Functional zinc(II) phthalocyanines bearing Schiff base complexes as oxidation catalysts for bleaching systems

Oxidation catalysis is used to increase the performance of hydrogen peroxide in laundry bleach applications. Bleach catalysts provide cost‐effective, energy‐saving and environmentally friendly bleach systems yielding perfect stain removal at lower temperatures. This comparative study is based on the synthesis of bis[bis(salicylhydrazonephenoxy)manganese(III)] phthalocyaninatozinc(II) ( 2 ), bis[bis(salicylhydrazonephenoxy)cobalt(III)] phthalocyaninatozinc(II) ( 3 ) and bis[bis(salicylhydrazonephenoxy)iron(III)] phthalocyaninatozinc(II) ( 4 ) as tri‐nuclear complexes consisting of two Schiff base complexes substituting a zinc phthalocyanine. Complexion on the periphery to obtain complexes 2 , 3 , 4 was performed through the reaction of a Schiff base‐substituted phthalocyanine using MnCl₂?4H₂O, CoCl₂?6H₂O or FeCl₃?6H₂O salts in basic condition in dimethylformamide. Fourier transform infrared, ¹H NMR, ¹³C NMR, UV–visible, inductively coupled plasma optical emission and mass spectra were applied to characterize the prepared compounds. The bleach performances of the three phthalocyanine compounds 2 , 3 , 4 were examined by the degradation of morin as hydrophilic dye. The degradation progress in the presence of catalysts 2 , 3 , 4 /H₂O₂ combination in aqueous solution was investigated using an online spectrophotometric method. It was found that the catalysts 2 , 3 , 4 exhibited better bleaching performance at 25 °C than tetraactylethylethylenediamine as bleach activator used in powder detergent formulations for stain removal. Copyright © 2015 John Wiley & Sons, Ltd.     

Ruthenium complexes of Schiff base ligands as efficient catalysts for catechol–hydrogen peroxide reaction

Zeolite Y-encapsulated ruthenium(III) complexes of Schiff bases derived from 3-hydroxyquinoxaline-2-carboxaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYqpd, RuYqap and RuYqab, respectively) and the Schiff bases derived from salicylaldehyde and 1,2-phenylenediamine, 2-aminophenol, or 2-aminobenzimidazole (RuYsalpd, RuYsalap and RuYsalab, respectively) have been prepared and characterized. These complexes, except RuYqpd, catalyze catechol oxidation by H₂O₂ selectively to 1,2,4-trihydroxybenzene. RuYqpd is inactive. A comparative study of the initial rates and percentage conversion of the reaction was done in all cases. Turn over frequency of the catalysts was also calculated. The catalytic activity of the complexes is in the order RuYqap > RuYqab for quinoxaline-based complexes and RuYsalap > RuYsalpd > RuYsalab for salicylidene-based complexes. The reaction is believed to proceed through the formation of a Ru(V) species.     

New olefin metathesis catalysts bearing polyether clamp in N-heterocyclic carbenes ligands

Synthesis of new type of the Hoveyda–Grubbs catalysts containing modified N-heterocyclic carbene ligands is described herein. New catalysts bear different in size polyether clamp embracing N,N′-2,4-dimethylphenyl substituents in N-heterocyclic carbene. New complexes were tested in model RCM, enyne and CM reactions. They showed comparable activity to that of commercially available Grubbs second generation and Hoveyda–Grubbs second generation complexes. Complex with larger polyether clamp proved Z-stereoselective in a macrocycle formation and yielded more Z isomers than commercial complexes in CM reactions. The catalysts are stable and easy to purify.     

