Title Ligand Research Articles

Chiral oxazoline ligands containing a 1,2,4-triazine ring and their application in the Cu-catalyzed asymmetric Henry reaction

Eleven members of new ligand class incorporating a chiral oxazoline and a 1,2,4-triazine ring have been synthesized via Pd-catalyzed amination reaction of 3-halo-1,2,4-triazines with 2-(o-aminophenyl)oxazolines. Buchwald–Hartwig amination of 3-halo-1,2,4-triazines was investigated to establish the best conditions for synthesis of the title ligands. Catalytic activity of the new ligands was evaluated in the asymmetric Henry reaction of nitromethane with a variety of aromatic and aliphatic aldehydes. The β-hydroxy nitroalkanes were obtained in high yields (up to 95%), and moderate-to-good enantioselectivity (up to 82% ee).

ChemInform Abstract: Chiral Dihydrobenzofuran‐Based Diphosphine (BICMAP): Optical Resolution and Application to Rhodium(I)‐Catalyzed Asymmetric 1,4‐Addition of Aryl‐ and Alkenylboronic Acids to Cyclic Enones.

AbstractThe (S)‐isomer of the title ligand is successfully applied for various boronic acid additions and the preparation of flavanone (X).

Bis(Tetramethylselenophosphoramidoyl) Methylamine Complexes of Cd(Ii) and Zn(Ii): Synthesis and Multinuclear (31P, 77Se, and 113Cd) Nmr Characterization in Solution

Five new complexes ZnL2(ClO4)2 (1), CdL2(ClO4)2 (2), CdL2(BF4)2 (3), CdLCl2 (4), and CdL(NO3)2 (5) [L = ((Me2N)2PSe)2NMe] have been synthesized and characterized by elemental analysis, infrared (IR) and multinuclear (31P, 77Se, and 113Cd), and nuclear magnetic resonance (NMR) spectroscopy. The 31P and 77Se NMR data showed that the title ligand is coordinated in a bidentate fashion to the metal center via its both P=Se groups. The solution structure of the cadmium complexes was further confirmed by its 113Cd NMR spectra, which displayed a quintuplet for the perchlorate complex and a triplet for each of the nitrate and chloride complexes, respectively due to coupling with four (two ligands) and two (one ligand) equivalent phosphorus nuclei, consistent with a four-coordinate tetrahedral geometry for the cadmium center. The results are discussed and compared with the corresponding oxo and thio analogues.

Biscyclometalated Ruthenium Complexes Bridged by 3,3′,5,5′-Tetrakis(N-methylbenzimidazol-2-yl)biphenyl: Synthesis and Spectroscopic and Electronic Coupling Studies

A series of biscyclometalated ruthenium complexes bridged by the title ligand were prepared by either an oxidative dimerization of corresponding monometallic complexes or treatment of the bridging ligand with Ru(L)Cl(3) (L = capping ligand). The electronic properties of these complexes were examined by electrochemical and spectroscopic analysis and DFT/TDDFT calculations. The degree of metal-metal electronic coupling of these complexes was estimated on the basis of intervalence charge-transfer transition analysis of corresponding mixed-valent complexes. These studies indicated that the electronic coupling was strongly dependent on the electronic nature of the terminal ligands. A hole-transfer superexchange mechanism was used to understand the underlying electron-transfer processes.

Synthesis, Structure, and Solution Study of a Mercury(II) Complex with the Ligand [1‐(2‐Methoxyphenyl)‐3‐(4‐chlorophenyl)]triazene

