An unsymmetrical tripodal ligand with an N2OS donor set: coordination chemistry with nickel(II)ions and aerial oxidation to the sulfinate complex

The synthesis of the previously unknown tripodal ligand H4-1 is reported. The tetradentate ligand is equipped with a completely unsymmetrical N2OS donor set. It reacts with Ni(OAc)2. 4H2O or Ni(ClO4)2.6H2O to give the multinuclear nickel(II) complexes [Ni(H-1-Imin)(OAc)]2 (2) (which contains a coordinated Schiff base obtained by reation of the primary amine with the acetone solvent) and [Ni3(H3-1)(H2-1)2]-ClO4.H2O.3 MeCN (3), respectively. A solution of 3 in DMF is readily oxidized upon exposure to air or by aqueous H2O2 to yield [Ni(H2-1-sulfinate)]2. 2MeOH (4). The molecular structures of 2-4 have been determined by X-ray diffraction. Complex 2 exhibits a strongly distorted, octahedral coordination geometry around each nickel(II)ion. The primary amino group of the ligand in this case reacted with the solvent acetone to yield a Schiff base which is coordinated to the metal center. The molecular structure of the trinuclear complex cation in 3 consists of two subunits: a nickel atom with a square-planar N2S2 coordination geometry and two other nickel atoms with a trigonal-bipyramidal N2O2S coordination environment. The dinuclear complex 4 shows distorted octahedral geometry around each nickel(II) ion. The thiolato groups of the ligands are oxidized to sulfinato groups which are O,O-bound to the nickel center. This coordination mode is unusual for nickel sulfinate complexes.     

An unusual oxidation of an NCH3 group to an NCHO group by osmium tetroxide

Treatment of pyrodelphinine (1) with osmium tetroxide afforded a mixture of the cis-hydroxylation product 2 and an unexpected product 3 in the ratio of 4:1, respectively. Similarly, oxidation of delphinine (5) afforded α-oxodelphinine (6; 75%) and oxidation of mesaconitine (8) furnished oxonitine (9; 92%). Thus a very selective oxidation of the N-methyl group of delphinine and mesaconitine is effected osmium tetroxide.     

Oxidations catalyzed by osmium compounds. Part 1: Efficient alkane oxidation with peroxides catalyzed by an olefin carbonyl osmium(0) complex

A carbonyl osmium(0) complex with π-coordinated olefin, (2,3-η-1,4-diphenylbut-2-en-1,4-dione)undecacarbonyl triangulotriosmium (1), efficiently catalyzes oxygenation of alkanes (cyclohexane, cyclooctane, n-heptane, isooctane, etc.) with hydrogen peroxide, as well as with tert-butyl hydroperoxide and meta-chloroperoxybenzoic acid in acetonitrile solution. Alkanes are oxidized to corresponding alcohols, ketones (aldehydes) and alkyl hydroperoxides. Thus, heating cyclooctane with the 1-H₂O₂ combination at 70 °C gave products with turnover number as high as 2400 after 6 h. The maximum obtained yield of all products was equal to 20% based on cyclohexane and 30% based on H₂O₂. The oxidation of linear and branched alkanes exhibits very low regio- and bond-selectivity parameters and this testifies that the reaction proceeds via attack of hydroxyl radicals on C-H bonds of the alkane. The oxygenation products were not formed when the reaction was carried out under argon atmosphere and it can be thus concluded that the oxygenation occurs via the reaction between alkyl radicals and atmospheric oxygen. In summary, the Os(0) complex is much more powerful generator of hydroxyl radicals than any soluble derivative of iron (which is an analogue of osmium in the Periodic System).     

