Heterotrinuclear manganese(II) and vanadium(IV) Schiff base complexes as epoxidation catalysts

The catalytic epoxidation of styrene using urea-hydrogen peroxide and heterotrinuclear Cu(II) complexes with general formula (ML ⁿ )₂Cu(acac)₂, where n = 1–3 and M = VO²⁺ or Mn²⁺ is reported. Schiff base complexes ML ⁿ involving a 3,4-diaminopyridine bridge with free coordination site were used as the ligand, where (Lⁿ)²⁻ is [(5-x-Sal)₂Py]² and x = H, Br or NO₂. The complexes were characterized by physico-chemical and spectroscopic methods. The electrochemical properties of M were modified upon trinuclear complex formation. The trinuclear complexes show high catalytic activity, with up to 86% conversion and 93% selectivity, while no catalytic properties were observed for the monomeric complexes. The catalyst could be reused with some loss of activity.     

Electrochemical properties of vanadium(III,IV,V)-salen complexes in acetonitrile. Four-electron reduction of O2 by V(III)-salen

The coordination chemistry and electrochemistry of complexes of vanadium(III,IV,V) with salen (H2 salen = N,N'-ethylenebis(salicylideneamine) were reexamined in an attempt to uncover the origin of puzzling results reported in a previous study (Inorg. Chem. 1994, 33, 1056). Microelectrodes were utilized to allow measurements in the absence of supporting electrolyte. The source of the puzzling results was identified and the modifications required in the previous interpretations are specified. Corrected values of formal potentials and diffusion coefficients are also given. The acid-induced disproportionation of V(IV)O(salen), as originally proposed by Bonadies et al. (J. Chem. Soc., Chem. Commun. 1986, 1218; Inorg. Chem. 1987, 26, 1218), was largely supported by the present results. The equilibrium constant for this disproportionation reaction was measured. The stoichiometry and kinetics of the reaction between O2 and the V(III)-salen complex were examined, and a possible mechanism for this four-electron reduction of O2 is suggested.     

Synthesis and electrochemistry of vanadium(IV) Schiff base complexes

The electrochemical properties of vanadyl(IV) derivatives, namely salen Schiff base complexes of the type [VO(Salen)] (5-BrSalen, 5-NO₂Salen, 5-MeOSalen, salpn (bis(salicylaldehyde)-1,3-propanediamine, 5-BrSalpn, 5-NO₂Salpn, 5-MeOSalpn, Me₂Salen, Salophen, 5-BrSalophen, and 5-MeOSalophen) were investigated. The equatorial Schiff base ligands affect the oxidation potentials via interaction with the d-orbitals of the vanadyl metal ion. The cathodic peak potential (E_pc) becomes less negative according to the sequence MeO- < H- < Br- < NO_2?.     

Characterization and antidiabetic activity of salicylhydrazone Schiff base vanadium(IV) and (V) complexes

Transition Metal Chemistry - Twenty-four oxidovanadium(IV,V) complexes with tridentate Schiff base ligands based on 5-nitrosalicylaldehyde, 5-methoxysalicylaldehyde, or 5-sulfosalicylaldehyde and...     

Schiff base tantalum(V) complexes

Summary Complexes of pentachlorotantalum with the Schiff bases: bis(vanillin)benzidine, bis(vanillin)-o-dianisidine, bis(acetylacetone)benzidine, bis(p-dimethylaminobenzaldehyde)-o-dianisidine, bis(anisaldehyde)-1, 3-propanediamine and bis(p-dimethylaminobenzaldehyde)-o-phenylenediamine have been prepared and characterized by molar conductance, decomposition temperature, elemental and t.g. analyses and i.r. spectral measurements. The conductances reveal that pentachlorotantalum (1 mole) interacts with all the ligands (1 mole), all five chloride ions thus forming simple adducts. A comparative study of the i.r. spectra of the parent ligands and their complexes allows the coordination sites to be ascertained. The studies show that tantalum(V) chloride prefers to form complexes of high coordination number.     

