Unsymmetrical Ligand Research Articles

Synthesis, characterization, and crystal structures of molybdenum complexes of unsymmetrical electron-poor dithiolene ligands

Mo(S2C2(CF3)2)3, 1a, has proven a useful p-dopant in organic electronics. To develop more soluble p-dopants, MoS92− was treated with alkynes CF3CCCO2Me and CF3CCCOCF3 to give the dianions of the corresponding tris(dithiolene) complexes, 1b2− and 1c2−, respectively, which were then oxidized to neutral molybdenum tris[1-(methoxycarbonyl)-2-(trifluoromethyl)-ethane-1,2-dithiolene], 1b, and molybdenum tris[1-(trifluoroethanoyl)-2-(trifluoromethyl)ethane-1,2-dithiolene], 1c, using NO+PF6−. The crystal structures of (NEt4+)21b2−, (NEt4+)21c2−, and neutral 1c have been determined. In all three cases, the metal coordination is approximately trigonal prismatic and the major isomer is cis (approximately C3v). The structure of 1b2− is distorted by a twist towards pseudo-octahedral coordination similar to that seen in structures of 1a2− and Mo(S2C2(CO2Me)2)32−, 1d2−, salts, and that of 1c exhibits marked folds between the planes formed by the ligand atoms and those formed by the Mo and coordinated S atoms, similar to those seen in the structure of 1a. On the other hand, the metal dithiolene core of 1c2− is essentially undistorted from C3v symmetry. The oxidant strength of the neutral molecules increases in the order 1d<1b<1a<1c, with the potentials ranging from −0.02 to +0.39V versus the ferrocenium/ferrocene couple.

Synthesis, characterization and catecholase-like activity of new Schiff base metal complexes derived from visnagin: Theoretical and experimental study

A new tetradentate, unsymmetrical Schiff base ligand (H2L) containing a donor set of N2O2 and its mononuclear Cu(II) and Fe(II) complexes ([CuL] and [FeL]), were synthesized and characterized on the basis of their elemental analysis, FT-IR, Raman, 1H and 13C NMR spectra, electronic and mass spectra, molar conductivity and magnetic susceptibility measurements. Density functional theory (DFT) calculations were performed in order to clarify molecular structures, 1H NMR and 13C NMR chemical shift values, frontier molecular orbitals (FMOs), nonlinear optical properties and map of molecular electrostatic potential (MEP) of the title molecules. In agreement with trials, the results provide a full explanation of the highest efficiency observed for the compounds in relation to the electronic and the structural characteristics. The catecholase-like activity of the complexes toward the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) to the corresponding quinone showed that both complexes have moderate catalytic activity. [FeL] shows higher activity (kcat = 26.4 h−1) than that of [CuL] (kcat = 23.4 h−1).

Investigation of ligand steric effect on the hydrogen gas produced via a nickel-catalyzed dehydrogenation of ammonia-borane utilizing unsymmetrical triazolylidene ligands

Seven new unsymmetrical triazolylidene ligands 4-(4-R-phenyl)-1-R′-1,2,4-triazoly-1-lidene (where R=H, CH3, CF3, F; and R′=CH3, iPr, Bzl, methylcyclohexane) were employed in a nickel-catalyzed dehydrogenation of ammonia borane to investigate the steric effects associated with the different N(1) substitutions in the triazole ring. The bulkier substituents benzyl and methylcyclohexane afforded the highest weight percent H2 gas produced. To quantify the steric effect, both percent buried volume (%Vbur) and solid angle G parameter (%) were employed. The G-parameter is a more useful tool when only the crystal structures of the precursor ligands are available.

Geometrical isomers of tris(β-diketonato)metal(III) complexes for M = Cr or Co: Synthesis, X-ray structures and DFT study

Solid state crystal data of three tris(β-diketonato)metal(III) complexes (M=Cr or Co), representative of the three different molecular symmetries that these complexes can obtain, namely D3, C3 or C1 symmetry, are presented and compared with related experimental structures. Density functional theory calculations show that both fac and mer isomers of tris(β-diketonato)metal(III) complexes containing unsymmetrical β-diketonato ligands can exist, in agreement with experimental NMR data. The orbital ordering for both the S=3/2 [Cr(acac)3] and S=0 [Co(acac)3] (Hacac=acetylacetone) complexes in order of increasing orbital energy is: dxy<dxz,dyz<dz2,dx2-y2.