AbstractThe title ligand, [1‐(2‐methoxyphenyl)‐3‐(4‐chlorophenyl)]triazene, HL (1), was prepared. In a reaction with Hg(NO3)2 it forms the complex [Hg(C26H22Cl2N6O2)], [HgL2] (2). Both compounds were characterized by means of X‐ray crystallography, CHN analysis, FT‐IR, 1H NMR, and 13C NMR spectroscopy. In the structure of compound 1, two independent fragments are present in the unit cell. They exhibit trans arrangement about the –N=N– double bond. The dihedral angles between two benzene rings in both fragments are 4.36 and 18.79 Å, respectively. Non‐classic C–H···N hydrogen bonding and C–H···π interactions form a layer structure along the crystallographic ab plane [110]. In compound 2, the HgII atom is hexacoordinated by two tridentate [1‐(2‐methoxyphenyl)‐3‐(4‐chlorophenyl)]triazenide ligands through a N2O2 set. In addition, in the structure of 2, monomeric complexes are connected to each other by C–H···π stacking interactions, resulting in a 2D architecture. These C–H···π edge‐to‐face interactions are present with H···π distances of 3.156 and 3.027 Å. The results of studies of the stoichiometry and formation of complex 2 in methanol solution were found to support its solid state stoichiometry.

ChemInform Abstract: Ionic‐Salt‐Tagged Ferrocenyl Diphosphine—Imine Ligands and Their Application to Palladium‐Catalyzed Asymmetric Allylic Etherification.

AbstractThe title ligands are successfully applied to the asymmetric allylic etherification of the acetates and benzoates (I).

Transition metal complexes of new glyoxylato-aroylhydrazones and their role in l-ascorbic acid oxidation inhibition

We report here the synthesis of new ligands of the aroylhydrazone family. Glyoxylato-aroylhydrazones (gly-AH) with lipophilic character were designed for possible biological applications where metal chelation is desired. They were found to coordinate readily with a number of metals and the crystal structures of the copper and zinc complexes, M(py)2L (M=Cu, Zn); LH2 (L2)=N′-(2-hydroxy-3-(pentan-3-yl)benzylidene)-2-mesityl-2-oxoacetohydrazide have been determined. The complexes both display a distorted trigonal bipyramidal coordination geometry around the metals. Ascorbate oxidase and ascorbate peroxidase mimicking reactions were carried out to determine the ability of the title ligands to inhibit metal-induced oxidation of l-ascorbic acid via complexes generated in situ.

ChemInform Abstract: Palladium (II) Complexes with the Unsymmetrical H‐Spirophosphorane Ligand HP(OCMe2CMe2O)(OCH2CMe2NH): Synthesis, Structural and Catalytic Studies.

AbstractThe mononuclear palladium complexes (I) and (II), prepared from the title ligand, catalyze the Heck and Hiyama coupling reactions.

ChemInform Abstract: Selective Arylation of Aldehydes with Di‐Rhodium(II)/NHC Catalysts.

AbstractNovel title ligands are designed and complex (I) is found to show enhanced activity in the arylation of aldehydes with boronic acids.

ChemInform Abstract: Novel Olefin—Phosphorus Hybrid and Diene Ligands Derived from Carbohydrates.

AbstractVarious title ligands are designed and tested in the reaction of (Ia) with boronic acid (II).

Oxazoles revisited: On the nature of binding of benzoxazole and 2-methylbenzoxazole with the zinc and palladium halides

A synthetic and structural (X-ray) investigation into the bonding modes of benzoxazole (box) and 2-methylbenzoxazole (Mebox) ligands with halide precursors of Zn and Pd has been undertaken to clarify earlier discrepancies concerning the nature of the bonding mode(s) of the two azoles. In four structurally characterised examples, all contain the title ligands in a κ(1)N bonding motif. Calculations at the density functional level (DFT) of theory (B3LYP) confirm the ground state stability of this class of coordination for several hypothetical Pd and Zn (gas phase) compounds. The attempt to obtain suitable crystalline material of PdCl(2)(box)(2) (i.e., 5) leads to substantial complex degradation. One minor product of this process has been identified (X-ray) as the diarylformamidinato complex C(26)H(22)N(4)O(4)Pd, presumably formed via a complex combination of the decomposition products of both free box and 5.

ChemInform Abstract: Dithiophosphonates and Related P/S‐Type Ligands of Group 11 Metals

AbstractReview: 73 refs.

