A route to magnetically separable nanocatalysts: Combined experimental and theoretical investigation of alkyl substituent role in ligand backbone towards epoxidation ability

We have prepared two chiral Schiff base ligands, H₂L¹ and H₂L², and one achiral Schiff base ligand, H₂L³, by treating 2,6‐diformyl‐4‐methylphenol separately with (R )‐1,2‐diaminopropane, (R )‐1,2‐diaminocyclohexane and 1,1′‐dimethylethylenediamine, in ethanolic medium, respectively. The complexes MnL¹ClO₄ ( 1 ), MnL²ClO₄ ( 2 ), MnL³ClO₄ ( 3 ), FeL¹ClO₄ ( 4 ), FeL²ClO₄ ( 5 ) and FeL³ClO₄ ( 6 ) have been obtained by reacting the ligands H₂L¹, H₂L² and H₂L³ with manganese(III) perchlorate or iron(III) perchlorate in methanol. Circular dichroism studies suggest that ligands H₂L¹ and H₂L² and their corresponding complexes have asymmetric character. Complexes 1 – 6 have been used as homogeneous catalysts for epoxidation of alkenes. Manganese systems have been found to be much better than iron counterparts for alkene epoxidation, with 3 as the best catalyst among manganese systems and 6 as the best among iron systems. The order of their experimental catalytic efficiency has also been rationalized by theoretical calculations. We have observed higher enantiomeric excess product with catalysts 1 and 4 , so they were attached to surface‐modified magnetic nanoparticles to obtain two new magnetically separable nanocatalysts, Fe₃O₄@dopa@MnL¹ and Fe₃O₄@dopa@FeL⁴. They have been characterized and their alkene epoxidation ability has been investigated. These catalysts can be easily recovered by magnetic separation and recycled several times without significant loss of catalytic activity. Hence our study focuses on the synthesis of a magnetically recoverable asymmetric nanocatalyst that finds applications in epoxidation of alkenes and at the same time can be recycled and reused.     

Syntheses,crystal structures and solvatochromic properties of dinuclear oxalato-bridged copper(II) complexes

Three dinuclear copper(II) complexes, [Cu₂(L¹)₂(μ-ox)](ClO₄)₂?2(CH₃CN), [Cu₂(L²)₂(μ-ox)](ClO₄)₂?H₂O, and [Cu₂(L³)₂(μ-ox)](ClO₄)₂ where ox = oxalato; L = N,N-dimethyl,N′-benzylethane-1,2-diamine, L¹, N,N-diethyl,N′-benzylethane-1,2-diamine, L², N,N-diisoprophyl,N′-benzylethane-1,2-diamine, L³, were prepared and characterized by elemental analyses, spectral (IR, UV–Vis) data and molar conductance measurements. The crystal structures of [Cu₂(L¹)₂(μ-ox)](ClO₄)₂?2(CH₃CN) and [Cu₂(L³)₂(μ-ox)](ClO₄)₂ have been determined by single-crystal X-ray analysis. Solvatochromic behaviors were investigated in various solvents, showing positive solvatochromism. The effect of steric hindrance around the copper ion imposed by N-alkyl groups of the diamine chelates on the solvatochromism property of the complexes is discussed. Solvatochromism was also studied with different solvent parameter models using stepwise multiple linear regression method.     

Synthesis,characterization, and structures of copper(I) complexes with N,N′-bis[1-(4-chlorophenyl)ethylidene]ethane-1,2-diamine and N,N′-bis[1-(4-nitrophenyl)ethylidene]ethane-1,2-diamine

Two ligands, N,N′-bis[1-(4-chlorophenyl)ethylidene]ethane-1,2-diamine (L¹ ) and N,N′-bis- [1-(4-nitrophenyl)ethylidene]ethane-1,2-diamine (L² ) and their corresponding copper(I) complexes, [Cu(L ¹)₂]ClO₄ (1) and [Cu(L ²)₂]ClO₄ (2), have been synthesized and characterized by CHN analyses, ¹H-NMR, IR, and UV–Vis spectroscopy. The crystal structures of L¹ and [Cu(L ¹)₂]ClO₄ (1) were determined from single crystal X-ray diffraction. L¹ lies across a crystallographic inversion center and the C=N is approximately coplanar with the benzene ring and adopts E configuration. The coordination polyhedron about copper(I) in 1 is best described as a distorted tetrahedron. Quasireversible redox behavior is observed for the complexes.     

