Ruthenacycles and Iridacycles as Transfer Hydrogenation Catalysts

Molecules, Journal Year: 2021, Volume and Issue: 26(13), P. 4076 - 4076

Published: July 3, 2021

In this review, we describe the synthesis and use in hydrogen transfer reactions of ruthenacycles iridacycles. The review limits itself to metallacycles where a ligand is bound bidentate fashion either ruthenium or iridium via carbon-metal sigma bond, as well dative bond from heteroatom an N-heterocyclic carbene. Pincer complexes fall outside scope. Described are applications (asymmetric) hydrogenation aldehydes, ketones, imines, reductive aminations. Oxidation reactions, i.e., classical Oppenauer oxidation, which reverse hydrogenation, dehydrogenations oxidations with oxygen, described. Racemizations alcohols secondary amines also catalyzed by

Language: Английский

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Modular Pincer-type Pyridylidene Amide Ruthenium(II) Complexes for Efficient Transfer Hydrogenation Catalysis

Inorganic Chemistry, Journal Year: 2018, Volume and Issue: 57(18), P. 11761 - 11774

Published: Sept. 5, 2018

A set of bench-stable ruthenium complexes with new N,N,N-tridentate coordinating pincer-type pyridyl-bis(pyridylideneamide) ligands was synthesized in excellent yields, the pyridylidene amide meta or para position ( m-PYA and p-PYA, respectively). While complex [Ru( p-PYA)(MeCN)3]2+ is catalytically silent transfer hydrogenation, its isomer m-PYA)(MeCN)3]2+ shows considerable activity turnover frequencies at 50% conversion TOF50 = 100 h-1. Spectroscopic, electrochemical, crystallographic analyses suggest considerably stronger donor properties zwitterionic ligand compared to partially π-acidic p-PYA analogue, imparted by valence isomerization. Further catalyst optimization achieved exchanging ancillary MeCN imines (4-picoline), amines (ethylenediamine), phosphines (PPh3, dppm, dppe). The most active comprised pincer PPh3, m-PYA)(PPh3)(MeCN)2]2+, which reached a 430 h-1 under aerobic conditions up 4000 absence oxygen. presence oxygen reversibly deactivates species, compromises activity, but not longevity catalyst. Ligand exchange kinetic studies NMR spectroscopy indicate that strong trans effect phosphine critical for high activity. Diaryl, aryl-alkyl, dialkyl ketones were hydrogenated conversion, α,β-unsaturated produced selectively saturated ketone as only product due exclusive C═C bond distinctly different selectivity from other hydrogenation catalysts.

Language: Английский

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Discovery of methoxy-naphthyl linked N-(1-benzylpiperidine) benzamide as a blood-brain permeable dual inhibitor of acetylcholinesterase and butyrylcholinesterase

European Journal of Medicinal Chemistry, Journal Year: 2020, Volume and Issue: 207, P. 112761 - 112761

Published: Aug. 28, 2020

Language: Английский

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Optimization of Synthetically Versatile Pyridylidene Amide Ligands for Efficient Iridium‐Catalyzed Water Oxidation

Chemistry - A European Journal, Journal Year: 2018, Volume and Issue: 24(24), P. 6386 - 6398

Published: Feb. 14, 2018

The synthetic versatility of pyridylidene amide (PYA) ligands has been exploited to prepare and evaluate a diverging series iridium complexes containing C,N-bidentate chelating aryl-PYA for water oxidation catalysis. phenyl-PYA lead structure 1 was modified (i) electronically through introduction one, two, or three electron-donating methoxy substituents on the aryl ring, (ii) by incorporating long aliphatic chains pyridyl fragment PYA unit, (iii) altering positions from para-PYA its ortho- meta-isomers. Electrochemistry indicated no substantial electronic effect chains, only minor changes electron density at when modifying ligand site, yet alteration if is (E1/2 =+0.72 V), para- =+0.64 meta-isomer =+0.56 V vs. saturated calomel electrode; SCE). In catalysis, alkyl did not induce any rate enhancement compared with compound, whereas MeO groups incorporated in group enhanced catalytic activity turnover frequency (TOFmax )=1600 h-1 original Ph-PYA system gradually as more were introduced up TOFmax =3300 tris(MeO)-substituted system. variation substitution had impact revealed weak trend sequence ortho>meta>para. high tris(MeO) ortho-PYA isomer attributed efficient hydrogen bonding, which assists O-H bond activation proton transfer. Remarkably, merging two optimized motifs, that is, an unit ortho isomer, into single new failed improve activity. Computational analysis suggests too much congestion active hinders turnover. These results illustrate complexity design subtle effects play

Language: Английский

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A mesoionic nitrogen-donor ligand: structure, iridium coordination, and catalytic effects

Dalton Transactions, Journal Year: 2017, Volume and Issue: 47(3), P. 659 - 662

Published: Dec. 6, 2017

A mesoinic pyridylideneamide ligand (PYA) was synthetized and fully characterized coordinated to an iridium(iii) center. This represents the first example of a mesoionic N-donor ligand. Structural spectroscopic analysis revealed unique properties which were exploited in chemically driven water oxidation catalysis.

