molar ratios were employed, both at 60 °C. Full article

(This article belongs to the Special Issue Organometallic Homogeneous Catalysis)

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10 pages, 1466 KiB

Open AccessArticle

A Mixed Heterobimetallic Y/Eu-MOF for the Cyanosilylation and Hydroboration of Carbonyls

by Estitxu Echenique-Errandonea, Mireya E. López-Vargas, Juana M. Pérez, Sara Rojas, Duane Choquesillo-Lazarte, José M. Seco, Ignacio Fernández and Antonio Rodríguez-Diéguez

Catalysts 2022, 12(3), 299; https://doi.org/10.3390/catal12030299 - 6 Mar 2022

Cited by 7 | Viewed by 3146

Abstract

Herein, to the best of our knowledge, the first heterobimetallic Y/Eu porous metal–organic framework (MOF), based on 3-amino-4-hydroxybenzoic acid (H₂L) ligand, with the following formulae {[Y_3.5Eu_1.5L₆(OH)₃(H₂O)₃]·12DMF}_n (in advance, [...] Read more.

Herein, to the best of our knowledge, the first heterobimetallic Y/Eu porous metal–organic framework (MOF), based on 3-amino-4-hydroxybenzoic acid (H₂L) ligand, with the following formulae {[Y_3.5Eu_1.5L₆(OH)₃(H₂O)₃]·12DMF}_n (in advance, namely Y/Eu-MOF), is described. The three-dimensional structure has been synthesized by solvothermal routes and thoroughly characterized, by means of single crystal X-ray diffraction, powder X-ray diffraction, electronic microscopy, ICP-AES, electrophoretic mobility, and FTIR spectra. Intriguingly, the porous nature allows for coordinated solvent molecules displacement, yielding unsaturated metal centers, which can act as a Lewis acid catalyst. This novel supramolecular entity has been tested in cyanosilylation and hydroboration reactions on carbonyl substrates of a diverse nature, exhibiting an extraordinary activity. Full article

(This article belongs to the Section Photocatalysis)

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16 pages, 2964 KiB

Open AccessArticle

Highly-Ordered PdIn Intermetallic Nanostructures Obtained from Heterobimetallic Acetate Complex: Formation and Catalytic Properties in Diphenylacetylene Hydrogenation

by Igor S. Mashkovsky, Pavel V. Markov, Galina O. Bragina, Galina N. Baeva, Alexander V. Rassolov, Ilya A. Yakushev, Michael N. Vargaftik and Alexander Yu. Stakheev

Nanomaterials 2018, 8(10), 769; https://doi.org/10.3390/nano8100769 - 28 Sep 2018

Cited by 27 | Viewed by 5240

Abstract

Formation of PdIn intermetallic nanoparticles supported on α-Al₂O₃ was investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and hydrogen temperature-programmed desorption (H₂-TPD) methods. The metals were loaded as heterobimetallic Pd(μ-O₂CMe)₄In(O₂CMe) [...] Read more.

Formation of PdIn intermetallic nanoparticles supported on α-Al₂O₃ was investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and hydrogen temperature-programmed desorption (H₂-TPD) methods. The metals were loaded as heterobimetallic Pd(μ-O₂CMe)₄In(O₂CMe) complex to ensure intimate contact between Pd and In. Reduction in H₂ at 200 °C resulted in Pd-rich PdIn alloy as evidenced by XRD and the disappearance of Pd hydride. A minor amount of Pd₁In₁ intermetallic phase appeared after reduction at 200 °C and its formation was accomplished at 400 °C. Neither monometallic Pd or in nor other intermetallic structures were found after reduction at 400–600 °C. Catalytic performance of Pd₁In₁/α-Al₂O₃ was studied in the selective liquid-phase diphenylacetylene (DPA) hydrogenation. It was found that the reaction rate of undesired alkene hydrogenation is strongly reduced on Pd₁In₁ nanoparticles enabling effective kinetic control of the hydrogenation, and the catalyst demonstrated excellent selectivity to alkene. Full article

(This article belongs to the Special Issue Organic-Inorganic Hybrid Nanomaterials)

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13 pages, 1009 KiB

Open AccessArticle

Efficient Suzuki–Miyaura C-C Cross-Couplings Induced by Novel Heterodinuclear Pd-bpydc-Ln Scaffolds

by Fu Ding, Yanli Li, Pingxuan Yan, Yan Deng, Dongping Wang, Yajing Zhang, Ileana Dragutan, Valerian Dragutan and Kangjun Wang

Molecules 2018, 23(10), 2435; https://doi.org/10.3390/molecules23102435 - 23 Sep 2018

Cited by 19 | Viewed by 6234

Abstract

An easy access to a series of previously unreported heterodinuclear Pd-Ln compounds, Pd-bpydc-La, Pd-bpydc-Ce and Pd-bpydc-Nd (bpydc = 2,2′-bipyridine-5,5′-dicarboxylate) has been developed. The Pd-Ln hybrid networks were effectively applied as catalysts in Suzuki–Miyaura C-C cross-coupling reactions of 4-bromoanisole and 4-bromobenzonitrile with phenylboronic acid, [...] Read more.