Synthesis and structural characterisation of rhodium hydride complexes bearing N-heterocyclic carbene ligands

Addition of excesses of N-heterocyclic carbenes (NHCs) IEt₂Me₂, IⁱPr₂Me₂ or ICy (IEt₂Me₂ = 1,3-diethyl-4,5-dimethylimidazol-2-ylidene; IⁱPr₂Me₂ = 1,3-diisopropyl-4,5-dimethylimidazol-2-ylidene; ICy = 1,3-dicyclohexylimidazol-2-ylidene) to [HRh(PPh₃)₄] (1) affords an isomeric mixture of [HRh(NHC)(PPh₃)₂] (NHC = IEt₂Me₂ (cis-/trans-2), IⁱPr₂Me₂ (cis-/trans-3), ICy (cis-/trans-4) and [HRh(NHC)₂(PPh₃)] (IEt₂Me₂(cis-/trans-5), IⁱPr₂Me₂ (cis-/trans-6), ICy (cis-/trans-7)). Thermolysis of 1 with the aryl substituted NHC, 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene (IMesH₂), affords the bridging hydrido phosphido dimer, [{(PPh₃)₂Rh}₂(μ-H)(μ-PPh₂)] (8), which is also the reaction product formed in the absence of carbene. When the rhodium precursor was changed from 1 to [HRh(CO)(PPh₃)₃] (9) and treated with either IMes (=1,3-dimesitylimidazol-2-ylidene) or ICy, the bis-NHC complexes trans-[HRh(CO)(IMes)₂] (10) and trans-[HRh(CO)(ICy)₂] (11) were formed. In contrast, the reaction of 9 with IⁱPr₂Me₂ gave [HRh(CO)(IⁱPr₂Me₂)₂] (cis-/trans-12) and the unusual unsymmetrical dimer, [(PPh₃)₂Rh(μ-CO)₂Rh(IⁱPr₂Me₂)₂] (13). The complexes trans-3, 8, 10 and 13 have been structurally characterised.     

Design and synthesis of new bidentate alkoxy-NHC ligands for enantioselective copper-catalyzed conjugate addition

A new family of chiral alkoxy-N-heterocyclic carbene (NHC) ligands has been designed for the enantioselective copper-catalyzed conjugate addition of dialkylzincs to enones. These new bidentate NHC ligands were synthesized in high overall yields using a five-step procedure starting from commercially available β-aminoalcohols. Influence of the temperature, base, solvent and copper source were studied in order to optimize the stereoselectivity of the addition. High reactivity and excellent enantioselectivity were obtained at ambient temperature with a range of cyclic enones and dialkylzinc. Addition to acyclic enones has also been studied.     

Schiff base complexes and their versatile applications as catalysts in oxidation of organic compounds: part I

Schiff bases and their complexes are good candidates as versatile compounds which are synthesized by the condensation of a primary amino compound with either aldehydes or ketones for a variety of industrial applications. They can act as catalysts in the catalytic oxidation of organic compounds. Recent researches in oxidation catalysis have focused on how to employ the metal‐catalyzed oxidation of organic substrates. This review summarizes the current developments of the last few decades for the oxidations of organic compounds that proceed through Schiff base complexes. The chemical syntheses of Schiff bases and their complexes are outlined.     

Synthesis and activity for ROMP of bidentate Schiff base substituted second generation Grubbs catalysts

The synthesis and characterisation of Schiff base substituted second generation Grubbs catalysts is described using the pyridine functionalised second generation catalyst and a Schiff base-Tl salt. The complexes are less active for the ROMP of COD (cycloocadiene) than their second generation analogues though their activity for the ROMP of DCPD (dicyclopentadiene) at high temperatures shows great potential due to the thermal stability of the catalysts.     

Ruthenium complexes with chelating carboxylate-NHC ligands as efficient catalysts for CH arylation in water

Ruthenium(ii) complexes with chelating N-heterocyclic carbene (NHC) ligands were studied in the arylation of phenyl group in 2-phenylpyridine and 1-phenylpyrazole with aryl chlorides in water. Complexes with NHC-ligands containing a hemilabile coordinating N-carboxylatomethyl group enable fast and selective ortho-CH-diarylation in the absence of carboxylate-assisting additives.     

