In The Zinc Research Articles

ЭЛЕКТРОХИМИЧЕСКОЕ ЛЕГИРОВАНИЕ ЦИНКОВЫХ ПОКРЫТИЙ ХРОМОМ И КОБАЛЬТОМ ИЗ ЭЛЕКТРОЛИТОВ, СОДЕРЖАЩИХ ГЕТЕРОЯДЕРНЫЕ КОМПЛЕКСЫ

The purpose of this work is the electrochemical alloying of zinc coatings with chromium and cobalt from glycine-containing electrolytes containing heteronuclear complexes. Currently, the development of electroplating is mainly aimed at creating environmentally safer industries. In solving these problems, low-waste technological processes with closed water circulation are introduced into industry, toxic substances are excluded from technological operations, and work is underway to reduce water consumption.An important area of work, in our opinion, is the production of alloyed coatings with effective performance characteristics. Obtaining such coatings allows the use of smaller thicknesses and longer service life, which helps to save material and energy resources, and in some cases solve environmental problems when replacing toxic metals, for example, cadmium. The processes of complexation in the zinc (II)-chromium (III)-cobalt (II) - glycine -water system were studied using NMR.The kinetics of the cathode process on zinc and steel electrodes has been studied by removing potentiodynamic polarization curves. It is suggested that the absence of characteristic current peaks on the polarization curves is due to the convergence of the electrode potentials of individual metal ions recovering from heteronuclear compounds, as well as the concomitant hydrogen release reaction.X-ray fluorescence analysis showed that in the studied current density range of 0.5-3.0 A/dm2, the content of alloying metals varies 0.01…2.00 for chromium and 0.1…3.6 for cobalt, respectively. The mass corrosion index for coatings alloyed with chromium and cobalt (cobalt content up to 1%) is 2 times less than for zinc coatings and is 0.05 g/m2·h.

Aminopolycarboxylate zinc(II) complexes with 1,10-phenanthroline and 2,2′-bipyridyl: kinetic studies in the surfactants solutions systems

Aminopolycarboxylate zinc(II) complexes with 1,10-phenanthroline and 2,2′-bipyridyl {[Zn(IDA)(H2O)2], [Zn(IDA)(bipy)(H2O)]·2H2O and [Zn(IDA)(phen)(H2O)]·2H2O} were synthesized. In order to confirm the composition and purity of the synthesized complex compounds, elemental analysis was used. Next, the kinetics of the substitution reaction of two water molecules in the zinc(II) iminodiacetate complex for 1,10-phenanthroline and 2,2′-bipyridyl in two surfactant solvents: CTAB and Triton X-100 were investigated. The kinetic studies were carried out using the stopped flow method. The kinetic research were carried out at 3 different temperatures: 288.15, 293.15 and 298.15 K and at different molar concentrations of the complex compound [Zn(IDA)(H2O)2]: 1 mM; 0.75 mM, 0.5 mM and 0.25 mM and at a constant molar concentration of ligands: i.e. 1,10-phenanthroline and 2,2′-bipyridyl, were 0.05 mM. Changes in absorbance during the kinetic run of the tested reactions were measured at a wavelength of 260 nm. Thanks to the conducted kinetic studies, the order of the reaction was determined, and the observable rate constants of the reaction rates of the substitution of two aqua molecules into the N-donor ligand were determined by the stopped—flow method using the Glint program. In the next step the thermodynamic parameters of complexes: {[Zn(IDA)(H2O)2], [Zn(IDA)(bipy)(H2O)]·2H2O and [Zn(IDA)(phen)(H2O)]·2H2O} in aqueous solutions by use potentiometric titrations were determined. The Hyperquad2018 program was used for determining of stability constants. In addition, the stoichiometry of complexes of zinc(II) with N-heterocyclic ligands in aqueous solutions was determined using the conductometric titrations.

