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, Journal Year: 2022, Volume and Issue: 144(30), P. 13865 - 13873

Published: July 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.

Language: Английский

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

Organometallics, Journal Year: 2022, Volume and Issue: 41(16), P. 2281 - 2290

Published: Aug. 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.

Language: Английский

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

Chemical Science, Journal Year: 2023, Volume and Issue: 14(19), P. 5141 - 5147

Published: Jan. 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

Language: Английский

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

Chemistry - A European Journal, Journal Year: 2023, Volume and Issue: 29(40)

Published: May 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.

Language: Английский

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

Organometallics, Journal Year: 2022, Volume and Issue: 41(14), P. 1806 - 1815

Published: April 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.

Language: 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, Journal Year: 2022, Volume and Issue: 24(34), P. 6310 - 6315

Published: Aug. 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.

Language: Английский

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

Catalysts, Journal Year: 2023, Volume and Issue: 13(3), P. 510 - 510

Published: March 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.

Language: Английский

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

Organometallics, Journal Year: 2024, Volume and Issue: 43(19), P. 2305 - 2313

Published: Sept. 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

Language: Английский

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Site-Selective Copper–N-Heterocyclic Carbene-Catalyzed C(sp²)–C(sp) Cross-Coupling of Aryl Thianthrenium Salts

Organic Letters, Journal Year: 2025, Volume and Issue: unknown

Published: March 23, 2025

This work demonstrates Cu–NHC (NHC = N-heterocyclic carbene) catalyzed alkynylation of aryl thianthrenium salts via thiazol-2-ylidene ligands, achieving a Pd-free Sonogashira coupling with broad substrate compatibility and functional group tolerance. Late-stage pharmaceutical rare alkynylative C–H functionalization/ring-opening pathways are enabled. Thiazol-2-ylidenes, featuring "half-umbrella"-shaped geometry, exhibit superior catalytic performance over traditional imidazol-2-ylidenes, underscoring their unique ligand efficacy. catalysis enables the use as versatile electrophiles for diverse cross-couplings under mild conditions.

Language: Английский

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Mechanistic Insights into Molecular Copper Hydride Catalysis: the Kinetic Stability of CuH Monomers toward Aggregation is a Critical Parameter for Catalyst Performance

Journal of the American Chemical Society, Journal Year: 2025, Volume and Issue: unknown

Published: March 31, 2025

The activity of molecular copper hydride (CuH) complexes toward the selective insertion unsaturated hydrocarbons under mild conditions has contributed significantly to versatile methodologies for upgrading these feedstocks. However, catalysts are particularly susceptible deleterious aggregation, leading depletion active CuH species. Little is known about mechanisms how it influences overall catalyst performance, and can be controlled. We address challenges with mechanistic studies on a model reaction unactivated alkene hydroboration catalyzed by (IPr*CPh3)CuH (LCuH). report comprehensive investigation this system, identifying an aggregation pathway that continuously depletes catalytically LCuH form inactive clusters during turnover. Deactivation controlled primarily competition between kinetics initial dimerization step into LCuH. therefore propose understanding performance must account step, revising previously explored thermodynamic where concentration species equilibria established monomers. With series (NHC)CuH congeners (NHC = N-heterocyclic carbene), we demonstrate ostensibly minor structural modifications ligand peripheries drastically affect kinetics, while maintaining reactivity on-cycle insertion. employed computational approach based dynamics simulations provide in-depth specific substantially increase kinetic stability monomeric catalysts. Our combined experimental suggest strategies rational design broadly applied systems deactivation via pathways.

Language: Английский

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