Vanadium complexes with quadridentate Schiff bases

The Schiff base ligands N,N′-(±)-trans-bis(3,5-dichloro-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H₂L¹) and N,N′-(±)-trans-bis(5-chloro-4-methyl-2-hydroxyacetophenone)-1,2-cyclohexanediamine (H₂L²) were derived from the condensation of trans-1,2-diaminocyclohexane with 3,5-dichloro-2-hydroxyacetophenone or 5-chloro-4-methyl-2-hydroxyacetophenone, respectively. Both these ligands formed well-defined complexes with vanadium (IV) and (V) under suitable experimental conditions. These complexes have been characterized by elemental analysis, molar conductivity, magnetic moments, infrared, electronic spectra, ESR, X-ray diffraction, and thermogravimetric analysis. X-ray diffraction study of [VO(L²)]·H₂O complex indicated its monoclinic crystal system with a = 9.8525, b = 23.6271, c = 9.0904 Å, and β = 97.87°. The complexes [VO(L¹)]·H₂O and [VO(L²)]·H₂O have been examined as catalysts for epoxidation of styrene in the presence of hydrogen peroxide as oxidant. The IR spectral data suggest that both the ligands behave as dibasic tetradentate chelating agent with ONNO donor atoms sequence toward cental metal ion.     

Aluminum complexes of sterically hindered tetradentate Schiff bases: Synthesis, structure, and reactivity toward -caprolactone

The sterically hindered Schiff bases tbmSalenH₂ [tbmSalen = N,N′-1,2-ethylenebis(3-tert-butyl-5-methylsalicylideneimine)] and tbmSalcenH₂ [tbmSalcen = N,N′-trans-1,2-cyclohexanediyl-bis(3-tert-butyl-5-methylsalicylideneimine)] afforded a series of aluminum complexes of the general formulae [Al(tbmSalen)X] and [Al(tbmSalcen)X] (X = Cl, Me, Et). The molecular structure of [Al(tbmSalcen)Cl] was determined by single-crystal X-ray structural analysis which revealed a five-coordinate aluminum center with a distorted square pyramidal geometry. The alkyl complexes were found to oligomerize -caprolactone.     

Synthesis and Characterization of a New (E,E)-Dioxime and its Homonuclear Complexes

N′-(4′-Benzo[15-crown-5]naphthylaminoglyoxime (H₂L) and its sodium chloride complex (H₂L·NaCl) have been prepared from 2-naphthylchloroglyoxime, 4′-aminobenzo[15-crown-5] and sodium bicarbonate or sodium bicarbonate and sodium chloride. Nickel(II), cobalt(II) and copper(II) complexes of H₂L and H₂L·NaCl have a metal–ligand ratio of 1:2 and the ligand coordinates through the two N atoms, as do most of the vic-dioximes. The BF₂⁺-capped Ni(II), Co(III) and mononuclear complexes of thevic-dioxime were prepared. The macrocyclic ligands and their transition metal complexes have been characterized on the basis of IR, ¹H NMR spectroscopy and elemental analyses data.     

Microstructure of 1,2-<Emphasis Type="Italic">trans</Emphasis>-and 1,4-<Emphasis Type="Italic">trans</Emphasis>-poly(penta-1,3-dienes)

Microstructures of 1,2-trans-and 1,4-trans-poly(penta-1,3-dienes) synthesized using different catalysts were determined by high resolution ¹³C NMR spectroscopy. The content of dyad combinations of the 1,4-and 1,2-structures was quantitatively determined in hydrogenated poly(penta-1,3-dienes) from the ratio of intensities of the characteristic signals of the carbon atoms of the methylene groups in the ¹³C NMR spectra. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1113–1118, June, 2007.     