A zinc(II) complex with tris(2-( N -methyl)benzimidazlylmethyl)amine and salicylate: synthesis,crystal structure,and DNA-binding

A five-coordinate zinc complex with tris(2-(N-methyl)benzimidazylmethyl)amine (Mentb) and salicylate, with composition [Zn(Mentb)(salicylate)](NO₃), was synthesized and characterized by elemental analysis, IR and UV-Vis spectral measurements. The crystal structure of the zinc complex shows that Zn(II) is bonded to tris(2-(N-methyl)benzimidazylmethyl)amine (Mentb) and a salicylate through four nitrogens and one oxygen, and the coordination geometry is best described as distorted trigonal-bipyramid. The DNA-binding of the Zn(II) complex and Mentb were investigated by spectrophotometric methods and viscosity measurements, and the results suggest that the Zn(II) complex binds to DNA via intercalation; the binding affinity of the Zn(II) complex to DNA is greater than Mentb. Additionally, Zn(II) complex exhibited potential to scavenge hydroxyl radical in vitro.     

Kinetic studies on the periodate oxidation of an iron(II) oxime‐imine complex

The iron(II) complex of H₂L (H₂L=3, 14‐dimethyl‐4, 7, 10, 13‐tetraazahexadeca‐3,13‐diene‐2,15‐dione dioxime, Coord. Chem. Rev., 33, 87 (1980)) is oxidized by periodate very rapidly in the range pH 2.0–7.0, and the kinetics of the reaction has been followed by stopped‐flow spectrophotometry at 30°C and ionic strength I=0.20 mol L⁻¹ (NaClO₄). The reaction is found to follow a simple second‐order kinetics as −d/dt [Fe^II(H₂L)²⁺]=k [Fe^II(H₂L)²⁺] [I(VII)], giving [Fe^III(L)]⁺ and IO₃⁻ as the final products. The reaction has been proposed to occur through a H‐bonded transition state formed probably between the protonated oxime group of the ligand and the oxygen atom on the periodate species, followed by an electron transfer from Fe^II centre to I^VII in a rate‐determining step. The I^VI species thus generated reacts in a fast step with another Fe^II complex. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 23–28, 1999     

Synthesis and characterization of luminescent zinc(II) and cadmium(II) complexes with N,S-chelating Schiff base ligands

The reactions of zinc(II) acetate with a variety of 2-substituted benzothiazolines afforded tetrahedral mononuclear complexes with a N 2S 2 donor set, [Zn(RPhC(H) NC 6H 4 S) 2]. The obtained zinc(II) complexes can be divided into three groups based on the characteristics of the absorption spectra; Group 1 (R = 2,4,6-triMe ( 1), 2,6-diCl ( 2)) showing an intense band at 250-300 nm and a weak band at 400-450 nm, Group 2 (R = 4-Cl ( 3), H ( 4), 4-Et ( 5), 4-OMe ( 6)) showing two intense bands at 250-300 nm and a weak band at 400-450 nm, and Group 3 (R = 4-NMe 2 ( 7), 4-NEt 2 ( 8)) showing an intense band at 250-300 nm and two very intense bands at 350-450 nm. The Group 2 and Group 3 complexes exhibited a strong emission on irradiating with ultraviolet light while the Group 1 complexes were not emissive at room temperature. However, all the zinc(II) complexes were luminescent in CH 2Cl 2/toluene glass at 77 K, and their emission peak energies were found to correlate with the Hammett constant of the substituent at para position of a pendent phenyl ring in each complex. Similar reactions of cadmium(II) acetate with 2-substituted benzothiazolines were also carried out to synthesize corresponding cadmium(II) complexes. While [Cd(RPhC(H) NC 6H 4 S) 2] (R = 2,4,6-triMe ( 9)) with bulky substituents at ortho positions of a pendent phenyl ring had a tetrahedral mononuclear structure, other cadmium(II) complexes [Cd 2(RPhC(H) NC 6H 4 S) 4] (R = 4-Et ( 10), 4-OMe ( 11), 4-NMe 2 ( 12)) possessed S-bridged dinuclear structures. These cadmium(II) complexes, which are assumed to have a mononuclear structure in solution, showed photophysical properties similar to those of the corresponding zinc(II) complexes.     

