Air-stable Complex Research Articles

Nonoxidovanadium(IV) Complex-Catalyzed Synthesis of 2-Amino-3-cyano-4H-pyrans/4H-chromenes, Biscoumarins, and Xanthenes under Green Conditions.

Reaction of [VIVO(acac)2] (Hacac = acetylacetone) with a Mannich base, N,N,N',N'-tetrakis(2-hydroxy-3,5-di-tert-butyl benzyl)-1,2-diaminoethane (H4L, I) in a 1:1 molar ratio in MeOH, leads to the formation of the nonoxidovanadium(IV) complex [VIVL] (1). Air stable complex 1 has been characterized using various spectroscopic techniques, DFT calculations, and single-crystal X-ray studies. 1 adopts distorted octahedral geometry where ligand coordinates through all coordination functionalities available. This complex has been used as a catalyst in the one-pot, three-component synthesis of 2-amino-3-cyano-4H-pyrans using 1,3-dicarbonyls (1,3-cyclohexanedione, dimedone, barbituric acid, and 4-hydroxycoumarin), malononitrile, and various substituted aromatic aldehydes in equimolar amounts employing ethanol as a green solvent. The catalytic reaction revealed that the multicomponent synthesis of 4H-pyrans and chromenes is greatly influenced by both types of 1,3-dicarbonyl compound employed and the nature of the substituent on the aromatic ring of the aldehyde. Synthesized catalyst has also been used in the synthesis of pharmacologically relevant oxygen-containing heterocycles, specifically, 1,8-dioxo-octahydro-1H-xanthenes and biscoumarins. The possible mechanism for the synthesized one-pot, multicomponent product has been proposed by isolating intermediate(s) generated during synthesis.

Half‐sandwich iridium complexes: Synthesis and catalytic activity in dehydrogenation of alcohols to carboxylic acids

A series of N,N‐chelate half‐sandwich iridium complexes were synthesized by a simple method with good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been successfully achieved by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half‐sandwich iridium catalyst system showed desirable stability and catalytic activity, and the achievement of a high TOF of 372.0 h−1 could be observed with an extremely low catalyst loading of only 0.05 mol%. Furthermore, the sustainable catalyst could be reused for a minimum of five cycles without obviously losing its activity, highlighting its potential application in industry. Structure of N,N‐chelate iridium complexes 1 and 3 were determined by single‐crystal X‐ray analysis.

Half-Sandwich Iridium Complexes: A Recyclable and Stable Catalyst for Dehydrogenation of Alcohols to Carboxylic Acids.

A series of acylhydrazone-based N,N-chelate half-sandwich iridium complexes have been synthesized through a facile route in good yields. The dehydrogenation of a series of aromatic and aliphatic primary alcohols to corresponding carboxylic acids has been accomplished catalyzed by the prepared air stable iridium complexes under mild reaction conditions. Carboxylic acids were obtained in high yields under open flask condition with broad substrates and good tolerance to sensitive functional groups. Such a half-sandwich iridium catalyst system exhibited high catalytic activity and stability, and a high TOF of 316.7 h-1 could be achieved with a catalyst loading as low as 0.05 mol %. Furthermore, the sustainable catalyst could be reused at least five times without obviously losing its activity, highlighting its potential application in industry. Molecular structure of iridium complex 1 was confirmed by single-crystal X-ray analysis.

Macrobicyclic Dibridgehead Di(trialkyl)pnictogens E((CH2) n )3E (E/n = As/10, As/12, As/14, Sb/14) and Their Cage-like Metal Complexes: Syntheses, Structures, and Homeomorphic Isomerizations.

