Symmetry Numbers of Activated Complexes

The conventional symmetry numbers σ_≠~' of activated complexes may lead to error in the rate constant expression of transition state theory, whereas the statistical factor ι~≠ or ι may violate the principle of detailed balance. A mathematically precise definition of the symmetry number σ_≠ of activated complex is given, i.e. σ_≠=_iN_4(?)/m, m is the number of physically distinct configurations of labelled transition state and N_i is the identical atoms in the activated complex. The identical atoms must belong to the same molecule of reactants and products. The present symmetry numbers σ_≠ of activated complexes assure not only obtaining correct rate constant expressions but also obeying the principle of detailed balance. It can be used with the statistical factor ι to construct the structures of transition states for unimolecular and bimolecular exchange reactions.     

Cleavage of Nucleotides by Lanthanide Metal Complexes

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Lanthanide Complexes for Oligomerization of Phenyl Isocyanate

IntroductionThestudyonthereactivitiesoflanthanidecomplexesto wardisocyanateshasattractedmuchattention .Ithasbeenre portedthatlanthanidealkoxides,1anddivalentdiaza pentadi enyllanthanidecomplexes2 canbeusedasthesinglecompo nentinitiatorsforisocyanatespolymerization .Recentlyourre searchgrouphasalsofoundthatlanthanoceneamide ,3diva lentaryloxideofsamarium4 ,5anddivalentsamarocene6 areallactivefortheoligomerizationofphenylisocyanate,andtheactivespeciesforthesethreesystemswereallsuccessfullyisolat…     

Syntheses and Crystal Structures of Hg(Ⅱ) and Ag(Ⅰ) Complexes Containing 2-Acetylpyridine-paminobenzoylhydrazone Ligand

The two complexes [HgI_2L](DMF)(1) and [AgL_2](ClO_4)(CH_3CN)(2) were synthesized from the reaction of Schiff base ligand(2-acetylpyridine-p-aminobenzoylhydrazone)(L) with HgI_2 or AgClO_4 respectively. The compounds are characterized by ~1H NMR,FTIR and elemental analysis. The structures of the ligand and two complexes are measured via single-crystal X-ray diffraction. In these two complexes,the structures are both distorted triangular bipyramids with five-coordinated centers.     

DFT Study of Hydrogen-Bonded 1,3,5-Triazine-Water Complexes

The 1,3,5-triazine-water hydrogen bonding interactions have been investigated using the density functional theory B3LYP method and 6-31 ＋＋G^＊＊ basis, obtaining one, two and seven energy minima of the ground states for the 1,3,5-triazine-water, 1,3,5-triazine-（water）2 and 1,3,5-triazine-（water）3 complexes respectively. The fully optimized geometries and binding energies were reported for the various stationary points. The global minima of 1,3,5-triazine-（water）2 and 1,3,5-triazine-（water）3 complexes have a hydrogen bond N…H-O and a chain of water molecules, terminated by a hydrogen bond O…H-C. The binding energies are 13.38, 39.52 and 67.79 kJ/mol for the most stable 1,3,5-triazine-water, 1,3,5-triazine-（water）2 and 1,3,5-triazine-（water）3 complexes respectively, after the basis set superposition error and zero point energy corrections. The H-O symmetric stretching modes of water in the complexes are red-shifted relative to those of the monomer water. In addition, the NBO analysis indicates that inter-molecule charge transfer is 0.02145 e, 0.02501 e and 0.02777 e for the most stable 1 ： 1, 1 ： 2 and 1 ： 3 complexes between 1,3,5-triazine and water, respectively.     

Synthetic and Structural Studies of N-Heterocyclic Carbene Complexes of Nickel

Transition metal complexes of stable N-heterocyclic carbenes have recently gained increasing attention as pre-catalysts for a number of important reactions primarily based on the analogy between N-heterocyclic carbenes and strong ó-donating tertiary phosphines,[1] Although a large number of transition-metal carbene complexes have been reported, very few incorporate chelating carbenes were reported.[2,3] Therefore, we have set out to prepare and study transition-metal compounds with chelating di-N-heterocyclic carbenes, and we now report new dicationic tetra(carbine)nickel(Ⅱ) complexes in this class (Scheme 1). Their structures have been determined by single-crystal X-ray diffraction studies (Figure 1).     