Fe[5NO2-sal-N(1,4,7,10)]: a new iron(II) complex exhibiting an unusual two-step spin conversion afforded by a hexadentate ligand with a N4O2, donor set

The new Fe[5NO₂-sal-N(1,4,7,10)] spin-crossover complex has been investigated by Mössbauer spectroscopy, magnetic susceptibility measurements, and X-ray diffraction powder studies as a function of temperature. The spin conversion occurs in two steps separated by a 30° broad spin equilibrium domain involving 50% of HS and LS complex molecules. A single structural phase characterizes this complex from 300 to 90 K. This is the first iron (II) spin-crossover complex including a N₄O₂ donor set.     

Reaction of an osmium(VI) nitrido complex with cyanide: formation and reactivity of an osmium(III) hydrogen cyanamide complex

Reaction of [Os(VI)(N)(L(1))(Cl)(OH(2))] (1) with CN(-) under various conditions affords (PPh(4))[Os(VI)(N)(L(1))(CN)(Cl)] (2), (PPh(4))(2)[Os(VI)(N)(L(2))(CN)(2)] (3), and a novel hydrogen cyanamido complex, (PPh(4))(2)[Os(III){N(H)CN}(L(3))(CN)(3)] (4). Compound 4 reacts readily with both electrophiles and nucleophiles. Protonation and methylation of 4 produce (PPh(4))[Os(III)(NCNH(2))(L(3))(CN)(3)] (5) and (PPh(4))[Os(III)(NCNMe(2))(L(3))(CN)(3)] (6), respectively. Nucleophilic addition of NH(3), ethylamine, and diethylamine readily occur at the C atom of the hydrogen cyanamide ligand of 4 to produce osmium guanidine complexes with the general formula [Os(III){N(H)C(NH(2))NR(1)R(2)}(L(3))(CN)(3)](-) , which have been isolated as PPh(4) salts (R(1) = R(2) = H (7); R(1) = H, R(2) = CH(2)CH(3) (8); R(1) = R(2) = CH(2)CH(3) (9)). The molecular structures of 1-5 and 7 and 8 have been determined by X-ray crystallography.     

Inner-sphere oxidation of 2-aminomethylpyridinecobalt(II) complex by N-bromosuccinimide

The kinetics of the oxidation of the 2-aminomethylpyridineCo^II complex by N-bromosuccinimide (NBS), have been studied in aqueous solutions under various conditions, and obey the following rate law:Rate = [NBS][Co(L)(H₂O)₂]²⁺[k₂₊k₃/[H⁺]]An inner-sphere mechanism is proposed for the oxidation pathway for both protonated and deprotonated complex species, with the formation of an intermediate, which is slowly converted into the final oxidation products. The reaction rate is increased by increasing the pH, T, [complex], and decreased by increasing ionic strength over the range studied.     

Concomitant polymorphism in an organometallic ruthenium(II) complex with an N,N′‐donor ligand

The simultaneous crystallization of different polymorphs, i.e. concomitant polymorphism, is a phenomenon which, when properly recognized and studied, can provide useful information for a variety of disciplines. It is rare for ruthenium complexes, although it has been observed. In the synthesis of the ruthenium(II) complex chlorido(η⁶‐p‐cymene)(dimethyl 2,2′‐bypyridine‐4,5‐dicarboxylate‐κ²N,N′)ruthenium(II) hexafluoridophosphate, [RuCl(C₁₀H₁₄)(C₁₄H₁₂N₂O₄)]PF₆, concomitant polymorphs were crystallized under the same conditions. The colour of both crystals was orange, but the shapes, as well as the orientation of the p‐cymene and methoxycarbonyl groups, were different. The crystal structures of both isomers show approximately the same bond lengths. In the asymmetric unit, there is one cation and one anion. Due to the absence of strong hydrogen bonds, only weak intermolecular interactions were observed. The Hirshfeld surface and two‐dimensional fingerprint plots of both isomers satisfactorily explain the difference in the melting points.     

