Photolytic reaction of chromium and molybdenum carbene complexes with imines : Synthesis of cepham, oxapenam, and oxacepham derivatives

A variety of substituted β-lactams, including a cepham analog, were synthesized by the photochemical reaction of [(methoxy)(methyl)carbene]chromium complexes with substituted imines. Oxazines and oxazolines were inert towards chromium carbene complexes. Oxazines were converted to bicyclic β-lactams by the photolytic reaction of molybdenum carbene complexes. Oxazolines were considerably less reactive and produced only low yields of β-lactam product and an equivalent amount of the corresponding oxazinone, incorporating two (MeO)(Me)C(CO) groups.     

Dinuclear gold(I)-N-heterocyclic carbene complexes: Synthesis,characterization, and catalytic application for hydrohydrazidation of terminal alkynes

Dinuclear gold(I)-N-heterocyclic carbene complexes were developed for the hydrohydrazidation of terminal alkynes. The gold(I)-N-heterocyclic carbene complexes 2a-2b were synthesized in good yields from silver complexes synthesized in situ, which in turn were obtained from the corresponding imidazolium salts with Ag₂O in dichloromethane as a solvent. The new air-stable gold(I)-NHC complexes, 2a - 2b, were characterized using NMR spectroscopy, elemental analysis, infrared, and mass spectroscopy studies. The gold(I) complex 2a was characterized using X-ray crystallography. Bis-N-heterocyclic carbene–based gold(I) complexes 2a - 2b exhibited excellent catalytic activities for hydrohydrazidation of terminal alkynes yielding acylhydrazone derivatives. The working catalytic system can be used in gram-scale synthesis. In addition, the catalytic reaction mechanism of the hydrohydrazidation of terminal alkynes by gold(I)-NHC complex was studied in detail using density functional theory.     

Addition of S-H bonds across electron-deficient olefins catalyzed by well-defined copper(I) thiolate complexes

A series of monomeric (NHC)Cu(SR) (R = Ph or CH2Ph; NHC = N-heterocyclic carbene) complexes have been synthesized and fully characterized including single-crystal X-ray diffraction studies. These complexes catalyze the addition of S-H bonds across electron-deficient olefins to regioselectively produce "anti-Markovnikov" products.     

(N‐heterocyclic carbene)PdCl(N‐heterocyclic carboxylate) complexes: Synthesis and catalytic activities towards arylation of benzoxazoles with aryl halides

A series of N‐heterocyclic carboxylate‐stabilized N‐heterocyclic carbene palladium complexes have been synthesized and fully characterized. The solid‐state structures indicate that each of the palladium centers is coordinated by an N‐heterocyclic carbene, a chloride and a bidentate N,O‐donor N‐heterocyclic carboxylate ligand. The catalytic performance of the complexes was screened and the results revealed that the complexes exhibit moderate to high catalytic activities for the direct C─H bond arylation of benzoxazoles with aryl bromides.     

New Fischer carbene complexes of rhodium(i): preparation and 2-cyclopentenone ring synthesis by annelation to alkynes

A new type of metal carbene complexes of group 9, specifically a cationic Fischer carbene of rhodium(I), has been synthesized from chromium carbene complexes via double transfer of carbene and CO ligands. These complexes reveal a different reactivity than other transition metal carbenes, including their chromium precursors, toward neutral and electron-poor alkynes, giving selectively polysubstituted cyclopentenones.     

Latent ruthenium carbene complexes with six-membered N- and S-chelate rings

New ruthenium carbene complexes with chelating N- and S-benzylidene ligands were synthesized by the reactions of second- and third-generation Grubbs catalysts with ortho-vinylbenzyl-substituted amines or sulfides. These complexes were shown to exhibit catalytic activity in ring-opening metathesis polymerization and ring-closing metathesis.     