New indenylidene-type metathesis catalysts bearing unsymmetrical N-heterocyclic ligands with mesityl and nitrobenzyl substituents.

New indenylidene-type second generation catalysts bearing modified unsymmetrically substituted N-heterocyclic carbene ligands were synthesized. The complexes contain an N-mesityl and N′-nitrobenzyl substituted NHC ligand. The precursors of free carbenes—imidazolinium salts—were obtained in an easy and environment-friendly way (under aqueous or neat conditions). The new catalysts were prepared by reaction of in situ generated carbenes with a 1st generation indenylidene catalyst, containing pyridine ligands instead of tricyclohexylphosphine. The complexes were tested in RCM, CM, and ene-yne metathesis model reactions in commercial-grade solvents in air. Their activities were compared with that of commercially available indenylidene catalyst. The structures of complexes and their stability were investigated using static DFT calculations with mixed basis set.Graphical abstractElectronic supplementary materialThe online version of this article (doi:10.1007/s00706-016-1697-7) contains supplementary material, which is available to authorized users.

N-Trifluoromethyl NHC Ligands Provide Selective Ruthenium Metathesis Catalysts

We report the synthesis of ruthenium metathesis catalysts containing unsymmetrical N-trifluoromethyl NHC ligands. These complexes have been fully characterized, and a Ru–F interaction has been identified in the solid state by X-ray crystallographic analysis for three catalysts with Ru–F distances between 2.629(2) and 2.652(2) A. The influence of the N-trifluoromethyl NHC ligands on the initiation rates and activation parameters was studied. The activity of these catalysts was evaluated in benchmark olefin metathesis reactions and compared to the standard second-generation Grubbs catalyst. Remarkably, N-trifluoromethyl catalysts display an unusually high selectivity for the formation of terminal olefins (up to 90%) in the ethenolysis of ethyl oleate. Much improved selectivity is demonstrated for alternating copolymerization of cyclooctene and norbornene as well. These results underline the importance of electronic effects exerted by the NHC ligand.

Highly phosphorescent platinum(II) complexes based on rigid unsymmetric tetradentate ligands

A new class of highly phosphorescent Pt(II) complexes (Pt1–Pt3) based on rigid unsymmetric tetradentate ligands (L1-L3) were designed and synthesized. L1-L3 ligands are an analogue to N,N-di(2-phenylpyrid-6-yl)aniline (L) except that one coordination phenyl group in L is replaced by other motifs with different electron donating/accepting capabilities. The effect associated with the modulation of a single coordination group within each ligand on the photophysical and electroluminescent properties of Pt1–Pt3 was investigated systematically. Among Pt1–Pt3, Pt1 has the highest HOMO due to the presence of a strong electron-donating group (3-methylindole), and exhibits the narrowest bandgap; Pt2 has the lowest HOMO due to the lack of strong donor group within the structure, and shows the widest bandgap. Organic light-emitting diodes (OLEDs) based on these three complexes showed yellowish green to greenish yellow electroluminescence with high efficiency. Notably, the device based on Pt1 at the doping level of 10 wt% achieved a maximum efficiency of 53.0 cd A−1, 35.9 lm W−1 and 16.3% with CIE coordinates of (0.44, 0.53).

Lanthanide–Organic Frameworks Constructed from an Unsymmetrical Tricarboxylate for Selective Gas Adsorption and Small‐Molecule Sensing

AbstractBy using the new unsymmetrical tricarboxylate ligand 5‐(6‐carboxynaphthalen‐2‐yl)isophthalic acid (H3L), three lanthanide–organic frameworks, [LnL(H2O)2]·DMF·H2O [Ln = Eu (1), Tb (2), and Ho (3); DMF = N,N‐dimethylformamide], have been synthesized solvothermally and characterized by single‐crystal X‐ray diffraction, powder X‐ray diffraction, thermogravimetric analysis (TGA), FTIR spectroscopy, and elemental analysis. The single‐crystal X‐ray diffraction analysis showed that the three metal–organic frameworks (MOFs) are isostructural and display 3D networks with the (3,6)‐connected flu‐type topology. Furthermore, the gas adsorption and photoluminescence properties of the three MOFs were investigated. The compounds exhibited selective adsorption toward CO2 over CH4 at ambient temperature and different luminescence responses to small molecules, especially nitrobenzene.

