Multimetallic synergic sedation of a labile sodium atrane: synthesis and characterization of a tetranuclear sodium atrane cation complex

A series of sodium and aluminum atrane complexes of Na(3)L(THF)(5) (1), [AlLMe][Na(4)L(THF)(6)] (2), AlL(THF) (3), AlNaLMe(THF)(2) (4), and AlNaLOBn(THF)(2) (5), wherein L = tris(2-oxy-4,6-di-tert-butyl-benzyl)amine, were synthesized and characterized by NMR, X-ray crystallography, and elemental analysis. The trinuclear sodium atrane complex of Na(3)L(THF)(5) (1) is labile at room temperature; however, the tetranuclear sodium atrane cation in complex 2 can be stabilized by a multimetallic synergetic effect due to a firm interaction ring of -[Na-O-benzene](3)-. Complex 2 is also the first example of a sodatrane and alumatrane ion-paired complex in which both the cationic and anionic moieties contain an atrane ligand.     

Structural characterization of a new cobalt(II) complex of 1-benzyl-5-methyl-1<Emphasis Type="Italic">H</Emphasis>-imidazole

The preparation of a cobalt(II) chloride complex with a N-donor ligand 1-benzyl-5-methyl-1H-imidazole of formula [CoCl₂(1-benzyl-5-methyl-1H-imidazole)₂] is described. The isolated complex was characterized by UV, IR spectroscopy and crystallographic studies. Single crystal X-ray diffraction analysis of the complex reveals its monomeric tetra-coordinated nature. The coordination polyhedron around the cobalt center can be described as a quasi-regular tetrahedron. The Co–N distances for this compound are 2.0111(17) Å and 2.0118(17) Å, while the Co–Cl distances are 2.2582(7) Å and 2.2549(7) Å. The crystal packing can be described as layers parallel to (101) plane alternating along the b axis, and it is stabilized by π–π stacking between the imidazole and phenyl rings. The shortest centroid–centroid distance is 3.6002(14) Å.     

Frequency measuring system using mirror gap stabilized Fabry-Perot interferometer

The mirror gap of a Fabry-Perot interferometer was stabilized with two laser diodes; one locked to the line frequency 385,243,555.14445 MHz of the F=3<--1 in 5D(3/2)<--5S(1/2) (87Rb) and the other to the 385,284,566.3663 MHz of the F=4<--2 in 5D(5/2)<--5S(1/2) (87Rb) [Opt. Commun. 102 (1993) 432]. The length of the mirror gap was adjusted to generate the zero-cross points simultaneously at both of the two line positions. The fringe signals obtained from an interferometer thus stabilized can be used as frequency markers having accuracies of the order of 10(10) depending on the finesse of the interferometer used. Based on measurement using Cs D1 hyperfine lines reported by Udem et al. [Phys. Rev. Lett. 82 (1999) 3568], the uncertainty of markers in the region 50 THz apart from the reference lines is +/- 5 MHz.     

A spectrophotometric and thermodynamic study of the charge-transfer complexes of iodine with 2-aminomethyl-15-crown-5 in chloroform and 1,2-dichloroethane solutions

Interaction of 2-aminomethyl-15-crown-5 (AM15C5) with iodine has been investigated spectrophotometrically in chloroform and 1,2-dichloroethane (1,2-DCE) solutions. The observed time dependence of the charge-transfer band and subsequent formation of I(3)(-) in solution were related to the slow transformation of the initially formed 1:1 AM15C5.I(2) outer complex to an inner electron donor-acceptor (EDA) complex, followed by fast reaction of the inner complex with iodine to form a triiodide ion. The pseudo-first-order rate constants were evaluated from the absorbance- and conductivity-time data. The stoichiometry and formation constants of the resulting EDA complexes have also been determined. Thermodynamic parameters, Delta H degrees and Delta S degrees , of the complexes have been determined from the temperature dependence of stability constants by Van't Hoff equation. The results indicate that iodine complexes of AM15C5 in both solvents are enthalpy stabilized but entropy destabilized. The influence of solvent properties on the kinetics and stability of the resulting charge-transfer complexes are discussed.     

