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In contrast to V(V) complexes with various organic ligands, a simple vanadate without any additive is inactive in neutral medium toward the oxidation of alkanes with H2O2. In this work, we discovered that the insufficient activation of H2O2 upon coordination to the simple vanadate – the commonly accepted reason for the low catalytic activity of the vanadate – cannot explain this phenomenon. Two main findings are reported here on the basis of DFT calculations. First, the generally accepted Fenton-like mechanism of the generation of the active oxidizing species (HO˙) in a vanadate/H2O2(aq)/MeCN system was revisited. A new mechanism based on the tremendous activation of the OOH ligand in the intermediate [V(OO)2(OOH)(H2O)] toward the homolytic O–O bond cleavage is not only feasible but significantly more favourable than the Fenton-like pathway. The surprisingly low activation barrier calculated for the HO˙ generation (15.4 kcal mol−1) demonstrates the efficiency of this process. The presence of easily oxidizable non-innocent OO ligands in this intermediate explains such an activation. Second, it was found that the generated HO˙ radicals may be easily captured by the V atom soon after their formation followed by the elimination of the molecular oxygen. This side reaction of the H2O2 dismutation efficiently consumes the produced HO˙ radicals decreasing their concentration in the reaction mixture and preventing the following oxidation of alkanes. [ABSTRACT FROM AUTHOR]

In this work, four new ruthenium complexes [Ru(η6-p-cymene)(L1)Cl] 1, [Ru(η6-p-cymene)(L2)Cl] 2, [Ru(η6-p-cymene)(L3)Cl] 3 and [Ru(η6-p-cymene)(L4)Cl] 4 [HL1 = (2-cyanophenyl)glycine; HL2 = (5-chloro-2-cyanophenyl)glycine; HL3 = (2-cyano-3-fluorophenyl)glycine; HL4 = (4-cyanophenyl)glycine] were synthesized and well characterized by several spectroscopic and analytical techniques. Complexes 1 and 3 were found to be fluorescent in most of the solvents; however, 2 and 4 were found to be fluorescent mostly in EtOAc, DMF and ethanol. Amongst these four complexes, 3 has shown selective sensing against CO32− and SO42− anions by quenching of fluorescence. The LOD values are found to be in the sub-micromolar range. Investigations of the sensing mechanism performed by computation and NMR studies indicate a possible adduct formation between the NH group of the ligand and the anion(s) through hydrogen bond formation, which ultimately might lead to proton transfer to the bi-negative anion. The quantum yield of the complex 3 was found to decrease on addition of CO32− and SO42− anions from 0.46 to 0.13 and 0.12, respectively. The Job's plot indicates the binding between the probe and anion in a 1 : 1 ratio for both CO32− and SO42− anions. Along with that, all the complexes were found to be biocompatible when tested against several cell lines showing very high IC50 values. It can also be observed that 1 is capable of penetrating within the cells and can act as a cell imaging agent showing fluorescence, and thus can be used for bio-imaging purposes. [ABSTRACT FROM AUTHOR]

Two new benzimidazole Schiff base copper(II) compounds [Cu(5-CH2PPh3-2-salmethylben)(NO3)(H2O)][BF4]·2/3(H2O)·1/3(MeOH) (1) and [Cu(5-CH2NEt3-2-salmethylben)(Cl)][BF4] (2) were synthesised by mixing 2-(1-methyl-1H-benzo[d]imidazol-2-yl)aniline, (3-formyl-4-hydroxybenzyl)triphenylphosphonium chloride or N,N-diethyl-N-(3-formyl-4-hydroxybenzyl)ethanaminium chloride and Cu(NO3)2·3H2O or CuCl2·2H2O in the presence of tetrafluoroborate in a binary mixture of MeOH : H2O under refluxing conditions. The structures of the compounds were established by elemental analysis, FT-IR, ESI-MS analytical techniques and, for 1, by single-crystal X-ray diffraction analysis. Absorption and fluorescence spectroscopic methods were performed to evaluate the calf thymus DNA interactions with the compounds. The calculated binding constants (Kb) of 3.14 × 105 M−1 for 1 and 3.20 × 105 M−1 for 2 were established. The intercalative DNA binding mode was also verified by molecular docking studies. Both compounds demonstrated a notable in vitro cytotoxic effect against human A-549 (lung carcinoma), MCF-7 (breast cancer) and HeLa (cervical cancer) cancer cell lines. A substantial repressive effect on the proliferation of MCF-7 cells (breast cancer cells) was observed for compound 1. The mechanism of action for the effective antiproliferative activity of 1 has additionally been confirmed by means of various biological studies such as morphological assessment through AO/EB, detection of apoptotic induction via Hoechst/PI dual staining, flow cytometry for detection of cell cycle arrest, quantitative analysis of apoptotic cells, DNA degradation, generation of reactive oxygen species (ROS) and by apoptotic induction through mitochondrial staining. [ABSTRACT FROM AUTHOR]

