Thiazol-2-ylidenes as N-Heterocyclic carbene ligands with enhanced electrophilicity for transition metal catalysis

Communications Chemistry, Год журнала: 2022, Номер 5(1)

Опубликована: Май 6, 2022

Over the last 20 years, N-heterocyclic carbenes (NHCs) have emerged as a dominant direction in ligand development transition metal catalysis. In particular, strong σ-donation combination with tunable steric environment make NHCs to be among most common ligands used for C-C and C-heteroatom bond formation. Herein, we report study on electronic properties of thiazol-2-ylidenes. We demonstrate that thiazole heterocycle enhanced π-electrophilicity result class highly active carbene electrophilic cyclization reactions form valuable oxazoline heterocycles. The evaluation steric, electron-donating π-accepting well structural characterization coordination chemistry is presented. This mode catalysis can applied late-stage drug functionalization furnish attractive building blocks medicinal chemistry. Considering key role ligands, anticipate N-aryl thiazol-2-ylidenes will broad interest modern chemical synthesis.

Язык: Английский

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Isolation of a Cu–H Monomer Enabled by Remote Steric Substitution of a N-Heterocyclic Carbene Ligand: Stoichiometric Insertion and Catalytic Hydroboration of Internal Alkenes

Journal of the American Chemical Society, Год журнала: 2022, Номер 144(30), С. 13865 - 13873

Опубликована: Июль 19, 2022

Transient Cu-H monomers have long been invoked in the mechanisms of substrate insertion catalysis. Their role from aggregates has mostly inferred since ligands to stabilize these monomeric intermediates for systematic studies remain limited. Within last decade, new sterically demanding N-heterocyclic carbene (NHC) led isolable dimers and, some cases, spectroscopic characterization solution. We report an NHC ligand, IPr*R, containing para R groups CHPh2 and CPh3 on ligand periphery isolation a monomer internal alkenes. This reactivity not reported (NHC)CuH complexes despite their common application Cu-H-catalyzed hydrofunctionalization. Changing impacts relative concentration monomers, rate alkene insertion, reaction trisubstituted alkene. Specifically, = CPh3, (IPr*CPh3)CuH was isolated provided >95% (10 mM C6D6). In contrast, CHPh2, solutions [(IPr*CHPh2)CuH]2 are 80% dimer 20% (IPr*CHPh2)CuH at 25 °C based 1H, 13C, 1H-13C HMBC NMR spectroscopy. Quantitative 1H kinetic cyclopentene into form corresponding Cu-cyclopentyl demonstrate strong dependence monomer. Only (IPr*CPh3)CuH, which high concentration, underwent regioselective alkene, 1-methylcyclopentene, give (IPr*CPh3)Cu(2-methylcyclopentyl), crystallographically characterized. also demonstrated that catalyzes hydroboration methylcyclopentene with pinacolborane.

Язык: Английский

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Pd–PEPPSI N-Heterocyclic Carbene Complexes from Caffeine: Application in Suzuki, Heck, and Sonogashira Reactions

Organometallics, Год журнала: 2022, Номер 41(16), С. 2281 - 2290

Опубликована: Авг. 11, 2022

The first synthesis of Pd-PEPPSI N-heterocyclic carbene complexes derived from the abundant and renewable natural product caffeine is reported. catalysts bearing 3-chloro-pyridine, pyridine N-methylimidazole ancillary ligands were readily prepared corresponding N9-Me imidazolium salt by direct deprotonation coordination to PdX2 in presence N-heterocycles or ligand displacement PdX2(Het)2. model Pd-PEPPSI-caffeine complex has been characterized x-ray crystallography. successfully employed Suzuki cross-coupling aryl bromides, amides, Heck Sonogashira cross-coupling. Computational studies determine frontier molecular orbitals bond order analysis complexes. This class offers an entry utilize benign sustainable biomass-derived Xanthine NHC popular systems organic catalysis.

Язык: Английский

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ItOct (ItOctyl) – pushing the limits of ItBu: highly hindered electron-rich N-aliphatic N-heterocyclic carbenes

Chemical Science, Год журнала: 2023, Номер 14(19), С. 5141 - 5147

Опубликована: Янв. 1, 2023

ItBu (ItBu = 1,3-di-tert-butylimidazol-2-ylidene) represents the most important and versatile N-alkyl N-heterocyclic carbene available in organic synthesis catalysis. Herein, we report synthesis, structural characterization catalytic activity of ItOct (ItOctyl), C2-symmetric, higher homologues ItBu. The new ligand class, including saturated imidazolin-2-ylidene analogues has been commercialized collaboration with MilliporeSigma: ItOct, 929 298; SItOct, 492 to enable broad access academic industrial researchers within field inorganic synthesis. We demonstrate that replacement t-Bu side chain t-Oct results highest steric volume carbenes reported date, while retaining electronic properties inherent N-aliphatic ligands, such as extremely strong σ-donation crucial reactivity carbenes. An efficient large-scale imidazolium imidazolinium SItOct precursors is presented. Coordination chemistry Au(i), Cu(i), Ag(i) Pd(ii) well beneficial effects on catalysis using complexes are described. Considering tremendous importance catalysis, metal stabilization, anticipate class ligands will find wide application pushing boundaries existing approaches

Язык: Английский

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N-Heterocyclic Carbene Complexes of Nickel(II) from Caffeine and Theophylline: Sustainable Alternative to Imidazol-2-ylidenes

Organometallics, Год журнала: 2022, Номер 41(14), С. 1806 - 1815

Опубликована: Апрель 5, 2022

Xanthines, such as caffeine and theophylline, are abundant natural products that often present in foods. Leveraging renewable benign resources for ligand design organometallic chemistry catalysis is one of the major missions green sustainable chemistry. In this Special Issue on Sustainable Organometallic Chemistry, we report first nickel–N-heterocyclic carbene complexes derived from Xanthines. Well-defined air- moisture-stable, half-sandwich, cyclopentadienyl [CpNi(NHC)I] nickel–NHC prepared theophylline. The model complex has been characterized by X-ray crystallography. evaluation steric, electron-donating, π-accepting properties presented. High activity Suzuki–Miyaura cross-coupling demonstrated. data show carbenes both earth 3d transition metal represent a alternative to classical imidazol-2-ylidenes.