含ONN席夫碱和2,2'-联吡啶的铜三元配合物的合成、晶体结构及电化学性质

合成了一个新颖的含ONN席夫碱配体N-水杨醛基-2-氨乙基苯并咪唑(HL),并在甲醇体系中合成了它的配合物ICu(L)(bipy)]ClO4(bipy为2,2'-联吡啶).利用X-射线单晶衍射法测定了配合物的晶体结构.配合物[Cu(L)(bipy)lClO4的晶体属于单斜晶系,C2/c空间群,a=2.585 5(8)nm,b=1.4355(5)nm,c=1.6242(5)nm,β=124.434(5)°,Z=8.在配合[Cu(L)(bipy)lClO4中,每个铜离子的配位数为5,分别和配体L的1个氧原子和2个氮原子及2,2'-联吡啶的2个氮原子配位,形成畸变的三角双锥配位环境.配合物[Cu(L)(bipy)]ClO4巾的氧键和π-π相互作用将配合物[Cu(L)(bipy)]ClO4连接成二维网络结构.用红外光谱、紫外-可见光谱对配合[Cu(L)(bipy)]ClO4进行了表征,并用循环伏安法对配合物进行了电化学性质的研究.     

Synthesis and characterization of a coordinated oxoborane: Lewis acid stabilization of a boron-oxygen double bond

The first example of a stable oxoborane monomer (LB=O) stabilized by complexation to AlCl3 has been prepared by the reaction of LAlCl2 with BCl3 followed by treatment with H2O in CH2Cl2 (L = [HC(CMe)2(NC6F5)2]). DFT calculations reveal that considerable boron-oxygen double bond character is retained in this complex.     

Synthesis, reactivity and applications of zinc-zinc bonded complexes

The discovery of decamethyldizincocene [Zn(2)(η(5)-Cp*)(2)] (Cp* = C(5)Me(5)), the first complex containing a covalent zinc-zinc bond, by Carmona in 2004 initiated the search for this remarkable class of compounds. Low-valent organozinc complexes can either be formed by ligand substitution reactions of [Zn(2)(η(5)-Cp*)(2)] or by reductive coupling reactions of Zn(ii) compounds. To the best of our knowledge, until now 25 low-valent Zn-Zn bonded molecular compounds stabilized by a variety of sterically demanding, very often chelating, organic ligands have been synthesized and characterized. There are two major reaction pathways of [Zn(2)(η(5)-Cp*)(2)]: it can either react with cleavage of the Zn-Zn bond or by ligand substitution. In addition, upon reaction with late transition metal complexes, [Zn(2)(η(5)-Cp*)(2)] was found to form novel intermetallic complexes with Cp*Zn and Cp*Zn(2) acting as unusual one-electron donor ligands. Very recently, the potential capability of [Zn(2)(η(5)-Cp*)(2)] to serve as a suitable catalyst in hydroamination reactions was demonstrated. Finally, the recent work on Cd-Cd bonded coordination compounds is reviewed.     

Complex Formation of Crown Ethers and Cations in Water–Organic Solvent Mixtures: Part XI. Effects of the Preferential Solvation of Benzo-15-Crown-5 and Acid-Base Properties of the Mixtures on the Thermodynamic Functions for Complex Formation of Benzo-15-Crown-5 with Na+ in Propan-1-ol–Water Mixtures at 298.15 K

The thermodynamic functions of complex formation of benzo-15-crown-5 ether (B15C5) and sodium cation (Na⁺) in the mixtures of propan-1-ol (PrOH) with water at 298.15 K have been calculated from experimental measurements. The equilibrium constants of B15C5/Na⁺ complex formation have been determined by conductivity measurements. The enthalpic effect of complex formation has been measured by a calorimetric method. The complexes are enthalpy stabilized but entropy destabilized in the PrOH–H₂O mixtures. The effects of preferential solvation of B15C5 by molecules of the organic solvent, solvation of the sodium cation, as well as the acid-base properties of propan-1-ol–water mixtures on the complex formation processes are discussed.     