A five-coordinate copper(II) perchlorate complex with tris(N-methylbenzimidazol-2-ylmethyl)amine and salicylate

A five-coordinate copper(II) complex with the tripod ligand tris(N-methylbenzimidazol-2-ylmethyl)amine (Mentb) and salicylate, with the composition [Cu(Mentb) (salicylate)](ClO₄) · 2DMF, was synthesized and characterized by elemental and thermal analyses, electrical conductivity, IR and UV-Vis spectral measurements. The crystal structure of the complex has been determined by single-crystal X-ray diffraction. The Cu(II) is five-coordinate with four N atoms from the Mentb ligand and an O atom of the monodentate salicylate ligand. The N₄O donors are in a distorted trigonal-bipyramid geometry. Cyclic voltammograms indicate a quasireversible Cu²⁺/Cu⁺ couple. The X-band EPR spectrum of the complex confirms the trigonal-bipyramidal structure with g_∥ < g _⊥ and a very small value of A_∥ (41 × 10^?4 cm^?1).     

Photoinduced and chemical oxidation of coordinated imine to amide in isomeric osmium(II) complexes of N-arylpyridine-2-carboxaldimines. Synthesis,characterization, electron transfer properties,and structural studies

The reaction of N-arylpyridine-2-carboxaldimine [C(5)H(4)NC(H)NC(6)H(4)R] (HL) with ammonium hexabromoosmate (NH(4))(2)[OsBr(6)] in boiling 2-methoxyethanol afforded a violet solution from which two geometrical isomers of [OsBr(2)(HL)(2)] (1 and 2) were isolated. These are characterized by analytical and spectroscopic data. (1)H NMR spectral data were used for the identification of the isomers. The blue-violet isomer, 1 (designated as ctc), has a 2-fold symmetry axis and gave rise to resonances for only one coordinated HL. The geometry of the ctc-isomer was, however, revealed from the X-ray structure determination of a representative example. The red-violet isomer (2, designated as ccc), on the other hand, is unsymmetrical and gave rise to a large number of proton resonances. The isomeric complexes, [OsBr(2)(HL)(2)], showed intense MLCT transitions in the visible region. This transition, in the ccc-isomer, is slightly (10 nm) red shifted in comparison to the ctc-isomer. These diimine complexes showed one metal based reversible oxidation assignable to the Os(III)/Os(II) process followed by two irreversible oxidations at more anodic potentials (>1.4 V). In addition to these, the complexes also showed two irreversible ligand reductions at high cathodic potentials (<-1.4 V). An unusual type of photochemical transformation of the azomethine function of coordinated HL in osmium compounds 1 is studied. When an air equilibrated acetonitrile solution of 1 was exposed to a xenon lamp, it underwent oxidation affording the mixed ligand, amido complexes of general formula [OsBr(2)(HL)(LO)], 3 (LO = C(5)H(4)NC(O)-N-C(6)H(4)R), in an excellent yield (>95%). This transformation (1 --> 3) was achieved chemically when H(2)O(2) was used as an oxidant. Notably, the chemical oxidation with H(2)O(2) also led to the formation of a tetravalent complex, [OsBr(2)(LO)(2)], 4, as a minor product. Compound 3 was characterized by various spectroscopic and analytical techniques. The room temperature magnetic moment of 3 corresponds to a t(2)(5) configuration for the osmium(III) center. EPR spectra of the amido complexes were recorded at 77 K in 1:1 dichloromethane-toluene glass, and they were anisotropic in nature. FAB mass spectra of 3 displayed intense peaks due to parent molecular ions. For example, the complex [OsBr(2)(HL(1))(L(1)O)], 3a, showed a strong peak at m/z 729 amu. The electronic spectrum of compound 3 consisted of a broad LMCT transition (ca. 525 nm; epsilon, 3000 M(-1) cm(-1)). The cyclic voltammogram of compound 3 consisted of two responses, one each on the positive and negative side of SCE, corresponding to Os(IV)/Os(III) (ca. 0.8V) and Os(III)/Os(II) (ca. -0.3V) couples, respectively. There has been a large cathodic shift of potential for the Os(III)/Os(II) couple in 3 in comparison to that in the parent complex, 1. The diamido compound [OsBr(2)(LO)(2)], 4, is diamagnetic and insoluble in common solvents. The X-ray structure determination of a representative sample, 4a, is reported. The molecule contains a C(2)-symmetry axis with bromide ions in relative cis positions. The Os-N(amide) bond lengths are considerably shorter than the Os-N(pyridine) lengths. All other bond lengths and angles fall within the expected range.     