Crown-ether styryl dyes

The surface enhanced Raman scattering (SERS) spectra of styryl dyes containing a crown-ether group and a heteroaromatic residue with sulfoalkyl (1a) or alkyl (1b)N-substituent and of their complexes with Mg²⁺ cations were recorded in the 10^–4–10^–8 mol L^–1 concentration range. A model for the interaction of compoundsla,b with a silver surface during their adsorption on an electrochemically treated electrode was suggested. Fastcis-trans relaxation of the adsorbed molecules1a,b and complexes (1a,b)Mg²⁺ was found. It was shown that at [1a] = 10^–5 mol L^–1 and moderate molar ratios (C _Mg/[1a] = 3/1 to 9/1) in acetonitrile solutions, (trans-1a)Mg²⁺ complexes are joined into head-to-tail type dimers. An excess of Mg²⁺ cations (C_Mg/[1a] > 100) leads to dissociation of the dimers yielding (trans-1a)(Mg²⁺)₂ complexes. The formation of dimers from complexes (trans-1a)Mg²⁺ is accompanied by a substantial distortion of the planar structure oftrans-1a. This may be an important factor influencing the efficiency of photocycloaddition involving dimers of (trans-1a)Mg²⁺.For part 15, see Ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2429–2436, December, 1995.The work was carried out with financial support of the Russian Foundation for Basic Research (Project No. 94-03-08760) and, to some extent, of INTAS (Grant No. 93-1829) and of the International Science Foundation (Grant No. MHAOOO).     

Synthesis and characterization of complexes of lanthanide nitrates with N,N′-dinaphthyl-N,N′-diphenyl-3,6-dioxaoctanediamide

Solid complexes of lighter lanthanide nitrates with N,N′-dinaphthyl-N,N′-diphenyl-3,6-dioxaoctanediamide (DDD), Ln(NO₃)₃(DDD) (Ln = La---Nd, Sm) have been prepared in non-aqueous media. These complexes have been characterized by elemental analysis, conductivity measurements, IR spectra, electronic spectra and TG-DTA techniques. In all the complexes, DDD and NO₃⁻ are coordinated to the lanthanide ions as tetradentate and bidentate ligands, respectively. The differences in the IR and electronic spectra between these complexes and lanthanide nitrate complexes with N,N,N′,N′-tetraphenyl-3,6-dioxaoctanediamide (TDD) are discussed.     

Mercury(II) cyanide complexes with alkyldiamines: solid-state/solution NMR,computational, and antimicrobial studies

Mercury cyanide complexes of alkyldiamines (1–6), [Hg(L)(CN)₂] (where L?=?en (1,2-diaminoethane), pn (1,3-diaminopropane), N-Me-en, N, N′-Me₂-en, N, N′-Et₂-en, and N, N′-ipr₂-en), have been synthesized and characterized by elemental analysis, IR, ¹³C, and ¹⁵N solution NMR in DMSO-d₆, as well as ¹³C, ¹⁵N, and ¹⁹⁹Hg solid-state NMR spectroscopy. Complexes 1 and 2 have been studied computationally, built and optimized by GAUSSIAN03 using DFT at B3LYP level with LanL2DZ basis set. Binding modes of en and bn (where bn?=?1,4-diaminobutane) toward Hg(CN)₂ are completely different. Complexes with en and pn show chelating binding to Hg(II), while bn behaves as a bridging ligand to form a polymeric structure, [Hg(CN)₂-bn]_∞ [B.A. Al-Maythalony, M. Fettouhi, M.I.M. Wazeer, A.A. Isab. Inorg. Chem. Commun., 12, 540 (2009).]. The solution ¹³C NMR of the complexes demonstrates a slight shift of the ?C≡N (0.9 to 2?ppm) and ?C–NH₂ (0.25 to 6?ppm) carbon resonances, while the other resonances are relatively unaffected. ¹⁵N labeling studies have shown involvement of alkyldiamine ligands in coordination to the metal. The principal components of the ¹³C, ¹⁵N, and ¹⁹⁹Hg shielding tensors have been determined from solid-state NMR data. Antimicrobial activity studies show that the complexes exhibit higher antibacterial activities toward various microorganisms than Hg(CN)₂.     