Dynamic [2]catenanes based on a hydrogen bonding-mediated bis-zinc porphyrin foldamer tweezer: a case study

This paper describes the self-assembly of a new class of three-component dynamic [2]catenanes, which are driven or stabilized by intramolecular hydrogen bonding, coordination, and electrostatic interaction. One of the component molecules 2, consisting of an aromatic oligoamide spacer and two peripheral zinc porphyrin units, was designed to adopt a folded preorganized conformation, which is stabilized by consecutive intramolecular three-centered hydrogen bonds. Component molecule 3 is a linear secondary ammonium bearing two peripheral pyridine units, which was designed to form a 1:1 complex with 24-crown-8 (5). The 1H NMR and UV-vis experiments in CDCl3-CD3CN (4:1 v/v) revealed that, due to the preorganized U-shaped feature, 2 could efficiently bind 3 through the cooperative zinc-pyridine coordination to generate highly stable 1:1 complex 2.3. Adding 5 to the 1:1 solution of 2 and 3 led to the formation of dynamic three-component [2]catenane 2.3.5 as a result of the threading of 3 through 5. 1H NMR studies indicated that in the 1:1:1 solution (3 mM) [2]catenane 2.3.5 was generated in 55% yield at 25 degrees C. The yield was increased with the reduction of the temperature and [2]catenane could be produced quantitatively in a 1:1:2 solution ([2]=3 mM) at -13 degrees C. Replacing 3 with 1,2-bis(4,4'-bipyridinium)ethane (4) in the three-component solution could also give rise to similar dynamic [2]catenane 2.4.5 albeit in slightly lower yield.     

Synthesis,Structure and Property of a 1D Coordination Polymer [Mn{5-（NO2）sal}2（phen）]n with 5-Nitrosalicylate Ligand

A new coordination polymer [Mn{5-（NO2）sal}2（phen）]n （5-（NO2）sal = 5-nitrosalicylate, phen = 1,10-phenanthroline） was synthesized by a hydrothermal reaction and characterized by elemental analysis, IR and X-ray single-crystal diffraction. The title complex crystallizes in orthorhombic, space group Pbcn with α = 25.747（8）, b = 13.220（4）, c = 7.009（3） A, V= 2386（1）A^3, Z = 4, R = 0.0427 and wR = 0.0890. The 5-nitrosalicylate anions doubly bridge the Mn（Ⅱ） atoms to form a one-dimensional polymeric chain with repeated eight-membered ring units （Mn-O-C-O）2. The crystal structure is stabilized by intra- and interchain hydrogen bonding interactions. The cyclic voltammetric behavior of the title complex is also reported.     

Kinetico-mechanistic information about alkene hydroamination with aniline in bromide-rich ionic media: importance of solvolysis

The study of the [PtBr(4)](2-) reactivity with hexene and aniline in highly ionic (Bu(4)P)Br/CH(2)Br(2) media has been studied from a Kinetico-Mechanistic perspective. The results indicate bromide ion association to the square-planar starting material to produce a stable diamagnetic compound that can be described as an ion pair of a [PtBr(5)](3-) square-pyramidal complex stabilized by several phosphonium countercations. While this species reacts rapidly with aniline, producing the known square-planar complex [PtBr(3)(PhNH(2))](-) with release of the apical bromide of the square-pyramidal intermediate, the reaction with hexene, producing the square-planar [PtBr(3)(hexene)](-) complex, is much slower. The thermal and pressure activation parameters determined for these processes fully agree with the proposed reactivity. The gross features of the platinum-catalyzed hydroamination mechanism, occurring via much higher energy transition states, are not necessarily altered by these new findings, given the fact that all ligand exchange reactions occur with relatively low activation barriers. Nevertheless, the nature of the catalyst resting state needs revision as demonstrated. The importance of explicitly considering the solvent for reactions conducted in noninnocent highly organized media is also highlighted.     