Photolyses of trans-Fe(CO)3(As((CH2) n )3As) (n = a, 10; b, 12; c, 14) in the presence of PMe3, or reactions of trans-[Fe(CO)2(NO)(As((CH2) n )3As)]+ BF4 - and n-Bu4N+ Cl-, afford the air stable title complexes As((CH2) n )3As (8a-c) in 79-34% yields. With 8a, the in, in and out, out isomers are separable and each is crystallographically characterized. With 8b,c, the isomers rapidly interconvert by homeomorphic isomerization, but each crystallizes (contrathermodynamically) as an out, out isomer. Reactions of 8c with H2O2 or 8b with BH3 give 8c·2O or 8b·2BH3, respectively (85-94%). Reactions of 8c with MCl2 (M = Pt, Pd, Ni), Rh(CO)(Cl), and Fe(CO)3 sources afford the corresponding cage-like complexes trans-ML n (As((CH2)14)3As) (86-51%). The crystal structures of 8c·2O and the PtCl2 and PdCl2 adducts are determined and compared to those of 8a-c and diphosphorus analogs. The corresponding distibine Sb((CH2)14)3Sb is analogously prepared, but precursors necessary for the bismuth analog could not be accessed due to the diminished BiR3 Lewis basicity.

Radical coupling of aryl halides to arenes facilitated by Ni(COD)(DQ) and other nickel sources.

The air-stable complex Ni(COD)(DQ) (COD = 1,5-cyclooctadiene, DQ = duroquinone) promotes the coupling of aryl halides to arenes in the presence of KOtBu. This complex has recently been shown to perform coupling reactions based on organonickel intermediates, but in this case the coupling reactions proceed via aryl radicals as shown by our newly developed assay for aryl radicals. Coupling with this nickel source is more efficient than with Ni(COD)2, Ni(PPh3)4 and Ni(acac)2, all of which we also show to operate through aryl radical pathways.

Well-defined Cu(I) complexes based on [N,P]-pyrrole ligands catalyzed a highly endoselective 1,3-dipolar cycloaddition.

We herein report the synthesis and catalytic application of a new family of dinuclear Cu(I) complexes based on [N,P]-pyrrole ligands. The Cu(I) complexes (4a-d) were obtained in good yields and their catalytic properties were evaluated in the1,3-dipolar cycloaddition of azomethine ylides and electron-deficient alkenes. The air-stable complexes 4a-d exhibited high endo-diasteroselectivity to obtain substituted pyrrolidines, and the catalytic system showed excellent reactivity and wide substitution tolerance.

Air stable N-heterocyclic carbene silver complexes: synthesis, characterization, and antibacterial activity

A new benzimidazolium salt containing a 2,5-dimethylbenzyl substituent and six N-heterocyclic carbene (NHC) silver complexes were prepared. The complexes were characterized by NMR, FTIR, and LC-MS spectroscopic methods and elemental analyses. They are stable in solution for a week. The antibacterial properties of the Ag(I) complexes against two Gram-positive and two Gram-negative bacteria were investigated. Inhibition zone and minimum inhibitory concentration (MIC) data establish that these NHC-Ag(I) complexes possess antibacterial activities; 2b showed the highest antibacterial activity overall against Gram-positive and Gram-negative bacteria.

Hydroxypyridine/Pyridone Interconversions within Ruthenium Complexes and Their Application in the Catalytic Hydrogenation of CO2

Reaction of a new ligand 6-DiPPon (6-diisopropylphosphino-2-pyridone) with 0.5 equiv of [RuCl2(p-cymene)]2 resulted in the formation of a mixture of [RuCl2(p-cymene)(κ1-P-6-DiPPon)]2 (1) and [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]Cl ([2]Cl) (where 6-DiPPin = 6-diisopropylphosphino-2-hydroxypyridine). The ratio between the two products can be controlled by the nature of the solvent. The similar reaction between 6-DiPPon and [RuCl2(p-cymene)]2 in the presence of AgOTf and Na[BArF24] (where BArF24 = [{3,5-(CF3)2C6H3}4B]-) resulted in the formation of the complexes [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]OTf, ([2]OTf) and [RuCl(p-cymene)(κ2-P,N-6-DiPPin)]BArF24 ([2]BArF24), respectively. Reactions between complex [2]Cl, [2]OTf, or [2]BArF24 and a base (either DBU or NaOMe) resulted in the deprotonation of the hydroxyl functional group to form a novel neutral orange-colored dearomatized complex, 3. The identity of complex 3 was confirmed as [RuCl(p-cymene)(κ2-P,N-6-DiPPon*)], where 6-DiPPon* is the anionic species (6-diisopropylphosphino-2-oxo-pyridinide), which contains the deprotonated moiety. The new 6-DiPPon ligand and its corresponding air stable half-sandwich derivative ruthenium complexes 1, [2]OTf, [2]BArF24, and 3 were all isolated in good yields and fully characterized by spectroscopic and analytical methods. The interconversions between the neutral and anionic forms of the ligands 6-DiPPon, 6-DiPPin, and 6-DiPPon* offer the potential for novel secondary sphere interactions and proton shuttling reactivity. The consequences for this have been explored in the activation of H2 and the subsequent catalytic hydrogenations of CO2 into formate salts in the presence of a base.