New Cu(II) complexes with polydentate chelating Schiff base ligands: Synthesis, structures, characterisations and biochemical activity studies

We have reported herein the synthesis of three new Cu(II) complexes of tri- and tetradentate Schiff base ligands containing N₃ or N₄ donor set along with terminal NNN⁻ or SCN⁻ ligands: [L¹Cu(NCS)]ClO₄ (1), [L²Cu(NCS)₂] (2) and [L³Cu(NNN)]ClO₄ (3) [L¹ = NC₅H₄C(CH₃)=N(CH₂)₃N=C(CH₃)C₅H₄N, L²= Me₂N–(CH₂)₃–N=C(CH₃)C₅H₄N and L³ = NC₅H₄CH=N–(CH₂)₄–N=CHC₅H₄N]. The complexes have been systematically characterised by elemental, spectroscopic and electrochemical techniques. Antimicrobial activities of the Schiff base ligands and their metal complexes have been studied using the disc diffusion method on the strains of Candida tropicalis and Bacillus megaterium. Structures of all the complexes have been unequivocally established from single crystal X-ray diffraction analyses that show the monomeric units containing a five-coordinated copper center in highly distorted square pyramidal geometry with thiocyanate or azide anion coordinated as terminal ligand. The complexes 1 and 3 crystallise in monoclinic (P2₁/c) and 2 in triclinic (P-1) space group, respectively.     

Synthesis,Crystal Structure and Properties of Two Macrocyclic Dinuclear Complexes

Two macrocyclic dinuclear complexes, [Cu₂L¹](PF₆)₂ and [Cu₂L²](ClO₄)₂, were synthesized by cyclo-condensation between N,N′-bis(3-formyl-5-methylsalicylidene)ethylenediimine or N,N′- bis(3-formyl-5-n-butylsalicylidene)ethylenediimine and ethylenediamine in the presence of Cu²⁺ ions. The crystal structures of the complexes were studied. The variable-temperature magnetic susceptibilities and cyclic voltammograms of the complexes were measured. The magnetic and electrochemical properties of the complexes were discussed. The results show that the complexes display very strong antiferromagnetic exchanges and that all copper(II) complexes undergo a one-electron transfer process.     

Syntheses and X-ray crystal structures of five- and six-coordinate copper(II) complexes of N,N,N′,N′-tetraalkylpyridine-2,6-dicarboxamides containing–OClO3 and–OSO2CF3 counter ions

Reactions of anhydrous copper(II) chloride with NaX (1 : 1 or 1 : 2) and AgX (1 : 2) containing appropriate N,N,N′,N′-tetraalkylpyridine-2,6-dicarboxamides(O-daap) in CH₃CN yield monosubstituted five-coordinate [Cu(L₁)Cl(CF₃SO₃)] (1), [Cu(L₂)Cl(ClO₄)] (2), [Cu(L₃)Cl(ClO₄)] (3), and six-coordinate [Cu(L₂)(CF₃SO₃)₂] · H₂O (4) (X = ?OClO₃ and–OSO₂CF₃; L₁ = N,N,N′,N′-tetraethylpyridine-2,6-dicarboxamides; L₂ = N,N,N′,N′-tetraisopropylpyridine-2,6-dicarboxamides; L₃ = N,N,N′,N′-tetraisobutylpyridine-2,6-dicarboxamides). The structures of these complexes have been determined by X-ray crystallography. The Cu²⁺ in 1–3 adopts distorted square-pyramidal geometry, while 4 exhibits octahedral structure. Steric factors in conjunction with lattice effects and the nature of the anions are responsible for the variety in coordination spheres. These compounds undergo extensive intermolecular H-bonding to give to 2-D sheets extending along various planes.     