Dinuclear metal complexes of Schiff base ligands as catalysts for oxidation and epoxidation reactions

Dinuclear copper(II) complexes (Cu₂ L_nCl₃), nickel(II) complexes (Ni₂ L_nCl₃) and cobalt(II) complexes (Co₂L ₂ ⁿ Cl₂) from Schiff base ligands are synthesised, characterised and used as catalysts for oxidation of 3,5-DTBC to 3,5-DTBQ. (Cu₂L_nCl₃) are found to be more efficient than the other complexes. Dinuclear iron(III) complexes of composition (Fe₂L₂Cl₂) and ruthenium (III) complexes of composition Ru₂L ₂ ⁿ Cl₆(PPh₃)₂ and Ru₂L ₂ ⁿ Cl₂(PPh₃)₂ catalyse epoxidation of styrene and cyclohexene. Catalytic activities of ruthenium(III) complexes are much greater than those of analogous iron(III) complexes.     

Synthesis and structural chemistry of arene-ruthenium half-sandwich complexes bearing an oxazolinyl-carbene ligand

Reaction of a series of directly connected oxazoline-imidazolium salts with silver(I) oxide and subsequent transmetallation with [Ru(p-cymene)Cl₂]₂ and anion exchange with KPF₆ cleanly gave the corresponding 2-oxazolinyl-(N-mesityl)imidazolidene(chloro)ruthenium(II) half-sandwich complexes [RuCl(oxcarb)(p-cymene)]PF₆, two derivatives of which were characterized by X-ray diffraction. Abstraction of the chloro ligand furnished the dicationic aqua complexes [Ru(H₂O)(oxcarb)(p-cymene)](PF₆)₂ which possess a similar coordination geometry. The syntheses were found to be highly diastereoselective, since only one diastereoisomer could be observed in all ruthenium complexes upon reaction of the chiral enantiopure oxazoline-imidazolium salts. Their potential as transfer hydrogenation and Lewis acid catalysts has been probed.     

A new class of ruthenium complexes containing Schiff base ligands as promising catalysts for atom transfer radical polymerization and ring opening metathesis polymerization

A novel series of Schiff base ruthenium complexes that are active catalysts in the field of atom transfer radical polymerization (ATRP), have been prepared. Moreover, when activated with trimethylsilyldiazomethane (TMSD), these species exhibit good catalytic activity in the ring opening metathesis polymerization (ROMP) of norbornene and cyclooctene. The activity for both the ROMP and ATRP reaction is dependent on the steric bulk and electron donating ability of the Schiff base ligand. The control over polymerization in ATRP was verified for the two substrates that exhibit the highest activity, namely MMA and styrene. The results show that the optimal ATRP equilibrium leading to a controlled polymerization, can be established by adjusting the steric and electronic properties of the Schiff base ligand.     

NHC-Pd(II)-Im (NHC = N-heterocyclic carbene; Im = 1-methylimidazole) complexes as efficient catalysts for Suzuki-Miyaura coupling reactions of aryl chlorides

A new type of well-defined N-heterocyclic carbene (NHC)-palladium chloride-imidazole complexes derived from IPrHCl or IMesHCl, PdCl₂ and 1-methylimidazole exhibits high catalytic activity in the room-temperature Suzuki-Miyaura coupling reactions of aryl or heteroaryl chlorides. Moreover, the large-scale (20.0 mmol) couplings in the presence of 0.01 mol% catalyst loading can also give the corresponding coupling products in high yields.     

