Homocoupling of arylboronic acids catalyzed by simple gold salts

A range of arylboronic acids undergo a homocoupling reaction in the presence of catalytic amount of gold salts to yield symmetrical biaryls. Alkenylboronic acids, arylboronic esters, and arylborates also participate in the gold-catalyzed homocoupling reaction.     

Homocoupling of arylboronic acids and potassium aryltrifluoroborates catalyzed by protein-stabilized palladium nanoparticles under air in water

Palladium nanoparticles stabilized primarily within the protein cavity of a highly thermostable Dps protein (DNA binding protein from starved cells) from the thermophilic bacterium Thermosynechoccus elongatus provide an efficient catalyst for the homocoupling of boronic acids and potassium aryltrifluoroborates in water under aerobic phosphine-free conditions. Symmetrical biaryls have been isolated in good to excellent yields. Potassium aryltrifluoroborates give similar or better results than the corresponding arylboronic acids.     

Very mild, enantioselective synthesis of propargylamines catalyzed by copper(I)-bisimine complexes

The stereoselective addition of aryl- and alkylacetylene derivatives to imines was studied. The reaction is catalyzed by copper complexes of enantiomerically pure bisimines, readily prepared in very high yields from the commercially available binaphthyl diamine. A very simple experimental procedure allowed to obtain at room temperature optically active propargylamines in high yields and enantioselectivity. Interestingly, bisimine/copper(I) complexes were able to promote the direct, enantioselective, catalytic addition to imines of alkylacetylenes. The effects of catalyst loading and other reaction parameters on the stereochemical outcome of the transformation were investigated. The extremely convenient methodology, the mild reaction conditions, and the possibility of a modular approach for developing new and more efficient bisimine-based chiral ligands make the present methodology very attractive.     

Remarkable co-catalysis by copper(I) oxide in the palladium catalyzed cross-coupling of arylboronic acids with ethyl bromoacetate

Copper(I) oxide can effectively co-catalyze the Suzuki type cross-coupling reactions of arylboronic acids with ethyl bromoacetate. As an alternative protocol for introducing the methylenecarboxy group into functionalized molecules, this reaction occurs in the absence of highly toxic thallium compounds or special ligands and should be convenient and practical.     

Aerobic oxidation of primary alcohols under mild aqueous conditions promoted by a dinuclear copper(II) complex

A sugar-discriminating dinuclear copper(II) complex was investigated for its ability to promote aerobic oxidation of primary benzylic alcohols in the presence of TEMPO and base. The transformation of benzyl alcohol to benzaldehyde was chosen as exploratory model reaction. The constitution of the catalytically active species was deducted from isothermal titration calorimetry and kinetic experiments, and the catalytic reaction was characterized both in aqueous organic and aqueous solution. The dinuclear complex is found to selectively oxidize primary over secondary alcohols in aqueous solution at ambient temperature with a turnover rate of 9 h⁻¹. A mechanism for the catalytic cycle is proposed.     

铜配合物催化的环状烯烃的光化学顺、反异构化反应

在大于300nm光波照射下,氯化亚铜或乙酰丙酮基铜(I)等低价铜配合物可以有效地催化中大环环状烯烃的顺、反异构化反应,对在大于250nm光波照射下,顺,顺-1,5-环辛二烯分子内环加成形成三环[3.3.0.0^2^.^6]-辛烷的反应机制,进行了讨论。     

Enantioselective 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds catalyzed by rhodium(I)-chiral phosphoramidite complexes

A chiral bidentate phosphoramidite (5a) was synthesized from Shibasaki’s linked-(R)-BINOL and P(NMe₂)₃ as a new ligand for rhodium(I)-catalyzed asymmetric 1,4-addition of arylboronic acids to α,β-unsaturated carbonyl compounds. The effects of 5a and Feringa’s monodentate phosphoramidite (4, R¹, R² = Et) on the yields and enantioselectivities were fully investigated. The reaction was significantly accelerated in the presence of a base such as KOH and Et₃N, allowing the reaction to be completed at the lower temperatures than 50 °C. The addition to cyclic enones such as 2-cyclopentenone, 2-cyclohexenone and 2-cycloheptenone at 50 °C in the presence of an [Rh(coe)₂Cl]₂-4 (R¹, R² = Et) complex resulted in enantioselectivities up to 98%, though it was less effective for acyclic enones (0–70% ee). On the other hand, a complex between [Rh(nbd)₂]BF₄ and 5a completed the addition to cyclic enones within 2 h at room temperature in the presence of Et₃N with 86–99% yields and 96–99.8% ee. This catalyst was also effective for acyclic enones, resulting in 62–98% yields and 66–94% ee. The 1,4-additions of arylboronic acids to unsaturated lactones and acyclic esters with rhodium(I)-phosphoramidites complexes were also investigated.     