Two mixed-valence vanadium(III,IV) phosphonoacetates with 16-ring channels: H2(DABCO)[V(IV)O(H2O)V(III)(OH)(O3PCH2CO2)2].2.5H2O and H2(PIP)[V(IVO)(H2O)V(III)(OH)(O3PCH2CO2)2].2.5H2O

Two isostructural mixed-valence vanadium phosphonoacetates H2(DABCO)[V(IV)O(H2O)V(III)(OH)(O3PCH2CO2)2].2.5H2O (1) and H2(PIP)[V(IV)O(H2O)V(III)(OH)(O3PCH2CO2)2].2.5H2O (2) have been synthesized. They crystallize in the orthorhombic space group Pnna with a = 7.0479(10) A, b = 15.307(2) A, and c = 17.537(3) A for 1 and a = 7.0465(9) A, b = 15.646(2) A, and c = 17.396(2) A for 2. X-ray single-crystal diffraction reveals that 1 and 2 have a three-dimensional open framework featuring 16-ring ellipsoid channels that are filled with doubly protonated 1,4-diazabicyclo[2,2,2]octanium/piperazinium cations and water molecules. According to the classification in metal-organic frameworks, 1 and 2 contain infinite (-O-V-)(infinity) chains that are cross-linked by "metalloligand" [VO(H2O)(O3PCH2CO2)2](4-) into a 3-D net of the sra topology. The temperature dependence of the magnetic susceptibility of 1 shows that the chi(m)T value in the range of 60-320 K is constant of 1.105 cm3 K mol(-1)/V2 unit, and upon further cooling, the chi(m)T value rapidly increases to 1.81 cm3 K mol(-1) at 2 K. The corresponding effective magnetic moment (mu(eff))/V2 unit varies from 2.97 mu(B) at 320 K to 3.80 mu(B) at 2 K. The magnetic data in the range of 2-320 K follow the Curie-Weiss law with C = 1.074 cm3 K mol(-1) and Theta= -1.34 K.     

Schiff base complexes of silicon(IV)

Reactions of silicon tetraacetate with different types ofSchiff bases have been investigated in anhydrous benzene. Monofunctional bidentate, C₆H₅CHNXOH and HORCHNC₆H₅ [whereX=CH₂CH₂, CH₂CH(CH₃) or o-C₆H₄ and R=o-C₆H₄ or 2,1-C₁₀H₆], bifunctional tridentate, o-HOC₆H₄CHNYOH [whereY=CH₂CH₂ or CH₂CH(CH₃)] and bifunctional tetradentateSchiff bases, o-HOC₆H₄C(CH₃)N(CH₂) _n NC(CH₃)C₆H₄OH-o (wheren=2 or 3) have been shown to yield derivatives of the type, Si(OAc)_4– m L _m, Si(OAc)_4–2 n L _n and Si(OAc)₂ L (wherem=1,2 or 3;n=1 or 2 and HL, H₂ L and H₂ L represent the molecules of monofunctional bidentate, bifunctional tridentate and bifunctional tetradentateSchiff bases resp.) and have been found to be monomeric in boiling benzene. Tentative structures based on IR and in a few cases PMR spectra have been indicated for the resulting derivatives.With 2 Figures     

Synthesis and characterization of titanium (IV) Schiff base complexes,part III1. Octahedral titanium (IV) complexes of some dibasic terdentate Schiff base ligands

Summary Complexes of the X₂Ti(SB) type, where X is OMe, OEt and OPr-i and SB is the dianion of salicylaldehyde-2-hydroxyanil (H₂SAP), acetylacetone-2-hydroxyanil (H₂AAP) and acetylacetone-2-mercaptoanil (H₂ASP), have been prepared and characterized by means of conductivity, molecular weight, i.r., n.m.r and mass spectral measurements. The ONO and ONS donor ligands are terdentate and the titanium(IV) atom attains six-coordinationvia dimerization of the complexes. The tendency of (i-PrO)₂Ti(AAP), where AAP is the dianion of acetylacetone-2-hydroxyanil, to become monomeric and to disproportionate to Ti(AAP)₂ and Ti(OPr-i)₄ was also investigated. Spectral data are also presented for the octahedral complexes of the Ti(SB)₂ type, where SB is the dianion of H₂SAP, H₂AAP, H₂ASP or of the related ONO donor ligands salicylaldehyde-2-hydroxyethylimine (H₂SAE), salicylaldehyde-3-hydroxypropylimine (H₂SPA), and diisopropylethanolamine (H₂DIP).Presented in part at the 166th ACS National Meeting, Chicago, Illinois, Aug. 26–31, 1973; No. INORG. 50.     

New Schiff base complexes of ruthenium(III) and their use as catalysts for O-allyl systems isomerization

Seven new ruthenium(III) complexes of the general formula [RuCl(PPh₃)LL′] · xH₂O (LL′ = [ONNO] = symmetrical and unsymmetrical Schiff base derivatives of trans-1,2-diaminocyclohexane and 2-hydroxynaphthaldehyde as well as R-salicylaldehydes, x = 0–3) have been synthesized. The complexes were characterized by physico-chemical and spectroscopic techniques. The catalytic activities of the complexes in the isomerization reaction of selected O-allyl systems, i.e., 1,4-diallyloxybutane and 4-allyloxybutan-1-ol have been studied. Some of the complexes showed high efficiency and E-stereoselectivity in double bond migration of allyl group to 1-propenyl group and high selectivity of isomerization of allyloxyalcohol to cyclic acetal.     

