Manganese complexes as models for manganese-containing pseudocatalase enzymes: Synthesis,structural and catalytic activity studies

Manganese complexes of the type [TpMn(X)] and [TpMn(μ-N₃)(μ-X)MnTp] (X = acetylacetonate, acac; picolinate, pic and Tp = Tp^Ph,Me for acac, Tp = Tp^ipr2 for pic complexes) having Tp^Ph,Me (hydrotris(3-phenyl,5-methyl-pyrazol-1-yl)borate)/Tp^ipr2 (hydrotris(3,5-diisopropyl-pyrazol-1-yl)borate) as a supporting ligand have been synthesized and structurally characterized. IR and X-ray structures suggest that complexes 7 and 9 are binuclear with azido and bidentate ligands (acac/pic) bridging, whereas complexes 6 and 8 are mononuclear with a 5-coordinated metal center. In complex 9 the picolinate is coordinated as tridentate in a η₃-fashion, but in complex 7 acac behaves as bidentate, whereas azide is coordinated in a bridging bidentate μ-1,3-manner in both 7 and 9. Since the coordination geometry of the manganese ions in complex 9 is very similar to the active site structure of manganese-containing pseudocatalase, we have tested the catalytic activity of the same towards the disproportionation of hydrogen peroxide. The catalytic results indicated that complex 9 has reasonably good catalase activity and may be suitable, structurally as well as functionally, as a model for the pseudocatalase enzyme.     

Mononuclear transition metal complexes with sterically hindered carboxylate ligands: Synthesis, structural and spectral properties

The metal coordination geometry in the active site of metalloproteins are very different from the one of small inorganic complexes, due to the inflexibility of the ligand set from amino acid side chains different from freely moving ligand set in synthesis. Using the sterically hindered 2,6-di-(p-fluorophenyl)benzoate(L) ligand, a series of mononuclear Co(II), Ni(II) and Cu(II) complexes of general formula [M(L)₂(Hdmpz)₂] (where, Hdmpz = 3,5-dimethyl pyrazole) have been synthesized and characterized by the variety of spectroscopic methods. A distorted octahedral geometry in case of nickel, tetrahedral geometry for cobalt and square pyramidal in copper was observed in the X-ray studies, which also revealed that the uncoordinated oxygen atom of the carboxylate group forms intramolecular hydrogen bonding with the N-H group of the coordinated 3,5-dimethylpyrazole in case of cobalt and copper.     

Synthesis, crystal structures and magnetic properties of trinuclear oxo-centered homo- and mixed-valence manganese pivalate complexes with imidazole (Im) and 1-methylimidazole (1-MeIm): and

Two new μ₃-oxo-centered trinuclear manganese complexes, one of them a homo-valence (1) pivalate complex and the other a mixed-valence (2) pivalate complex (where Im = imidazole, 1-MeIm = 1-methylimidazole), have been synthesized and characterized by IR spectroscopy, thermogravimetric analysis, X-ray crystallography and magnetochemistry. Complexes 1 and 2 are μ₃-oxo-trinuclear compounds with the three manganese atoms bridged by six pivalate groups. At each axial position there is an Im (1) or 1-MeIm (2) molecule. In both compounds, the manganese coordination geometry is slightly distorted octahedral, consisting of the oxygen of the central triangle, four oxygen atoms from bridging pivalate ligands, and a terminal Im or 1-MeIm nitrogen atom. The crystal packing of 1 involves hydrogen bonding between complex cations [Mn₃O(Piv)₆(Im)₃]⁺ and outersphere pivalate ions, whereas in compound 2 interactions of the C–Hπ type, formed by both the aromatic and methyl C–H groups of 1-MeIm molecules, are present. Magnetic studies reveal that both compounds represent antiferromagnetically coupled, spin-frustrated triangular systems exhibiting weak to moderate exchange coupling constants.     