Spectral Properties of Extracted Complexes of MetalPicrates with Crown Ethers

The investigation on UV-visible spectra of species formed by extracting some metal picrates with benzo-15-crown-5(B15C5) and dibenzo-18-crown-6(DB18C6) verified that there are some interactions of picrate anion with K , Na and rare earth ions in loaded organic phase. By the study of the charge transfer band and absorption spectra of picrate anion, it can be determined whether an ion pair has been formed and either a 1 : 1 contact ion pair or a 1 : 2 crown-separated ion pair involved in organic phase can be distinguished for an ion-pair extraction.     

Complexes of 2,2′-bipyrimidine with some lanthanides

Complexes of the lanthanide ions, La³⁺, Eu³⁺, Ce³⁺, Yb³⁺ and Ho³⁺ as well as that of Y³⁺ with the ligand 2,2′-bipyrimidine have been prepared and their physico-chemical properties studied.     

Selective Hydrogenation of Avermectin Catalyzed by Iridium-Phosphine Complexes

A series of new iridium complexes, IrCl（COD）（TMOPP） （1） [COD=1,5-cyclooctadiene, TMOPP=tris（4- methoxyphenyl）phosphine], IrCl（COD）（TFMPP） （2） [TFMPP = tris（4-trifluoromethylphenyl）phosphine], IrCl（COD）（BDNA） （3） [BDNA= 1,8-bis（diphenylphosphinomethyl）naphthalene], IrCl（COD）（BISBI） （4） [BISBI= 2,2＇-bis（diphenylphosphinomethyl）biphenyl] and IrCl（COD）（BDPB） （5） [BDPB= 1,2-bis（diphenylphosphinomethyl）benzene], were synthesized and characterized by NMR spectra and elemental analyses. In order to obtain the relationships between complex structures and their catalytic properties, IrCl（COD）（DPPM） （6） [DPPM = bis（diphenylphosphino）methane], IrCl（COD）（DPPE） （7） [DPPE= 1,2-bis（diphenylphosphino）ethane], IrCl（COD）（DPPP） （8） [DPPP=1,3-bis（diphenylphosphino）propane] and IrCl（COD）（TPP） （9） [TPP=triphenylphosphine], were also synthesized according to the reported methods. The hydrogenation results showed that the low electronic density at the central metal was favorable to increase the catalytic activity for the hydrogenation of avermectin, but decrease the selectivity to ivermectin. The complex with a large chelating ring and a bulky chelating backbone would easily cause the cleavage of C-O bond in avermectin to give a byproduct avermectin aglycon.     

Octahedral Complexes in the Polymerization of α-Olefins

Summary : A series of dimethyl titanium benzamidinate complexes has been prepared containing various functional groups at the aromatic ring. These functional groups were selected to study their electronic or steric effects at the cationic metal center in the polymerization of propylene. Quantitative structure activity relationship (QSAR) studies showed that a linear relationship is observed only for the Taft Parameter (Es). Mono- and bis-benzamidinate complexes were found to produce similar polymers indicating that alike active species are obtained regardless of the starting complex. Deuterium labeled 2-D-propene showed that a new epimerization mechanism for this type of complexes is operative.     

Synthesis of Terminal Amino Substituted Cyclopentadienyl Titanium Complexes

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Synthesis,Structure and Reactivity of Lanthanocene Complexes

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Freeze-Dried Complexes of Furosemide with β-Cyclodextrin Derivatives

A freeze-drying method was used to prepare complexes of furosemide (guest) with three derivatives of -cyclodextrin (hosts) in different molecular ratios in order to increase the aqueous solubility and rate of dissolution of the drug, and also to study the influence of this method on different parameters of the guest and the host, such as the diffusion rate constant and the partition coefficient, and additionally the surface tension activity of the host (if any). The hosts were found to have significant, increasing effects on the solubility and the rate of dissolution of furosemide. X-ray diffraction confirmed the host–guest interaction, in support of the earlier results. The freeze-drying method increased the diffusion rate of the drug in complex form, while the partition coefficient varied with the type of -cyclodextrin in the product. It is well known that CD derivatives are highly surface active which gives rise to their hemolytic action. Our observations showed that their presence with furosemide in complex form might decrease (if not diminish) the hemolytic action.     

Inclusion Complexes of Conjugated Nitroolefins in β-Cyclodextrin

Physical studies such as Powder X-ray,FT-IR, UV, ¹H and ¹³C NMR clearly identifya 1 : 1 inclusion complex formed between-cyclodextrin and nitroolefins such as-nitrostyrene, 1-nitrocyclohexene in thesolid state as well as in solution. The olefins lieshallow inside the cavity leaving the nitro groupoutside the torus. It has been found that the complexis capable of reacting with a-phenyl-N-p-methylphenyl nitrone ina 1,3-dipolar cycloaddition with excellent rateacceleration and regioselection. The NaBH₄reduction of the complex in the solid state leads tothe corresponding nitroalkane.     