COMPLEX FORMATION IN THE SYSTEM ZINC (II)-CHROMIUM (III) -COBALT (II)-GLYCINE-WATER

The study of complex formation processes is the scientific basis for the development of electrolytes in electroplating. The data on complexation in the zinc (II)–chromium (III)–cobalt (II)–glycine–water system were obtained. The study of complex formation in the zinc (II)-chromium (III)-cobalt (II)-glycine-water system is relevant due to the possibility of developing electrolytic galvanizing processes and obtaining appropriate coatings with high corrosion resistance. In addition, the alloying of zinc electroplating coatings with chromium, cobalt makes it possible to replace the use of toxic cadmium coatings and use their smaller thicknesses. The solutions were thermostated at 25 °C. The HI 2215 pH/ORPMeter was used to measure pH. The spin-lattice relaxation time T1 was measured on a pulsed NMR spectrometer "Minispecmq20" with a frequency of 19.75 MHz. The constants of the formation of complexes and their accumulation shares were calculated according to the CPESSP program. The paper presents data on previously conducted studies of chromium(III)–water, zinc(II)–glycine–water, chromium(III)–glycine–water and zinc(II)–chromium(III)–glycine–water systems. Data on complexation in the chromium (III)-cobalt (II)-glycine-water system were obtained. The formation of a heteronuclear complex CrCoGly83- has been established. The compositions of heteronuclear compounds, their accumulation fractions and formation constants were established: CrCoZn(HGly)5Gly34+ (lgK= 2.31±0.01); CrCoZn(HGly)3Gly52+ (lgK= -1.36±0.05) and CrCoZn(HGy)2Gly6+ (lgK= -4.23±0.09). The maximum proportion of accumulation of heteronuclear complexes, as studies have shown, is observed in the pH range of 2...6. In this paper, considerations are made about the electrochemical reactivity of heteronuclear compounds. In particular, it is noted that the electrochemical reduction of more electronegative metals, if they are in a heteronuclear complex, should occur with less overvoltage of the reaction. For citation: Berezin N.B., Chevela V.V., Mezhevich Zh.V., Ivanova V.Yu. Complex formation in the system zinc (II)-chromium (III) -cobalt (II)-glycine-water. ChemChemTech [Izv. Vyssh. Uchebn. Zaved. Khim. Khim. Tekhnol.]. 2023. V. 66. N 6. P. 31-36. DOI: 10.6060/ivkkt.20236606.6789.

The Cathodic Reduction of Zn (II) on the Zn and Au Electrode in the Zinc(II)–NH4Cl System

The Cathodic Reduction of Zn (II) on the Zn and Au Electrode in the Zinc(II)–NH4Cl System

Solid-State Structural Transformation and Photoluminescence Properties of Supramolecular Coordination Compounds

The combination of strong coordination bonds and hydrogen bonding interactions were used to generate a series of supramolecular coordination materials (SCMs), which was achieved by reacting a bis-pyridyl amide ligand, namely N-(4-pyridyl)nicotinamide (4PNA) with copper(II), zinc(II), and cadmium(II) benzoates. The SCMs were structurally characterized using X-ray diffraction and the key intermolecular interactions were identified via Hirshfeld surface analysis. The role of solvent molecules on the supramolecular architecture was analyzed by synthesizing the SCMs in different solvents/solvent mixtures. A solvent-mediated solid-state structural transformation was observed in copper(II) SCMs and we were able to isolate the intermediate form of the crystal-to-crystal transformation process. The luminescence experiments revealed that complexation enhanced the fluorescence properties of 4PNA in the zinc(II) and cadmium(II) SCMs, but a reverse phenomenon was observed in the copper(II) SCMs. This work demonstrated the tuning of supramolecular assembly in coordination compounds as a function of solvents for generating SCMs with diverse properties.

The crystal structures and Hirshfeld surface analyses of a cadmium(II) and a zinc(II) mononuclear complex of the new tetrakis-substituted pyrazine ligand N,N',N'',N'''-[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(N-methyl-aniline).

The whole mol-ecule of the cadmium(II) complex, di-iodido-{N,N',N'',N'''-[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(N-methyl-aniline)-κ3 N 2,N 1,N 6}cadmium(II), [CdI2(C36H40N6)], (I), of the ligand N,N',N'',N'''-[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(N-methyl-aniline) (L), is generated by a twofold rotation symmetry; the twofold axis bis-ects the cadmium atom and the nitro-gen atoms of the pyrazine ring. The ligand coordinates in a mono-tridentate manner and the cadmium atom has a fivefold CdN3I2 coordination environment with a distorted shape. In the zinc(II) complex, dichlorido{N,N',N'',N'''-[pyrazine-2,3,5,6-tetra-yltetra-kis-(methyl-ene)]tetra-kis-(N-methyl-aniline)-κ3 N 2,N 1,N 6}zinc(II) di-chloro-methane 0.6-solvate, [ZnCl2(C36H40N6)]·0.6CH2Cl2, (II), ligand L also coordinates in a mono-tridentate manner and the zinc atom has a fivefold ZnN3Cl2 coordination environment with a distorted shape. It crystallized as a partial di-chloro-methane solvate. In the crystal of I, the complex mol-ecules are linked by weak C-H⋯I contacts, forming ribbons propagating along [100]. In the crystal of II, the complex mol-ecules are linked by a series of C-H⋯π inter-actions, forming layers lying parallel to the (11) plane. In the crystals of both compounds there are metal-halide⋯π(pyrazine) contacts present. The Hirshfeld analyses confirm the importance of the C-H⋯halide contacts in the crystal packing of both compounds.