Synthesis, Characterization And Antimicrobial Study of Pd(II) and Pt(II) complexes of 4-methyl-5-Imidazolecarboxaldehyde Thiosemicarbazone

Schiff bases are regarded as “privileged ligands” due to their capability to form complexes with a wide range of transition metal ions yielding stable and intensely colored metal complexes. In this study, equimolar amounts of 4-methyl-5-imidazolecarboxaldehyde and thiosemicarbazide were combined and the Schiff base 4-methyl-5-imidazolecarboxaldehyde thiosemicarbazone was prepared as a new bidentate complexing agent. The synthesized ligand was reacted with palladium (II) and platinum (II) ions yielding air-stable complexes. For characterization purpose, mass spectra and x-ray analysis of the ligand and infrared spectra, electronic spectra, thermal analysis, proton nuclear magnetic resonance and 13-carbon nuclear magnetic resonance spectra studies were carried out on the obtained ligand and its complexes. The characterization data showed that the ligand acts as a bidentate coordinate to the metal ions through azomethine nitrogen and sulfur atom. An in vitro antimicrobial investigation was also carried out for the free ligand and its metal complexes against four bacteria; Bacillus cereus, Staphylococcus aureus (Gram-positive), Escherichia coli and Salmonella typhimurium (Gram-negative) and one Fungi; Candida albicans. The results showed that the antimicrobial activity of the prepared complexes showed higher activity than the free ligand.

E-selective Semi-hydrogenation of Alkynes under Mild Conditions by a Diruthenium Hydride Complex.

The synthesis, characterization and catalytic activity of a new class of diruthenium hydrido carbonyl complexes bound to the tBu PNNP expanded pincer ligand is described. Reacting tBu PNNP with two equiv of RuHCl(PPh3 )3 (CO) at 140 °C produces an insoluble air-stable complex, which was structurally characterized as [Ru2 (tBu PNNP)H(μ-H)Cl(μ-Cl)(CO)2 ] (1) using solid-state NMR, IR and X-ray absorption spectroscopies and follow-up reactivity. A reaction with KOtBu results in deprotonation of a methylene linker to produce [Ru2 (tBu PNNP* )H(μ-H)(μ-OtBu)(CO)2 ] (3) featuring a partially dearomatized naphthyridine core. This enables metal-ligand cooperative activation of H2 analogous to the mononuclear analogue, [Ru(tBu PNP*)H(CO)]. In contrast to the mononuclear system, the bimetallic analogue 3 catalyzes the E-selective semi-hydrogenation of alkynes at ambient temperature and atmospheric H2 pressure with good functional group tolerance. Monitoring the semi-hydrogenation of diphenylacetylene by 1 H NMR spectroscopy shows the intermediacy of Z-stilbene, which is subsequently isomerized to the E-isomer. Initial findings into the mode of action of this system are provided, including the spectroscopic characterization of a polyhydride intermediate and the isolation of a deactivated species with a partially hydrogenated naphthyridine backbone.

Chiral oxazolidines acting as transient hydroxyalkyl-functionalized N-heterocyclic carbenes: an efficient route to air stable copper and gold complexes for asymmetric catalysis.