The effect of polyether ligands on the solution structure of [Li]-α-(phenylthio)benzyllithium in tetrahydrofuran: A H,Li-HOESY NMR study

[⁶Li]-α-(phenylthio)benzyllithium 1-⁶Li was studied in THF/[D₈]THF solution (1:1) in the presence of several acyclic and cyclic polyether ligands by ¹H,⁶Li-HOESY, ¹H and ¹³C NMR spectroscopy. The question whether these ligands are bonded to lithium or not is important for physical–organic investigations as well as for studies of the ground state of (stereoselective) reactions of organolithium compounds in the presence of such ligands. Dimethoxyethane is not bonded to lithium under these conditions. The acyclic ethers diglyme and triglyme coordinate only weakly to the organolithium compound and form contact ion pairs (CIPs) at 25°C. At −80°C, CIPs are in equilibrium with separated ion pairs (SIPs). Very stable complexes of 1-⁶Li are obtained with crown ether ligands. Addition of 12-crown-4 and 15-crown-5, respectively, results in the exclusive formation of SIPs at 25°C and −80°C. With 18-crown-6, a CIP–SIP equilibrium is observed at 25°C which is shifted entirely to the SIP side at −80°C. Graphical analyses of the ¹H and ¹³C NMR spectra of the polyether complexes of 1-⁶Li revealed correlations between the chemical shifts of the para phenyl carbon C-5, the para phenyl proton H-5, the benzylic carbon C-1, and the proton–carbon coupling constant J(C-1,H-1) of 1-Li, which are useful probes for the charge distribution within the carbanionic moiety of 1-⁶Li in the respective complexes, and thus for the ion pair character as a function of the polyether complexation of lithium.     

Co(III) complexes of Me-salpn and Me-salbn and the ring size effect on the coordination modes and electrochemical properties: The crystal structures of trans-[Co(Me-salpn)(py)2]PF6 and cis-α-[Co(Me-salbn)(4-Mepy)2]BPh4 · 4-Mepy

The synthesis and characterization of a series of cobalt(III) complexes of the general type [Co(N₂O₂)(L₂)]⁺ are described. The N₂O₂ Schiff base ligands used are Me-salpn (H₂Me-salpn = N,N′-bis(methylsalicylidene)-1,3-propylenediamine) (1–3) and Me-salbn (H₂Me-salbn = N,N′-bis(methylsalicylidene)-1,4-butylenediamine) (4–5). The two ancillary ligands L include: pyridine (py) 1, 3-metheylpyridine (3-Mepy) 2, 1-methylimidazole (1-MeIm) 3, 4-methylpyridine (4-Mepy) 4 and pyridine (py) 5. These complexes have been characterized by elemental analyses, IR, UV–Vis, and ¹H NMR spectroscopy. The crystal structures of trans-[Co^III(Me-salpn)(py)₂]PF₆, 1, and cis-α-[Co^III(Me-salbn)(4-Mepy)₂]BPh₄ · 4-Mepy, 4, have been determined by X-ray diffraction. Examination of the solution and crystalline structures revealed that the outer coordination sphere of the complexes exerts a noticeable influence on the inner coordination sphere of the Co(III) ion. The electrochemical reduction of these complexes at a glassy carbon electrode in acetonitrile solution indicates that the first reduction process corresponding to Co^III–Co^II is electrochemically irreversible, which is accompanied by the dissociation of the axial (R-py)–cobalt bonds. It has also been observed that the Co(III) state is stabilized with increasing the flexibility of the ligand environment.     

Substituted pyridine coordinated N,N-trans and N,N-cis cyclopalladated complexes of (S)-4-tert-butyl-2-phenyl-2-oxazoline: Crystal structures, spectral study and catalysis of the decomposition of PS pesticides

Three pyridine coordinated cyclopalladated complexes: (S)-chloro{2-[2-(4-tert-butyl)oxazolinyl]phenyl-C,N}(4-R-pyridine)palladium(II) (R = H, 2; R = CF₃, 3; R = NMe₂, 4), have been synthesized and structurally characterized. While the crystal structure shows that 2 has a normal N,N-trans-conformation in the coordination sphere of palladium(II), 3 and 4 exhibit uncommon N,N-cis-conformations. From ¹H NMR measurements, the major coordination isomer in deuterated chloroform solution is N,N-trans configuration for three palladacycles. It was found that the three complexes catalyze effectively the methanolysis of the PS pesticides including chiral thiophosphates but show different activity depending on the substituents of co-coordinated pyridine ring in 2–4.     