Lewis acid stabilized methylidene and oxoscandium complexes

The methylidene scandium complex (PNP)Sc(mu3-CH2)(mu2-CH3)2[Al(CH3)2]2 (PNP = N[2-P(CHMe2)2-4-methylphenyl]2-) can be prepared from the reaction of (PNP)Sc(CH3)2 and 2 equiv of Al(CH3)3. The Lewis acid stabilized methylidenes candium complex has been crystallographically characterized, and its bonding scheme analyzed by DFT. In addition, we report preliminary reactivity studies of the Sc-CH2 ligand with substrates such as H2NAr and OCPh2. While the former results in an Br?nsted acid-base reaction, the latter reagent produces the olefin H2C CPh2 along with the novel oxoscandium complex (PNP)Sc(mu3-O)(mu2-CH3)2[Al(CH3)2]2, quantitatively.     

CARBONIUM CYCLIZATION--STUDIES ON LIGNANS CONTAINING THE DIBENZOCYCLOOCTADIENE SYSTEM.Ⅱ

The major products of carbonium cyclization of 1 are 2 and 3;2 is unstable and undergoes aerial oxidation to give 4.Asimilar product(6)from 5 is somehow stabilized by the extra ben-zoyloxy group(or OH)and can be stored without deterioration.     

Properties of a suggested commensurate monolayer solid of Kr/NaCl(001)

It is shown that a commensurate square monolayer solid of Kr/NaCl(001) can be stabilized with a model incorporating a rather large energy corrugation amplitude. Then a square bilayer is formed under a compression and preempts the formation of an incommensurate triangular monolayer lattice. The lattice dynamics of the commensurate monolayer may be complex, because the modeling admits the possibility that it has a (2 × 2) unit cell with four Kr atoms.     

On the formation of resonantly stabilized C5H3 radicals--a crossed beam and ab initio study of the reaction of ground state carbon atoms with vinylacetylene

The formation of polycyclic aromatic hydrocarbons in combustion environments is linked to resonance stabilized free radicals. Here, we investigated the reaction dynamics of ground state carbon atoms, C((3)P(j)), with vinylacetylene at two collision energies of 18.8 kJ mol(-1) and 26.4 kJ mol(-1) employing the crossed molecular beam technique leading to two resonantly stabilized free radicals. The reaction was found to be governed by indirect scattering dynamics and to proceed without an entrance barrier through a long-lived collision complex to reach the products, n- and i-C(5)H(3) isomers via tight exit transition states. The reaction pathway taken is dependent on whether the carbon atom attacks the π electron density of the double or triple bond, both routes have been compared to the reactions of atomic carbon with ethylene and acetylene. Electronic structure/statistical theory calculations determined the product branching ratio to be 2:3 between the n- and i-C(5)H(3) isomers.     

Bond‐Strengthening Backdonation in Aminoborylene‐Stabilized Aminoborylenes: At the Intersection of Borylenes and Diborenes

Singly NHC‐coordinated (aminoboryl)aminoborenium salts react with Na₂[Fe(CO)₄] to yield stable coordination complexes of aminoborylene‐stabilized aminoborylenes, which exhibit exceptional σ‐donor properties. Upon photolytic CO extrusion from the metal center, the diboron ligand adopts a novel η³‐BBN coordination mode, where bond‐strengthening backdonation from the metal center into the vacant B?B π‐orbital is observed. This bonding situation can be alternatively described as a Fe‐diaminodiborene complex. In a related reduction of CAAC‐stabilized (aminoboryl)aminoborenium with KC₈, the reduced species can be captured with nucleophiles to form three‐coordinate (diaminoboryl)borylenes, where both amino groups have migrated to the distal boron atom. Collectively, these reactions illustrate the isomeric flexibility imparted by amino groups on this reduced diboron system, thus opening multiple avenues of novel reactivity.     