Salicylaldoxime in manganese(III) carboxylate chemistry: Synthesis, structural characterization and physical studies of hexanuclear and polymeric complexes

The use of salicylaldehyde oxime (H₂salox) in manganese(III) carboxylate chemistry has yielded new members of the family of hexanuclear compounds presenting the [Mn₆(μ₃-O)₂(μ₂-OR)₂]¹²⁺ core, complexes [Mn^III₆(μ₃-O)₂(O₂CPh)₂(salox)₆(L₁)₂(L₂)₂] (L₁ = py, L₂ = H₂O (1); L₁ = Me₂CO, L₂ = H₂O (2); L₁ = L₂ = MeOH (3)). Addition of NaOMe to the acetonitrile reaction mixture, afforded the 1D complex [Mn^III₃Na(μ₃-O)(O₂CPh)₂(salox)₃(MeCN)]_n (4), whereas addition of NaClO₄ to the acetone reaction mixture afforded an analogous 1D complex [Mn^III₃Na(μ₃-O)(O₂CPh)₂(salox)₃(Me₂CO)]_n (5). The structures of 1–3 present the [Mn₆(μ₃-O)₂(μ₂-OR)₂]¹²⁺ core and can be described as two [Mn₃(μ₃-O)]⁷⁺ triangular subunits linked by two μ₂-oximato oxygen atoms of the salox²⁻ ligands, which show the less common μ₃-κ²O:κO′:κN coordination mode. The benzoato ligands are coordinated through the usual syn,syn-μ₂-κO:κO′ mode. The 1D polymeric structures of 4 and 5 consist of alternating [Mn₃(μ₃-O)]⁷⁺ subunits and Na⁺ atoms linked through two μ₃-κ²O:κO′:κN and one μ₄-κ²O:κ²O′:κN salox²⁻ ligands as well as one syn,anti-μ₂-κO:κO′ benzoato ligand. DC and AC magnetic susceptibility studies on 1 revealed the stabilization of an S = 4 ground state, and indications of single-molecule magnetism behavior, whereas the DC experimental data from polycrystalline sample of 5 are indicative of antiferromagnetic interactions within the [Mn₃] subunit. Solid state ¹H NMR data of 1 were used to probe the spin-lattice relaxation of the system.     

Chloro and azido bonded manganese complexes: synthesis,structural, and magnetic studies

Two manganese complexes, [Mn₂(tptz)₂Cl₄] · CH₃CN (1) and [Mn(tptz(ac)(N₃)(H₂O)] · H₂O (2) (where tptz = 2,4,6-tri(2-pyridyl)-1,3,5-triazine, ac = acetate anion), were synthesized and characterized by elemental analyses, infrared spectra, and UV–Vis absorption spectral analyses. The structures of both the complexes were determined by single crystal X-ray diffraction analysis. Complex 1 is binuclear with chloro-bridged manganese ions at the Mn–Mn separation of 3.777(27) Å. Each manganese center in 1 is six coordinate with three nitrogens from a tridentate tptz, three chlorides (one terminal and two bridging), adopting a centrosymmetric distorted octahedral geometry. Various hydrogen bonds form 2-D spiral structures in 1 with Mn–Mn separation of 7.421(2) Å along a-axis and 9.121(2) Å along b-axis. Complex 2 is seven coordinate with pentagonal bipyramidal geometry. The metal center coordinates to three nitrogens from tptz, two oxygens from acetate, one nitrogen from azide, and one oxygen from water. It has a 1-D layered structure, where three independent molecules are linked by uncoordinated water present in the lattice. Magnetic susceptibility in the temperature range 5–300 K for 1 shows the presence of antiferromagnetic interaction between the local high-spin manganese(II) ions with J = ?0.17 cm^?1.     

Organic carboxylate anions effect on the structures of a series of Mn(II) complexes based on 2-phenylimidazo[4,5-f]1,10-phenanthroline ligand

In our efforts to tune the structures of Mn(II) complexes by selection of organic carboxylic acid ligands, six new complexes [Mn(PIP)₂Cl₂] (1), [Mn(PIP)₂(4,4′-bpdc)(H₂O)]·2H₂O (2), [Mn(PIP)₂(1,4-bdc)] (3), [Mn(PIP)(1,3-bdc)] (4), [Mn(PIP)₂(2,6-napdc)]·H₂O (5), and [Mn(PIP)(1,4-napdc)]·H₂O (6) were obtained, where PIP=2-phenylimidazo[4,5-f]1,10-phenanthroline, 4,4′-H₂bpdc=biphenyl-4,4′-dicarboxylic acid, 1,4-H₂bdc=benzene-1,4-dicarboxylic acid, 1,3-H₂bdc=benzene-1,3-dicarboxylic acid, 2,6-H₂napdc=2,6-naphthalenedicarboxylic acid, 1,4-H₂napdc=1,4-naphthalenedicarboxylic acid. All complexes have been structurally characterized by IR, elemental analyses, and single crystal X-ray diffraction. Structural analyses show that complexes 1 and 2 possess mononuclear structures, complexes 3, 4, and 5 feature chain structures, and complex 6 exhibits a 2D (4,4) network. The structural difference of 1–6 indicates that organic carboxylate anions play important roles in the formation of such coordination architectures. Furthermore, the thermal properties of complexes 1–6 and the magnetic property of 4 have been investigated.     