A rare ferromagnetically coupled asymmetric doubly azido bridged copper(II) dimer with an N,N, O donor Schiff base

A new end-to-end (EE) doubly azido bridged dinuclear complex [Cu₂L₂(μ_1,3-N₃)₂] (1) [where L = (E)-4-(2-(dimethylamino)ethylimino)-1,1,1-trifluoropentan-2-one)] has been synthesized and characterized by elemental and spectroscopic techniques. Single crystal X-ray diffraction analysis reveals that the dimeric complex possesses a center of inversion. Each copper atom in 1 is in a distorted square pyramidal geometry with a CuN₄O chromophore as revealed from the τ value, 0.19. The four basal positions are occupied by two imine N and one keto O atom of the Schiff base and one N atom from the azide anion. Another N atom from a coordinated azide occupies the apical position. Temperature dependent magnetic susceptibility of 1 was fitted using the Bleaney–Bowers expression which led to the parameters J = 13.6 cm⁻¹ and R = 3.4 × 10⁻⁵. It indicates a ferromagnetic interaction through the double azido bridges connecting the individual copper Schiff base units.     

Crystal structure of copper(II) complex with N,N-bis(2-benzimidazolylmethyl)benzylamine

The copper(II) complex with N,N-bis(2-benzimidazolylmethyl)benzylamine has been synthesized and its crystal structure was determined by X-ray diffraction methods.     

Crystal structure of a dimeric copper(II) complex with N,N -diethylethylenediamine (dien): a model for the thermally and photoinduced violet forms of the bis(dien)copper(II) cation

The molecular structure of the violet dimer bis(μ-hydroxo)bis(N,N-diethylethyl- enediamine)dicopper(II) perchlorate supports the hypothesis that the photoinduced phase of the monomer bis(N,N-diethylethylenediamine)copper(II) perchlorate, similar to the corresponding, high temperature, thermally induced phase, features tetrahedral distortion of the square planar coordination.     

Diastereospecific and diastereoselective syntheses of Ruthenium(II) complexes using N,N' bidentate ligands aryl-pyridin-2-ylmethyl-amine ArNH-CH2-2-C5H4N and their oxidation to imine ligands

Coordination of N,N' bidentate ligands aryl-pyridin-2-ylmethyl-amine ArNH-CH2-2-C5H4N 1 (Ar = 4-CH3-C6H4, 1a; 4-CH3O-C6H4, 1b; 2,6-(CH3)2-C6H3, 1c; 4-CF3-C6H4, 1d) to the moieties [Ru(bipy)2]2+, [Ru(eta5-C5H5)L]+ (L = CH3CN, CO), or [Ru(eta6-arene)Cl]2+ (arene = benzene, p-cymene) occurs under diastereoselective or diastereospecific conditions. Detailed stereochemical analysis of the new complexes is included. The coordination of these secondary amine ligands activates their oxidation to imines by molecular oxygen in a base-catalyzed reaction and hydrogen peroxide was detected as byproduct. The amine-to-imine oxidation was also observed under the experimental conditions of cyclic voltammetry measurements. Deprotonation of the coordinated amine ligands afforded isolatable amido complexes only for the ligand (1-methyl-1-pyridin-2-yl-ethyl)-p-tolyl-amine, 1e, which doesn't contain hydrogen atoms in a beta position relative to the N-H bond. The structures of [Ru(2,2'-bipyridine)2(1b)](PF6)2, 2b; [Ru(2,2'-bipyridine)(2)(1c)](PF6)2, 2c; trans-[RuCl2(COD)(1a)], 3; and [RuCl2(eta6-C6H6)(1a)]PF6, 4a, have been confirmed by X-ray diffraction studies.     