Synthesis and structure of catena cadmium complex with 2-hydroxo-1-naphthaldehyde thiosemicarbazono tetradentate ligand

The title ligand (H2L) and its complex [CdL(py)2]py (L= C12H9N3OS dianionic) have been synthesized and characterized. The complex structure determination indicates that Cd( II ) atom has a distorted octahedral coordination geometry. As an unusual tetradentate ligand, one L2 chelates one Cd( II ) atom using the O, S atoms and one N atom of the hydrazino group while its another N atom links to the neighbouring Cd atom. The bridging hydrazono groups extend the compound into a catena chain. The naphthoxy rings of each neighboring unit are alternatively arranged at opposite sides of the chain, and the ring planes on the same side are parallel.

ChemInform Abstract: Synthesis of Novel Chiral Oxazoline‐Schiff Base Ligands for the Catalytic Asymmetric Chlorination of β‐Keto Esters.

AbstractA number of title ligands is prepared in order to test their effectiveness in asymmetric chlorination of β‐keto esters.

Syntheses, characterization, X-ray crystal structures and emission properties of copper(II), zinc(II) and cadmium(II) complexes of pyridyl–pyrazole derived Schiff base ligand – Metal selective ligand binding modes

The varying coordination modes of the title ligand, L [5-methyl-1-(pyridin-2-yl)- N′-[pyridin-2-ylmethylidene]pyrazole-3-carbohydrazide] towards the different metal centers is reported by preparation and characterization of Cu(II), Zn(II) and Cd(II) complexes, [Cu(L)NO 3.H 2O](NO 3) ( 1) [Zn(L) 2](ClO 4) 2·2DMF ( 2) and [Cd(L)(I) 2] ( 3) respectively. In 1, the neutral ligand serves as tetradentate 4 N donor where both pyridine and pyrazole nitrogen atoms of pyridyl–pyrazole part are coordinatively active, leaving the carbonyl oxygen of the carbohydrazide part inactive. The same pyridine and pyrazole N atoms remain abstained from the coordination process towards the Zn(II) and Cd(II) metal centers. For 2 and 3 the ligand behaves as a tridentate NNO donor where the two nitrogen atoms come from azomethine, pyridine of pyridine-2-carbaldehyde parts and O from carbonyl oxygen atoms (carbohydrazide part). The complex 1 and 2 are distorted octahedral while complex 3 adopts distorted square pyramidal geometry. All the complexes are X-ray crystallographically characterized.

DITHIOPHOSPHONATES AND RELATED P/S-TYPE LIGANDS OF GROUP 11 METALS

Within the phosphor-1,1,-dithiolate class of compounds, the dithiophosphonato ligand [S2PAr(OR′)]− (typically Ar = aryl or ferrocenyl; R′ = alkyl) has emerged as an interesting choice for the preparation of a variety of new metal complexes. This review focuses on the dithiophosphonates and certain related thio species of the group 11 coinage metals, copper, silver and gold, with particular emphasis on structure and coordination modes. Amongst these three metals a rich coordination and structural chemistry had been developed and reported. For copper, a number of new complexes ranging from a single metal center, to di-, tetra-, and Cu14 clusters had been prepared. For silver, the number of reported complexes is not yet abundant but range in nuclearity from Ag2 to Ag28, which gives an indication of the potential scope. For gold, the majority of complexes are dinuclear gold(I) of the type [AuS2PR(OR′)]2 where the variety of R′ can be enormous. A few silver and gold complexes with the title ligand had also been subjected to theoretical studies. New coordination modes have also been observed, particularly in cases where previously isolated complexes have been subjected to further reaction with phosphines. Copper and silver complexes have not yet shown the rich luminescent properties as gold, and developments of the latter are described also.

