Tuning, via counter anions, the morphology and catalytic activity of CeO2 prepared under mild conditions

Advanced synthetic methods under mild and controlled conditions for the synthesis of nanocrystals with specific shapes and exposed surfaces are very important for understanding the surface related properties and to explore their structure-property relationship for various potential applications. Here, we report the synthesis of highly uniform CeO(2) nanorods and nanoflowers in large scale using non-hydrothermal homogeneous precipitation method with urea as a precipitating agent and CTAB as a shape directing agent. Uniform microstructures of CeO(2) samples were selectively synthesized using chloride and nitrate as the counter anions. The samples were characterized by thermal analysis, X-ray diffraction, N(2) adsorption-desorption isotherms, SEM, TEM, UV-Vis-DRS, and Raman spectroscopy, and temperature programmed reduction as well as desorption methods. The results show that the physicochemical and optical properties of CeO(2) samples significantly differ with their surface microstructure and morphology. They also strongly influence the redox property, oxygen storage capacity, and surface acidity of the CeO(2) samples. The CeO(2) samples with different morphologies were tested for their soot oxidation activity. The CeO(2) sample with nanorod morphology was found to be more active due to larger CeO(2)/soot interface than the CeO(2) sample with nanoflower morphology.     

Structures, preparation and catalytic activity of ruthenium cyclopentadienyl complexes based on pyridyl-phosphine ligand

Ruthenium complexes [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(PPh₃)Cl] (1) and [(η⁵-C₅H₅)Ru(κ²-P-N-PPh₂Py)(PPh₃)]⁺ (1a) containing diphenyl-2-pyridylphosphine (PPh₂Py) are reported. Coordinated PPh₂Py in the complex [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(PPh₃)Cl] (1) exhibits monodentate behavior. In presence of NH₄PF₆ in methanol at room temperature it afforded chelated complex [(η⁵-C₅H₅)Ru(κ²-P,N-PPh₂Py)(PPh₃)]⁺ (1a). Further, 1 reacted with various species viz., CH₃CN, NaCN, NH₄SCN and NaN₃ to afford cationic and neutral complexes [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(PPh₃)L]⁺ and [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(PPh₃)L] [L = CH₃CN (1b); CN⁻ (1c); N₃⁻ (1d) and SCN⁻ (1e)] and it’s reaction with N,N-donor chelating ligands dimethylglyoxime (H₂dmg) and 1,2-phenylenediamine (pda) gave cationic complexes [(η⁵-C₅H₅)Ru(κ¹-P-PPh₂Py)(κ²-N-N)]PF₆ [κ²-N-N = dmg (1f) and pda (1g)]. The complexes 1-1g have been characterized by physicochemical techniques and crystal structures of 1, 1a, 1c, 1e and 1f have been determined by single crystal X-ray analyses. Catalytic potential of the complex 1 has been evaluated in water under aerobic conditions. It was observed that the complex 1 selectively catalyzes reduction of aldehyde into alcohol.     

Effect of ligand structure of Schiff base oxovanadium(IV) complexes on their catalytic activity in aerobic oxidation of alcohols

Two kinds of immobilized bidentate Schiff base oxovanadium(IV) complexes are prepared via polymer reactions and coordination reactions with chloromethylated cross-linked polystyrene (CMCPS) microspheres as matrix. Benzaldehyde (BA)-functionalized CPS microspheres, BA-CPS microspheres, were prepared through nucleophilic substitution with CMCPS microsphere as precursor and p-hydroxy benzaldehyde as reagent, and then Schiff base reactions were carried out with 3-aminopyridine (AP) and glycine (GL) as reagents, respectively, obtaining two kinds of bidentate Schiff base ligand-bonded microspheres, BAAP-CPS microspheres and BAGL-CPS microspheres. Finally, through coordination reactions with vanadyl sulfate (VOSO₄) as reagent, the two kinds of immobilized bidentate Schiff base oxovanadium(IV) complex microspheres, CPS-[VO(BAAP)₂] and CPS-[VO(BAGL)₂], were obtained. The two immobilized complexes, VO(BAAP)₂ and VO(BAGL)₂, are N,N- and N,O-type bidentate Schiff base oxovanadium(IV) complexes and their ligands have different chemical structures. The two catalyst microspheres were used in oxidation of cyclohexanol and benzyl alcohol with molecular oxygen as oxidant and their catalytic activities are compared. The experimental results show that both solid catalysts can catalyze the transformation reactions of cyclohexanol and benzyl alcohol to their corresponding carbonyl compounds under mild conditions. However, CPS-[VO(BAAP)₂] microspheres have much higher catalytic activity and better stability than CPS-[VO(BAGL)₂] microspheres. For the immobilized bidentate Schiff base oxovanadium(IV) catalysts, the catalytic property is closely related to the chemical structures of the ligands, and for this, a theoretical explanation is given.     