Novel (N‐heterocyclic carbene)Pd(pyridine)Br2 complexes for carbonylative Sonogashira coupling reactions: Catalytic efficiency and scope for arylalkynes,alkylalkynes and dialkynes

New N,N′‐substituted imidazolium salts and their corresponding dibromidopyridine–palladium(II) complexes were successfully synthesized and characterized. Reactions of palladium bromide with the newly synthesized N,N′‐substituted imidazolium bromides ( 2a and 2b ) in pyridine afforded the corresponding new N‐heterocyclic carbene pyridine palladium(II) complexes ( 3a and 3b ) in high yields. Their single‐crystal X‐ray structures show a distorted square planar geometry with the carbene and pyridine ligands in trans position. Both complexes show a high catalytic activity in carbonylative Sonogashira coupling reactions of aryl iodides and aryl diiodides with arylalkynes, alkylalkynes and dialkynes.     

Synthesis and biological activity of ester- and amide-functionalized imidazolium salts and related water-soluble coinage metal N-heterocyclic carbene complexes

N-Heterocyclic carbene (NHC) ligand precursors, namely, HIm(A)Cl [1,3-bis(2-ethoxy-2-oxoethyl)-1H-imidazol-3-ium chloride] and HIm(B)Cl {1,3-bis[2-(diethylamino)-2-oxoethyl]-1H-imidazol-3-ium chloride}, functionalized with hydrophilic groups on the imidazole rings have been synthesized and were used in the synthesis of corresponding carbene complexes of silver(I) and copper(I), {[Im(A)]AgCl}, {[Im(A)]CuCl}, and {[Im(B)](2)Ag}Cl. Related Au(I)NHC complexes {[Im(A)]AuCl} and {[Im(B)]AuCl} have been obtained by transmetalation using the silver carbene precursor. These compounds were characterized by several spectroscopic techniques including NMR and mass spectroscopy. HIm(B)Cl and the gold(I) complexes {[Im(A)]AuCl} and {[Im(B)]AuCl} were also characterized by X-ray crystallography. The cytotoxic properties of the NHC complexes have been assessed in various human cancer cell lines, including cisplatin-sensitive and -resistant cells. The silver(I) complex {[Im(B)](2)Ag}Cl was found to be the most active, with IC(50) values about 2-fold lower than those achieved with cisplatin in C13*-resistant cells. Growth-inhibitory effects evaluated in human nontransformed cells revealed a preferential cytotoxicity of {[Im(B)](2)Ag}Cl versus neoplastic cells. Gold(I) and silver(I) carbene complexes were also evaluated for their ability to in vitro inhibit the enzyme thioredoxin reductase (TrxR). The results of this investigation showing that TrxR appeared markedly inhibited by both gold(I) and silver(I) derivatives at nanomolar concentrations clearly point out this selenoenzyme as a protein target for silver(I) in addition to gold(I) complexes.     

Pincer-type bis(carbene)-derived complexes of nickel(II): Synthesis, structure, and catalytic activity

Air- and moisture-stable NHC (N-heterocyclic carbene)-derived CNC-type pincer complexes of nickel(II) 4a-d were successfully synthesized, and their structures were fully characterized using X-ray crystallography and analytical and spectroscopic methods. These complexes exhibit a high catalytic activity for the Suzuki-Miyaura coupling reaction of aryl bromides and chlorides with aryl- and alkenylboronic acids, providing an array of biphenyls and stilbenes generally in high yields.     

Cycloadditions and annulations of transition metal carbene complexes

The synthetic aspects of several reactions from the multifaceted chemistry of Fischer carbene complexes are examined. Their benzannulation reactions with acetylenes are utilized in the synthesis of anthracyclinones via two approaches which differ by beginning at opposite ends of the molecule with either an aryl or an alkenyl substituted chromium carbene complex. The latter has been employed in a formal synthesis of daunomycinone. The Diels-Alder reactions of ,β-acetylenic chromium carbene complexes provide for a facile entry into substituted cyclohexenyl chromium carbene complexes that are subsequently employed in benzannulation reactions. These tandem cycloaddition/annulation reactions are incorporated into model studies for the synthesis of anthracyclinones and wentilactone A. Their potential is also demonstrated for coupling to yet a third reaction of organochromium compounds ; aromatic nucleophilic substitutions on arene chromium tricarbonyl complexes. The annulations of β,β-disubstituted alkenyl complexes provides for a regio- and stereoselective synthesis of 2,4-cyclohexadienones under neutral conditions at near ambient temperatures.     