Synthesis, characterization, and photophysical properties of a thiophene-functionalized bis(pyrazolyl) pyridine (BPP) tricarbonyl rhenium(i) complex

A bromo tricarbonyl rhenium(I) complex with a thiophene-functionalized bis(pyrazolyl) pyridine ligand (L), ReBr(L)(CO)(3) (1), has been synthesized and characterized by variable temperature and COSY 2-D (1)H NMR spectroscopy, single-crystal X-ray diffraction, and photophysical methods. Complex 1 is highly luminescent in both solution and solid-state, consistent with phosphorescence from an emissive (3)MLCT excited state with an additional contribution from a LC (3)(pi-->pi*) transition. The single-crystal X-ray diffraction structure of the title ligand is also reported.

Macrocyclic complexes : Synthesis and characterization of cobalt(II), nickel(II) and copper(II) complexes with [14]1,4,5,7,8,11,12,14-octaaza-2,3,9,10-tetraoxo-1,4,5,6,6,7,8,11,12,13,13,14-dodecahydrocyclotetradecane (OTCT)

A series of macrocyclic complexes of the titled ligand have been isolated by the action of formaldehyde (H 2 CO) on bis-(1,4-diamino-1,4-diaza-2,3-dioxobutane) complexes of cobalt(II), nickel(II) and copper(II). The coordination template effect governs the steric course of the reaction. The structures of the complexes have been elucidated on the basis of IR, electronic, ESR spectral data, magnetic properties, electrochemical studies and thermal data. Electrochemical studies show that all the complexes show two well defined reduction curves corresponding to the formation of species where the metal ion can be formally assigned an oxidation state of +I and zero respectively.

Mixed-ligand complex formation equilibria of CuII with histidine and biguanide

Combined spectrophotometric and computer-based pH-metric investigations on the mixed-ligand complex formation equilibria of Cu II with histidine [(C 3 H 3 N 2 )CH 2 CH(NH 2 )COOH, hisH ± ] and biguanide [NH 2 C-(=NH)NHC(=NH)NH 2 , Bg] in aqueous solution at a constant ionic strength (I = 0.1 mol dm ―3 ) and 25 ± 1°C, provided evidence of binary [Cu(hism) + ], [Cu(hism-H)], [Cu(hism) 2 ], [Cu(hism)(hism-H) ― ], [Cu(hism-H) 2 2― ] and [Cu(Bg) 2+ ] and ternary [Cu(hism)(Bg) + ], [Cu(hism-H)(Bg)], [Cu(Bg)(OH) + ] and [Cu(Bg-H)(OH)] complexes. Histidine provides both histamine-like [(NH 2 , N-imidazole i.e. (hism ― )] and mixed histamine-like glycine-like [(NH 2 , N-imidazole) (NH 2 , COO-) i.e. (hism ― )(gly ― )] chelation, barring simple glycine-like (gly ― ) chelation. Binding affinity of Cu II for (NH 2 , =NH) bidentate chelating biguanide is so strong that the histidine-imidazole deprotonated mixed-ligand complex, [Cu(hism-H)(Bg)] decomposes at pH > 10 to biguanide (=NH) deprotonated ternary hydroxo complex, [Cu(Bg-H)(OH)], setting free the his- ligand ion in solution, a phenomenon of great biological significance, in regard to medicinal applications of the title ligands and their metal derivatives.

Crystal structure, NMR and theoretical investigations on 2-( o-hydroxy-anilino)-1,4-napthoquinone

Crystal structure, 1H NMR and cyclic voltammetric investigations of 2-( o-hydroxy-anilino)-1,4-napthoquinone (HAN), resulting from coupling of aminophenol with 2-hydroxy-1,4-napthoquinone, have been carried out. X-ray structure reveals that the HAN ligand crystallizes in orthorhombic space group Pca2 1 with Z = 4, forming a chain via inter-molecular O2⋯H1A O1 and C15 H15⋯O3 interactions. Both 1H NMR and cyclic voltammetry experiments suggest the titled ligand is associated and exists as dimer in d 6-DMSO while the monomer has been predicted in CDCl 3 solution. Density functional calculations can be utilized to gauge the strength of hydrogen-bonded interactions from the 1H chemical shifts in the NMR spectra. Self-consistent reaction field (SCRF) calculations further support the inferences drawn from cyclic voltammetry experiments.