Synthesis, characterization, and molecular structures of di- and triorganotin(IV) complexes with 9-anthracenecarboxylic acid: The structural diversity in organotin 9-anthracenecarboxylates

The di- and triorganotin(IV) derivatives of anthracenecarboxylic acid, Ph₂MeSnOC(O)C₁₄H₉ (2), Me₃SnOC(O)C₁₄H₉ (3), Me₂Sn[OC(O)C₁₄H₉]₂ · CH₃OH (4) Ph₃SnOC(O)C₁₄H₉ · CH₃OH (5), Ph₂EtSnOC(O)C₁₄H₉ (6), Ph₂Sn[OC(O)(C₁₄H₉)]₂ (7) and PhMe₂SnOC(O)C₁₄H₉ (8) were synthesized by the reaction of Ph₂MeSnI, Me₃SnCl, Me₂SnCl₂, Ph₃SnCl, Ph₂EtSnI, Ph₂SnCl₂, and PhMe₂SnI with 9-anthracenecarboxylic acid, respectively, with the aid of potassium iso-propoxide. All complexes were characterized by elemental analysis, mass spectrometry, IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectroscopes. The molecular structures of complexes 2, 3 and 4 were determined by single crystal X-ray analysis. The X-ray structures reveal that complex 2 and 3 adopt a polymeric trans-C₃SnO₂ trigonal bipyamidal configuration with the oxygen atoms occupying axial positions. Complex 4 adopts a monomeric structure with two carboxylates coordinated to tin in a monodentate form from axial and equatorial positions, and with the coordination number raised to five as the methanol occupies the apical position of the trigonal bipyramid.     

High-spin iron(III) complexes: structural,spectroscopic, and photochemical studies

Reaction of FeCl₃ with one equivalent of acac (acac = pentane-2,4-dionate) and KTp^Me2 (Tp^Me2 = hydrotris(3,5-dimethyl-pyrazol-1-yl)borate) yielded Tp^Me2Fe(acac)Cl (3), which upon reaction with methanolic solution of sodium azide resulted in the formation of a six coordinate compound Tp^Me2Fe(acac)N₃ (4) with a single azide. When the reaction of FeCl₃ and KTp^Me2 was performed with two equivalents of sodium azide and one equivalent of 3,5-dimethylpyrazole (Pz^Me2H), a six coordinate cis azide compound [Tp^Me2Fe(Pz^Me2H)(N₃)₂] (5) was obtained. These compounds were characterized by spectroscopic methods and single crystal X-ray crystallography. Electrochemical studies of 5 show that it can be irreversibly reduced at relatively lower potential than 4. The photolysis of 5 was performed at 77 K at different wavelengths (480, 419, and 330 nm) showing that 5 was photoreduced to a high-spin Fe(II) species instead of photooxidized to Fe(V).     

Synthesis,structural analysis,and thermal and spectroscopic studies of methylmalonate-containing zinc(II) complexes

The synthesis, crystal structure, thermal analysis and spectroscopic studies of five zinc(II) complexes of formulae [Zn(Memal)(H₂O)]_n (1) and [Zn₂(L)(Memal)₂(H₂O)₂]_n (2-5) [H₂Memal = methylmalonic acid, and L = 4,4′-bipyridine (4,4′-bpy) (2), 1,2-bis(4-pyridyl)ethylene (bpe) (3), 1,2-bis(4-pyridyl)ethane (bpa) (4) and 4,4′-azobispyridine (azpy) (5)] are presented here. The crystal structure of 1 is a three-dimensional arrangement of zinc(II) cations interconnected by methylmalonate groups adopting the μ₃-κ²O:κO’:κO”:κO”’ coordination mode to afford a rare (10,3)-d utp-network. The structures of the compounds 2-5 are also three-dimensional and they consist of corrugated square layers of methylmalonate-bridged zinc(II) ions which are pillared by bis-monodentate 4,4′-bpy (2), bpe (3), bpa (4) and azpy (5) ligands. The Memal ligand in 2-5 adopts the μ₃-κO:κO′:κO′′:κO′′′ coordination mode. Each zinc(II) ion in 1-5 is six-coordinated with five (1)/four (2-5) methylmalonate-oxygen atoms, a water molecule (1-5) and a nitrogen atom from a L ligand (2-5) building distorted octahedral environments. The rod-like L co-ligands in 2-5 appear as useful tools to control the interlayer metal-metal separation, which covers the range 8.4311(5) Å (2) – 9.644(3) Å (5). The influence of the co-ligand on the fluorescence properties of this series of compounds has been analyzed and discussed by steady-state and time resolved spectroscopy on all five compounds in the solid state.     