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex as an efficient catalyst for oxidation of alcohols with tert-butyl hydroperoxide

A polymer-supported diacetatobis(2-quinolylbenzimidazole)copper(II) complex [PS–(QBIM)₂Cu(II)] was synthesized by functionalization of chloromethylated polystyrene cross-linked with 6.5 % divinyl benzene with 2-(2′-quinolyl)benzimidazole and subsequent treatment with Cu(OAc)₂ in methanol. The complex was characterized by physical, analytical and spectroscopic techniques. Electronic and ESR spectra, together with magnetic susceptibility measurements, indicated that the complex was paramagnetic with distorted octahedral geometry around the copper. The complex was found to be active toward oxidation of various alcohols including phenol, benzyl alcohol and cyclohexanol using 70 % aqueous tert-butyl hydroperoxide under mild conditions. Under the optimized reaction conditions, cyclohexanol gave 100 % conversion to cyclohexanone, benzyl alcohol gave 98 % yield of benzaldehyde and phenol gave 89 % yield of catechol and 4 % of hydroquinone. The complex was recycled five times without much loss in catalytic activity.     

Reduction of (imine)Pt(IV) to (imine)Pt(II) complexes with carbonyl-stabilized phosphorus ylides

A novel method is reported for generation of the difficult-to-obtain (imine)Pt(II) compounds that involves reduction of the corresponding readily available Pt(IV)-based imines by carbonyl-stabilized phosphorus ylides, Ph3P=CHCO2R, in nonaqueous media. The reaction between neutral (imino)Pt(IV) compounds [PtCl4[NH=C(Me)ON=CR1R2]2] [R1R2 = Me2, (CH2)4, (CH2)5, (Me)C(Me)=NOH], [PtCl4[NH=C(Me)ONR2]2] (R = Me, Et, CH2Ph), (R1 = H; R2 = Ph or C6H4Me; R3 = Me) as well as anionic-type platinum(IV) complexes (Ph3PCH2Ph)[PtCl5[NH=C(Me)ON=CR2]] [R2 = Me2, (CH2)4, (CH2)5] and 1 equiv of Ph3P=CHCO2R (R = Me, Et) proceeds under mild conditions (ca. 4 h, room temperature) to give selectively the platinum(II) products (in good to excellent isolated yields) without further reduction of the platinum center. All thus prepared compounds (excluding previously described Delta4-1,2,4-oxadiazoline complexes) were characterized by elemental analyses, FAB mass spectrometry, IR and 1H, 13C[1H], 31P[1H] and 195Pt NMR spectroscopies, and X-ray single-crystal diffractometry, the latter for [PtCl2[NH=C(Me)ON=CMe2]2] [crystal system tetragonal, space group P4(2)/n (No. 86), a = b = 10.5050(10) A, c = 15.916(3) A] and (Ph3PCH2CO2Me)[PtCl3(NCMe)] [crystal system orthorhombic, space group Pna2(1) (No. 33), a = 19.661(7) A, b = 12.486(4) A, c = 10.149(3) A]. The reaction is also extended to a variety of other Pt(II)/Pt(IV) couples, and the ylides Ph3P=CHCO2R are introduced as mild and selective reducing agents of wide applicability for the conversion of Pt(IV) to Pt(II) species in nonaqueous media, a route that is especially useful in the case of compounds that cannot be prepared directly from Pt(II) precursors, and for the generation of systematic series of Pt(II)/Pt(IV) complexes for biological studies.