Upon the intriguing stereoselective formation of organobismuth(V) complexes

The preparation of triphenylbismuth(V) 3a-k and antimony(V) 4e-k bis-carboxy ester complexes is described. A range of studies in solution suggest that the diastereoselective formation of (RR,SS)-3a-j is governed by the thermodynamic stability of rapidly interconverting epimeric species. Diastereoselectivity is absent in the case of the corresponding Sb complexes, leading to the conclusion that a combination of both ligand-ligand (steric) and metal-ligand (hyperconjugative) interactions govern stereoselectivity. The formation of homochiral complexes (RR,SS)-3a-j is rationalised using a simple model, invoking for the first time a palindromic BiPh3 propeller moiety, which correlates the chirality of the trans axial carboxy-ester ligands. The X-ray crystal structures of both hetero- and homochiral diastereoisomeric antimony complexes (4h and 4i, respectively) are presented in support of this model.     

Structural characterization and catalytic activities of copper complexes with pyridine-amine-phosphine-oxide ligand

A new tetradentate containing pyridine, amine and phosphine oxide donor systems (1) was synthesized by the condensation of o-diphenylphosphinoaniline with 2-pyridinecarbaldehyde. Reaction of 1 with equal molar amount of CuCl₂ and Cu(ClO₄)₂ provided the formation of [CuCl₂(1)] (4) and [[Cu(1)(H₂O)](ClO₄)₂] (5), respectively. The ligand 1 behaves as a tridentate in 4, while as a tetradentate in 5. Both complexes were characterized by EPR, UV-Vis spectroscopy and X-ray diffraction. Both copper(II) complexes are in a square-pyramidal geometry. Single crystal structure of the copper complex reveals that the copper center is surrounded by three nitrogen donors and two chloride for 4; three nitrogen donors, water and oxygen donor from the moiety of phosphine oxide for 5. Complexation of 1 with CuCl in dichloromethane resulted in the formation of the corresponding copper(I) species, which catalyzed the oxidation of benzylic alcohols under aerobic conditions.     

Radical scavenging and catalytic activity of metal-phenolic complexes

A series of metal-ligand complexes were prepared by the reaction of various metal ions, namely, Cu(II), Mn(II), or Fe(II) with phenolic derivatives of [catechol, chlorogenic acid (CGA), n-propyl gallate (nPG), 3-hydroxy anthranilic acid, resveratrol, and rutin] and characterized by UV-vis spectroscopy. The metal/ligand complexing ratio and complexation constants have been determined. The complexes were probed for their reactivity toward various free radicals (e aq-, CO2*-, and O2*-). Pulse radiolysis studies showed that the one-electron reduction of metal/phenol complexes by CO2*- radicals was metal-centered, and this was confirmed by the formation of an initial adduct with CO2*- radicals. Rate constants for the scavenging of superoxide anions with metal complexes ranged between 10(7)-10(9) dm3 mol(-1) s(-1) and those for the reaction of e aq- with the metal complexes were in the range of (1-5) x 10(9) dm3 mol(-1) s(-1), depending on the pH of the solution. Cyclic and differential pulse voltammetric studies showed that the reduction potential of the complexes are found to range between -0.022 to 0.45 V vs normal hydrogen electrode.     

Synthesis and catalytic activity of novel Ni-N complexes

A series of nickel complexes with 1,3-xylylenediamine, 1,2-diaminobenzene and 1,2-aminobenzylamine were first synthesized and characterized. The reaction of these amines with Ni(OAc)₂ · 4H₂O and NiCl₂ · 6H₂O in methanol or tetrahydrofuran resulted in the production of four novel nickel complexes I, II, III, and IV. The structure of each complex was determined by X-ray diffraction analysis. Each complex was also characterized using elemental analysis, ¹H NMR and IR. The complexes were then used to catalyze the Henry reaction, and good catalytic results (65?C99%) were achieved. The catalytic activity of the complexes was determined by ¹H NMR.     