Antihypertensive Effects in Vitro and in Vivo of Novel Angiotensin-Converting Enzyme Inhibitory Peptides from Bovine Bone Gelatin Hydrolysate.

In this study, we investigated the antihypertensive effects in vitro and in vivo of novel angiotensin-converting enzyme inhibitory (ACEI) peptides purified and identified from bovine bone gelatin hydrolysate (BGH). Thirteen ACEI peptides were identified from BGH, and among which, RGL-(Hyp)-GL and RGM-(Hyp)-GF exhibited high ACE inhibition with IC50 values of 1.44 and 10.23 μM. Molecular docking predicted that RGM-(Hyp)-GF and ACE residues of Glu384, His513, and Lys511 formed hydrogen-bonding interactions at distances of 2.57, 2.99, and 2.42 + 3.0 Å. RGL-(Hyp)-GL formed hydrogen bonds with Lys511 and Tyr523 and generated hydrogen-bonding interactions with His387 and Glu411 in the zinc(II) complexation motif at distances of 2.74 and 3.03 + 1.93 Å. The maximal decrements in systolic blood pressure in spontaneously hypertensive rats induced by one-time gavage of RGL-(Hyp)-GL and RGM-(Hyp)-GF at 30 mg/kg were 31.3 and 38.6 mmHg. RGL-(Hyp)-GL had higher enzyme degradation resistance than that of RGM-(Hyp)-GF in vitro incubation in rat plasma, and they were sequentially degraded into pentapeptides and tetrapeptides within 2 h. Our results indicate that BGH can serve as a nutritional candidate to control blood pressure.

A Pseudo-Octahedral Cobalt(II) Complex with Bispyrazolylpyridine Ligands Acting as a Zero-Field Single-Molecule Magnet with Easy Axis Anisotropy.

The homoleptic mononuclear compound [Co(bpp-COOMe)2 ](ClO4 )2 (1) (bpp-COOMe=methyl 2,6-di(pyrazol-1-yl)pyridine-4-carboxylate) crystallizes in the monoclinic C2/c space group, and the cobalt(II) ion possesses a pseudo-octahedral environment given by the two mer-coordinated tridentate ligands. Direct-current magnetic data, single-crystal torque magnetometry, and EPR measurements disclosed the easy-axis nature of this cobalt(II) complex, which shows single-molecule magnet behavior when a static field is applied in alternating-current susceptibility measurements. Diamagnetic dilution in the zinc(II) analogue [Zn(bpp-COOMe)2 ](ClO4 )2 (2) afforded the derivative [Zn0.95 Co0.05 (bpp-COOMe)2 ](ClO4 )2 (3), which exhibits slow relaxation of magnetization even in zero field thanks to the reduction of dipolar interactions. Theoretical calculations confirmed the overall electronic structure and the magnetic scenario of the compound as drawn by experimental data, thus confirming the spin-phonon Raman relaxation mechanism, and a direct quantum tunneling in the ground state as the most plausible relaxation pathway in zero field.

Fast Interchange of Coordinated and Guest Dimethylformamide Molecules in the Zinc(II) Lactate Terephthalate Metal–Organic Framework

Mobility of N,N-dimethylformamide (dmf) molecules in a homochiral metal–organic framework [Zn2(bdc)(S-lac)(dmf)]·dmf (bdc = 1,4-benzenedicarboxylate; S-lac = L-(−)-lactate) has been studied using 13C, 1H, and 2H solid-state NMR and DSC experiments. The compound exhibits a phase transition in the vicinity of 240 K, associated with disordering of the dmf molecules. In the high-temperature phase, the dmf molecules undergo intense diffusion accompanied by the exchange between the molecules coordinated with Zn and guest molecules in the framework pores. The activation energy of the molecular migration including exchange between coordinated and guest molecules was estimated to be 37 kJ/mol.