Synthesis and structural characterization of mixed carbene-carboxylate complexes of palladium(II)

Mixed carbene-carboxylate complexes of Palladium(II) have been prepared by reacting {1,1^′-dimethyl-3,3^′-methylenediimidazoline-2,2^′-diylidene} palladium(II) diiodide (1) [Angew. Chem. 107 (1995) 2602; Angew. Chem. Int. Ed. Engl. 34 (1995) 2371; J. Organomet. Chem. 557 (1998) 93] with AgO₂CR, where R=CF₃, CF₂CF₃ and CF₂CF₂CF₃. In this manner, {1,1^′-dimethyl-3,3^′-methylenediimidazoline-2,2^′-diylidene} palladium(II) bis(trifluo-roacetate) (2), {1,1^′-dimethyl-3,3^′-methylenediimidazoline-2,2^′-diylidene} palladium(II) bis(pentafluoropropionate) (3) and {1,1^′-dimethyl-3,3^′-methylenediimidazoline-2,2^′-diylidene} palladium(II) bis(heptafluorobutyrate) (4) were obtained. All three complexes were fully characterized by ¹H-, ¹³C- and ¹⁹F NMR spectroscopy as well as ESI mass spectrometry. X-ray crystal structure analyses of complexes 3 and 4 reveal mononuclear species with a square planar metal center coordinated by a cis-chelating dicarbene and two monodentate carboxylate ligands. The results show that the introduction of a cis-chelating N,N-heterocyclic carbene ligand stabilizes the palladium-carboxylate moiety effectively.     

Synthesis and structural characterization of ruthenium complexes with 1-aryl-imidazole-2-thione

Treatment of [RuCl₂(PPh₃)₃] with 2 equiv. Himt^MPh (Himt^MPh?=?1-(4-methyl-phenyl)-imidazole-2-thione) in the presence of MeONa afforded cis-[Ru(κ ²-S,N-imt^MPh)₂(PPh₃)₂] (1), while interaction of [RuCl₂(PPh₃)₃] and 2 equiv. Himt^MPh in tetrahydrofuran (THF) without base gave [RuCl₂(κ ¹-S-Himt^MPh)₂(PPh₃)₂] (2). Treatment of [RuHCl(CO)(PPh₃)₃] with 1 equiv. Himt^MPh in THF gave [RuHCl(κ ¹-S-Himt^MPh)(CO)(PPh₃)₂] (3), whereas reaction of [RuHCl(CO)(PPh₃)₃] with 1 equiv. of the deprotonated [imt^MPh]^? or [imt^NPh]^? (imt^NPh?=?1-(4-nitro-phenyl)-2-mercaptoimidazolyl) gave [RuH(κ ²-S,N-imt^RPh)(CO)(PPh₃)₂] (R?=?M 4a, R?=?N 4b). The ruthenium hydride complexes 4a and 4b easily convert to their corresponding ruthenium chloride complexes [RuCl(κ ²-S,N-imt^MPh)(CO)(PPh₃)₂] (5a) and [RuCl(κ ²-S,N-imt^NPh)(CO)(PPh₃)₂] (5b), respectively, in refluxing CHCl₃ by chloride substitution of the RuH. Photolysis of 5a in CHCl₃ at room temperature afforded an oxidized product [RuCl₂(κ ²-S,N-imt^MPh)(PPh₃)₂] (6). Reaction of 6 with excess [imt^MPh]^? afforded 1. The molecular structures of 1·EtOH, 3·C₆H₁₄, 4b·0.25CH₃COCH₃, and 6·2CH₂Cl₂ have been determined by single-crystal X-ray crystallography.     