Synthesis,crystal structure,and antibacterial activity of mononuclear nickel(II) and cobalt(III) Schiff-base complexes

Four new mononuclear complexes, [Ni(L¹)(NCS)₂] (1), [Ni(L²)(NCS)₂] (2), [Co(L¹)(N₃)₂]ClO₄ (3), and [Co(L²)(N₃)₂]ClO₄ (4), where L¹ and L² are N,N′-bis[(pyridin-2-yl)methylidene]butane-1,4-diamine and N,N′-bis[(pyridin-2-yl)benzylidene]butane-1,4-diamine, respectively, have been prepared. The syntheses have been achieved by reaction of the respective metal perchlorate with the tetradentate Schiff bases, L¹ and L², in presence of thiocyanate (for 1 and 2) or azide (for 3 and 4). The complexes have been characterized by microanalytical, spectroscopic, single crystal X-ray diffraction and other physicochemical studies. Structural studies reveal that 1–4 are distorted octahedral geometries. The antibacterial activity of all the complexes and their constituent Schiff bases have been tested against Gram-positive and Gram-negative bacteria.     

Formation of various polymeric frameworks by dicarboxylate-like ligands: Synthesis and crystal structures of polymeric complexes of sodium perchlorate with flexible double betaines

Three crystalline complexes of sodium perchlorate with different flexible double betaines [Na ₂(L¹)(ClO₄)(H₂O) _n ](ClO₄) _n (1), [Na ₃(L²)(ClO₄)₃(H₂O)_{2 n} ] (2), and [Na(L ³)(CH₃OH)_n]-(ClO₄) _n ·xnH₂O (x=0.25) (3) [^–O₂CCH₂N⁺Me₂–(CH₂) _n -N⁺Me₂CH₂CO₂ ^–,n=2 L¹;n=3 L²;n=4 L³] have been synthesized and characterized by single-crystal X-ray structure analysis. Complex (1) comprises tetranuclear sodium units consolidated by betaine and aqua ligands, which are bridged by half of the ClO₄ ^– anions to form layers matching the (200) planes, the remaining uncoordinated ClO₄ ^– anions being accommodated between adjacent layers. Complex (2) possesses a double-layer polymeric structure with the sodium atoms bridged by ligand oxygen atoms to form columns running parallel to thea axis, which are interconnected by double-betaine ligands lying parallel to theac plane. All of the ClO₄ ^– groups and water molecules are coordinated to the metal atoms. In complex (3) the chains composed of alternating eight-membered and four-membered metallocycles are cross-linked by the betaine ligands, which lie in the (020) and (01/1) families of planes, to yield a three-dimensional network. All of the ClO₄ ^– groups and water molcules fill the resulting infinite channels running parallel to thea axis. Two unusual carboxylate coordination modes are identified, namely ₃-O andhapto-3-O plushapto-2-O in (1) and (2), respectively.     

Synthesis and characterization of Cu(II) complexes of tetradentate and tridentate symmetrical Schiff base ligands involving <Emphasis Type="Italic">o</Emphasis>-phenelenediamine,salicylaldehyde and diacetylmonoxime

A mononuclear complex [CuL] (1), a binuclear complex [Cu₂LCl₂(H₂O)] (2), a trinuclear complex [Cu₃L₂](ClO₄)₂ (3) involving o-phenylenediamine and salicylaldehyde and another binuclear complex of a tridentate ligand (H₂L¹) [Cu₂L₂¹](CH₃COO)₂ (4) involving o-phenylenediamine and diacetylmonoxime have been synthesized, where H₂L = N,N′-o-phenylenebis(salicylideneimine) and H₂L¹ = 3-(2-aminophenylimino)butan-2-one oxime. All the complexes have been characterized by elemental analyses, spectral and magnetic studies. The binuclear complex (2) was characterized structurally where the two Cu(II) centers are connected via an oxygen-bridged arrangement.     

Hydrogen-bonded assemblies of trinuclear metal string complexes

Three kinds of trinuclear metal string complexes, [Ni₃(dpa)₄(L¹)₂]?·?H₂O?·?C₂H₅OH (L¹?=?(E)-3-(2-hydroxyl-phenyl)-acrylic acid) (1), [Ni₃(dpa)₄(L²)₂]?·?2C₂H₅OC₂H₅ (L²?=?(E)-3-(3-hydroxyl-phenyl)-acrylic acid) (2) and [Ni₃(dpa)₄(L³)₂]?·?3CH₂Cl₂?·?1.5CH₃OH (L³?=?(E)-3-(4-hydroxyl-phenyl)-acrylic acid) (3). (dpa^??=?bis(2-pyridyl)amido), have been synthesized. The structures of 1 and 2 have been analyzed by the X-ray single-crystal diffraction showing hydrogen-bonded networks.     