Facile high-yield synthesis of unsymmetric end-off compartmental double Schiff-base ligands: easy access to mononuclear precursor and unsymmetric dinuclear complexes

Novel approach to unsymmetric end-off compartmental ligands with a selective high-yield synthesis and access to unsymmetric dinuclear complexes.

Three novel metal–organic frameworks based on an unsymmetrical rigid carboxylate ligand for luminescence sensing of nitrobenzene derivatives and magnetic properties

Three novel metal–organic frameworks, formulated as [Co(HDCPN)(4,4′-bibp)]·1.5H2O (1), [Cd3(DCPN)2(4,4′-bibp)2H2O]·1.5H2O (2) and [Mn3(DCPN)2(4,4′-bibp)3(H2O)4] (3) (H3DCPN = 6-(3,5-dicarboxylphenyl)nicotinic acid and 4,4′-bibp = 4,4′-bis(imidazolyl)biphenyl), have been solvothermally synthesized based on an unsymmetrical rigid carboxylate ligand. Single-crystal X-ray diffraction analysis shows that complex 1 is an sql/Shubnikov tetragonal plane network with mononuclear Co(II) ions, which is connected by O2⋯H2⋯O1 hydrogen bonds to generate a 3D framework. Complex 2 is a new 3D (3,10)-c network based on trinuclear Cd clusters. Complex 3 is an extended 3D (3,10)-c network based on trinuclear Mn clusters, which belongs to 3,10T3 (MOF.ttd). Complex 2 exhibits potential application for the luminescence sensing of nitrobenzene derivatives. Furthermore, the variable-temperature magnetic susceptibilities of complexes 1 and 3 indicate that they exhibit antiferromagnetic behavior and ferromagnetic behavior between metal ions, respectively.

Synthesis and Characterization of a New Unsymmetrical Potentially Pentadentate Schiff Base Ligand and Related Complexes with Manganese(II), Nickel(II), Copper(II), Zinc(II) and Cadmium(II)

New unsymmetric thioether Schiff base amine, 2-(2-aminoethylthio)-N-(thiophene-2-ylmethylene)aniline was prepared by reaction of 2-aminothiophenol with N-(2-bromoethyl)phthalimide and then by thiophene-2-carbaldehyde. Then, the phthalimide group converted to the amine by hydrazine hydrate. The new potentially pentadentate N3S2 donor unsymmetrical Schiff base ligand, 2-(2-(pyridine-2-ylmethyleneamino)ethylthio)-N-(thiophene-2-ylmethylene)aniline (L) was prepared via [1 + 1] condensation of pyridine-2-carbaldehyde with this amine. Manganese(II), nickel(II), copper(II), zinc(II) and cadmium(II) complexes of this ligand were prepared by adding metal salts to an ethanolic solution in this ligand. The thioether amine, ligand (L) and unsymmetric Schiff base complexes are characterized by the appropriate spectroscopic methods such as infrared (IR), UV-Vis, 1H nuclear magnetic resonance (NMR), 13C NMR studies, X-ray, microanalysis and mass spectrometry.

Homochiral and heterochiral Mn(II) coordination frameworks: spontaneous resolution dependent on dipyridyl ligands.

An unsymmetric tetracarboxylic ligand collaborates with 4,4'-bipyridine to induce spontaneous resolution to form homochiral 3D coordination frameworks, while the use of longer dipyridyl ligands instead of 4,4'-bipyridine leads to isoreticular but heterochiral frameworks.

Six- and seven-coordinate Fe(ii) and Zn(ii) compounds ligated by unsymmetric xanthene-based ligands: characterization and magnetic properties

We present new ligand platforms for pentagonal bipyramidal metal complexes, and the characterization of the corresponding Zn(ii)- and Fe(ii)-containing compounds.

Ruthenium complexes bearing an unsymmetrical pincer ligand with a 2-hydroxypyridylmethylene fragment: active catalysts for transfer hydrogenation of ketones

Five ruthenium(ii) complexes were synthesized, including (HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)Cl2 (3), [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2Cl][PF6] (4) and [(HO-C5H3N-CH2-C5H3N-C5H4N)Ru(PPh3)2OH][PF6] (5) bearing an unsymmetrical pincer NNN ligand with a 2-hydroxypyridylmethylene fragment, and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][Cl]2 (6) and [(CH3O-C5H3N-CH2-C5H3N-C5H4N)2Ru][PF6]2 (7) containing 2-methoxypyridylmethylene moieties. 4 reacts with H2O at room temperature to give 5 whose crystal structure reveals the existence of intramolecular hydrogen-bonding between its two -OH groups. 3 exhibits high catalytic activity for transfer hydrogenation of ketones.