Novel dibasic Schiff bases with three tridentate sites were obtained from the condensation of the triketone 2,4,6-triacetylphloroglucinol (H3ptk) with four different hydrazides, benzoyl hydrazide (bhz), furoyl hydrazide (fah), isonicotinoyl hydrazide (inh) and nicotinoyl hydrazide (nah): H6ptk(bhz)3I, H6ptk(fah)3II, H6ptk(inh)3III and H6ptk(nah)3IV. These ligand precursors I–IV, each being an ONO donor, are tricompartmental building blocks able to form trinuclear complexes having C3 symmetry. The reaction of I–IV with [VIVO(acac)2] leads to the formation of [{VIVO(H2O)}3(ptk(bhz)3)] 1, [{VIVO(H2O)}3(ptk(fah)3)] 2, [{VIVO(H2O)}3(ptk(inh)3)] 3, and [{VIVO(H2O)}3(ptk(nah)3)] 4. In methanol/aqueous solutions of M2CO3 (M+ = Na+, K+ and Cs+), these complexes are slowly converted into dioxidovanadium(V) compounds, namely, M3[(VVO2)3{ptk(bhz)3}]·6H2O [M+ = K+5, Na+9, Cs+13], M3[(VVO2)3{ptk(fah)3}]·6H2O [M+ = K+6, Na+10, Cs+14], M3[(VVO2)3{ptk(inh)3}]·6H2O [M+ = K+7, Na+11, Cs+15] and M3[(VVO2)3{ptk(nah)3}]·6H2O [M+ = K+8, Na+12, Cs+16]. All ligand precursors and complexes are characterized by various techniques such as FT-IR, UV/Visible, EPR, NMR (1H, 13C and 51V), elemental analysis, thermal studies, cyclic voltammetry (CV) and single-crystal X-ray analysis. X-ray diffraction studies of complexes K2.7[{(VVO2)3ptk(fah)3}]·11.5H2O·MeOH 6a, Cs3[{(VVO2)3ptk(bhz)3}]·7H2O 13a and Cs3[{(VVO2)3ptk(nah)3}]·7.3H2O 16a reveal their distorted square pyramidal geometry by coordinating through phenolate oxygen (of ptk), azomethine nitrogen and enolate oxygen (of hydrazide) atoms. The reactivity of complexes 5–16 and their catalytic potential were screened towards their peroxidase mimetic activity in the oxidation of dopamine to aminochrome driven by H2O2 as an oxidant. The conversion of dopamine to aminochrome with different catalysts was monitored by HPLC showing high activity under mild conditions with good conversions within 1 h. Kinetic studies using compounds 13–16 as catalyst precursors reveal that the reaction follows a Michaelis–Menten-like kinetics. [ABSTRACT FROM AUTHOR]

