Conversion constants for redox potentials measured versus different reference electrodes in acetonitrile solutions at 25°C

Syntheses of new porous frameworks with specific pore size and type are of considerable interest for the appearance of zeolite-like functionalities. It is useful to take advantage of metal complex-assembled compounds because of designable frameworks, high microporosity, and flexible frameworks based on a variety of coordination geometries of metal centers and multifunctionality of bridging organic parts. Many recent reports show that the synthesis procedures are developing from serendipitious to rational level. Therefore, the micropore chemistry of metal complex-based assemblages is directed toward not only new frameworks but also functionalities such as gas and small molecule adsorption, ion exchange, heterogeneous catalysis, photo-chemical and -physical properties. For chemical and physical functionalities robustness of a framework is required even in the absence of guest molecules in the cavity. The stability is largely dependent on the structural dimensionality of the assemblages. A wide variety of st...

Functional Micropore Chemistry of Crystalline Metal Complex-Assembled Compounds

The chemistry of lithium enolates is used to demonstrate that complex structures held together by noncovalent bonds (“supramolecules”) may dramatically influence the result of seemingly simple standard reactions of organic synthesis. Detailed structural data have been obtained by crystallographic investigations of numerous Li enolates and analogous derivatives. The most remarkable features of these structures are aggregation to give dimers, tetramers, and higher oligomers, complexation of the metal centers by solvent molecules and chelating ligands, and hydrogen-bond formation of weak acids such as secondary amines with the anionoid part of the enolates. The presence in nonpolar solvents of the same supramolecules has been established by NMR-spectroscopic, by osmometric, and by calorimetric measurements. The structures and the order of magnitude of the interactions have also been reproduced by ab-initio calculations. Most importantly, supramolecules may be product-forming species in synthetic reactions of Li enolates. A knowledge of the complex structures of Li enolates also improves our understanding of their reactivity. Thus, simple procedures have been developed to avoid complications caused by secondary amines, formed concomitantly with Li enolates by the common methods. Mixtures of achiral Li enolates and chiral Li amides can give rise to enantioselective reactions. Solubilization by LiX is observed, especially of multiply lithiated compounds. This effect is exploited for alkylations of N-methylglycine (sarcosine) CH2 groups in open-chain oligopeptides. Thus, the cyclic undecapeptide cyclosporine, a potent immunosuppressant, is converted into a THF-soluble hexalithio derivative (without epimerization of stereogenic centers) and alkylated by a variety of electrophiles in the presence of either excess lithiumdiisopropyl amide or of up to 30 equivalents of lithium chloride. Depending on the nature of the LiX additive, a new stereogenic center of (R) or (S) configuration is created in the peptide chain by this process. A structure-activity correlation in the series of cyclosporine derivatives thus available is discussed.

Structure and Reactivity of Lithium Enolates. From Pinacolone to Selective C‐Alkylations of Peptides. Difficulties and Opportunities Afforded by Complex Structures

The effect of structural parameters on the exchange coupling constant of the title complexes of Cu(II), Ni(II), and Mn(II) is studied by means of density functional calculations on model compounds....

Magnetic Coupling in End-On Azido-Bridged Transition Metal Complexes: A Density Functional Study

Structural and functional evolution of metallacrowns.

A number of palladium(II) and platinum(II) bis-chelates have been prepared which contain one kind of symmetric or unsymmetric β-diketonate anions, or involve two different β-diketonate anions. Existence of the cis and trans isomers in solution of the binary chelates of unsymmetric β-diketones was confirmed by 1H and 13C NMR spectroscopy. Geometrical isomerization of the palladium(II) complexes to attain equilibrium in solution is fast, while the platinum(II) complexes are quite inert. The mixed-ligand chelates are stable in solution, showing no sign of disproportionation. The isomeric pairs of bis(1-phenyl-1,3-butanedionato)palladium(II), bis(2,4-hexanedionato)palladium(II), and bis(1,1,1-trifluoro-2,4-pentanedionato)platinum(II) were isolated, and molecular structure of the cis isomer of the first complex was determined by X-ray analysis.