A coordination polymer consisting of two different one‐dimensional copper(II) chains

The title compound, catena‐poly[[[diaqua(methanol‐κO)copper(II)]‐μ‐N‐(4‐methylpyrimidin‐2‐yl‐κN¹)pyrazin‐2‐amine‐κ²N¹:N⁴] [[aqua(aqua/methanol‐κO)(perchlorato‐κO)copper(II)]‐μ‐N‐(4‐methylpyrimidin‐2‐yl‐κN¹)pyrazin‐2‐amine‐κ²N¹:N⁴] tris(perchlorate) methanol monosolvate 1.419‐hydrate], {[Cu(C₉H₉N₅)(CH₃OH)(H₂O)₂][Cu(C₉H₉N₅)(ClO₄)(CH₃OH)_0.581(H₂O)_1.419](ClO₄)₃·CH₃OH·1.419H₂O}_n, is a one‐dimensional straight‐chain polymer of N‐(4‐methylpyrimidin‐2‐yl)pyrazin‐2‐amine (L) with Cu(ClO₄)₂. The complex consists of two crystallographically independent one‐dimensional chains in which the Cu^II atoms exhibit two different octahedral coordination geometries. The L ligand coordinates to two Cu^II centres in a tridentate manner, with the pyrazine ring acting as a bridge linking the Cu^II coordination units and building an infinite one‐dimensional chain. Extensive hydrogen bonding among perchlorate anions, water molecules and L ligands results in three‐dimensional networks.     

Copper(II), Cobalt(II), and Nickel(II) Complexes of two Novel Pyridine‐derived Macrocyclic Ligands bearing o‐ and pNitrobenzyl Pendant Groups

The pendant‐armed ligands L¹ and L² were synthesized by N‐alkylation of the four secondary amine groups of the macrocyclic precursor L using o‐nitrobenzylbromide (L¹) and p‐nitrobenzylbromide (L²). Nitrates and perchlorates of Cu^II, Ni^II and Co^II were used to synthesize the metal complexes of both ligands and the complexes were characterized by microanalysis, MS‐FAB, conductivity measurements, IR and UV‐Vis spectroscopy and magnetic studies. The crystal structures of L¹, [CuL¹](ClO₄)₂·CH₃CN·H₂O, [CuL²](ClO₄)₂·6CH₃CN, [CuL²][Cu(NO₃)₄]·5CH₃CN·0.5CH₃OH and [NiL²](ClO₄)₂·3CH₃CN·H₂O were determined by single crystal X‐ray crystallography. These structural analysis reveal the free ligand L¹, three mononuclear endomacrocyclic complexes {[CuL¹](ClO₄)₂·CH₃CN·H₂O, [CuL²](ClO₄)₂·6CH₃CN and [NiL²](ClO₄)₂·3CH₃CN·H₂O} and one binuclear complex {[CuL²][Cu(NO₃)₄]·5CH₃CN·0.5CH₃OH} in which one of the metals is in the macrocyclic framework and the other metal is outside the ligand cavity and coordinated to four nitrate ions.     

Synthesis,characterization, and antitumor activities of two copper(II) complexes with pyrazole derivatives

Two mononuclear copper(II) complexes with pyrazole derivatives, 1,1′-(anthracen-9-ylmethylene)bis(1H-pyrazole) (L¹ ) and 9-(4-(di(1H-pyrazol-1-yl)methyl)phenyl)-9H-carbazole (L² ), of formulae [CuL¹(CH₃CN)₂](ClO₄)₂ (1) and [CuL²(CH₃CN)₂](ClO₄)₂ (2) were prepared. Both complexes were confirmed by IR, MS, ¹H NMR, and elemental analyses. Complex 1 was also characterized by X-ray crystallography, confirming that copper(II) is coordinated by four nitrogen atoms from two L¹ and two oxygen atoms from two perchlorates. Furthermore, all ligands and complexes were tested in vitro for their antitumor activities using mouse melanoma cell line B16-F10, HepG2 human hepatoma cell line, and A549 human lung adenocarcinoma cell line. Both complexes displayed potent cytotoxicity and are promising substrates for further investigations.     