A series of 5-coordinate oxidovanadium(IV) complexes based on 2-(2′-hydroxyphenyl)imidazole (HPIMH), with substituent groups of different electronegativities on the phenolic para position (HPIMX; X = –H, –Br, –OMe and –NO2), were synthesized and characterized. Three of these complexes were characterized by single crystal X-ray diffraction, [VIVO(PIMH)2], [VIVO(PIMBr)2] and [VIVO(PIMNO2)2], as well as a dioxidovanadium(V) compound ([VVO2(PIMH)(PIMH2)]). The complexes were tested for their catalytic activities in the oxidation of dibenzothiophene (DBT), the major refractory organosulfur compound found in fuel. The nitro substituted compound [VIVO(PIMNO2)2] had the highest catalytic oxidation activity followed by: [VIVO(PIMH)2] > [VIVO(PIMBr)2] > [VIVO(PIMMeO)2]. The decrease in activity is attributed to the different electronegativities of the substituent groups, which influence the electron density on the metal center, the V＝O bond distances and infrared stretching bands. Geometry index (τ) values calculated from single crystal X-ray diffraction (SC-XRD) data and DFT studies provided further insights on the trend in activity observed. SC-XRD, EPR, 51V NMR and UV-Vis spectroscopies, and DFT studies were instrumental in studying the mechanism of the catalyzed reaction and proposal of intermediate species. Both radical and non-radical pathways are plausible for the catalytic oxidation and participation of reactive oxygen species in both pathways is also postulated. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of an oxidovanadium(iv) [VIVO(L)(acac)] (1) and of two dioxidovanadium(v) [VVO2(L′)] (2) and [VVO2(L)] (2a) complexes of the Schiff base formed from the reaction of 4-(p-fluorophenyl) thiosemicarbazone with pyridine-2-aldehyde (HL) are described. The oxidovanadium(iv) species [VIVO(L)(acac)] (1) was synthesized by the reaction of VIVO(acac)2 with the thiosemicarbazone HL in refluxing ethanol. The recrystallization of [VIVO(L)(acac)] (1) in DMF, CH3CN or EtOH gave the same product i.e. the dioxidovanadium(v) complex [VVO2(L)] (2a); however, upon recrystallization of 1 in DMSO a distinct compound [VVO2(L′)] (2) was formed, wherein the original ligand L− is transformed to a rearranged one, L′−. In the presence of DMSO the ligand in complex 1 is found to undergo methylation at the carbon centre attached to imine nitrogen (aldimine) and transformed to the corresponding VVO2-species through in situ reaction. The synthesized HL and the metal complexes were characterized by elemental analysis, IR, UV–Vis, NMR and EPR spectroscopy. The molecular structure of [VVO2(L′)] (2) was determined by single crystal X-ray crystallography. The methylation of various other ligands and complexes prepared from different vanadium precursors under similar reaction conditions was also attempted and it was confirmed that the imine methylation observed is both ligand and metal precursor specific. Complexes 1 and 2 show in vitro insulin-like activity against insulin responsive L6 myoblast cells, higher than VIVO(acac)2, with complex 1 being more potent. In addition, the in vitro cytotoxicity studies of HL, and of complexes 1 and 2 against the MCF-7 and Vero cell lines were also done. The ligand is not cytotoxic and complex 2 is significantly more cytotoxic than 1. DAPI staining experiments indicate that an increase in the time of incubation and an increase of concentration of the complexes lead to the increase in cell death. [ABSTRACT FROM AUTHOR]

The single compartmental Schiff base N,N′-ethylenebis(salicylaldimine) (H2L) and [SnPh2Cl2] were utilized to synthesize heterobimetallic 3d metal–Sn complexes, the CoIIISnIV compound [{SnPhCl2}(1κO2N2,2κO2-μ-L)(μ-OMe){CoPh}] (1), the NiIISnIV compound [{SnPh2Cl2}(1κO2N2,2κO2-μ-L)Ni] (2) and the CuIISnIV compound [{SnPh2Cl2}(1κO2N2,2κO2-μ-L)Cu] (3). Attempting to prepare the ethoxido bridged compound analogous to 1 (in ethanol) gives the phenylcobalt(iii) complex [Co(κO2N2)Ph(H2O)] (1A). Single crystal X-ray structure analyses reveal that 1 is derived from an intermetallic (Sn to Co) phenyl shift and that 1A is a transmetallated product; in compounds 2 and 3, the phenyl groups remain coordinated to SnIV but one of the π rings interacts with the 3d-metal. Thus, while systems 1 and 1A show the lability of the phenyl ligand, 2 and 3 reveal its flexible nature. Theoretical DFT calculations demonstrate that the conceivable Ph group shift occurs in the oxidized CoIII intermediate [{SnIVPh2Cl2}(κO2N2-μ-L){CoIII(MeO)}] (5) rather than in the corresponding CoII species [{SnIVPh2Cl2}(κO2N2-μ-L){CoII(MeOH)}] (4). Their catalytic studies in the Baeyer–Villiger oxidation of cyclohexanone into ε-caprolactone with two different oxidants reveal that the sacrificial aldehyde method (with dioxygen/benzaldehyde) is better than that with aqueous H2O2 (30%). The effects of various reaction parameters such as solvent, catalyst amount, temperature, time and heating method were studied allowing the achievement of yields up to 83% with 89% selectivity. [ABSTRACT FROM AUTHOR]