Language: Английский

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Resin-supported iridium complex for low-temperature vanillin hydrogenation using formic acid in water

RSC Advances, Journal Year: 2021, Volume and Issue: 11(26), P. 15835 - 15840

Published: Jan. 1, 2021

Biorefinery seeks to utilize biomass waste streams as a source of chemical precursors with which feed the industry. This goal replace petroleum main feedstock, however this task requires development efficient catalysts capable transforming substances derived from into useful products. In study, we demonstrate that highly-active iridium complex can be solid-supported and used low-temperature catalyst for both decomposition formic acid (FA) produce hydrogen, hydrogenation vanillyl alcohol (VA) 2-methoxy-4-methylphenol (MMP) vanillin (V); lignin-derived feedstock. These products are promising epoxy resins thus an approach their production without need petroleum. contrast other require temperatures exceeding 100 °C, here accomplish at temperature <50 °C in water under autogenous pressure. provides avenue towards biorefinery lower energy demands, is central decentralization broad implementation. We found high activity transfers solid-support accelerating rate determining step; FA hydrogen carbon dioxide. The yield VA MMP independently tuned depending on temperature. simplicity expands utility molecular metal complexes new opportunities biorefinery.

Language: Английский

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Olefin Dimerization and Isomerization Catalyzed by Pyridylidene Amide Palladium Complexes

Organometallics, Journal Year: 2018, Volume and Issue: 37(20), P. 3619 - 3630

Published: Sept. 24, 2018

A series of cationic palladium complexes [Pd(N∧N′)Me(NCMe)]+ was synthesized, comprising three different N∧N′-bidentate coordinating pyridyl–pyridylidene amide (PYA) ligands with electronic and structural properties depending on the PYA position (o-, m-, p-PYA). Structural investigation in solution revealed cis/trans isomeric ratios that correlate donor ligand, highest cis for complex having most donating o-PYA ligand lowest weakest p-PYA system. The catalytic activity alkene insertion dimerization showed a strong correlation setting. While bearing more electron m- produced butenes within 60 30 min, respectively, much slower only reached 50% conversion ethylene 2 h. Likewise, methyl acrylate as polar monomer efficient stronger units, reaching 32% ratio vs insertion. Mechanistic investigations about allowed detection, first time, by NMR spectroscopy both cis- trans-Pd-ethyl intermediates and, furthermore, trans to isomerization Pd-ethyl resting state rate-limiting step inducing conversion. These induce rapid double-bond terminal internal alkenes through chain-walking process, which prevents polymerization also higher olefins, leading selectively dimerization.

Language: Английский

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Highly Efficient Transfer Hydrogenation Catalysis with Tailored Pyridylidene Amide Pincer Ruthenium Complexes

Chemistry - A European Journal, Journal Year: 2020, Volume and Issue: 26(58), P. 13226 - 13234

Published: May 26, 2020

The rational optimization of homogeneous catalysts requires ligand platforms that are easily tailored to improve catalytic performance. Here, it is demonstrated pyridylidene amides (PYAs) provide such a platform custom-shape transfer hydrogenation with exceptional activity. Specifically, series meta-PYA pincer ligands differently substituted PYA units has been synthezised and coordinated ruthenium(II) centres form bench-stable tris-acetonitrile complexes [Ru(R-PYA-pincer)(MeCN)3 ](PF6 )2 (R=OMe, Me, H, Cl, CF3 ). Analytic studies including 1 H NMR spectroscopy, cyclic voltammetry, X-ray crystallography reveal direct influence the substituents on electronic properties ruthenium center. active in ketones, activities directly encoded by substitution pattern. Their perfomance improves further upon exchange an ancillary MeCN PPh3 . While [Ru(R-PYA-pincer)(PPh3 )(MeCN)2 were only isolated for R=H, situ protocol was developed generate these R=OMe, using 1:2 ratio This together short catalyst pre-activation provided highly systems. most pre-catalyst featured methoxy-substituted reached turnover frenquencies 210 000 h-1 under exceptionally low loading 25 ppm benchmark substrate benzophenone, representing one systems known date.

Language: Английский

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Structural, Electronic, and Catalytic Modulation of Chelating Pyridylideneamide Ruthenium(II) Complexes

Organometallics, Journal Year: 2020, Volume and Issue: 39(13), P. 2383 - 2391

Published: June 17, 2020

A family of Ru(cym)-type complexes bearing different pyridylideneamide (PYA) ligands has been prepared. Incorporation diverse potentially coordinating sites afforded a series chelating hybrid containing PYA nitrogen as one donor site and second variable constituted cyclometalated aryl ring (complex 3a), pyridine (3b), pyridylidene (3c), another unit (3d), or triazolylidene ligand (3e). Structural electrochemical analyses indicate considerable electronic variation in this with decreasing ability from phenyl > ≈ pyridine. This trend allows the properties metal center to be tailored reveals strong ligands, surpassing those pyridine-derived N-heterocyclic carbenes. The effect these tunable was demonstrated transfer hydrogenation catalysis, for which direct correlation between catalytic activity established.

Language: Английский

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Sterically and Electronically Flexible Pyridylidene Amine Dinitrogen Ligands at Palladium: Hemilabile cis/trans Coordination and Application in Dehydrogenation Catalysis

Chemistry - A European Journal, Journal Year: 2022, Volume and Issue: 28(68)

Published: Sept. 6, 2022

Ligand design is crucial for the development of new catalysts and materials with properties. Herein, synthesis unique hemilabile coordination properties bis-pyridylidene amine (bis-PYE) ligands to palladium, preliminary catalytic activity these complexes in formic acid dehydrogenation are described. The synthetic pathway form cationic [Pd(bis-PYE)Cl(L)]X a cis-coordinated N,N-bidentate bis-PYE ligand flexible provides access diversity Pd

Language: Английский

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