Tetradentate Schiff base oxovanadium(IV) complexes

Summary Eleven oxovanadium(IV) complexes of tetradentate Schiff bases, obtained by condensating two moles of an o-hydroxycarbonyl compound with a diamine, have been prepared and characterized by elemental analysis, m.p., and i.r. and electronic spectra. The i.r. and electronic spectra of the free ligand and the complexes are compared and discussed. The Gaussian analysis of the vis. spectra of the complexes, normally C₁ or C_s, in MeCN yielded four peaks at ca. 12000, 15000, 17700 and 20000–23000cm^–1, assigned to the four d-d transitions.     

Formation of iron(III) cluster complexes with a new (N2O2) Schiff base

Two new series of Fe(III) Schiff-base complexes have been prepared and characterized by elemental and thermogravimetric analyses, IR, electronic, ESR and Mössbauer spectra. The Fe(III) complexes possess octahedral, pseudo-octahedral or pseudo-tetrahedral geometries around Fe(III), depending on the nature of the Schiff-base ligand used.     

Bis(β‐enaminoketonato) vanadium (III or IV) complexes as catalysts for olefin polymerization

Bis(β‐enaminoketonato) vanadium(III) complexes ( 2a–c ) [O(R₁)C?C(H)_xC(R₂)?NC₆H₅]₂VCl(THF) and the corresponding vanadium(IV) complexes ( 3a–c ) [O(R₁)C?C(H)_xC(R₂)? NC₆H₅]₂VO (R₁ = ? (CH₂)₄? , R₂ = H, x = 0, a ; R₁ = ? C₆H₅, R₂ = H, x = 1, b ; R₁ = ? C₆H₅, R₂ = ? C₆H₅, x = 1, c ) have been synthesized from VCl₃(THF)₃ and VOCl₂(THF)₂, respectively, by treating with 2.0 equivalent β‐enaminoketonato ligands in tetrahydrofuran. Structures of 2b and 3a–c were further confirmed by X‐ray crystallographic analysis. The complexes were investigated as the catalysts for ethylene polymerization in the presence of Et₂AlCl. Complexes 2a–c and 3a–c exhibited high catalytic activities (up to 23.76 kg of PE/mmol_V h bar), and afforded polymers with unimodal molecular weight distributions at 70 °C indicating the good thermal stability. The catalytic behaviors were influenced not only by the oxidation state of the catalyst precursors but also by the ligand structures. Complexes 2a–c and 3a–c were also effective catalyst precursors for ethylene/1‐hexene copolymerization. The influence of polymerization parameters such as reaction temperature, Al/V molar ratio and hexene feed concentration on the ethylene/hexene copolymerization behaviors have bee also investigated in detail. In addition, the agents such as AlMe₃, AlⁱBu₃, MeMgBr, MgCl₂, and ZnEt₂ were applied to control the molecular weight and molecular weight distribution modal. © 2010 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 3062–3072, 2010     

Schiff base complexes derived from trichlorooxovanadium(V)

Summary The synthesis, characterization and geometrical features of penta- and hexa-coordinated oxovanadium(V) complexes, [(VOCl₂)(SB)] and [(VOCl)(SB)₂] (where SBH represents a monobasic Schiff base) are described. The isolated products are coloured, crystalline monomeric solids, which are nonelectrolytes. On the basis of spectral (i.r.,¹H n.m.r. and u.v.) and magnetic susceptibility measurements distorted trigonal bipyramidal and octahedral geometries are proposed for [(VOCl₂)(SB)] and for the [(VOCl)(SB)₂] type complexes, respectively.     

Binuclear vanadium(V) and vanadium(IV,V) complexes of dihydrocaffeic,caffeic and ferulic acids

Summary Binuclear complexes of dihydrocaffeic, caffeic and ferulic acids with vanadium were prepared and studied. The suggested square-pyramidal structures with catecholic-type coordination are supported by various spectroscopic, magnetic and thermogravimetric data.     

Highly-oxidised, sulfur-rich, mixed-valence vanadium(IV/V) complexes

The reactions of [V(2)(micro-S(2))(2)(S(2)CNR(2))(4)] (R = alkyl) with NOBF(4) produce highly-oxidised, sulfur-rich, V(iv/v) complexes, [V(2)(micro-S(2))(2)(S(2)CNR(2))(4)]BF(4), that exhibit 15-line EPR spectra and structures consistent with Class III mixed-valence behaviour.     