Metal-bound isocyanides demonstrate a very rich chemistry towards 1,3-dipoles of the allyl anion type such as nitrones. Depending on the metal centre, dipole nature and substituent in isocyanides, cycloadducts, imine + isocyanates or metallacycles may be formed. In this work, the reasons for such diversity, intimate details of the reaction mechanism and main factors determining the chemoselectivity in the reaction between Au(iii)-bound isocyanides ([AuCl3(C≡NR)]) and cyclic nitrones −O–Ṉ+=C(H)XXX̱ (XXX = CH2CH2CMe2, CH2CH2CH2, OCH2CMe2, CH2OCMe2 and CH2CH2O) are analysed in detail by theoretical (DFT) methods. The formation of cycloadducts is controlled by the LUMOπ*(C≡N) of isocyanides and it occurs in a stepwise manner via the initial nucleophilic addition of nitrone at the C atom of C≡NR (except for nitronate −O–Ṉ+=C(H)CH2CH2O̱). The imine + isocyanate products are formed upon oxygen transfer from nitrones to isocyanides, and N–O bond cleavage is the main factor determining this process. A metallacycle is formed upon decomposition of the cycloadduct, and this process includes deprotonation of the oxadiazoline CH group/N–O bond cleavage and Cl− elimination/cyclization. The main factor controlling the metallacycle formation is the acidity of the endocyclic CH group in the cycloadduct. Effects of the substituent R in C≡NR and the nitrone nature on the reactivity are analysed. [ABSTRACT FROM AUTHOR]

A series of new benzimidazole containing compounds 2-((1-R-1-H-benzimidazol-2-yl)phenyl-imino)naphthol HL1–3 (R = methyl, ethyl or propyl, respectively) have been synthesized by Schiff base condensation of 2-(1-R-1-H-benzo[d]imidazol-2-yl)aniline and 2-hydroxy-1-naphthaldehyde. The reactions of HL1–3 with Cu(NO3)2·2.5H2O led to the corresponding copper(ii) complexes [Cu(L)(NO3)] 1–3. All the compounds were characterized by conventional analytical techniques and, for 1 and 3, also by single-crystal X-ray analysis. The interactions of complexes 1–3 with calf thymus DNA were studied by absorption and fluorescence spectroscopic techniques and the calculated binding constants (Kb) are in the range of 3.5 × 105 M−1–3.2 × 105 M−1. Complexes 1–3 effectively bind DNA through an intercalative mode, as proved by molecular docking studies. The binding affinity of the complexes decreases with the size increase of the N-alkyl substituent, in the order of 1 ＞ 2 ＞ 3, which is also in accord with the calculated LUMOcomplex energies. They show substantial in vitro cytotoxic effect against human lung (A-549), breast (MDA-MB-231) and cervical (HeLa) cancer cell lines. Complex 1 exhibits a significant inhibitory effect on the proliferation of the A-549 cancer cells. The antiproliferative efficacy of 1 has also been analysed by a DNA fragmentation assay, fluorescence activated cell sorting (FACS) and nuclear morphology using a fluorescence microscope. The possible mode for the apoptosis pathway of 1 has also been evaluated by a reactive oxygen species (ROS) generation study. [ABSTRACT FROM AUTHOR]

A new quinazoline functionalized benzimidazole-based fluorogenic chemosensor H3L is synthesized and fully characterized by conventional techniques including single crystal X-ray analysis. It acts as a highly selective colorimetric and fluorescence sensor for Cu2+ ions in DMF/0.02 M HEPES (1 : 1, v/v, pH = 7.4) medium. Reaction of H3L with CuCl2 forms a mononuclear copper(ii) [Cu(Cl)(H2L)(H2O)] (H2L–Cu2+) complex which is characterized by conventional techniques and quantum chemical calculations. Electronic absorption and fluorescence titration studies of H3L with different metal cations show a distinctive recognition only towards Cu2+ ions even in the presence of other commonly coexisting ions such as Li+, Na+, K+, Mg2+, Ca2+, Fe2+, Fe3+, Mn2+, Co2+, Ni2+, Zn2+, Cd2+ and Hg2+. Moreover, H2L–Cu2+ acts as a metal based highly selective and sensitive chemosensor for S2− ions even in the presence of other commonly coexisting anions such as F−, Cl−, Br−, I−, SO42−, SCN−, AcO−, H2PO4−, PO43−, NO3−, ClO4−, NO2−, HSO4−, HSO42−, S2O32−, S2O82−, CN−, CO32− and HCO3− in DMF/0.02 M HEPES (1 : 1, v/v, pH = 7.4) medium. Quantification analysis indicates that these receptors, H3L and H2L–Cu2+, can detect the presence of Cu2+ and S2− ions at very low concentrations of 1.6 × 10−9 M and 5.2 × 10−6 M, respectively. The propensity of H3L as a bio-imaging fluorescent probe for detection of Cu2+ ions and sequential detection of S2− ions by H2L–Cu2+ in Dalton lymphoma (DL) cancer cells is also shown. [ABSTRACT FROM AUTHOR]