Trinuclear nickel and cobalt complexes containing unsymmetrical tripodal tetradentate ligands: syntheses, structural, magnetic, and catalytic properties

The coordination chemistries of the tetradentate N2O2-type ligands N-(2-pyridylmethyl)iminodiethanol (H2pmide) and N-(2-pyridylmethyl)iminodiisopropanol (H2pmidip) have been investigated with nickel(ii) and cobalt(ii/iii) ions. Three novel complexes prepared and characterized are [(Hpmide)2Ni3(CH3COO)4] (1), [(Hpmide)2Co3(CH3COO)4] (2), and [(pmidip)2Co3(CH3COO)4] (3). In 1 and 2, two terminal nickel(ii)/cobalt(ii) units are coordinated to one Hpmide(-) and two CH3CO2(-). The terminal units are each connected to a central nickel(ii)/cobalt(ii) cation through one oxygen atom of Hpmide(-) and two oxygen atoms of acetate ions, giving rise to nickel(ii) and cobalt(ii) trinuclear complexes, respectively. Trinuclear complexes 1 and 2 are isomorphous. In 3, two terminal cobalt(iii) units are coordinated to pmidip(2-) and two CH3CO2(-). The terminal units are each linked to a central cobalt(ii) cation through two oxygen atoms of pmidip(2-) and one oxygen atom of a bidentate acetate ion, resulting in a linear trinuclear mixed-valence cobalt complex. 1 shows a weak ferromagnetic interaction with the ethoxo and acetato groups between the nickel(ii) ions (g = 2.24, J = 2.35 cm(-1)). However, 2 indicates a weak antiferromagnetic coupling with the ethoxo and acetato groups between the cobalt(ii) ions (g = 2.37, J = -0.5 cm(-1)). Additionally, 3 behaves as a paramagnetic cobalt(ii) monomer, due to the diamagnetic cobalt(iii) ions in the terminal units (g = 2.53, |D| = 36.0 cm(-1)). No catalytic activity was observed in 1. However, 2 and 3 showed significant catalytic activities toward various olefins with modest to good yields. 3 was slightly less efficient toward olefin epoxidation reaction than 2. Also 2 was used for terminal olefin oxidation reaction and was oxidised to the corresponding epoxides in moderate yields (34-75%) with conversions ranging from 47-100%. The cobalt complexes 2 and 3 promoted the O-O bond cleavage to ∼75% heterolysis and ∼25% homolysis.

Chemical consequences of pyrazole orientation in Ru(II) complexes of unsymmetric quinoline-pyrazole ligands.

A series of homoleptic Ru(II) complexes including the tris-bidentate complexes of a new bidentate ligand 8-(1-pyrazol)-quinoline (Q1Pz) and bidentate 8-(3-pyrazol)-quinoline (Q3PzH), as well as the bis-tridentate complex of bis(quinolinyl)-1,3-pyrazole (DQPz) was studied. Together these complexes explore the orientation of the pyrazole relative to the quinoline. By examining the complexes structurally, photophysically, photochemically, electrochemically, and computationally by DFT and TD-DFT, it is shown that the pyrazole orientation has a significant influence on key properties. In particular, its orientation has noticeable effects on oxidation and reduction potentials, photostability and proton sensitivity, indicating that [Ru(Q3PzH)3](2+) is a particularly good local environment acidity-probe candidate.

Synthesis and structural studies of 1,4-di(2-pyridyl)-1,2,3-triazole and its transition metal complexes; a versatile and subtly unsymmetric ligand.

The synthesis of the 'click' derived 1,4-di(2-pyridyl)-1,2,3-triazole () chelator/ligand from 2-azidopyridine and 2-ethynylpyridine using Cu(i) and TBTA by microwave assisted synthesis is presented. The complexes of the subtly unsymmetric ligand with Cu(i), Pt(ii), Co(ii), and Ag(i) were structurally characterised by using conventional methods, as well as using single crystal and powder diffraction analysis. The results of the studies showed formation of discrete molecules displaying preferential binding of the d-metal cations through the pyridyl nitrogen N1 and the proximal triazolyl nitrogen N2 i.e. the 2-(1H-1,2,3-triazol-4-yl)pyridine or 'regular' chelate moiety despite the presence of a second potential binding pocket i.e. the 2-(1H-1,2,3-triazol-1-yl)pyridine chelate or 'inverse' moiety. This binding selectivity was corroborated through the study of the self-assembly of with Cu(i) and Ag(i) using (1)H NMR titration in CD3CN solution, as well as using UV-Vis absorption titrations; the former showing a broadening of the proton peaks associated with that chelate pocket.