The Solvation of Carbenes: π and O-Ylidic Complexes of p-Nitrophenylchlorocarbene

p-Nitrophenylchlorocarbene (PNPCC) was studied by laser flash photolysis with UV-vis detection in solution at ambient temperature. The π → p (316 nm) and σ → p (628 nm) absorptions of PNPCC were replaced in π- or O-donor solvents by absorptions due to π- or O-ylidic complexes or O-ylides. Donors included anisole, 1,3-dimethoxybenzene, 1,3,4,5-tetramethoxybenzene, diethyl ether, 18-crown-6, and dibenzo-18-crown-6. Suggestive evidence was also obtained for weak π-complexation of PNPCC by benzene. Computational studies aided in understanding the carbene complex and O-ylide absorption spectra, and they provided structures and energetics for these species.     

Homocoupling of Aryl Iodides Catalyzed by Cyclopalladated Complexes of Tertiary Arylamines

Homocoupling of aryl iodides catalyzed by cyclopalladated complexes of tertiary arylamines gives symmetric biaryls with good yields in DMA or ionic liquid [Bmim]BF4. This catalytic alternative of the Ullmann reaction has proved to be sensitive to both electronic and steric factors of substrates.     

Syntheses and Crystal Structures of Two New Ag(Ⅰ) Complexes with Betaine Derivative: Structure Changes via Metal-to-ligand Ratio

Two new Ag(I) complexes {Ag2(L)(NO3)(H2O)}n(1) and {Ag(L)}n·nH2O(2) have been synthesized via the reaction of silver nitrate and betaine derivative 1-carboxymethylpyridinium-3-carboxylate(L) by only changing the metal-to-ligand ratio. The results of X-ray crystallographic analysis indicate that complexes 1 and 2 both crystallize in the monoclinic space group P21/c with a = 5.0809(14), b = 17.390(5), c = 13.399(4), β = 91.677(5)o, V = 1183.4(6)3, Z = 4, Mr = 475.90, Dc = 2.671 g/cm3, F(000) = 912, μ = 3.352 mm-1, S = 1.259, the final R = 0.0320 and wR = 0.0831 for 2036 observed reflections with I 2σ(I) for 1 and a = 12.180(2), b = 5.0283(10), c = 14.396(3), β = 94.87(3)o, V = 878.5(3)3, Z = 4, Mr = 306.02, Dc = 2.314 g/cm3, F(000) = 600, μ = 2.294 mm-1, S = 1.053, the final R = 0.0283 and wR = 0.0684 for 2011 observed reflections with I 2σ(I) for 2. Complexes 1 and 2 both feature a unique 2D structure. For 1, the 2D undulated network consists of 1D infinite helical chains running parallel to the b axis, while for 2, the 2D network is made up of 1D tubes along the b axis. Moreover, the Ag…Ag interactions in complexes 1 and 2 are also discussed.     

The Synthesis of Glycosyl Phosphite-Pt（Ⅱ） Complexes

Ethylene glycol phosphorochloridite 1 or catechol phosphorochloridite 2 reacted with isopropylidene derivatives of D-glucose, D-galactose, D-mannose and D-fructose, a series of glycosyl phosphites were obtained. These glycosyl phosphites form optically active complexes with simple Pt (Ⅱ) salts. Pt (Ⅱ) is coordinated to the phosphorus atom, most of the metal complexes are quite stable.     

Studies on Electrophilic Substitution of Quasi-Aromatic Metal Ion Complexes

The electrophilic substitution reaction occurring to the chelate ring of the complexes could be regarded as an indication of quasi-aromaticity of the ring systems, no catalyst was used and only triethylamine was employed, implying that the aroylating agents with different p-substituents are polarized enough to be effective electrophiles to attack the methine carbon of the electron-rich substrate 1. This property is probably the clue to polarization of the ligand electrons by the nickel( Ⅱ ) ion and to the participation of the nickel( Ⅱ ) in the π-bond systems of the two coordinated conjugated rings. The linearity relationship between vd-d maxima, E1/2OX(1) and σp are obtained, respectively. The electronic environment of central metal ion as well as the aromaticity of the ring system are affected by the electronic properties of the p-substituents. A comparison of the electrochemical results with each other showed .that when the electronegativity of the substituent was higher, the oxidation(Ni2+/Ni3+)