We report the synthesis and characterization of several novel aminopyridine –l-amino acid derived CuII-complexes. The ligands are prepared by a one-pot reductive alkylation of the l-amino acid scaffold and the respective aminopyridine CuII-complexes were obtained by reaction with CuCl2 or Cu(acetato)2. All compounds were characterized by spectroscopic techniques, as well as ESI-MS. Two of the CuII-complexes were characterized by single-crystal X-ray diffraction, one of them, [CuII(L)(CH3COO)] (HL = (S)-3-phenyl-2-(pyridin-2-ylmethylamino)propanoic acid), being the first ever reported aminopyridine-class CuII complex bearing a tridentate N,N,O donor set and a monodentate acetato ligand. The complexes are tested as catalysts in the oxidative coupling of 2-naphthol in organic solvent–water mixtures using dioxygen as the terminal oxidant. The effect of variables such as ligand denticity and substituents, as well as solvent, temperature and oxidant intake, on the overall performance is studied. In general, moderate to low conversions of 2-naphthol to 1,1′-bi-2-naphthol (BINOL) are obtained. The catalysts also showed moderate to low enantioselectivity. Some aspects of the reaction mechanism were elucidated by spectroscopy, electrochemical and theoretical studies. It was found that basic additives are important for activity, but these also increase the formation of secondary oxidation products. The addition of peroxide scavengers such as KI resulted in an increase of conversion, the yield of BINOL and enantioselectivity. [ABSTRACT FROM AUTHOR]

The cyanamides NCNR² (R² = Me2, Ph2, C5H10) react with ZnX2 (X = Cl, Br, I) in a 2 : 1 molar ratio at RT, giving a family of zinc(II) complexes [ZnX2(NCNR²)2] (R² = Me2, X = Cl 1, X = Br 2, X = I 3; R² = C5H10, X = Cl 4, X = Br 5; X = I 6; R² = Ph2, X = Cl 7, X = Br 8, X = I 9; 75-92% yields). Complexes 7 and 8 undergo ligand redistribution in wet CH2Cl2 solutions giving the [Zn(NCNPh2)4(H2O)2][Zn2(µ-X)2X4] (X = Cl 10, Br 11) species that were characterized by 1H NMR, HRESI-MS, and X-ray diffraction. Halide abstraction from 1-3 by the action of AgCF3SO3 or treatment of Zn(CF3SO3)2 with NCNR² (R² = Me2, C5H10) leads to labile complexes [Zn(CF3SO3)2(NCNR²)3] (R² = Me2, 12; C5H10, 13). Crystallization of 12 from wet CH2Cl2 or from the reaction mixture gave [Zn(NCNMe2)3(H2O)2](SO3CF3)2 (12a) or [Zn(CF3SO3)2(NCNMe2)2]8 (12b), whose structures were determined by X-ray diffraction. The ZnII-mediated hydration was observed for the systems comprising ZnX2 (X = Cl, Br, I), 2 equiv. NCNR² (R² = Me2, C5H10, Ph2) and ca. 40-fold excess of water and conducted in acetone at 60 °C (R² = Me2, C5H10) or 80 °C (R² = Ph2) in closed vials, and it gives the urea complexes [ZnX2{OC(NR²)NH2}] (R² = Me2, X = Cl 13, X = Br 14, X = I 15; R = C5H10, X = Cl 16, X = Br 17; X = I 18; R² = Ph2, X = Cl 19, X = Br 20, X = I 21; 57-81%). In contrast to the ZnII-mediated hydration of conventional nitriles, which proceeds only in the presence of co-catalyzing oximes or carboxamides, the reaction with cyanamides does not require any co-catalyst. Complexes 1-9, 12-19 were characterized by ¹H, 13C{¹H} NMR, IR, HRESI-MS, and X-ray crystallography (for 1-3, 8, 9, 13-15, and 17), whereas 20 and 21 were characterized by HRESI+-MS and ¹H and 13C{¹H} NMR (for 20). The structural features of the cyanamide complexes 1, 2, 7, and 8 were interpreted by theoretical calculations at the DFT level. [ABSTRACT FROM AUTHOR]