Synthesis, isolation and characterization of cationic gold(I) N-heterocyclic carbene (NHC) complexes

A number of cationic gold(I) complexes have been synthesized and found to be stabilized by the use of N-heterocyclic carbene ligands. These species are often employed as in situ-generated reactive intermediates in gold catalyzed organic transformations. An isolated, well-defined species was tested in gold-mediated carbene transfer reactions from ethyl diazoacetate.     

Quinoline-functionalized N-heterocyclic carbene complexes of iridium: Synthesis, structures and catalytic activities in transfer hydrogenation

Iridium complexes containing quinoline-functionalized N-heterocyclic carbene (NHC) ligands have been synthesized by the transmetalation route from silver carbene precursors. The silver complexes undergo a facile reaction with [Ir(COD)Cl]₂ (COD = 1,5-cyclooctadiene) to yield a series of carbene complexes [(NHC)Ir(COD)Cl] (NHC = 3-methyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2a); 3-n-butyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2b); 3-benzyl-1-(8-quinolylmethyl)imidazole-2-ylidene (2c); 1,3-di(8-quinolylmethyl)imidazole-2-ylidene (2d). The coordinated COD was replaced by carbon monoxide to yield the corresponding carbonyl species [(NHC)Ir(CO)₂Cl] (3). Complexes 2 and 3 have been characterized by IR, ESI-MS, ¹H and ¹³C NMR and elemental analyses. The molecular structures of complexes 2b and 2c have been confirmed by single-crystal X-ray diffraction. Two analogous Ir(I) complexes 5 and 6 with naphthalene-containing NHC have also been synthesized and characterized. These Ir(I) complexes in the current work have been proved to be active catalysts in the transfer hydrogenation of ketones to alcohols using 2-propanol as the hydrogen source.     

N-Heterocyclic carbene adducts of cyclopalladated ferrocenylimines: Synthesis,characterization and catalytic activity for the Suzuki–Miyaura reaction

A series of novel air-stable carbene adducts of cyclopalladated ferrocenylimines have been synthesized and characterized. The structures of these complexes were determined by single-crystal X-ray analysis. These adducts have been successfully applied to the Suzuki–Miyaura coupling reaction under aerobic conditions. Good to excellent yields were obtained in short reaction times with a lower loading of the catalyst.     

Well‐Defined N‐Heterocyclic Carbene‐Palladium Complexes as Efficient Catalysts for Domino Sonogashira Coupling/Cyclization Reaction and C‐H bond Arylation of Benzothiazole

Well‐defined and air‐stable PEPPSI (Pyridine Enhanced Precatalyst Preparation Stabilization and Initiation) themed palladium bis‐N‐heterocyclic carbene complexes have been developed for the domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with a variety of terminal alkynes and C‐H bond arylation of benzothiazole with aryl iodides. The PEPPSI themed palladium complexes, 2a and 2b were synthesized in good yields from the reaction of corresponding imidazolium salts with PdCl₂ and K₂CO₃ in pyridine. The new air‐stable palladium‐NHC complexes were characterized by NMR spectroscopy, X‐ray crystallography, elemental analysis, and mass spectroscopy studies. The PEPPSI themed palladium(II) bis‐N‐heterocyclic carbene complexes 2a and 2b exhibited excellent catalytic activities for domino Sonogashira coupling/cyclization reaction of 2‐iodophenol with terminal alkynes yielding benzofuran derivatives. In addition, the palladium complexes, 2a and 2b successfully catalyzed the direct C‐H bond arylation of benzothiazole with aryl iodides as coupling partners in presence of CuI as co‐catalyst.     