New examples of metalloaromatic Al-clusters: (Al4M4)Fe(CO)3 (M = Li, Na and K) and (Al4M4)2Ni: rationalization for possible synthesis

Ab initio calculations reveal that all-metal antiaromatic molecules like Al4M4 (M = Li, Na and K) can be stabilized in half sandwich (Al4M4)Fe(CO)3 and full sandwich (Al4M4)2Ni complexes. The formation of the full sandwich complex [(Al4M4)2Ni] from its organometallic precursor depends on the stability of the organic-inorganic hybrid (C4H4)Ni(Al4Li4).     

16-electron elongated dihydrogen complex stabilized by agostic interaction

A 16-electron dicationic dihydrogen complex [Ru(eta2-H...H)(PP)2][OTf]2 [4; PP = (C6H5CH2)2PCH2CH2P(CH2C6H5)2] has been prepared and characterized by protonating the precursor hydride complex [Ru(H)(PP)2)][OTf] (2) using HOTf. The hydride and dihydrogen complexes are stabilized via agostic interaction of the ortho C-H fragment of the phenyl ring on the benzyl group. The intact nature of the H-H bond in this derivative was established from the short spin-lattice relaxation time and the observation of a substantial J(H,D) of 22.0 Hz for the HD isotopomer. The H-H bond distance calculated from J(H,D) is 1.05 A, which falls under the category of elongated dihydrogen ligands.     

Interplay between solvent and counteranion stabilization of highly unsaturated rhodium(III) complexes: facile unsaturation-induced dearomatization

Abstraction of the chloride ligand from the PCN-based chloromethylrhodium complex 2 by AgX (X=BF(4)(-), CF(3)SO(3)(-)) or a direct C-C cleavage reaction of the PCN ligand 1 with [(coe)(2)Rh(solv)(n)](+)X(-) (coe=cyclooctene) lead to the formation of the coordinatively unsaturated rhodium(III) complexes 3. Compound 3 a (X=BF(4)(-)) exhibits a unique medium effect; the metal center is stabilized by reversible coordination of the bulky counteranion or solvent as a function of temperature. Reaction of [(PCN)Rh(CH(3))(Cl)] with AgBAr(f) in diethyl ether leads to an apparent rhodium(III) 14-electron complex 4, which is stabilized by reversible, weak coordination of a solvent molecule. This complex coordinates donors as weak as diethyl ether and dichloromethane. Upon substitution of the BF(4)(-) ion in [(PCN)Rh(CH(3))]BF(4) by the noncoordinating BAr(f)(-) ion in a noncoordinating medium, the resulting highly unsaturated intermediate undergoes a 1,2-metal-to-carbon methyl shift, followed by beta-hydrogen elimination, leading to the Rh-stabilized methylene arenium complex 5. This process represents a unique mild, dearomatization of the aromatic system induced by unsaturation.     

Insights into the mechanism of N2O reduction by reductively activated N2O reductase from kinetics and spectroscopic studies of pH effects

Nitrous oxide reductase (N2OR) from Achromobacter cycloclastes (Ac) can be reductively activated with reduced methyl viologen over a broad range of pH. Activated Ac N2OR displays a complex activity profile as a function of the pH at which catalytic turnover is measured. Spectroscopic and steady-state kinetics data suggest that [H+] has multiple effects on both the activation and the catalytic reactions. These experimental results are in good agreement with previous theoretical studies, which suggested that the transition state is stabilized by H-bonding interactions between the active site and an N2O-derived intermediate bound to the catalytic CuZ cluster.