Photonics of zinc(II) and boron(III) chelates with methyl- and phenyl-substituted dipyrromethenes and azadipyrromethenes

A comparative study of spectral, luminescent, and photophysical parameters has been carried out for a series of zinc(II) and boron(III) chelates with dipyrromethene ligands of a similar structure: tetramethyl- and tetraphenylpyrrodimethenes bearing the substituents on the pyrrole rings and tetraphenylazapyromethene. In some cases, the luminescence efficiency of the chelates depends on the excitation wavelength. The replacement of the central atom boron(III) by zinc(II) results in not only a twofold increase in the number of coordinated chromophoric ligands and the absorption coefficient, but also an increase in the contribution of nonradiative processes to excitation energy deactivation and, hence, a decrease in the yield of fluorescence. The efficiency of intersystem crossing is higher in the zinc(II) dipyrromethene complexes than in the corresponding boron-chelated dipyrromethenes (BODIPYs), resulting in the appearance of phosphorescence in frozen solutions. It has been found that the replacement of the meso-spacer in the dipyrromethene ligand by the nitrogen atom not only shifts the absorption and fluorescence band maximums to longer wavelengths, but also decreases the fluorescence efficiency and leads to the appearance of long-lived luminescence even in aza-BODIPY. An analysis of the results has shown that these behavior can be due to involvement of the nπ* (πσ*, σπ*) states localized on the meso-nitrogen in the deactivation of excitation energy.

The copper(II) and zinc(II) coordination mode of HExxH and HxxEH motif in small peptides: The role of carboxylate location and hydrogen bonding network

Copper(II) and zinc(II) complexes with two hexapeptides encompassing HExxH and HxxEH motif were characterized by means of a combined experimental and theoretical approach. Parallel tempering and density functional theory (DFT) investigations show the presence of different hydrogen bonding networks between the copper(II) and zinc(II) complexes with the two peptides, suggesting a significant contribution of these non-covalent interactions to the stability constant values. The glutamate carboxylate group has a direct role in metal ion binding. The location of this amino acid along the sequence of the investigated peptides is critical to determine thermodynamic and spectroscopic features of the copper(II) complex species, whereas is less relevant in the zinc(II) complexes formation. Electrospray ionization mass spectrometry (ESI-MS) characterization of the zinc(II) complex species show that in the [ZnH−2L] two deprotonated amide nitrogen atoms are involved in the metal coordination environment, an uncommon behavior in zinc(II) complexes for multi-histidine ligands.

Hydrogen-bonded 1D nanotubes and 2D layers of group 12 metal complexes with a pyridylurea ligand

A series of group 12 metal complexes, [ZnCl2L2]·H2O (1), [ZnBr2L2]·0.75EtOH (2a), [ZnBr2L2]·0.8H2O (2b), [ZnI2L2] (3), [HgCl2L2] (4), [HgBr2L2] (5), and [HgI2L] (6), have been synthesized from a naphthyl-substituted pyridylurea ligand N-(1-naphthyl)-N′-(3-pyridyl)urea (L) and zinc(II) or mercury(II) halides. In the zinc(II) dichloro complex, 1, the chloride ions participate not only in metal coordination but also in N–H⋯Cl hydrogen bonding with the urea NH groups, giving an overall layered structure. In contrast, the coordinated bromide and iodide anions in 2 and 3 are not involved in hydrogen bonding; instead, the urea groups undergo self-association to form nano-tubular structures with various pore sizes stacked by the semi-macrocyclic [ZnX2L2] synthons. Most interestingly, although different solvent molecules [EtOH (2a) and H2O (2b)] can be encapsulated in the nano-tubular zinc dibromo complexes, a competitive experiment conducted in the EtOH/H2O mixed solvents showed that the nanotube can selectively capture the EtOH molecule, as confirmed by X-ray single-crystal diffraction and solid-state fluorescence studies. With the tetrahedral mercury(II) ion, complexes 4 and 5 are isomorphous 2D sheet structures held by N–H⋯O hydrogen bonds and π–π stacking interactions. The 2D sheets are further linked by C–H⋯Cl/Br weak interactions into a hydrogen-bonded 3D framework. Notably, compound 6 contains an uncommon trigonal-planar HgII center and forms a 1D chain structure via the typical urea⋯urea hydrogen bonding and π–π stacking interactions of L, which further aggregates to a 2D parallelogram grid framework through C–H⋯I weak interactions. The solid-state fluorescent properties of L and the complexes 1–6 have also been investigated at room temperature.