丁撑桥联蝶状铁硫原子簇配合物[(μ-ZS)Fe2(CO)6[μ-S(CH2)4-S-μ[(μ-ZS)Fe2(CO)6]的合成结构及构象

双Grignard试剂BrMg(CH2)4MgBr可还原断裂两分子μ-S2Fe2(CO)6的硫-硫键,生成丁撑桥联双簇铁硫中间物A, [(μ-BrMgS)Fe2(CO)6]μ-S(CH2)4S-μ-[(μ-BrMgS)Fe2(CO)6], A于原位(in situ)进一步同卤代烃、氯甲醚、氯代酮、氯代酯或酰氯作用, 共得到10个结构新颖的丁撑桥联双簇铁硫配合物B, [(μ-ZS(Fe2(CO)6]μ-S(CH2)4S-μ[(μ-ZS)Fe2(CO)6]. 除通过IR、^1H NMR及碳氢分析证实上述配合物的结构和推得某些配合物可能的构象外, 还用X衍射法确证了其中一个配合物B(1)的结构和构象.     

Stereochemical influence of the ligand on the structure of manganese complexes: implications for catalytic epoxidations

Manganese complexes of the ligand HphoxCOOR (R=H or Me) have been synthesized and characterized by X-ray analysis, ESI-MS, ligand-field spectroscopy, electrochemistry, and paramagnetic 1H NMR. The ligands, chirally pure or racemic, influence the structures of the complexes formed. Manganese(III) complexes of the ligand HphoxCOOMe are square-pyramidal or octahedral with two ligands bound in a trans fashion in the solid state. The racemic ligand (RS-HphoxCOOMe) as well as the enantiopure ligand (R-HphoxCOOMe) forms manganese complexes with similar solid-state structures. Ligand-exchange reactions occur in solution giving rise to meso complexes as confirmed by ESI-MS and deuteration studies. The manganese(III) complex of R-HphoxCOOH is octahedral, with two dianionic ligands bound in a fac-cct fashion in a tridentate manner. The manganese(III) complex of RS-HphoxCOOH is also octahedral with two dianionic ligands now bound in a trans fashion in a didentate manner and with two water molecules occupying axial sites. The paramagnetic 1H NMR spectra of the complexes have been interpreted on the basis of the relaxation times with the help of the inversion-recovery pulse technique. The binding of imidazole with the metal center depends on the chirality of the ligands in the metal complexes of HphoxCOOMe. Imidazole coordination was found to occur with the metal complex that contains two ligands with the same chirality (R and R) (R-1), while no imidazole coordination was found upon reaction with the metal complex that contains two ligands with opposite chirality (R and S) (RS-1). Epoxidation reactions of various alkenes with H2O2 as the oxidant reveal that the complexes give turnover numbers in the range of 10-35, the epoxide being the major product. The catalytic activity depends on the additives used, and a clear base effect is observed. The turnover numbers have been found to be higher in the complexes where no binding of N-Meim is observed. The latter fact unambiguously shows that imidazole binding is not a prerequisite for higher turnover numbers, in contrast to the Mn-Schiff base catalysts.     

聚合负载三氯化镨配合物的合成、表征及催化活性

合成并表征了聚(苯乙烯(S)-丙烯酸(A))镨配合物(SAAC·Pr).红外光谱表明了它的配位结构.计算了共聚物中单体单元的序列分布.苯乙烯和丙烯酸单元长序列分布随其在共聚物中含量的增加而增加.当丙烯酸长序列分布高时,配合物的催化活性低.苯乙烯和丙烯酸的平均链长分别为 nS=3, nA=1时,配合物的催化活性最高.     

Formation,characterization and catalytic activity of PD-polyheteroarylenes complexes

High molecular weight polybenzimidazoles, poly[(N-phenyl)benzimidazoles], polynaphthoylenebenzimidazoles and poly(naphthoylene-s-triazoles) were obtained using well-known polycyclodehydration processes as well as new reactions for their preparation -reductive polyheterocyclization and “activated” poly-cyclocondensation. Treatment of polymers obtained with PdCl₂ led to the formation of Pd-containing polyheteroarylenes complexes. Pd^II bound to the polymers was reduced to Pd° by treatment with hydrogen or NaBH₄. Pd-polyheteroarylenes complexes obtained may be used as catalysts for the hydrogenation of alkenes and alkynes, for the selective hydrogenation of the triple bonds of unsaturated hydrocarbons in the presence of double bonds etc. Of especially great interest is the utilization of Pd-polybenzimidazole as catalyst for carbonylation of nitrobenzene and different halogen-substitited nitrobenzenes in the presence of alcohols leading to the formation of carbamates.     