Structural and magnetic properties of metal complexes with pyridine-2,6-dicarboxylate and 5-(4-bromophenyl)-2,4′-bipyridine

A series of complexes has been synthesized based on pyridine-2,6-dicarboxylate (L1) as the bridging ligand and 5-(4-bromophenyl)-2,4′-bipyridine (L2) as the pendant with different metal ions such as Ni^II, Co^II, and Cu^II, under hydrothermal conditions. In nickel and cobalt complexes [M(L1)(L2)₂ · H₂O]_n (M = Ni²⁺ or Co²⁺), the metal ions are bridged by L1 to form 1D coordination zigzag polymeric chains with L2 pendants possessing hexa-coordinated distorted octahedral geometries. While the copper ions are penta-coordinated by L1 and L2 with distorted square pyramidal geometries forming the tetranuclear cluster with the formula [Cu₄(L1)₄(L2)₄] · 2H₂O. It has been found that both the structure and magnetic property of these complexes are metal ions dependent. Intramolecular antiferromagnetic interactions were observed in the nickel and cobalt 1D coordination polymers, while ferromagnetic coupling was found in the tetranuclear copper cluster. Density functional theory calculations suggested that the O–C–O bridges of L1 in a basal–apical mode are responsible for intracluster intermetallic ferromagnetic exchange for the tetranuclear copper cluster.     

Synthesis and crystal structures of nickel(II) supramolecules containing hexaazamacrocycles and aromatic carboxylate ligands

Two new nickel(II) complexes, {[Ni(L)(4,4′-bpdc)] · 3H₂O} _n (1) and {[Ni(L)(2,6-ndc)] · 2CH₃CN} _n (2) (L = 1,8-dihydroxylethyl-1,3,6,8,10,13-hexaazacyclotetradecane, 4,4′-bpdc = 4,4′-biphenyldicarboxylate, 2,6-ndc = 2,6-naphthalenedicarboxylate), have been synthesized and structurally characterized by spectroscopic and X-ray diffraction methods. Compound 1 shows a 3-D supramolecule which is composed of two different series of 1-D coordination polymers, where each 1-D chain runs in different directions and interacts by π–π stacking at the intersection. Compound 2 contains 1-D coordination polymers in which 1-D chains run in the same direction. The 1-D chains are interconnected by hydrogen bonds in an undulated fashion to form a 3-D supramolecule.     

Fluoro aromatic imine nickel(0) complexes: Synthesis and structural studies

The reaction of [Ni(dippe)]₂(μ-H)₂ with a series of fluoroaromatic imines affords nickel(0) complexes of the type [(dippe)Ni(η²-C,N)-PhHCNR′Ph], dippe = 1,2-bis(diisopropylphosphine)ethane. Solution NMR experiments as well as X-ray diffraction studies confirmed the π-coordination of the ligand through the CN moiety; the resulting complex found to adopt a distorted tetrahedral geometry around the nickel center. The compounds are thermally stable and decomposition is only observed after long periods of heating above 150 °C.     

Synthesis, crystal structure and antibacterial activity of a group of mononuclear manganese(II) Schiff base complexes

Five mononuclear complexes of manganese(II) of a group of the general formula, [MnL(NCS)₂] where the Schiff base L = N,N′-bis[(pyridin-2-yl)ethylidene]ethane-1,2-diamine (L¹), (1); N,N′-bis[(pyridin-2-yl)benzylidene]ethane-1,2-diamine (L²), (2); N,N′-bis[(pyridin-2-yl)methylidene]propane-1,2-diamine (L³), (3); N,N′-bis[(pyridin-2-yl)ethylidene]propane-1,2-diamine (L⁴), (4) and N,N′-bis[(pyridin-2-yl)benzylidene]propane-1,2-diamine (L⁵), (5) have been prepared. The syntheses have been achieved by reacting manganese chloride with the corresponding tetradentate Schiff bases in presence of thiocyanate in the molar ratio of 1:1:2. The complexes have been characterized by IR spectroscopy, elemental analysis and other physicochemical studies, including crystal structure determination of 1, 2 and 4. Structural studies reveal that the complexes 1, 2 and 4 adopt highly distorted octahedral geometry. The antibacterial activity of all the complexes and their respective Schiff bases has been tested against Gram(+) and Gram(−) bacteria.     

Synthesis,crystal structures,and catalytic properties of phenoxo-bridged dinuclear manganese(III) complexes with bis-Schiff bases

Two structurally similar centrosymmetric phenoxo-bridged dinuclear manganese(III) complexes, [Mn₂(L¹)₂(N₃)₂] (1) and [Mn₂(L²)₂(NCS)₂] (2), were prepared from the tetradentate bis-Schiff base ligands, N,N’-bis(salicylidene)propane-1,2-diamine (H₂L¹) and N,N’-bis(salicylidene)ethane-1,2-diamine (H₂L²), respectively, in the presence of pseudohalides. The complexes have been characterized by FTIR, elemental analyses, and molar conductivity. Structures of the complexes have been confirmed by single-crystal X-ray determination. The bis-Schiff base ligands coordinate with Mn through their phenolate oxygen and imino nitrogen. Each Mn is an octahedral. The complexes showed that they exhibit high activity in catalytic olefin oxidation.     