Synthesis, characterization, and antimicrobial activity of silver carbene complexes derived from 4,5,6,7-tetrachlorobenzimidazole against antibiotic resistant bacteria

Silver N-heterocyclic carbene complexes have been shown to have great potential as antimicrobial agents, affecting a wide spectrum of both Gram-positive and Gram-negative bacteria. A new series of three silver carbene complexes (SCCs) based on 4,5,6,7-tetrachlorobenzimidazole has been synthesized, characterized, and tested against a panel of clinical strains of bacteria. The imidazolium salts and their precursors were characterized by elemental analysis, mass spectrometry, (1)H and (13)C NMR spectroscopy, and single crystal X-ray diffraction. The silver carbene complexes, SCC32, SCC33, and SCC34 were characterized by elemental analysis, (1)H and (13)C NMR spectroscopy, and single crystal X-ray diffraction. These complexes proved highly efficacious with minimum inhibitory concentrations (MICs) ranging from 0.25 to 6 μg mL(-1). Overall, the complexes were effective against highly resistant bacteria strains, such as methicillin-resistant Staphylococcus aureus (MRSA), weaponizable bacteria, such as Yersinia pestis, and pathogens found within the lungs of cystic fibrosis patients, such as Pseudomonas aeruginosa, Alcaligenes xylosoxidans, and Burkholderia gladioli. SCC33 and SCC34 also showed clinically relevant activity against a silver-resistant strain of Escherichia coli based on MIC testing.     

Metallocene Carbene Complexes and Related Compounds of Titanium,Zirconium, and Hafnium

The structure and creativity spectrum of transition-metal carbene complexes has been widened significantly by the bent metallocenes of titanium, zirconium, and hafnium. Proceeding from metal carbonyls and reactive (butadiene)-, (aryne)-, or (olefin) MCp₂ complexes, many new Fischer-type metaloxycarbene complexes of Zr, Hf, V, Nb, Cr, Mo, W, Mn, Re, Fe, Ru, Os, Co, Ni, and Rh have been synthesized. The incorporation of titanocene, zirconocene, or hafnocene fragments allows new types of carbene complexes to be prepared. For the (alkylidenamido)metallocene complexes , metallocene ylides , and binuclear (μ-alkynyl)metallocene compounds, some metalligand π bonding is indicated. Metallocene complexes with metallaoxirane units, , show similar chemical behavior to that of binuclear (μ-methylene)complexes . The methylene groups of zirconaoxirane complexes, which are derived from carbon monoxide, may be expelled as ethylene by thermally induced CC coupling. With metal hydrides, CH₂ transfer with insertion into the metal–hydride bond occurs. In one case, methylene insertion into a metal–carbon bond can even be observed. These reactions of Ti-group metallaoxiranes could be models for postulated intermediates in the Fischer–Tropsch synthesis.     

Pyridinium-derived N-heterocyclic carbene complexes of platinum: synthesis, structure and ligand substitution kinetics