Gamma-ray irradiation and characterization of synthesized bidentate and tetradentate Schiff base ligands and their complexes with some transition metal ions

Salen ligands are essential for coordinating a diverse group of metals in their respective oxidation states. This creates significant complexes of salen metals that are used in different fields. Condensation of ehylenediamine (en) with p-methoxybenzaldehyde (L¹) or o-hydroxyacetophenone (L²) with a ratio 1: 2 (en: p-methoxybenzaldehyde or o-hydroxyacetophenone) or by the interaction of o-phenylenediamine (phen) with o-hydroxybenzaldehyde (L³) or p-hydroxybenzaldehyde (L⁴) with a ratio 1: 2 (phen: o-hydroxybenzaldehyde or p-hydroxybenzaldehyde) has been used to prepare four symmetrical Schiff bases (L¹-L⁴). The UV–vis spectroscopy has been used to investigate the diverse electronic transitions associated with the Schiff bases molecules as well as how these transitions are impacted by diverse polarities of solvents. Elemental analysis, FT-IR, UV–vis spectra, molar conductivity, and ¹H NMR have been used to characterise all the compounds obtained in this process. The continuous variation applied alongside molar ratio spectral methods showed the formation of different complexes arising from the reaction of the ligand (L^1-L⁴) with the metal ions Mn(II), Fe(III) and Cu(II) is 1: 1 and/ or 1: 2 (M: L). A series of universal buffer solutions (20 % ethanol v/v) with varying pH values were used in spectrophotometry to determine the acid dissociation constants of the L² and L⁴ ligands. Gamma radiation was applied to examine the compounds’ irradiation stability. Additionally, the absorptions of the main functional groups were screened using FT-IR spectra before and after Gamma irradiation. The results show that all the compounds are stable after irradiation process; therefore, it could be used as enhancing agents in cancer therapy.     

Catalytic amination reactions mediated by Co(II) Schiff base complexes

Co(acacen), 1, (acacen = 2,11-dihydroxy-4,9-dimethyl-5,8-diaza-2,4,8,10-dodecatetraene dianion) was found to be a highly efficient catalyst for the allylic amination of non activated alkenes, using N-(p-toluensulfonyl)iminophenyliodinane (PhINTs) as nitrene precursor. This reactivity has been extended to the less reactive C-H bond of toluene. The effect of reaction times and of added cosolvent on yields and selectivities was investigated. Under the best conditions, allylic amines were obtained in a 40-70% isolated yield. A complex derived from the stoichiometric reaction of Co(acacen), 1, with PhINTs has been isolated and spectroscopically characterized. Such a complex, although not able to transfer its NTs moiety to alkenes, is still active in catalyzing allylic amination of cyclohexene.     

Synthesis,characterization and crystal structure of a dioxomolybdenum(VI) complex with a N,O type bidentate Schiff base ligand as a catalyst for homogeneous oxidation of olefins

The synthesis of a Mo(VI) Schiff base complex, cis-[MoO₂{(4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenolate)₂}], cis-[MoO₂(L)₂] where L = 4,6-bis(tert-butyl)-2-{(benzyl)iminomethyl}phenol, derived from benzylamine and 3,5-di-tert-butylsalycilaldehyde is reported. Full characterization of this complex was accomplished with elemental analyses, spectroscopic studies (NMR, IR and electronic) and X-ray structure analysis. This complex was tested as a catalyst for the homogeneous oxidation of olefins. The Mo(VI) complex is catalytically active for the epoxidation of aliphatic substrates at 80 °C, yielding the epoxide as the sole product in yields up to 100% and turnover numbers up to 5000. Under the optimized conditions styrene was oxidized in an 81% conversion to produce styrene oxide, benzaldehyde, and acetophenone.     

Rotamers of palladium complexes bearing IR active N-heterocyclic carbene ligands: Synthesis, structural characterization and catalytic activities