Язык: Английский

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Sonogashira Cross-Coupling of Aryl Ammonium Salts by Selective C–N Activation Catalyzed by Air- and Moisture-Stable, Highly Active [Pd(NHC)(3-CF₃-An)Cl₂] (An = Aniline) Precatalysts

Organic Letters, Год журнала: 2022, Номер 24(34), С. 6310 - 6315

Опубликована: Авг. 24, 2022

We report the Sonogashira cross-coupling of aryl ammonium salts catalyzed by air- and moisture-stable [Pd(NHC)(3-CF3-An)Cl2] (An = aniline). This highly active Pd(II)–NHC complex features broad scope excellent C–N activation selectivity in challenging alkynylative salts. Full structural characterization computational studies demonstrate effect pyridine to aniline replacement as effective stabilizing ancillary ligand well-defined Pd(II)–NHCs. Considering high reactivity recent commercialization (Millipore Sigma, no. 915165), this catalyst represents an attractive approach bonds synthetic interest.

Язык: Английский

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Pt^II−N‐Heterocyclic Carbene Complexes in Solvent‐Free Alkene Hydrosilylation

Chemistry - A European Journal, Год журнала: 2023, Номер 29(40)

Опубликована: Май 17, 2023

Herein, we report the catalytic activity of a series platinum(II) pre-catalysts, bearing N-heterocyclic carbene (NHC) ligands, in alkene hydrosilylation reaction. Their structural and electronic properties are fully investigated using X-ray diffraction analysis nuclear magnetic resonance spectroscopy (NMR). Next, our study presents structure-activity relationship within this group pre-catalysts gives mechanistic insights into catalyst activation step. An exceptional performance one complexes is observed, reaching turnover number (TON) 970 000 frequency (TOF) 40 417 h-1 at 1 ppm loading. Finally, an attractive solvent-free open-to-air protocol, featuring efficient platinum removal (reduction residual Pt from 582 to 5.8 ppm), disclosed.

Язык: Английский

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Bulky NHC–Cobalt Complex-Catalyzed Highly Markovnikov-Selective Hydrosilylation of Alkynes

Catalysts, Год журнала: 2023, Номер 13(3), С. 510 - 510

Опубликована: Март 2, 2023

The hydrosilylation of alkynes is one the most attractive and, at same time, challenging catalytic transformations, usually demanding use noble transition metals. We describe a system, based on cobalt(0) complex and bulky N-heterocyclic carbene (NHC) ligands, permitting highly effective broad scope silanes. application NHC ligands allowed decrease in amount cobalt necessary for an reaction run to 2.5 mol% provided excellent selectivity towards α-vinylsilanes. developed method tolerates number substituted aryl, alkyl, silyl acetylenes. Moreover, it suitable both tertiary secondary Our findings confirm that steric hindrance around metal center can effectively increase activity catalyst ensure better than those analogous complexes bearing smaller ligands.

Язык: Английский

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IPr^# Complexes─Highly-Hindered, Sterically-Bulky Cu(I) and Ag(I) N-Heterocyclic Carbenes: Synthesis, Characterization, and Reactivity

Organometallics, Год журнала: 2024, Номер 43(19), С. 2305 - 2313

Опубликована: Сен. 21, 2024

Metal-N-heterocyclic carbene (M-NHC) complexes are well-known as an important class of organometallic compounds widely used in transition-metal catalysis. Taking into account that the steric hindrance around metal center is one major effects M-NHC catalysis, development new, sterically hindered ongoing interest this field research. Herein, we report synthesis and characterization exceedingly hindered, well-defined, air- moisture-stable Cu(I) Ag(I) complexes, [Cu(NHC)Cl] [Ag(NHC)Cl], recently discovered IPr

Язык: Английский

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Tunable Unsymmetrical Ferrocene Ligands Bearing a Bulky Di-1-adamantylphosphino Motif for Many Kinds of C_sp²–C_sp³ Couplings

ACS Catalysis, Год журнала: 2022, Номер 12(9), С. 5123 - 5135

Опубликована: Апрель 15, 2022

A class of ferrocene-based unsymmetrical bidentate ligands containing a di(1-adamantyl)phosphino group, Fc(PAd2)(PR2) (R = Ph, Cy, iPr, tBu) abbreviated as MPhos ligands, and their corresponding (MPhos)PdCl2 pre-catalysts were synthesized in very good yields fully characterized using techniques including single-crystal X-ray crystallography. These utilized for Csp2–Csp3 couplings many kinds name reactions such Murahashi–Feringa, Kumada–Corriu, Negishi, Suzuki–Miyaura with substrate scope isolated yields. About nine "drug-like" molecules also tested successfully to demonstrate potential applications active pharmaceutical ingredient (API) synthesis. The tunability the catalyst system enabled matching sterics electronics ligand that substrates have desirable results over five dozen systems selectivity.

Язык: Английский

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