Synthesis and characterization of group 12 complexes of N,N-methyl phenyl-N,N-butyl phenyl dithiocarbamate

Zn(II), Cd(II), and Hg(II) complexes of N-methyl-N-phenyl dithiocarbamate (L1) and N-butyl-N-phenyl dithiocarbamate (L2) formulated as ML1L2 have been synthesized and characterized by elemental analysis, FT–IR, 1H- and 13C-NMR spectroscopic techniques. Single-crystal X-ray structures of the Zn(II) and Hg(II) complexes are also reported. X-ray crystal structures revealed that in the zinc(II) complex, the dithiocarbamate is chelating and bridging, forming eight-member rings, while the Hg complex is monomeric with bidentate dithiocarbamate. In both complexes, the metals are in distorted tetrahedral geometry and the methyl and butyl groups of the dithiocarbamates exhibit compositional disorder between two positions.

Synthesis and structures of pyridinecarboxylate-containing zinc(II) complexes in dien and tren system

Four new zinc(II) complexes [Zn(dien)( μ-nic)] 2(BPh 4) 2·2CH 3OH ( 1), {[Zn(dien)(isonic)]BPh 4} n ( 2), [Zn(tren)(nic)]BPh 4 ( 3) and [Zn(tren)(isonic)]BPh 4 ( 4) (dien/tren = diethylenetriamine/triethylenetriamine, nic/isonic = nicotinate/isonicotinate anion) were synthesized and structurally characterized by IR, 1H NMR and single crystal X-ray diffraction. In the zinc(II) complexes of dien, both nicotinate and isonicotinate connect the zinc(II) ions via N,O-bis-monodentate mode. Complex 1 contains a centrosymmetric dinuclear unit bridged by two nicotinate anions in anti-parallel way. Complex 2 is characterized by an infinite one-dimensional zigzag chain bridged by isonicotinate anion in an end-to-end mode. The Zn···Zn distance is 6.782 for 1 and 8.805 Å for 2. While in the complexes of tren, both 3 and 4 are mononuclear complexes with nicotinate and isonicotinate coordinated to zinc(II) ion through only one oxygen atom of their carboxylate groups. The zinc(II) ions in all of the four complexes are in a distorted trigonal bipyramidal geometry. Complex 3 forms a dinuclear unit and complex 4 forms an infinite 2D sheet structure through intermolecular H-bonds. In all of the crystal lattices, the BPh 4 - counterions act to balance the electronic charge at the same time to construct different 3D structures through noncovalent interactions such as C–H···π, N–H···π and van der Waals interactions.

Thermodynamic characteristics of the complex formation in the zinc(II) ion-L-serine-water system

Using calorimetric method we determined the thermal effects of reactions of the L-serine complex formation with the doubly charged zinc ion. The heat effects of the reaction of amino acid solution with a solution of zinc(II) were measured at temperatures 288.15, 298.15, and 308.15 K and ionic strengths 0.25, 0.50, and 0.75, against the background of KNO3. The heats of dilution of zinc nitrate in the background electrolyte solution were determined under the same conditions, to introduce respective corrections. The thermochemical data were processed with accounting for all the possible equilibria. The standard thermodynamic characteristics of complex formation processes were calculated. The effects of concentration and temperature on the thermal effects of the complex formation of zinc(II) and L-serine in aqueous solution were estimated.

Thermodynamic characteristics of complex formation in the zinc(II)-glycylglycine system in aqueous solution

The heats of reaction of zinc(II) with glycylglycine at temperatures 288.15, 298.15, and 308.15 K and ionic strengths 0.25, 0.50, and 0.75 (potassium nitrate as a supporting electrolyte) were determined by calorimetry. The thermochemical results were processed with inclusion of stepwise equilibria. In addition to complexation reactions, “side” protolytic processes were considered. Standard heats of complexation in the system were found by extrapolation to the zero ionic strength by an equation with one individual parameter. The influence of the supporting electrolyte concentration and temperature on the thermodynamic characteristics of the complexation reactions in the glycylglycine-zinc(II) system was considered. The standard enthalpies of formation of ZnGlyGly+, Zn(GlyGly)2, and Zn(GlyGly) 3 − species in aqueous solution were calculated.