The Schiff bases H3dfmp(L)2 obtained by the condensation of 2,6-diformyl-4-methylphenol and hydrazones [L = isonicotinoylhydrazide (inh), nicotinoylhydrazide (nah) and benzoylhydrazide (bhz)] are prepared and characterized. By reaction of [VIVO(acac)2] and the H3dfmp(L)2 in methanol the VIVO-complexes [VIVO{Hdfmp(inh)2}(H2O)] (1), [VIVO{Hdfmp(nah)2}(H2O)] (2) and [VIVO{Hdfmp(bhz)2}(H2O)] (3) were obtained. Upon their aerial oxidation in methanol [VVO(OMe)(MeOH){Hdfmp(inh)2}] (4), [VVO(OMe)(MeOH){Hdfmp(nah)2}] (5) and [VVO(OMe)(MeOH){Hdfmp(bhz)2}] (6) were isolated. In the presence of KOH, oxidation of 1–3 results in the formation of [VVO2{H2dfmp(inh)2}]n·5H2O (7), K[VVO2{Hdfmp(nah)2}] (8) and K[VVO2{Hdfmp(bhz)2}] (9). All compounds are characterized in the solid state and in solution, namely by spectroscopic techniques (IR, UV-Vis, EPR, 1H, 13C and 51V NMR), and DFT is also used to calculate the VIV hyperfine coupling constants of VIV-compounds and 51V NMR chemical shifts of several VV-species and assign them to those formed in solution. Single crystal X-ray analysis of [VVO(OMe)(MeOH){Hdfmp(bhz)2}] (6) and [VVO2{H2dfmp(inh)2}]n·5H2O (7) confirm the coordination of the ligand in the dianionic (ONO2−) enolate tautomeric form, one of the hydrazide moieties remaining non-coordinated. In the case of 7 the free N(pyridine) atom of the inh moiety coordinates to the other vanadium center yielding a polynuclear complex in the solid state. It is also demonstrated that the VVO2-complexes are catalyst precursors in the oxidative bromination of styrene by H2O2, therefore acting as functional models of vanadium dependent haloperoxidases. Plausible intermediates involved in the catalytic process are established by UV-Vis, 51V NMR and DFT studies. [ABSTRACT FROM AUTHOR]

The previously predicted ability of the methyl group of nitromethane to form hydrogen bonding with halides is now confirmed experimentally based on X-ray data of novel nitromethane solvates followed by theoretical ab initio calculations at the MP2 level of theory. The cationic (1,3,5-triazapentadiene)PtII complexes [Pt{HN＝C(NC5H10)N(Ph)C(NH2)＝NPh}2](Cl)2, [1](Hal)2 (Hal = Cl, Br, I), and [Pt{HN＝C(NC4H8O)N(Ph)C(NH2)＝NPh}2](Cl)2, [2](Cl)2, were crystallized from MeNO2-containing systems providing nitromethane solvates studied by X-ray diffraction. In the crystal structure of [1][(Hal)2(MeNO2)2] (Hal = Cl, Br, I) and [2][(Cl)2(MeNO2)2], the solvated MeNO2 molecules occupy vacant spaces between lasagna-type layers and connect to the Hal− ion through a weak hydrogen bridge via the H atom of the methyl thus forming, by means of the Hal−⋯HCH2NO2 contact, the halide–nitromethane cluster "filling". The quantum-chemical calculations demonstrated that the short distance between the Hal− anion and the hydrogen atom of nitromethane in clusters [1][(Hal)2(MeNO2)2] and [2][(Cl)2(MeNO2)2] is not just a consequence of the packing effect but a result of the moderately strong hydrogen bonding. [ABSTRACT FROM AUTHOR]