Hydrogenation of olefins by π-arene ruthenium complexes : A role of π-arene ligand in catalytic activity

The divalent ruthenium complexes bearing benzene, mesitylene triphenylbenzene as a π-ligand were prepared and their catalytic activity for olefin hydrogenation was examined. They showed activity in the presence of a small amount of base. Particularly, the complex with triphenylbenzene was found to have extremely high activity. Discussion here is on a role of a π-arene ligand in the activity.     

Synthesis and catalytic activity of binuclear titanium imido complexes

Treatment of the N-P ligand ArPN(SiMe3)2 with TiCl4 affords the imido-bridged binuclear titanium complex [TiCl2(THF)(micro-NArP)]2 (ArP = m-C6H4PR2) which reacts with Ni(0) or Pd(ii) to give heterotrinuclear compounds, while activation with methylaluminoxane generates a new type of imido-based ethene polymerisation catalyst that is tolerant of -PR2 functional groups.     

Stereospecific synthesis and catalytic activity of L-histidylidene metal complexes

We report on the synthesis, metal coordination, and catalytic impact of histidylidene, a histidine-derived N-heterocyclic carbene (NHC) ligand. The histidinium salt 3, comprising methyl substituents at both heterocyclic nitrogens and protected at the C- and N-terminus of the amino acid, was rhodated and iridated by a transmetallation protocol using Ag(2)O. Ambient temperature and short reaction times were pivotal for full retention of configuration at the α-carbon. The stereospecificity of the reaction was conveniently probed by (31)P NMR spectroscopy after transmetallation with rhodium(I) and coordination of enantiopure (S)-Ph-binepine. The histidylidene rhodium complexes are highly efficient catalysts for the mild hydrosilylation of ketones. For the cationic complexes [Rh(cod)(histidylidene)(phosphine)](+), lowering the temperature shifted the rate-limiting step of the catalytic reaction to an earlier stage that is not enantioselective. Hence the asymmetric induction-which is governed by the chiral phosphine-did not improve at low temperature.     

Calculation of catalytic activity of transition metal complexes

A method is proposed for calculation of the catalytic activity of the complexes of transition metals. An effective Hamiltonian describing the behavior of the reagents in the presence of the catalyst is formulated, and a catalytic activity index tan2 is introduced. The isomerization of quadricyclane to norbornadiene is considered. It is shown that the index in the case of the catalytically active low-spin complex CoTPP is two orders of magnitude larger than in the case of the catalytically inactive high-spin complex MnTPP and the analogous Fe(III)TPP and MnPc complexes.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 24, No. 4, pp. 398–406, July–August, 1988.     

Synthesis and catalytic activity of histidine-based NHC ruthenium complexes

Main-chain C,N-protected histidine has been successfully alkylated at both side-chain nitrogens. The corresponding histidinium salt was metallated with ruthenium(II) by a transmetalation procedure, thus providing histidine-derived NHC ruthenium complexes. These bio-inspired complexes show appreciable activity in the catalytic transfer hydrogenation of ketones.     

Syntheses,structures and conformation of butylene-bridged butterfly-shaped Fe-S cluster complexes

Di-Grignard reagent BrMg(CH₂)₄MgBr can reductively cleave the S? S bond of two molecules of μ-S₂Fe₂(CO)₆ to give a double Fe-S cluster core intermediate A which contains a bridging butylene group. Reactions of A with alkyl halides, chloromethyl methyl ether, chloroketones, chloroesters or acyl chlorides in situ give ten structurally novel butylene-bridged double Fe-S core complexes B. For all the complexes B , the structures were confirmed by IR, ¹H NMR and elemental analysis while the conformers of some complexes B were deduced based on related ¹H NMR data. In addition, for Z = Me the structure and conformation of the complex B have been firmly established by an X-ray diffraction technique.