Thermochemical study of coordination equilibria in the zinc(II)-β-alanine-water system in aqueous solution

The heats of formation of β-alanine (HAla) complexes with Zn2+ ion at temperatures of 288.15, 298.15, and 308.15 K and ionic strengths of 0.25, 0.50, and 0.75 mol/l (KNO3) were determined by calorimetry; the heats of dilution of a zinc nitrate solution in supporting electrolyte solutions were found for introduction of appropriate corrections. The standard heats of complexation in the zinc(II)-β-alanine-water system were determined. The standard thermodynamic characteristics of zinc(II) complexation with β-alanine and standard enthalpies of formation of ZnAla+ and ZnAla2 complex species were calculated.

Carbon dioxide fixation by zinc(II) complexes with macrocyclic ligand

Two novel zinc(II) coordination complexes [Zn 2(L)(CO 3)]Br 2 · 7H 2O ( 1) and [Zn 2(L)(CO 3)]Br 2 · 0. 5CH 3COCH 3 · 5H 2O ( 2) with new macrocyclic ligand 3, 6, 9, 12, 20, 23, 26, 29-octaazatricyclo[29.3.1.1 14,18] hexatriaconta-1(34), 14, 16, 18(36), 31(35), 32-hexaene (L) were synthesized at an initial pH of ca. 9.5 with evaporation and diffusion methods, respectively. The dinuclear units of [Zn 2(L)] 4+ in both complexes are linked together by carbonate anions to form 1D infinite chain structure. The results show that carbon dioxide from air was absorbed and converted to carbonate anion in the formation of complexes 1 and 2. To the best of our knowledge, this is the first example of absorption and hydration of atmosphere carbon dioxide to form the 1D chain structure in the zinc(II) macrocyclic complexes.

Copper and zinc binding properties of the N-terminal histidine-rich sequence of Haemophilus ducreyi Cu,Zn superoxide dismutase

The Cu,Zn superoxide dismutase (Cu,ZnSOD) isolated from Haemophilus ducreyi possesses a His-rich N-terminal metal binding domain, which has been previously proposed to play a copper(II) chaperoning role. To analyze the metal binding ability and selectivity of the histidine-rich domain we have carried out thermodynamic and solution structural analysis of the copper(II) and zinc(II) complexes of a peptide corresponding to the first 11 amino acids of the enzyme (H(2)N-HGDHMHNHDTK-OH, L). This peptide has highly versatile metal binding ability and provides one and three high affinity binding sites for zinc(II) and copper(II), respectively. In equimolar solutions the MHL complexes are dominant in the neutral pH-range with protonated lysine epsilon-amino group. As a consequence of its multidentate nature, L binds zinc and copper with extraordinary high affinity (K(D,Zn)=1.6x10(-9)M and K(D,Cu)=5.0x10(-12)M at pH 7.4) and appears as the strongest zinc(II) and copper(II) chelator between the His-rich peptides so far investigated. These K(D) values support the already proposed role of the N-terminal His-rich region of H. ducreyi Cu,ZnSOD in copper recruitment under metal starvation, and indicate a similar function in the zinc(II) uptake, too. The kinetics of copper(II) transfer from L to the active site of Cu-free N-deleted H. ducreyi Cu,ZnSOD showed significant pH and copper-to-peptide ratio dependence, indicating specific structural requirements during the metal ion transfer to the active site. Interestingly, the complex CuHL has significant superoxide dismutase like activity, which may suggest multifunctional role of the copper(II)-bound N-terminal His-rich domain of H. ducreyi Cu,ZnSOD.

Stereoselective Conjugate Addition Reactions Using In Situ Metallated Terminal Alkynes and the Development of Novel Chiral P,N-Ligands

Abstract In this account, new methods for the catalytic and stereoselective conjugate addition of terminal alkynes are described. Our laboratories have disclosed asymmetric addition reactions to aldehydes and imines using a combination of a zinc or copper salt and a terminal alkyne. Under these conditions, terminal alkyne is transformed in situ into an alkynyl metal species. Recently, it was found that these in situ generated alkynyl metal species can undergo conjugate additions to alkylidene malonate-type acceptors. In the zinc(II) triflate-catalyzed system, a highly diastereoselective conjugate addition has been realized using a chiral oxazepene acceptor. Subsequently, alternative conjugate addition protocols have been developed which employ a terminal alkyne, substoichiometric amounts of copper and a highly eletrophilic Meldrum’s acid derived acceptor. This reaction can be made enantioselective using a novel atropisomeric P,N-ligand (PINAP). With this ligand, excellent enantioselectivities can be achieved for the conjugate addition of aromatic alkynes to various Meldrum’s acid derived acceptors.