Studies on ruthenium(II) Schiff base complexes as catalysts for transfer hydrogenation reactions

The reactions of [RuHCl(CO)(B)(EPh₃)₂] (B = EPh₃ or Py; E = P or As) and Schiff bases in 1:1 molar ratio led to the formation of [RuCl(CO)(EPh₃)(B)(L)] (E = P or As; B = PPh₃, AsPh₃ or Py; L = Schiff base ligand). The new complexes have been characterized by analytical and spectroscopic (IR, electronic and ¹H NMR) data. They have been assigned an octahedral structure. The new complexes were found to catalyse the transfer hydrogenation of ketones.     

o,o′-Alkylene dithiophosphato complexes of vanadium(IV) and vanadium(V)

Reactions of VO(acac)₂ with alkylene dithiophosphoric acids, POGOS₂H, and of VOCl₃ with the ammonium salts NH₄(POGOS₂) in 1:2 molar ratio gave the oxovanadium(IV) alkylene dithiophosphates, [VO(POGOS₂)₂], and monochloroxovanadium(V) alkylene dithiophosphates, [VOCl(POGOS₂)₂], respectively, where G = —CH₂CMe₂-CH₂—, —CH₂CEt₂CH₂—, —CHMeCH₂CMe₂— or —CMe₂CMe₂—. These complexes are green solids, soluble in common organic solvents and sensitive to moisture. They were characterized by elemental analysis, molecular weight and spectral studies including i.r. and n.m.r. (¹H, ¹³C and ³¹P), which suggested bidentate bonding of the POGOS₂ ligands to give a square pyramidal for the V^IV complexes and an octahedral geometry for the V^V complexes.     

Thorium(IV) complexes with tetradentate Schiff base ligands

Summary Some thorium(IV) complexes were synthesized with the tetradentate Schiff base ligands (N₂O₂ donor set) obtained by the condensation of ethylenediamine with salicylaldehyde (H₂salen) or acetylacetone (H₂ acacen). In all cases the neutral Schiff bases and not their anions are coordinated to the central thorium(IV) atom. The complexes have the general formula: ThL₂Xa (L = H₂ salen; X = Cl, Br, 1, NCS and L = lie acacen; X = Cl, 1, NCS, ClO₄) or ThLX₄ (L = H₂ salen; X = NO₃, ClO₄ and L = H₂ acacen; X = Br, NO₃). The stoichiometry and coordination number of the complexes was determined on the basis of elemental analysis, conductivity measurements, i.r. spectra and t.g.a./d.t.a. data. The coordination number of the complexes is either 12 or 8 for the bisor monocomplexes respectively.     

Synthesis,structural characterization,and ethylene polymerization behavior of (arylimido)vanadium(V) complexes bearing tridentate Schiff base ligands

A series of novel (arylimido)vanadium(V) complexes bearing tridentate salicylaldiminato chelating ligands, V(N‐2,6‐Me₂C₆H₃)Cl₂[(O‐2‐^tBu‐4‐R‐C₆H₃)CH?ND] (R = H, D = 2‐CH₃O? C₆H₄ ( 2a ); 2‐CH₃S? C₆H₄ ( 2b ); 2‐Ph₂P? C₆H₄ ( 2c ); 8‐C₉H₆N (quinoline) ( 2d ); CH₂C₅H₄N ( 2e ); R = ^tBu, D = 2‐Ph₂P? C₆H₄ ( 2f )), were prepared from V(NAr)Cl₃ by reacting with 1.0 equiv of the ligands in the presence of triethylamine in tetrahydrofuran. These complexes were characterized by ¹H, ¹³C, ³¹P, and ⁵¹V NMR spectra and elemental analysis. The structures of 2c and 2f were further confirmed by X‐ray crystallographic analysis. These (arylimido)vanadium(V) complexes are effective catalyst precursors for ethylene polymerization in the presence of Et₂AlCl as a cocatalyst and ethyl trichloroacetate as a reactivating agent. Complex 2c with a ? PPh₂ group in the sidearm was found to exhibit an exceptional activity up to 133800 kg polyethylene/mol_V h for ethylene polymerization at 75 °C, which is one of the highest activities displayed by homogeneous vanadium(V) catalysts at high temperature. Moreover, high molecular weight polymers with unimodal molecular weight distribution can be obtained, indicating the single site behavior of these catalysts. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2633‐2642     

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.