The preparation and properties of mono- versus bis(carbene) Pd(II) complexes bearing unsymmetrical cyano- and ester-functionalized NHC ligands as potential IR probes were studied in detail. Direct reaction of Pd(OAc)₂ with functionalized imidazolium salts afforded either bis(carbene) (3a, c) or monocarbene complexes (5, 6) with a N-coordinated imidazole co-ligand. The latter were exclusively obtained with N-ethylene substituted salts, which were found to undergo N-C cleavage reaction. The milder Ag-carbene transfer reaction on the other hand was tolerable to the length of the substituents and the nature of the functional groups. All bis(carbene) complexes (3a-c, 4a-c) were obtained as a inseparable mixture of square-planar trans-anti and trans-syn rotamers. The identity, ratio and dynamic equilibrium of these rotamers have been investigated and the relatively high rotational barrier for rotamers of 3a was estimated to be about 74 kJ mol⁻¹ at 380 K. All eight complexes were fully characterized by NMR and IR spectroscopies, ESI mass spectrometry and X-ray single crystal and powder diffraction. A preliminary catalytic study showed that ester-functionalized complexes 4a and 4b gave rise to highly active catalyst in the double Mizoroki-Heck coupling of aryl dibromides, while the in situ ester-hydrolyzed complexes were also active in the coupling of activated aryl chlorides.     

Transition metal complexes of tetradentate and bidentate Schiff bases as catalysts for ethylene polymerization: Effect of transition metal and cocatalyst

This article compares catalytic performance of ethylene polymerization in similar polymerization conditions of transition metal complexes having two ligands [O,N] (phenoxy‐imine) and having one tetradentate ligand [O,N,N,O] (salphen or salen). It is shown that the activity of both complex types as well as the product properties depend in the same way on the type of central metal in the complex and on the cocatalyst used. Although the type of ligand has some effect on the catalyst activity, yet it does not control the properties of the obtained products. The vanadium and zirconium complexes, irrespective of the cocatalyst used, yield linear polyethylene with high molecular weight (a few hundred thousand g/mol). Similar products are formed when titanium complexes activated with MAO are employed. On the other hand, the same titanium complexes in conjunction with Et₂AlCl, yield low molecular weight polyethylene (of a few thousand) and additionally a mixture of oligomers. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 565–575, 2009     

Half‐sandwich Ru (II) complexes containing (N,O) Schiff base ligands: Catalysts for base‐free transfer hydrogenation of ketones

Two new half‐sandwich Ru (II)(p‐cymene) complexes ( 1 and 2 ) containing dopamine‐based (N, O) Schiff base ligands ( L ¹ H and L ² H ) were synthesized and characterized by FT‐IR, UV–Visible and ¹H & ¹³C NMR spectral techniques, and elemental analyses. The spectroscopic and analytical data revealed monobasic bidentate coordination of the ligands with Ru ion. The molecular structures of L ¹ H , L ² H and 2 were further confirmed by single crystal X‐ray diffraction study. Complexes 1 and 2  have been employed as catalysts in the transfer hydrogenation of ketones using 2‐propanol as a hydrogen source at 85 °C under base‐free condition. Good to the excellent yield of secondary alcohols, gram scale synthesis, and high TON and TOF made this catalytic system interesting.     

Chromone-based Schiff base metal complexes as catalysts for catechol oxidation: Synthesis,kinetics and electrochemical studies

Two new Schiff base ligands with chromone moiety and their transition metal complexes were synthesized and characterized by elemental analyses, magnetic susceptibility, molar conductance and TGA analyses, FT IR, UV-Vis, NMR and mass spectroscopy. All the complexes synthesized have been investigated as functional models for catechol oxidase (catecholase) activity by employing 3,5-di-tert-butylcatechol as a model substrate. The two mononuclear copper(II) and two mononuclear iron(II) complexes show catecholase activity with turnover (k_cat) numbers lying in the range 27.2–1328.4 h^?1. According to the kinetic measurement results, the rate of catechol oxidation follows first order kinetics and iron(II) complexes were found to have higher catalytic activity than those of copper(II) complexes. Electron-donating substituent on Schiff base ligand enhanced the catalytic activity of metal complexes while the electron-withdrawing substituent led to a decrease in activity. The electrochemical properties of two Schiff bases and their metal complexes were also investigated by Cyclic Voltammetry (CV) using glassy carbon electrode (GCE) at various scan rates. Electrochemical processes of all the compounds were observed as irreversible.