A series of [(R-iso-BIPY)Pt(CH(3))L ](+)X(-) complexes [R-iso-BIPY = N-(2-pyridyl)-R-pyridine-2-ylidene; (R = 4-H, 1; 4-tert-butyl, 2; 4-dimethylamino, 3; 5-dimethylamino, 4); L = SMe(2), b; dimethyl sulfoxide (DMSO), c; carbon monoxide (CO), d; X = OTf(-) = trifluoromethanesulfonate and/or [BPh(4)](-)] were synthesized by cyclometalation of the [R-iso-BIPY-H](+)[OTF](-) salts 1a-4a ([R-iso-BIPY-H](+) = N-(2-pyridyl)-R-pyridinium) with dimethylplatinum-micro-dimethyl sulfide dimer. X-ray crystal structures for 1b, 2c-4c as well as complexes having bipyridyl and cyclometalated phenylpyridine ligands, [(bipy)Pt(CH(3))(DMSO)](+) (5c) and (C(11)H(8)N)Pt(CH(3))(DMSO) (6c), have been determined. The pyridinium-derived N-heterocyclic carbene complexes display localized C-C and C-N bonds within the pyridinium ligand that are indicative of carbene pi-acidity. The significantly shortened platinum-carbon distance, for "parent" complex 1b, together with NMR parameters and the nu(CO) values for carbonyl cations 1d-4d support a degree of Pt-C10 multiple bonding, increasing in the order 3 < 4 < 2 < 1. Degenerate DMSO exchange kinetics have been determined to establish the nature and magnitude of the trans-labilizing ability of these new N-heterocyclic carbene ligands. Exceptionally large second-order rate constants (k(2) = 6.5 +/- 0.4 M(-1).s(-1) (3c) to 2300 +/- 500 M(-1).s(-1) (1c)) were measured at 25 degrees C using (1)H NMR magnetization transfer kinetics and variable temperature line shape analysis. These rate constants are as much as 4 orders of magnitude greater than those of a series of structurally similar cationic bis(nitrogen)-donor complexes [(N-N)Pt(CH(3))(DMSO)](+) reported earlier, and a factor of 32 to 1800 faster than an analogous charge neutral complex derived from cyclometalated 2-phenylpyridine, (C(11)H(8)N)Pt(CH(3))(DMSO) (k(2) = 0.21 +/- 0.02 M(-1).s(-1) (6c)). The differences in rate constant are discussed in terms of ground state versus transition state energies. Comparison of the platinum-sulfur distances with second order rate constants suggests that differences in the transition-state energy are largely responsible for the range of rate constants measured. The pi-accepting ability and trans-influence of the carbene donor are proposed as the origin of the large acceleration in associative ligand substitution rate.     

Fluorescence and crystal structures of new mercury(II) macrocyclic N-heterocyclic carbene complexes with ether chains

Polyerther-linked mercury(II) carbene complexes are synthesized by the reaction of carbene precursores with mercury(II) acetate. The binuclear carbene complexes with the chloride ion linkage are easily prepared by the reaction of mononuclear mercury carbene complexes with tetrabutylammoium chloride. The crystal structures reveal that the fluorescence of mercury complexes are related to the coordination mode of the ligands.     

N-杂环卡宾Pd络合物的合成及其在Buchwald-Hartwig反应中的应用

合成鉴定了二个N-杂环卡宾环金属Pd络合物[1,3-N,N’-双{2,6-二取代基苯基}咪唑基-2-卡宾][N,N-二甲基卞胺-2-C,N]氯化钯(Ⅱ)(3a：取代基 = 异丙基；和3b：取代基 = 甲基)，评价了它们在氯代芳烃和各种胺偶联反应中的催化性能。发现NaOBu-t是效果较好的碱，及Pd周围有较大的立体位阻的3a在4-甲基氯苯与吗啡啉反应中较3b有更好的催化性能.     

Regioselective synthesis of substituted o-alkoxyphenol derivatives through thermal benzannulation of Fischer (alkenylcyclobutenyl)carbene complexes

A convenient, regioselective, and general synthetic method for producing highly substituted o-phenol-containing polycycles from Fischer (alkenylcyclobutenyl)carbene complexes has been described. The starting complexes have been synthesized by means of the [2 + 2] cycloaddition reaction of (alkenylethynyl)carbene complexes and a range of enol ethers, and in most cases, they have proven to be stable at room temperature and therefore isolable. The key step of the synthesis consists of the thermal benzannulation reaction of these novel pentacarbonyl dienyl Fischer complexes, which is an unprecedented transformation for these kinds of complexes. The unexpected behavior of (alkenylcyclobutenyl)carbene complexes has been rationalized in terms of their geometries.