Optically pure oxazolidines were synthesized in nearly quantitative yields from chiral hydroxyalkyl-functionalized imidazolinium salts. Acting as transient chiral diamino N-heterocyclic carbenes (NHCs), these oxazolidines allowed the efficient formation of well-defined copper(i) and gold(i) hydroxyalkyl-NHC complexes, which could be isolated, for the first time, as air stable complexes after silica gel chromatography. Interestingly, X-ray analysis of gold complexes revealed that the hydroxyl-function is not chelated to the metal. Computational studies suggested that both cyclisation to produce oxazolidine and O–H bond elimination to form the transient carbene (prior to coordination) occur through a concerted mechanism. The novel chiral copper-catalysts, as well as oxazolidines alone (copper free), demonstrated excellent performances in asymmetric conjugate addition and allylic alkylation with high regio- and enantio-selectivities (up to 99% ee).

Structural and multi-functional properties of novel thorium complex bearing higher analogue of guanidine base

New-fangled water mediated and air stable thorium complex of molecular formula (AgunH)2[Th(dip)3].H2O have been prepared by reacting thorium(IV) nitrate, dipicolinic acid (H2dip) and aminoguanidine bicarbonate (AgunH.HCO3) at appropriate molar ratio via., template method. The complex has been systematically characterized by chemical analysis, elemental, spectral, thermal and single crystal studies including luminescence and antioxidant properties. The IR spectrum of the resulting complex infers that the carboxylate anion behaves as a monodentate and facilitates to form a monomeric rather than polymeric environment. This is further confirmed by single crystal X-ray diffraction studies. Thermal stability of the title compound undergoes step-wise decomposition to endure ThO(CO3) as the end residue. The single crystal X-ray study reveals that the thorium complex crystallizes in the triclinic crystal system with centric space group (P-1) of Z = 2. Each dipicolinate anion (dip2−) exhibits tridentate coordination modes through a nitrogen atom of pyridine ring and oxygen atoms of the carboxylate groups to form nine coordination with tri-capped trigonal prismatic geometry. Further, the anionic complex is neutralized by two aminoguanidinium (AgunH+) cations and stabilized along with a lattice water molecule. This material shows enhanced luminescent properties, this is due to the crucial role of dipicolinate anion not for aminoguanidinium moiety. Whereas, the aminoguanidinium species is promote to act as a secondary antioxidant.

Synthesis, characterization, and antimicrobial activity of 4-imidazolecarboxaldehyde thiosemicarbazone and its Pt(II) and Pd(II) complexes

Schiff bases are versatile ligands, synthesized via condensation of primary amines with carbonyl compounds. In this study, equimolar amounts of 4-imidazolecarboxaldehyde and thiosemicarbazide were combined and the Schiff base 4-imidazolecarboxaldehyde thiosemicarbazone was prepared as a new bidentate complexing agent. The synthesized ligand was reacted with palladium (II) and platinum (II) ions yielding air-stable complexes. For characterization purpose, infrared spectra, mass spectra, electronic spectra, thermal analysis, proton nuclear magnetic resonance and 13-carbon nuclear magnetic resonance spectra studies were carried out on the obtained complexes and ligand. The characterization data showed that the ligand acts as a bidentate coordinate to the metal ions through azomethine nitrogen and sulfur atoms. An in vitro antimicrobial investigation was also carried out for the free ligand and its metal complexes against four bacteria; Bacillus cereus, Staphylococcus aureus (Gram-positive), Escherichia coli and Salmonella typhimurium (Gram-negative) and one Fungi; Candida albicans, to assess their antimicrobial properties by disc diffusion technique. Antimicrobial activity of the prepared complexes showed higher activity than the free ligand.