Cis‐Dioxomolybdenum(VI) complexes with unsymmetric linear tetradentate ligands: syntheses, structures and bromoperoxidase activities

Reactions of [MoO2(acetylacetonate)2], 2‐((2‐(2‐hydroxyethylamino)ethylamino)methyl)‐4‐R‐phenols (H2Ln, n = 1–5 for R = H, Me, OMe, Cl and Br, respectively) and KOH in 1:1:2 mole ratio in methanol afford a series of complexes having the general formula cis‐[MoO2(Ln)] (1, 2, 3, 4, 5) in 81–86% yields. The complexes have been characterized using elemental analysis, spectroscopy (infrared, UV–visible, and 1H NMR, 13C NMR and 13C‐DEPT NMR) and electrochemical measurements. The molecular structures of 1, 2, 3, 4 have been determined using single‐crystal X‐ray crystallography. In each of 1, 2, 3, 4, the ONNO‐donor 6,5,5‐membered fused chelate rings forming (Ln)2− and the two mutually cis oxo groups assemble a distorted octahedral N2O4 coordination sphere around the metal centre. In the crystal lattice, each of 1, 2, 3, 4 forms a one‐dimensional infinite chain structure via intermolecular NH⋅⋅⋅O hydrogen bonding interactions. In cyclic voltammograms, the diamagnetic complexes display an irreversible metal‐centred reduction in the potential range −0.73 to −0.88 V (vs Ag/AgCl). The physicochemical data are consistent with a very similar gross molecular structure for all of 1, 2, 3, 4, 5. All the complexes exhibit decent bromoperoxidase activities and are also able to effectively catalyse benzoin and methyl(phenyl)sulfide oxidation reactions. Copyright © 2015 John Wiley &amp; Sons, Ltd.

Synthesis and Crystal Structures of Co(II) Complexes Derived From Two Unsymmetrical Bis-Heterocyclic Ligands With Benzimidazole Moiety

Treatment of two kinds of unsymmetrical bis-heterocyclic ligands bearing benzimidazole moiety, 2-[2-(1,2,4-triazole-1-yl)ethyl]-1H-benzimidazole (L1) and 2-[2-(1,2,3-benzotriazole-1-yl)ethyl]-1H-benzimidazole (L2), with Co(II) chloride, resulted in two new complexes, [Co3(L2)4Cl6]·2H2O (1) and [Co(L1)Cl2]2 (2), with different aggregating patterns. Two complexes were characterized by single-crystal X-ray determinations. In the solid state, L1 assumes an anti conformation in compound 1, whereas L2 exists as a gauche conformer in compound 2. Complex 1 reveals a 1-D double-stranded chain structure consisting of both octahedrally and tetrahedrally coordinated Co(II) ions. Complex 2 is a mononuclear tetrahedral Co(II) species, which was hydrogen bonded with each other to give a 1-D linear chain.

Synthesis, Characterization, Spectral Studies, Antibacterial Evaluation, Thermodynamics and DFT Calculations of Dimethyltin(IV) Dichloride Schiff Base.

A number of new 1:1 complexes of SnMe(2)Cl(2) with unsymmetrical tetradentate Schiff base ligand with NNOS coordination sphere have been synthesized and fully characterized by a variety of physico-chemical techniques viz. elemental analysis, molar conductivity, (1)H and (119)Sn NMR, IR and mass spectroscopy. IR spectral data show that the fifth coordination position of tin atom is occupied by an oxygen atom of Schiff base ligands. In the light of titled techniques, trigonal bipyramidal geometry around the tin atom is proposed for the synthesized complexes. The in vitro antibacterial activities of the complexes against Staphylococcus aureus and Escherichia Coli have been studied. It was found that they possess significant antibacterial activity. Also, DFT/B3LYP method was used to analyze the electronic structures and study of the geometries. The thermodynamic formation constants of the complexes were determined spectrophotometrically at 25ºC in DMF solvent.