An easy access to a series of previously unreported heterodinuclear Pd-Ln compounds, Pd-bpydc-La, Pd-bpydc-Ce and Pd-bpydc-Nd (bpydc = 2,2′-bipyridine-5,5′-dicarboxylate) has been developed. The Pd-Ln hybrid networks were effectively applied as catalysts in Suzuki–Miyaura C-C cross-coupling reactions of 4-bromoanisole and 4-bromobenzonitrile with phenylboronic acid, under mild conditions. A systematic investigation revealed Pd-bpydc-Nd as the most active catalyst. In all cases, reaction yields varied with the base, catalyst loading and substantially augmented with temperature (from 30 to 60 °C). Substituent effects were operative when changing from 4-bromoanisole to 4-bromobenzonitrile. The key role played by the lanthanides, aromatic substrate and base, in modulating the Pd-catalytic cycle has been highlighted. Importantly, the new catalysts proved to be stable in air and vs. functionalities and are quite efficient in Suzuki–Miyaura carbon-carbon bond formation conducted in protic solvents. Full article

(This article belongs to the Special Issue Organometallic Catalysis in Organic Synthesis)

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18 pages, 396 KiB

Open AccessArticle

Enantioselective Synthesis of 2,2-Disubstituted Terminal Epoxides via Catalytic Asymmetric Corey-Chaykovsky Epoxidation of Ketones

by Toshihiko Sone, Akitake Yamaguchi, Shigeki Matsunaga and Masakatsu Shibasaki

Molecules 2012, 17(2), 1617-1634; https://doi.org/10.3390/molecules17021617 - 7 Feb 2012

Cited by 28 | Viewed by 9546

Abstract

Catalytic asymmetric Corey-Chaykovsky epoxidation of various ketones with dimethyloxosulfonium methylide using a heterobimetallic La-Li₃-BINOL complex (LLB) is described. The reaction proceeded smoothly at room temperature in the presence of achiral phosphine oxide additives, and 2,2-disubstituted terminal epoxides were obtained in high [...] Read more.

Catalytic asymmetric Corey-Chaykovsky epoxidation of various ketones with dimethyloxosulfonium methylide using a heterobimetallic La-Li₃-BINOL complex (LLB) is described. The reaction proceeded smoothly at room temperature in the presence of achiral phosphine oxide additives, and 2,2-disubstituted terminal epoxides were obtained in high enantioselectivity (97%–91% ee) and yield ( > 99%–88%) from a broad range of methyl ketones with 1–5 mol% catalyst loading. Enantioselectivity was strongly dependent on the steric hindrance, and other ketones, such as ethyl ketones and propyl ketones resulted in slightly lower enantioselectivity (88%–67% ee). Full article

(This article belongs to the Special Issue Asymmetric Catalysis)

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11 pages, 158 KiB

Open AccessArticle

Catalytic Asymmetric Nitro-Mannich Reactions with a Yb/K Heterobimetallic Catalyst

by Tatsuya Nitabaru, Naoya Kumagai and Masakatsu Shibasaki

Molecules 2010, 15(3), 1280-1290; https://doi.org/10.3390/molecules15031280 - 4 Mar 2010

Cited by 21 | Viewed by 9278

Abstract

A catalytic asymmetric nitro-Mannich (aza-Henry) reaction with rare earth metal/alkali metal heterobimetallic catalysts is described. A Yb/K heterobimetallic catalyst assembled by an amide-based ligand promoted the asymmetric nitro-Mannich reaction to afford enantioenriched anti-b-nitroamines in up to 86% ee. Facile reduction of the [...] Read more.

A catalytic asymmetric nitro-Mannich (aza-Henry) reaction with rare earth metal/alkali metal heterobimetallic catalysts is described. A Yb/K heterobimetallic catalyst assembled by an amide-based ligand promoted the asymmetric nitro-Mannich reaction to afford enantioenriched anti-b-nitroamines in up to 86% ee. Facile reduction of the nitro functionality allowed for efficient access to optically active 1,2-diamines. Full article

(This article belongs to the Special Issue Bifunctional Catalysis)

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7 pages, 37 KiB

Open AccessArticle

Effect of Microwaves in the Chiral Switching Asymmetric Michael Reaction

by S. Narasimhan and S. Velmathi

Molecules 2003, 8(2), 256-262; https://doi.org/10.3390/80200256 - 28 Feb 2003

Cited by 11 | Viewed by 8463

Abstract

Highly enantioselective Michael reactions of malonates with cyclic enones are achieved in remarkably less time under microwave irradiation using newly developed heterobimetallic catalysts. Full article

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