Synthesis of chiral vicinal C2 symmetric and unsymmetric bis(sulfonamide) ligands based on trans-1,2-cyclohexanediamine by aminolysis of N-tosylaziridines

The ring opening of N-tosylaziridines with aliphatic amines can be efficiently catalyzed by lithium perchlorate to provide derivatives of the trans-1,2-diamine in high yields. The reaction was used in desymmetrization of several cyclic N-tosylaziridines using chiral amines. Using this strategy, an efficient synthesis of chiral vicinal C₂ symmetric bis(sulfonamide) and unsymmetrical bis(sulfonamide) ligands based on trans-1,2-cyclohexanediamine was developed.     

Nucleophilic addition of bifunctional sulfimidosulfides to platinum(<Emphasis Type="SmallCaps">IV</Emphasis>)-coordinated nitriles

Reactions of the platinum(IV) nitrile complexes [PtCl₄(RCN)₂] (R = Me, CH₂Ph, Ph) with 1,2- and 1,4-PhS(=NH)C₆H₄SPh in CH₂Cl₂ afforded addition products of sulfimides and coordinated nitriles, viz., the [PtCl₄{NH=C(R)N=S(Ph)(C₆H₄SPh)}₂] complexes. The latter were isolated in 75—90% yields and characterized by elemental analysis, positive-ion FAB mass spectrometry, IR spectroscopy, and ¹H and ¹³C¹H NMR spectroscopy. The temperature dependence of the ¹H NMR spectra of the model [PtCl₄{NH=C(R)N=SPh₂}₂] complexes (R = Me, Et) in CD₂Cl₂ studied in a temperature range from +40 to -70 °C demonstrated that E—Z isomerization of the ligands is a dynamic process in a range from +40 to -10 °C. The activation free energy of this process was calculated.Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 8, pp. 1618–1622, August, 2004.     

Coordination Properties of Ga, In, and Tl Tetraphenylporphine Complexes in Reactions with Nitrogen-containing Extra Ligands

The formation of Ga^{3 +}, In^{3 +}, and Tl^{3 +} tetraphenylporphine mixed-ligand complexes (X)MTPP + L = (X)M(L)TPP (X = Cl^-, AcO^-, acac^-; L = N-methylimidazole, imidazole, pyridine, 3,5-dimethylpyrazole, dimethylformamide) in chloroform was studied by spectrophotometric titration and quantum-chemical calculations. The stability of the Ga, In, and Tl porphyrin extra complexes was found to depend on the nature of the acido and nitrogen-containing ligands. The geometric and energetic characteristics of the complexes of six-coordinate gallium and indium porphyrins were calculated. Correlations between calculated and experimental energies of formation and Gibbs energies were found. The cis- and trans-effects of ligands in the extra complexes of metal porphyrins were explained.     

Light-induced cis/trans isomerization of cis-[Pd(L-S,O)2] and cis-[Pt(L-S,O)2] complexes of chelating N,N-dialkyl-N′-acylthioureas: key to the formation and isolation of trans isomers