Syntheses,crystal structures and properties of dinuclear copper(I) complexes

Two dinuclear molecule-bridged Cu(I) complexes, (μ-bpym)[Cu(PPh₃)Cl]₂ (1), [(μ-bpym)(CuL)₂](ClO₄)₂·(CH₃CN)₂(H₂O) (2) (bpym = 2,2′-bipyrimidine, L = (R)-(+)-2,2′-bis(diphenylphospho)-1,1′-dinaphthalene) have been synthesized and characterized. The molecular structures of the two new dinuclear compounds exhibit bridging of two copper(I) centers by the symmetrically bis-chelating bpym ligand. Intriguingly, compound 1 features a remarkable “intramolecular organic sandwich” configuration where the central 2,2′-bipyrimidine bridging ligand interacts in π/π/π fashion with two phenyl rings from the coligands above and below the central plane, while chiral compound 2 exhibits second-order nonlinear optical effect and temperature-dependent luminescence. Upon decreasing the temperature from 298 to 10 K, compound 2 shows a red light emission.     

The nature of bond critical points in dinuclear copper(I) complexes

Closed-shell contacts between two copper(I) ions are expected to be repulsive. However, such contacts are quite frequent and are well documented. Crystallographic characterization of such contacts in unsupported and bridged multinuclear copper(I) complexes has repeatedly invited debates on the existence of cuprophilicity. Recent developments in the application of Bader's theory of atoms-in-molecules (AIM) to systems in which weak hydrogen bonds are involved suggests that the copper(I)-copper(I) contacts would benefit from a similar analysis. Thus the nature of electron-density distributions in copper(I) dimers that are unsupported, and those that are bridged, have been examined. A comparison of complexes that are dimers of symmetrical monomers and those that are dimers of two copper(I) monomers with different coordination spheres has also been made. AIM analysis shows that a bond critical point (BCP) between two Cu atoms is present in most cases. The nature of the BCP in terms of the electron density, ρ, and its Laplacian is quite similar to the nature of critical points observed in hydrogen bonds in the same systems. The ρ is inversely correlated to Cu-Cu distance. It is higher in asymmetrical systems than what is observed in corresponding symmetrical systems. By examining the ratio of the local electron potential-energy density (V(c)) to the kinetic energy density (G(c)), |V(c)|/G(c) at the critical point suggests that these interactions are not perfectly ionic but have some shared nature. Thus an analysis of critical points by using AIM theory points to the presence of an attractive metallophilic interaction similar to other well-documented weak interactions like hydrogen bonding.     

Amination and amidation of aryl iodides catalyzed by copper(I)-phenanthroline complexes

Four kinds of copper(I)-phenanthroline complexes ([Cu^I(phen)₂]Cl, [Cu^I(phen)Cl]₂, [Cu^I(phen)₂]BF₄, and Cu^I(phen)PPh₃Cl) were prepared and used as catalysts for amination and amidation of aryl iodide to investigate the influence on the yields of products due to differences of the structures. These complexes were found to work as catalysts on these reactions and showed that the differences of structures of copper(I) complexes significantly influenced the yield of aryl-nitrogen bond forming processes.     

Controlled radical polymerization catalyzed by copper(I)–sparteine complexes

Sparteine was found to be an efficient ligand because when complexed with copper(I) halide it generated a homogeneous catalyst for the atom transfer radical polymerization of styrene or methyl methacrylate, which was initiated by (1-bromoethyl)benzene in the former case and by p-toluenesulfonyl chloride in the latter. The plots of ln([M]₀/[M]) versus time and molecular weight versus monomer conversion exhibited linear dependencies, which indicated that the concentration of the living centers throughout polymerization was constant. The polydispersities of polystyrene and poly(methyl methacrylate) in both the bulk and solution polymerizations were quite low. An induction time was observed during the bulk polymerization of styrene; however, it was absent during the solution polymerization. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 4191–4197, 1999     

Reaction behaviour of dinuclear copper(I) complexes with m-xylyl-based ligands towards dioxygen

Intramolecular ligand hydroxylation was observed during the reactions of dioxygen with the dicopper(I) complexes of the ligands L(1)(L(1)=alpha,alpha'-bis[(2-pyridylethyl)amino]-m-xylene) and L(3)(L(3)=alpha, alpha'-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-m-xylene). The dinuclear copper(I) complex [Cu(2)L(3)](ClO(4))(2) and the dicopper(II) complex [Cu(2)(L(1)-O)(OH)(ClO(4))]ClO(4) were characterized by single-crystal X-ray structure analysis. Furthermore, phenolate-bridged complexes were synthesized with the ligand L(2)-OH (structurally characterized [Cu(2)(L(2)-O)Cl(3)] with L(2)=alpha, alpha'-bis[N-methyl-N-(2-pyridylethyl)amino]-m-xylene; synthesized from the reaction between [Cu(2)(L(2)-O)(OH)](ClO(4))(2) and Cl(-)) and Me-L(3)-OH: [Cu(2)(Me-L(3)-O)(mu-X)](ClO(4))(2)xnH(2)O (Me-L(3)-OH = 2,6-bis[N-(2-pyridylethyl)-N-(2-pyridylmethyl)amino]-4-methylphenol and X = C(3)H(3)N(2)(-)(prz), MeCO(2)(-) and N(3)(-)). The magnetochemical characteristics of compounds were determined by temperature-dependent magnetic studies, revealing their antiferromagnetic behaviour [-2J(in cm(-1)) values: -92, -86 and -88; -374].     