Synthesis, crystal structure and spectroscopic properties of two new complexes containing azido or dicyanamido bridges

Two new complexes, [Cu(L₁){N(CN)₂}]·ClO₄ (1) (L₁ is 1,8-dimethyl-1,3,6,8,10,13-hexa-azacyclotetradecane) and [Co(L₂)(N₃)₂]·ClO₄ (2) (L₂ is 5,7,7,12,14,14-hexamethyl-1,4,8,11-tetra-azacyclotetradecane) have been synthesized and characterized. The compounds crystallize in the monoclinic system P2₁ space group for 1 and P2₁/n for 2. Single crystal X-ray analysis reveals that the compound 1 assumes a one-dimensional structure via hydrogen-bonding interactions, in which each Cu(II) ion is coordinated by four nitrogen atoms from ligand L₁ and one nitrogen atom from [N(CN)₂]⁻ anion. For compound 2, each Co(III) ion is coordinated by four nitrogen atoms of ligand L₂ and two nitrogen atoms from N₃ ⁻ anion.     

Synthesis and structures of iron(iii) complexes based on azo derivatives of 5-oxo- and 5-thioxopyrazole

New potentially tridentate ligands, viz., 3-methyl-1-phenyl-4-(quinolin-8-ylhydrazono)pyrazol-5(1H)-one and 3-methyl-1-phenyl-4-(quinolin-8-ylhydrazono)pyrazole-5(1H)-thione (LH), and their complexes with Fe^III were synthesized. The structures of the ligands and metal chelates (FeL₂A; A = ClO₄ or FeCl₄) were studied by ¹H NMR spectroscopy and magnetochemistry. The FeL₂A complex (A = FeCl₄) was investigated by X-ray diffraction. These low-spin complexes have pseudooctahedral structures with the N₄X₂ ligand environment (X = O or S).     

Catalytic oxyfunctionalization of saturated hydrocarbons by non-heme oxo-bridged diiron(III) complexes: role of acetic acid on oxidation reaction

Oxo-bridged diiron(III) complexes [Fe₂O(L¹)₂(H₂O)₂](ClO₄)₄ (1) and [Fe₂O(L²)₂(H₂O)₂](ClO₄)₄ (2), where L¹ and L² are tetradentate N-donor N,N′-bis(2-pyridylmethyl)-1,2-cyclohexanediamine and N,N′-bis(2-pyridylmethyl)ethane-1,2-diamine respectively, have been isolated as synthetic models of non-heme iron oxygenases and characterized by physicochemical and spectroscopic methods. Both the complexes have been studied as catalysts for the oxyfunctionalization of saturated hydrocarbons using green hydrogen peroxide (H₂O₂) as oxidant under mild conditions. The selectivity (A/K) and regioselectivity (3°/2°) in oxidative C–H functionalization of alkanes suggests the involvement of metal-based intermediate in the oxygenation reaction. The catalytic efficiency is found to be strongly dependent on the presence of acetic acid. Remarkable increase in conversion and selectivity favoring the formation of alcohols in the oxidation of cyclohexane and cyclooctane and exclusive hydroxylation of adamantane with drastic enhancement of regioselectivity has been achieved by the addition of acetic acid in the presence of H₂O₂.

     

Dioxomolybdenum(VI) complexes of hydrazone phenolate ligands - syntheses and activities in catalytic oxidation reactions

The new cis-dioxomolybdenum (VI) complexes [MoO₂(L²)(H₂O)] (2) and [MoO₂(L³)(H₂O)] (3) containing the tridentate hydrazone-based ligands (H₂L² = N'-(3,5-di-tert-butyl-2-hydroxybenzylidene)-4-methylbenzohydrazide and H₂L³ = N'-(2-hydroxybenzylidene)-2-(hydroxyimino)propanehydrazide) have been synthesized and characterized via IR, ¹H and ¹³C NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction analysis. The catalytic activities of complexes 2 and 3, and the analogous known complex [MoO₂(L¹)(H₂O)] (1) (H₂L¹ = N'-(2-hydroxybenzylidene)-4-methylbenzohydrazide) have been evaluated for various oxidation reactions, viz. oxygen atom transfer from dimethyl sulfoxide to triphenylphosphine, sulfoxidation of methyl-p-tolylsulfide or epoxidation of different alkenes using tert-butyl hydroperoxide as terminal oxidant. The catalytic activities were found to be comparable for all three complexes, but complexes 1 and 3 showed better catalytic performances than complex 2, which contains a more sterically demanding ligand than the other two complexes.     