Transfer Hydrogenation of Aldehydes and Ketones in Air with Methanol and Ethanol by an Air-Stable Ruthenium–Triazole Complex

Coordination of 1,4-disubstituted 1,2,3-triazoles L₁ and L₂ with [(p-cymene)RuCl₂]₂ followed by dehydrochlorination in the presence of a base resulted in the formation of complexes 1 and 2, respectively. Both were tested for the transfer hydrogenation of aldehydes and ketones in air using ecologically benign and cheap ethanol as the hydrogen source in the presence of a catalytic amount of a base. Air-stable complex 1 was proved to be an active catalyst for the transfer hydrogenation of a wide variety of aromatic and aliphatic aldehydes and ketones bearing various functionalities. Catalyst 1 was also effective for the transfer hydrogenation of carbonyls using the simplest primary alcohol, methanol, under aerobic conditions. Under the present catalytic protocol, labile or reducible functionalities such as nitro, cyano, and ester groups were tolerated. Good selectivity was also observed for acyclic α,β-unsaturated carbonyls. However, this catalytic protocol was not selective for 2-cyclohexen-1-one as both alkene and keto moieties were reduced. The transfer hydrogenations are believed to proceed via a ruthenium-hydride intermediate. Finally, transfer hydrogenation of acetophenone using isopropanol as a commonly used hydrogen source was also performed and the sustainable and green credentials of these catalytic protocols utilizing methanol, ethanol, and isopropanol were compared with the help of the CHEM21 green metrics toolkit.

Syntheses, structures and mössbauer effect spectroscopy of triple-decker complexes incorporating decamethylferrocene

Two new triple-decker complexes were synthesized by the reaction of decamethylferrocene Cp∗FeCp∗ (Cp∗ = C5Me5) with ruthenium cations, [CpRu]+ (Cp = C5H5) and [Cp∗Ru]+. The reaction of [CpRu]+ with Cp∗FeCp∗ afforded a purple colored heterometallic complex [CpRu(μ-Cp∗)FeCp∗]+ by electrophilic addition of ruthenium to one Cp∗ ring of decamethylferrocene in 13.3% yield. In analogous manner, the reaction of [Cp∗Ru]+ with Cp∗FeCp∗ afforded a magenta colored complex [Cp∗Ru(μ-Cp∗)FeCp∗]+ in 22.5% yield. Two air stable triple-decker complexes incorporating decamethylferrocene, [CpRu(μ-Cp∗)FeCp∗]+ (1) and [Cp∗Ru(μ-Cp∗)FeCp∗]+ (2) have been characterized by NMR spectroscopy, elemental analysis, single-crystal X-ray diffraction analysis, cyclic voltammetry and temperature dependent 57Fe Mössbauer spectroscopy.

Palladium complexes of chalcogenoethanamine (S/Se) bidentate ligands: Applications in catalytic arylation of C[sbnd]H and O[sbnd]H bonds

This report describes the syntheses of N,E (E = S, Se) coordinated bidentate palladium complexes, by the reaction of N-(2-bromobenzyl)-2-(phenylthio/selanyl)ethanamine (3, 4) with [PdCl2(CH3CN)2]. The new ligands and palladium complexes were characterized by techniques like 1H, 13C{1H} NMR, IR, and elemental analysis. The coordination modes of ligand with palladium precursor in complexes 5 and 6 were authenticated by single crystal X-ray diffraction. The complexes possess distorted square planar geometry around palladium center. Thermally robust and air stable complexes 5 and 6 were used as catalyst for regioselective arylation of imidazole and O-arylation of phenol. In case of regioselective arylation of imidazole, the reaction proceeds smoothly under mild reaction conditions, only 2.0 mol% of catalyst loading is required to achieve high yield (76–92%). This protocol is applicable to a broad substrate scope showing excellent tolerance towards different functional groups. Whereas for O-arylation of phenol also only 2.0 mol% catalyst loading is sufficient to give good yield (71–92%) with excellent tolerance towards a broad range of functional groups. Among sulfur and selenium coordinated ligands, selenium ligand coordinated complex, was found to outperform the catalytic reactions in both cases as compare to sulfur ligand. The mercury and triphenylphosphine poisoning tests suggest homogeneous nature of catalysis.