Bis(β-diketonato)-palladram(II) and -platinum(II) Complexes

Synthesis and solution behavior of mononuclear palladium(II) and platinum(II) complexes containing pyridine-2-thiolate as a ligand. Crystal structure of chloro(pyridine-2-thiolato)- (triphenylphosphine)palladium(II)

Mixed-valence complexes of the type [CoII(µ-SO3)2(µ-L)2CoIII2(H2O)n(ROH)2–n](n= 0, 1, or 2; R = Me or Prn) have been prepared and characterized, where the deprotonated Schiff-base ligands L2– are either symmetrical, such as N,N′-ethylenebis(salicylideneiminate)(salen), N,N′-ethylenebis(α-methylsalicylideneiminate)(α,α′-Me2-salen), propane-1,3-diylbis(salicylideneiminate)(salpd), and propane-1,3-diylbis(α-methylsalicylideneiminate)(α,α′-Me2-salpd), or unsymmetrical such as propane-1,3-diyl(α-methylsalicylideneiminate)(salicylideneiminate)(α-Me-salpd). An X-ray structure determination of [COII(µ-SO3)2(µ-α,α′Me2-salpd)2CoIII2(PrnOH)2]·2PrnOH showed the presence of bridging phenolic oxygens and sulphite ions. The mixed-valence state CoIII(S= 0)–CoII(S=)–CoIII(S= 0) in these trinuclear complexes has been demonstrated by cryomagnetic measurements because the effective magnetic moments (4.40–5.00) at room temperature correspond to the monomeric complex of a cobalt(II) ion in a high-spin state. Down to 77 K, no spin-exchange interaction was observed between the cobalt(III) and cobalt(II) ions. I.r. spectra and thermal gravimetric-differential thermal analysis data have been obtained and discussed with regard to the co-ordination modes of the solvent molecules water, methanol, ethanol, and propan-1-ol.

Mixed oxidation state trinuclear cobalt complexes with bridging sulphito and Schiff-base ligands. Part 1. Preparation of the complexes [CoII(µ-SO3)2(µ-L)2COIII2(ROH)2](L = Schiff base anion, R = alkyl) and structure determination of [CoII(µ-SO3)2(µ-α,α′-Me2-salpd)2CoIII2(PrnOH)2]·2PrnOH

Synthesis and X-ray structures of octanuclear silver(I) cluster [Ag8(μ6-S){S2P(OC2H5)2}6] and its copper(I) analogue [Cu8(μ8-S){S2P(OC2H5)2}6]

A new complex, aquaoxo[N-(2-pyridylmethyl)iminodiacetato]vanadium(IV) dihydrate [VO(pmida)(H2O)]·2H2O has been synthesized and its crystal structure determined by the X-ray method. The triclinic crystals obtained from water or aqueous ethanol solution are twinned and contain 2 mol of lattice water. The unit cell contains four formula units and the structure was analyzed on the assumption that the space group is P\bar1. The positional and thermal parameters were refined to R=0.115. The vanadium atom has a distorted octahedral coordination and deviates by 0.39 A from the equatorial plane, which is composed of two cis carboxylate oxygens, a water molecule and the pyridine nitrogen. Vanadyl oxygen and tertiary nitrogen occupy the axial sites. Absorption spectra indicated that the structure is maintained in an aqueous solution of pH 3.0 to 4.9. This geometrical isomer seems to be formed selectively in an aqueous medium.

Keiji Matsumoto

Papers

Bis(β-diketonato)-palladram(II) and -platinum(II) Complexes

Synthesis and solution behavior of mononuclear palladium(II) and platinum(II) complexes containing pyridine-2-thiolate as a ligand. Crystal structure of chloro(pyridine-2-thiolato)- (triphenylphosphine)palladium(II)

Mixed oxidation state trinuclear cobalt complexes with bridging sulphito and Schiff-base ligands. Part 1. Preparation of the complexes [CoII(µ-SO3)2(µ-L)2COIII2(ROH)2](L = Schiff base anion, R = alkyl) and structure determination of [CoII(µ-SO3)2(µ-α,α′-Me2-salpd)2CoIII2(PrnOH)2]·2PrnOH

Synthesis and X-ray structures of octanuclear silver(I) cluster [Ag8(μ6-S){S2P(OC2H5)2}6] and its copper(I) analogue [Cu8(μ8-S){S2P(OC2H5)2}6]

Synthesis and structure of a hexa-coordinated vanadium(IV) complex aquaoxo[N-(2-pyridylmethyl)iminodiacetato]vanadium(IV) dihydrate.