Syntheses,characterization, and crystal structures of ruthenium(II)/(III) complexes with tridentate salicylaldiminato ligands

Treatment of [Ru(PPh₃)₃Cl₂] with one equivalent of tridentate Schiff base 2-[(2-dimethylamino-ethylimino)-methyl]-phenol (HL) in the presence of triethylamine afforded a ruthenium(III) complex [RuCl₃(κ²-N,N-NH₂CH₂CH₂NMe₂)(PPh₃)] as a result of decomposition of HL. Interaction of HL and one equivalent of [RuHCl(CO)(PPh₃)₃], [Ru(CO)₂Cl₂] or [Ru(tht)₄Cl₂] (tht = tetrahydrothiophene) under different conditions led to isolation of the corresponding ruthenium(II) complexes [RuCl(κ³-N,N,O-L)(CO)(PPh₃)] (2), [RuCl(κ³-N,N,O-L)(CO)₂] (3), and a ruthenium(III) complex [RuCl₂(κ³-N,N,O-L)(tht)] (4), respectively. Molecular structures of 1·CH₂Cl₂, 2·CH₂Cl₂, 3 and 4 have been determined by single-crystal X-ray diffraction.     

Tetranuclear Zn(II) complexes with compartmental and dicyanamido ligands: synthesis,structure, and luminescent properties

New tetranuclear compounds have been obtained by reacting binuclear complexes, [Zn₂L ⁿ (μ-OH)(H₂O)₂](ClO₄)₂, with sodium dicyanamide (HL ⁿ are end-off bicompartmental ligands resulting from condensation between 2,6-diformyl-p-cresol with N,N-dimethyl-ethylenediamine or 2-aminomethyl-pyridine). The complexes, [{L¹(μ-OH)Zn₂}(μ _1,5-dca)₂{Zn₂(μ-OH)L¹}](ClO₄)₂ (1) and [{Zn₂L²(μ ₃-OH)(dca)}₂](ClO₄)₂?·?2H₂O (2), have been characterized by single-crystal X-ray diffraction. The angular nature of the bridging dicyanamido induces the “M” shape of the tetranuclear cationic unit in 1. The tetranuclear cation, because of its particular shape, acts as a receptor toward one perchlorate ion, which is hydrogen bonded to the hydroxo groups. This tetranuclear unit in 2 has a defective heterocubane structure. The luminescence properties of the new tetranuclear complexes have been investigated.     

Zinc(II) and cadmium(II) complexes having racemic and enantiomeric ligands: [Zn(La)2](NO3)2 · CH3CH2OH and [Cd(Lb)2Cl](ClO4) (La = D,L and Lb = D-(+)-1,2, 2-trimethylcyclopentane-1,3-diamine)

Two d¹⁰ transition-metal complexes having racemic and enantiomeric 1,2,2-trimethylcyclopentane-1,3-diamine ligands, [Zn(L_a)₂](NO₃)₂ · CH₃CH₂OH (1) and [Cd(L_b)₂Cl](ClO₄) (2) (L_a = D,L-1,2,2-trimethylcyclopentane-1,3-diamine, L_b = D-(+)-1,2,2-trimethylcyclopentane-1,3-diamine or (1R,3S)-1,2,2-trimethylcyclopentane-1,3-diamine), were synthesized and characterized by X-ray single-crystal diffraction. They crystallize in the Pbca and P2₁2₁2₁ space groups, respectively, and have different coordination numbers and coordination geometry (four-coordinate tetrahedron for Zn(II) in 1 and five-coordinate square-based pyramid for Cd(II) in 2) mainly due to their different ionic radii.