Synthesis, characterization and biological activity of a Schiff base derived from o-amino benzoic acid and its Co(II), Cd(II) and Ni(II) complexes

Equimolar amounts of imidazoleacetophenone and 2-aminobenzoic acid were combined together and the Schiff base 4(1H-imidazole-yl)acetophenoneanthranilic acid was prepared as a new bidentate complexing agent. The synthesized ligand was reacted with cobalt(II), cadmium(II), and nickel(II) ions yielding air stable complexes. For quantification and characterization purposes, elemental analysis, infrared spectra, electronic spectra, proton nuclear magnetic resonance spectra and mass spectra studies were carried out on the obtained complexes and ligand. Thermogravimetric analysis and magnetic susceptibility measurements were also used for characterization. The ligand IR spectrum showed that the ligand acts as a bidentate coordinates to the metal ions through the nitrogen and oxygen atoms.Measurements of magnetic susceptibility for Ni(II) and Co(II) complexes were found to be 3.4 and 3.8 B.M., respectively, in the range normal for the octahedral geometry. The conductivity measurements revealed that the chelates are non-electrolytes. An in vitro antimicrobial investigation was also carried out for the free ligand and its metal complexes against a number of bacterial and fungal strains, to assess their antimicrobial properties by diffusion technique. Antimicrobial activity of the prepared complexes showed higher activity than the free ligand.

Water-Soluble Rhenium Phosphine Complexes Incorporating the Ph2C(X) Motif (X = O-, NH-): Structural and Cytotoxicity Studies.

Reaction of [ReOCl3(PPh3)2] or [ReO2I(PPh3)2] with 2,2'-diphenylglycine (dpgH2) in refluxing ethanol afforded the air-stable complex [ReO(dpgH)(dpg)(PPh3)] (1). Treatment of [ReO(OEt)I2(PPh3)2] with 1,2,3-triaza-7-phosphaadamantane (PTA) afforded the complex [ReO(OEt)I2(PTA)2] (2). Reaction of [ReOI2(PTA)3] with dpgH2 led to the isolation of the complex [Re(NCPh2)I2(PTA)3]·0.5EtOH (3·0.5EtOH). A similar reaction but using [ReOX2(PTA)3] (X = Cl, Br) resulted in the analogous halide complexes [Re(NCPh2)Cl2(PTA)3]·2EtOH (4·2EtOH) and [Re(NCPh2)(PTA)3Br2]·1.6EtOH (5·1.6EtOH). Using benzilic acid (2,2'-diphenylglycolic acid, benzH) with 2 afforded the complex [ReO(benz)2(PTA)][PTAH]·EtOH (6·EtOH). The potential for the formation of complexes using radioisotopes with relatively short half-lives suitable for nuclear medicine applications by developing conditions for [Re(NCPh2)(dpg)I(PTA)3] (7)[ReO4]- in a 4 h time scale was investigated. A procedure for the technetium analog of complex [Re(NCPh2)I2(PTA)3] (3) from 99mTc[TcO4]- was then investigated. The molecular structures of 1-7 are reported; complexes 3-7 have been studied using in vitro cell assays (HeLa, HCT116, HT-29, and HEK 293) and were found to have IC50 values in the range of 29-1858 μM.

Air stable and efficient rare earth Eu(ii) hydro-tris(pyrazolyl)borate complexes with tunable emission colors

Eu(ii) complexes with high air stability and tunable emission colors were synthesized and characterized.

A designed and potentially decadentate ligand for use in lanthanide(iii) catalysed biomass transformations: targeting diastereoselective trans-4,5-diaminocyclopentenone derivatives.

The goal of this study was to design a ligand system which can accommodate single lanthanide(iii)-ions and investigate the properties of the resulting complexes. The complexes of all the accesible lanthanides and yttrium with the new ligand LH6 = N,N'-dimethyl-N,N'-ethylene-bis(5-bromo-3-(1H-benzimidazol-2-yl)hydrazineylidene)-2-hydroxybenzylamine) were obtained in high yield at room temperature under aerobic reaction conditions. The corresponding compounds were characterised using X-ray diffraction, FT-IR, elemental analysis and the optical properties of all complexes were investigated using UV-vis and fluorescence spectroscopy. The air stable complexes efficiently transform biomass furfural to trans-4,5-cyclopentenones in high yield.