Cyclopalladated complexes catalyzed addition of arylboronic acids to aldehydes in neat water

Cyclopalladated ferrocenylimine complexes gave high yields for the addition of arylboronic acids with aldehydes in neat water using a weak acid as additive.     

Syntheses and characterization of two dioxygen-reactive dinuclear macrocyclic schiff-base copper(I) complexes

The dinuclear copper(I) complex [Cu(2)L(1)(CH(3)CN)(2)](ClO(4))(2) (1, L(1) = 3,6,9,17,20,23-hexaazatricyclo[23.3.1.1]triaconta-1(29),2,9,11(30),12(13),14,16,23,25,27-decaene) has been structurally characterized. As previously described, intramolecular ligand hydroxylation (at the aromatic ring) was observed when 1 was reacted with dioxygen. A stopped-flow analysis of the reaction of 1 with dioxygen under different conditions did not allow a "dioxygen intermediate" to be spectroscopically detected. Detailed NMR and electrochemical data on 1 are also presented and evaluated for the first time. No copper(II) complexes of L(1) could be characterized due to hydrolysis of the compounds. In contrast, complex 2-differing from 1 only in an increase in the size of the chelate rings-did not undergo intramolecular hydroxylation when it was oxidized. The crystal structure of 2 is also described.     

Hydrocarboxylation of unactivated internal alkynes with carboxylic acids catalyzed by dinuclear palladium complexes

Dinuclear palladium complexes catalyzed addition reactions of carboxylic acid O-H bond to unactivated internal alkynes. The reaction afforded a trans-adduct selectively.     

Cyclisations of alkynoic acids using copper(I) arylspiroborate complexes

In this study we have studied the synthesis, characterization and catalytic activity of phosphinocopper(I) complexes [Cu(PPh₃)₃(NCCH₃)][B(O₂C₆H₄-4-R)₂] (3a: R?=?H; 3b: R?=?Me; 3c: R?=?NO₂) and [Cu(PPh₃)₃(NCCH₃)][B(O₂C₆H₃-3,5-di-^tBu)₂] (3d) containing weakly coordinating arylspiroborate ligands bearing various electronic and sterically defined characteristics. All new compounds have been characterized fully including single crystal X-ray diffraction studies for 3a and 3c and confirm that the arylspiroborate ligands do not coordinate to the copper atoms. Using these new metal complexes as precatalysts in the cyclisation of short chain alkynoic acids gave the corresponding exo-dig cyclic lactones exclusively.     

Magnetic properties of spacer-armed dinuclear copper(II) complexes

The results of static magnetic susceptibility studies of spacer-armed dinuclear copper(II) complexes with dicarboxylic acid acylhydrazones are described. Weak exchange coupling between paramagnetic centers has been detected with an exchange parameter value of −2J ∼ 1–7 cm⁻¹. Short intermolecular contacts give rise to additional weak antiferromagnetic exchange coupling between copper cations comparable in terms of energy with superexchange inside the dinuclear complex (−zJ′ ∼ 0.6–5.0 cm⁻¹).     

Synthesis of 1,3,4-mercapto-oxadiazole mono- and dinuclear copper(I) and copper(II) complexes and their microbiological activity

Mono- and dinuclear Cu(I) and Cu(II) complexes of 1,3,4-mercapto-oxadiazole derivatives were prepared and characterized by elemental analyses and standard spectroscopic techniques. The complexes were formulated as Cu(G-OX)₂, Cu₂(G-OX)₄(H₂O)₄, Cu(G-OX)₂L₂and Cu₂(G-OX)₂(PPh₃)₂; (G = H, MeO, Cl; L = Ph₃P, Ph₃As). The microbiological activity of the complexes was investigated against bacteria and fungi. All the complexes were active against Candida albicans, while the reactivity against bacteria varied. The antimicrobial activity of the [Cu(MeO-OX)₂(H₂O)₂]₂ complex was exceptionally better than that observed for any other metal complex against both bacteria and fungi.     

Arene substitution by iridium complexes under mild conditions

[(C₅Me₅Ir)₂Cl₄] reacts with Al₂Me₆ in saturated hydrocarbons to give [C₅Me₅IrMe₄) or cis- and trans-[C₅Me₅Ir)₂Me₂(α-CH₂)₂], depending on workup conditions. In benzene or toluene solution the main product is [(C₅Me₅Ir)₂Me(Aryl)(α-CH₂)₂] (aryl = Ph or m- plus p-tolyl, ratio 2/1); if CO is introduced into the benzene solution the products are [C₅Me₅Ir(CO)R¹R²] (R¹ = Me, R² = Ph; R¹ = R² = Me or Ph).