Chloro-bridged complexes of copper(II) and manganese(II) derived from unsymmetric bidentate ligands: synthesis,crystal structure and characterization

Two new usymmetric bidentate Schiff-base ligands (2-pyridyl-2-furylmethyl)imine (L1) and (2-pyridyl-phenylmethyl)imine (L2) were prepared. The crystal structures of two chloro-bridged complexes [Cu₂(μ-Cl)₂(L1)₂Cl₂] (1) and [Mn (μ-Cl)₂(L2)] (2) derived from the each ligand have been confirmed by single-crystal X-ray diffraction analysis. The complexes were characterized by IR, elemental analysis and spectroscopic methods. In complex 1, the two copper atoms are five-coordinate involving a square-pyramidal geometry having a N₂Cl₃ donor set with the two chlorine atoms bridging the two copper atoms. In complex 2, the manganese atoms are both six-coordinate. In contrast to 1, all chlorine atoms in 2 are bridging chlorides and link adjacent manganese atoms together forming 1-D infinite chains.     

Synthesis, crystal structure and magnetic properties of three polynuclear manganese compounds bearing ferrocenecarboxylato ligands

The reactions of sodium ferrocenecarboxylate (FcCO₂Na) and Mn(ClO₄)₂ · 6H₂O in methanol in the presence of ancillary ligands of 1,10-phenanthroline (phen) or 2,2′-bipyridine (2,2′-bpy) produce three discrete polynuclear complexes bearing ferrocenecarboxylato ligands: [Mn₂(FcCO₂)₃(phen)₂](ClO₄) · 2CH₂Cl₂ (1), [Mn₃(FcCO₂)₆(2,2′-bpy)₂] · 2H₂O (2) and [Mn₄O₂(FcCO₂)₇(2,2′-bpy)₂]ClO₄ · 2CH₂Cl₂ · 6H₂O (3). It is shown that their composition and skeletons are tuned by the ancillary ligands and the ratios of starting materials. In dimanganese complex 1, both Mn(II) ions are pentacoordinated in a distorted trigonal bipyramidal geometry and bridged by three ferrocenecarboxylato ligands in a distorted syn-syn bridging mode, which is rare in triply carboxylato-bridged dimanganese complexes. Compound 2 presents a linear trinuclear [Mn₃(μ₂-η¹:η¹-O₂CFc)₄(μ₂-η¹:η²-O₂CFc)₂] core, in which six ferrocencarboxylato ligands show two different bridging modes. The cationic Mn₄O₂ core of 3 has a butterfly structure, in which two Mn(III) ions at “body” sites are bridged by an additional ferrocenecarboxylato ligand and they are further connected to the Mn(III) ions at “wing-tip” sites by ferrocenecarboxylato ligands. Magnetic susceptibilities of 1 and 2 were measured. Both of them mediate a weak antiferromagnetic coupling between the Mn(II) ions bridged by ferrocenecarboxylato ligands.     

Synthesis,structural characterization and biological activities of metal(II) complexes with Schiff bases derived from 5-bromosalicylaldehyde: Ru(II) complexes transfer hydrogenation

In this study, two novel Schiff base ligands (L¹ and L²) derived from condensation of methyl 2-amino-6-methyl-4,5,6,7-tetrahydrothieno[2,3-c]pyridine-3-carboxylate and methyl 2-amino-6-phenyl-4,5,6,7-tetrahydrobenzo[b]thiophene-3-carboxylate, both starting matter with 5-bromo-salicylaldehyde, and their Zn(II) and Ni(II) metal complexes have been prepared using a molar ratio of ligand:metal as 1:1 except the Ru(II) complexes 1:0.5. The structures of the obtained ligands and their metal complexes were characterized by elemental analysis, FT-IR, ¹H NMR, ¹³C NMR, UV–vis, thermal analysis methods, mass spectrometry, and magnetic susceptibility measurements. Antioxidant and antiradical activity of Schiff base ligands and their metal complexes were been evaluated in vitro tests. Antioxidant activities of metal complexes generally were more effectives than free Schiff bases. 1c and 2c were used as catalysts for the transfer hydrogenation (TH) of ketones. 1c, 2c complexes were found to be efficient catalyst for transfer hydrogenation reactions.