Irradiation cis-[M(Lⁿ-S,O)₂] complexes (M = Pt^II, Pd^II) derived from N,N-dialkyl-N′-benzoylthioureas (HLⁿ) with various sources of intense visible polychromatic or monochromatic light with λ < 500 nm leads to light-induced cis?→?trans isomerization in organic solvents. In all cases, white light derived from several sources or monochromatic blue-violet laser 405 nm light, efficiently results in substantial amounts of the trans isomer appearing in solution, as shown by ¹H NMR and/or reversed-phase HPLC separation in dilute solutions at room temperature. The extent and relative rates of cis/trans isomerization induced by in situ laser light (λ = 405 nm) of cis-[Pd(L²-S,O)₂] was directly monitored by ¹H NMR and ¹⁹⁵Pt NMR spectroscopy of selected cis-[Pt(L-S,O)₂] compounds in chloroform-d; both with and without light irradiation allows the δ(¹⁹⁵Pt) chemical shifts cis/trans isomer pairs to be recorded. The cis/trans isomers appear to be in a photo-thermal equilibrium between the thermodynamically favored cis isomer and its trans counterpart. In the dark, the trans isomer reverts back to the cis complex in what is probably a thermal process. The light-induced cis/trans process is the key to preparing and isolating the rare trans complexes which cannot be prepared by conventional synthesis as confirmed by the first example of trans-[Pd(L-S,O)₂] characterized by single-crystal X-ray diffraction, deliberately prepared after photo-induced isomerization in acetonitrile solution.     

Synthesis,spectral, catalytic,and thermal studies of vanadium complexes with quadridentate schiff bases

The paper reports the synthesis and characterization of vanadium complexes of N,N′-(±)-trans-bis(2,4-dihydroxyacetophenone)-1,2-cyclohexanediamine (H₂L¹) and N,N′-(±)-trans-bis(2,4-dihyroxy-5-nitroacetophenone)-1,2-chyclohexanediamine (H₂L²). All the complexes were characterized by elemental analysis, magnetic susceptibility measurements, infrared and electronic spectra, and thermogravimetric analysis. The X-ray patterns of the [VO(L¹)] · H₂O (I) and [VO(L²)] · H₂O (II) complexes show the monoclinic system with the unit cell parameters a = 26.1352, b = 11.7149, c = 6.0401 β = 115.38° and a = 29.3787, b = 12.9398, c = 5.9175 β = 96.84°, respectively. The complexes I and II catalyze the oxidation of styrene in the presence of hydrogen peroxide.     

Complexation of N4-Tetradentate Ligands with Nd(III) and Am(III)

To improve understanding of aza-complexants in trivalent actinide?Clanthanide separations, a series of tetradentate N-donor ligands have been synthesized and their complexation of americium(III) and neodymium(III) investigated by UV?Cvisible spectrophotometry in methanolic solutions. The six pyridine/alkyl amine/imine ligands are N,N??-bis(2-methylpyridyl)-1,2-diaminoethane, N,N??-bis(2-methylpyridyl)-1,3-diaminopropane, trans-N,N-bis(2-pyridylmethyl)-1,2-diaminocyclohexane (BPMDAC), N,N??-bis(2-pyridylmethyl)piperazine, N,N??-bis-[pyridin-2-ylmethylene]ethane-1,2-diamine, and trans-N,N-bis-([pyridin-2-ylmethylene]-cyclohexane-1,2-diamine. Each ligand has two pyridine groups and two aliphatic amine/imine N-donor atoms arranged with different degrees of preorganization and structural backbone rigidity. Conditional stability constants for the complexes of Am(III) and Nd(III) by these ligands establish the selectivity patterns. The overall selectivity of Am(III) over Nd(III) is similar to that reported for the terdentate bis(dialkyltriazinyl)pyridine molecules. The cyclohexane amine derivative (BPMDAC) is the strongest complexant and shows the highest selectivity for Am(III) over Nd(III) while the imines appear to prefer a bridging arrangement between two cations. These results suggest that this series of ligands could be employed to develop an enhanced actinide(III)?Clanthanide(III) separation system.     