The reaction between [VIVO(acac)2] and the ONN donor Schiff base obtained by the condensation of pyridoxal and 2-aminoethylbenzimidazole (Hpydx-aebmz, I) or 2-aminomethylbenzimidazole (Hpydx-ambmz, II) in equimolar amounts results in the formation of [VIVO(acac)(pydx-aebmz)] 1and [VIVO(acac)(pydx-ambmz)] 2, respectively. The aerobic oxidation of the methanolic solution of 1yielded [VVO2(pydx-aebmz)] 3and its reaction with aqueous H2O2gave the oxidoperoxidovanadium(v) complex, [VVO(O2)(pydx-aebmz)] 4. The formation of 4in solution is also established by titrations of methanolic solutions of 1with H2O2. By titrating solutions of 3and of 4with aqueous H2O2several distinct VV-pydx-aebmz species also containing the peroxido ligand are detected. The full geometry optimization of all species envisaged was done using DFT methods for suitable model complexes. The 51V NMR chemical shifts (δV) have also been calculated, the theoretical data being used to support assignments of the experimental chemical shifts. The 51V hyperfine coupling constants are calculated for 1, the obtained values being in good agreement with the experimental EPR data. Reaction between the VIVO2+exchanged zeolite-Y and Hpydx-aebmz and Hpydx-ambmz in refluxing methanol, followed by aerial oxidation results in the formation of the encapsulated VVO2-complexes, abbreviated herein as [VVO2(pydx-aebmz)]-Y 5and [VVO2(pydx-ambmz)]-Y 6. The molecular structure of 1, determined by single crystal X-ray diffraction, confirms its distorted octahedral geometry with the ONN binding mode of the tridentate ligand, with one acetylacetonato group remaining bound to the VIVO-centre. Oxidation of styrene is investigated using some of these complexes as catalyst precursors with H2O2as oxidant. Under optimised reaction conditions for the conversion of styrene in acetonitrile, a maximum of 68% conversion of styrene (with [VVO2(pydx-aebmz)]-Y) and 65% (with [VVO2(pydx-ambmz)]-Y) is achieved in 6 h of reaction time. The selectivity of the various products is similar for both catalysts and follows the order: benzaldehyde (ca.55%) > 1-phenylethane-1,2-diol > benzoic acid > styrene oxide > phenyl acetaldehyde. Speciation of the systems and plausible intermediates involved in the catalytic oxidation processes are established by UV-Vis, EPR, 51V NMR and DFT studies. Both non-radical (Sharpless) and radical mechanisms of the olefin oxidations were theoretically studied, and the radical pathway was found to be even more favorable than the Sharpless mechanism. [ABSTRACT FROM AUTHOR]

Reactions of copper(ii) with 3-phenylhydrazopentane-2,4-diones X-2-C6H4–NHNC{C(O)CH3}2bearing a substituent in the ortho-position [X = OH (H2L1) 1, AsO3H2(H3L2) 2, Cl (HL3) 3, SO3H (H2L4) 4, COOCH3(HL5) 5, COOH (H2L6) 6, NO2(HL7) 7or H (HL8) 8] lead to a variety of complexes including the monomeric [CuL4(H2O)2]·H2O 10, [CuL4(H2O)2] 11and [Cu(HL4)2(H2O)4] 12, the dimeric [Cu2(H2O)2(μ-HL2)2] 9and the polymeric [Cu(μ-L6)]n] 13ones, often bearing two fused six-membered metallacycles. Complexes 10–12can interconvert, depending on pH and temperature, whereas the Cu(ii) reactions with 4in the presence of cyanoguanidine or imidazole (im) afford the monomeric compound [Cu(H2O)4{NCNC(NH2)2}2](HL4)2·6H2O 14and the heteroligand polymer [Cu(μ-L4)(im)]n15, respectively. The compounds were characterized by single crystal X-ray diffraction (complexes), electrochemical and thermogravimetric studies, as well as elemental analysis, IR, 1H and 13C NMR spectroscopies (diones) and ESI-MS. The effects of the substituents in 1–8on the HOMO–LUMO gap and the relative stability of the model compounds [Cu(OH)(L8)(H2O)]·H2O, [Cu(L1)(H2O)2]·H2O and [Cu(L4)(H2O)2]·H2O are discussed on the basis of DFT calculations that show the stabilization follows the order: two fused 6-membered > two fused 6-membered/5-membered > one 6-membered metallacycles. Complexes 9, 10, 12and 13act as catalyst precursors for the peroxidative oxidation (with H2O2) of cyclohexane to cyclohexanol and cyclohexanone, in MeCN/H2O (total yields of ca. 20% with TONs up to 566), under mild conditions. [ABSTRACT FROM AUTHOR]

Deprotonation of the N-thiophosphorylated thioureas RC(S)NHP(S)(OiPr)2(R = Me2N, HLI; iPrNH, HLII; 2,6-Me2C6H3NH, HLIII, 2,4,6-Me3C6H2NH, HLIV, aza-15-crown-5, HLV) and reaction with CuI or Cu(NO3)2in aqueous EtOH leads to the polynuclear complexes [Cu4(LI–S,S′)4], [Cu8(LII–S,S′)8], and [Cu3(LIII–V–S,S′)3]. The structures of these compounds were investigated by IR, 1H, 31P{1H} NMR, UV-vis spectroscopy and elemental analyses. The crystal structures of [Cu4LI4], [Cu8LII8], [Cu3LIII,IV3]were determined by single-crystal X-ray diffraction. Reaction of the deprotonated ligands (LI–V)−with a mixture of CuI and 1,10-phenanthroline (phen) or PPh3leads to the mixed-ligand mononuclear complexes [Cu(phen)LI–V], [Cu(PPh3)LI–V]or [Cu(PPh3)2LI–V]. The same mixed-ligand complexes were obtained from the reaction of [Cu4LI4], [Cu8LII8], [Cu3LIII–V3]with phen or PPh3. [ABSTRACT FROM AUTHOR]

Plausible mechanisms of olefin epoxidation catalysed by a V–salan model complex [VIV(O)(L)(H2O)] (1, L = (CH2NHCH2CHCHO−)2) in the presence of H2O2are investigated and compared by theoretical methods using density functional theory. Three main routes, i.e.the Mimoun, Sharpless and biradical mechanisms, were examined in detail, and the Sharpless pathway was found to be the most favourable one. The reaction starts from the formation of an active catalytic species [VV(O)(OO)(LH)] (3c) upon interaction of 1with H2O2, then concerted, highly synchronous attack of the olefin to 3coccurs yielding the epoxide and catalyst [VV(O)2(LH)], the latter being oxidized by H2O2to 3c. The activation barrier strongly depends on the proton location in the catalyst molecule and is the lowest when one of the oxygen atoms of the salan ligand is protonated and the vanadium atom is penta-coordinated with one vacant coordination position (complex 3c). The olefin in this reaction acts as an electron donor (nucleophile) rather than as an electron acceptor (electrophile). [ABSTRACT FROM AUTHOR]

Diffusion of ammonia into CH2Cl2 solutions of the dialkylcyanamide complexes cis- or trans-[PtCl2(RCN)2] (R = NMe2, NEt2, NC5H10) at 20–25 °C leads to metal-mediated cyanamide–ammonia coupling to furnish, depending on reaction time, one or another type of novel bisguanidine compound, i.e. the molecular cis- or trans-[PtCl2{NHC(NH2)R}2] (cis-1–3 and trans-1–3) and the cationic cis- or trans-[Pt(NH3)2{NHC(NH2)R}2](Cl)2 (cis-4–6 and trans-4–6) complexes. Compounds cis-1–3 or trans-1–3 were converted to cis-4–6 or trans-4–6, accordingly, upon prolonged treatment with NH3 in CH2Cl2. The ammination of the relevant nitrile complexes cis- or trans-[PtCl2(RCN)2] (R = Et, CH2Ph, Ph) in CH2Cl2 solutions affords only the cationic compounds cis- or trans-[Pt(NH3)2{NHC(NH2)R}2](Cl)2 (cis-7–9 and trans-7–9). The formulation of 1–9 was supported by satisfactory C, H and N elemental analyses, agreeable ESI+-MS (or FAB+-MS), IR, 1H and 13C NMR spectroscopies. The structures of trans-1, trans-3, cis-4, trans-4, cis-7, and cis-9 were determined by single-crystal X-ray diffraction disclosing structural features and showing that the ammination gives ligated guanidines and amidines in the E- and Z-forms, respectively, where both correspond to the trans-addition of NH3 to the nitrile species. [ABSTRACT FROM AUTHOR]

Reactions of the nitrone CH3CHN(CH3)O and the nitrile oxide CH3CNO with the nitrile complexes trans-[MCl2(NCCH3)2] (M = Pt, 1; Pd, 2) were investigated by theoretical methods at B3LYP and, for some processes, CCSD(T) levels of theory. The mechanisms of substitutions and cycloadditions were studied in detail. The former occur via a concerted asynchronous mechanism of dissociative type. The calculations of the metal–ligand bond energies in the starting complexes and substitution products and the analysis of structural features of the transition states indicate that the M–N bond dissociation (rather than M–O bond formation) is the step, which controls the reactivity of 1 and 2 in substitutions. The different chemical behaviours of the Pt and Pd complexes towards the 1,3-dipoles were investigated. The exclusive isolation of cycloaddition rather than substitution products in any solvents in the case of 1 is both kinetically and thermodynamically controlled. The switch of the reaction mode from cycloaddition to substitution for 2 in CH2Cl2 solution is caused by the significantly lower Pd–N bond energy in comparison with the Pt–N bond energy, consistent with the higher lability of the Pd complexes. The different chemical behaviour of 2 in CH3CN and CH2Cl2 solvents is accounted for by the great excess of acetonitrile in the CH3CN solution rather than a different solvation character. The relative variation of Wiberg bond indices along the reaction path is proposed as a quantitative criterion for the classification of the reaction mechanism. [ABSTRACT FROM AUTHOR]