Synthesis and catalytic properties in olefin epoxidation of dioxomolybdenum(vi) complexes bearing a bidentate or tetradentate salen-type ligand

The monomeric cis-dioxomolybdenum(VI) complexes [MoO₂(oep-saldpen)] and [MoO₂Cl₂(oep-H₂saldpen)], with a tetradentate [N₂(imine)O₂] and bidentate [N₂(imine)] salen-type ligand functionalised with two pyrrole derivative pendant arms [oep-H₂saldpen = 1,2-diphenylethylenebis(3-oxyethylpyrrole)salicylideneimine], were synthesised and characterised by ¹H NMR, IR and Raman spectroscopy. The solid-state structure of the free ligand oep-H₂saldpen was determined by single crystal X-ray diffraction. Assignment of the vibrational spectra of the molybdenum complexes was supported by carrying out ab initio calculations for the possible isomers using [MoO₂(salen)] and [MoO₂Cl₂(H₂salen)] as model compounds [H₂salen = N,N′-ethylenebis(salicylideneimine)]. The oep-saldpen complexes were examined as catalysts for the epoxidation of cyclooctene, (R)-(+)-limonene, styrene, α-pinene, and cis and trans-β-methylstyrene, with tert-butyl hydroperoxide as the oxidant. Both complexes exhibited high selectivity for the epoxidation reaction, with the bis(chloro) complex being always the more active of the two.     

Hindered rotation of ligands in cis-[PtR2Cl2] complexes

The temperature dependence of the¹H NMR spectra ofcis-[Pt(II)R₂Cl₂] complexes was studied in DMSO at 18–100°C (R is 2-methyl and 2,5-dimethylpyridine). The broadening of the signals from the methyl groups or hydrogen atoms in theortho-positions of heteroaromatic ligands is due to the coexistence of two forms of thecis-complexes in solution. These forms arise from the hindered rotation of asymmetrical ligands around the Pt-N bond.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 424–425, February, 1993.     

Synthesis, characterization and solution behaviour of phosphoryl complexes of tin tetrafluoride

The preparation and characterization of a series of octahedral complexes [SnF₄L₂] (L = (Me₂N)₃PO (1), L = (R₂N)₂P(O)F; R = Me (2); Et (3) or L = R₂NP(O)F₂; R = Me (4); Et (5)) are described. These new adducts have been characterised by multinuclear (¹⁹F, ³¹P and ¹¹⁹Sn) NMR, IR spectroscopy and elemental analysis. The NMR data particularly the ¹⁹F NMR spectra showed that the complexes exist in solution as mixtures of cis and trans isomers. The solution behaviour of the complexes studied by variable temperature NMR in the presence of excess ligand indicated that, unlike in the SnCl₄ analogues, the ligand exchange at room temperature is slow for 1–3 and fast only for 4 and 5. The metal–ligand exchange barriers in [SnF₄L₂] and [SnCl₄L₂] systems were estimated and compared. The results indicate that in addition to the difference in the Lewis acidity between SnF₄ and SnCl₄ the nature of the substituents (fluorine atoms) on the phosphorus atom of the ligand can contribute considerably to the lability of the complex obtained.     

Cobalt(II) complexes of new biomimetic polydentate amide ligands. A spectroscopic,thermal and potentiometric study

Complexes of Co^II with N,N-bis-(3-carboxy-1-oxopropanyl)-1,2-ethylenediamine(L₁), N,N-bis-(3-carboxy-1-oxopropanyl)-1,2-phenylenediamine(L₂), N,N-bis-(2-carboxy-1-oxophenelenyl)-1,2-phenylenediamine(L₃) and N,N-bis-(3-carboxy-1-oxoprop-2-enyl)-1,2-phenylenediamine(L₄) have been prepared and characterized by elemental analysis, vibrational spectra, magnetic susceptibility measurements, electronic spectra and thermal studies. Stability constants of the complexes have been evaluated potentiometrically. Vibrational spectra indicate coordination of amide and carboxylate oxygens of the ligands along with two water molecules giving a MO₆ weak field octahedral chromophore. Electronic spectra support octahedral geometry around Co^II. The [Co(L₁)-(H₂O)₂] · 2H₂O complex has the maximum activation energy and [Co(L₃)(H₂O)₂] complex has the minimum activation energy. The order of stability constants of the Co^II complexes with various ligands is due to their -donor abilities.