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With the goal of understanding how the nature of the tridentate macrocyclic supporting ligand influences the relative stability of isomeric mu-eta 2:eta 2-peroxo- and bis(mu-oxo)dicopper complexes, a comparative study was undertaken of the O2 reactivity of Cu(I) compounds supported by the 10- and 12-membered macrocycles, 1,4,7-R3-1,4,7-triazacyclodecane (R3TACD; R = Me, Bn, iPr) and 1,5,9-triisopropyl-1,5,9-triazacyclododecane (iPr3TACDD). While the 3-coordinate complex [(iPr3TACDD)Cu]SbF6 was unreactive with O2, oxygenation of [(R3TACD)Cu(CH3CN)]X (R = Me or Bn; X = ClO4- or SbF6-) at -80 degrees C yielded bis(mu-oxo) species [(R3TACD)2Cu2(mu O)2]X2 as revealed by UV-vis and resonance Raman spectroscopy. Interestingly, unlike the previously reported system supported by 1,4,7-triisopropyl-1,4,7-triazacyclononane (iPr3TACN), which yielded interconverting mixtures of peroxo and bis(mu-oxo) compounds (Cahoy, J.; Holland, P. L.; Tolman, W. B. Inorg. Chem. 1999, 38, 2161), low-temperature oxygenation of [(iPr3TACD)Cu(CH3CN)]SbF6 in a variety of solvents cleanly yielded a mu-eta 2:eta 2-peroxo product, with no trace of the bis(mu-oxo) isomer. The peroxo complex was characterized by UV-vis and resonance Raman spectroscopy, as well as an X-ray crystal structure (albeit of marginal quality due to disorder problems). Intramolecular attack at the alpha C-H bonds of the substituents was indicated as the primary decomposition pathway of the oxygenated compounds through examination of the decay kinetics and the reaction products, which included bis(mu-hydroxo)- and mu-carbonato-dicopper complexes that were characterized by X-ray diffraction. A rationale for the varying results of the oxygenation reactions was provided by analysis of (a) the X-ray crystal structures and electrochemical behavior of the Cu(I) precursors and (b) the results of theoretical calculations of the complete oxygenated complexes, including all ligand atoms, using combined quantum chemical/molecular mechanics (integrated molecular orbital molecular mechanics, IMOMM) methods. The size of the ligand substituents was shown to be a key factor in controlling the relative stabilities of the peroxo and bis(mu-oxo) forms, and the nature of this influence was shown by both theory and experiment to depend on the ligand macrocycle ring size.

A crystalline pentahydrate and a crystalline 8/3 hydrate of nedocromil calcium (NC) were prepared. The relationships between these solid phases and the nature of the water interactions in their structures were studied through characterization by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), Karl Fischer titrimetry (KFT), hot-stage microscopy (HSM), ambient- or variable-temperature powder X-ray diffraction (PXRD), Fourier-transform infrared (FTIR) spectroscopy, solid-state nuclear magnetic resonance (SSNMR) spectroscopy, water uptake at various relative humidities (RH), intrinsic dissolution rate (IDR) and solubility measurements. The solubility and intrinsic dissolution rate of the pentahydrate in water at 25 degrees C are approximately 17% greater than the corresponding values for the 8/3 hydrate, corresponding to a greater Gibbs free energy of only 380 J.mol-1 (91 cal.mol-1) for the pentahydrate. The results of DSC, TGA, and FTIR and SSNMR spectroscopy indicate that the water of hydration is more loosely bound in the pentahydrate than in the 8/3 hydrate. On increasing the temperature in open-pan DSC and TGA, the water in the pentahydrate is released in four steps (three steps in crimped pans), whereas the water in the 8/3 hydrate is released in three steps (three steps also in crimped pans). These three stepwise dehydrations are fundamentally explained by their different water environments in the crystal structure of the 8/3 hydrate, which was determined by single-crystal XRD [crystal data: triclinic, space group P1, a = 13.2381(3) A, b = 13.3650(2) A, c = 17.8224(2) A, alpha = 68.202(1) degrees, beta = 86.894(1) degrees, gamma = 82.969(1) degrees, Z = 6]. The asymmetric unit contains three nedocromil anions and three calcium cations associated with eight water molecules. The nedocromil anions act as polyfunctional ligands to the Ca2+ ions, coordinating through both the carbonyl oxygen and the carboxylate oxygen atoms. The molecular conformations of the three nedocromil anions in the asymmetric unit are almost identical. However, the crystal structure contains two different calcium environments, one of which has the Ca2+ ion hydrated by four water molecules in the equatorial plane and by two carbonyl oxygens in its axial coordination sites. In the second environment, the Ca2+ ion has four carboxylate oxygen atoms in its equatorial plane and two water molecules in its axial coordination sites. Two of the carboxylate ligands are twisted out of the tricyclic ring, and the other two carboxylate ligands are nearly coplanar with the tricyclic ring. All of the eight water molecules in the 8/3 hydrate are linked to calcium and carboxylate ions and none are linked to other water molecules.

Solventothermal reactions of nickel acetate tetrahydrate with 1,2-dicyanobenzene in methanol and ethanol yield novel complexes in which nickel atoms are coordinated by modified phthalocyanine ligands with inner rings bearing methoxy and ethoxy substituents, respectively.

A key requirement for the generation of active copper catalysts for olefin aziridination has been identified by examination of a copper(II) complex supported by a new tridentate, mer-coordinating, pyridyl-appended diazacyclooctane ligand. Combined structural, spectroscopic, and electrochemical studies suggest that the high catalytic reactivity of complex 4 (shown) is rooted in facile access to an equatorial coordination site, occupied by a labile trifluoroacetate ligand in its X-ray crystal structure.

Chiral 12-metallacrown-4 complexes can now be obtained in high yield using resolved β-phenylalanine hydroxamic acids as organic scaffolding. These new copper(II) compounds bear a striking resemblance based on size and shape to Cu(II) tetraphenylporphyrin. This suggests that metallacrowns may be useful alternatives to metalloporphyrins in future applications which require high metal densities and well-defined chiral centers.

Oxygenation at the methyl instead of the usually more reactive methine position of a ligand isopropyl substituent occurred upon treatment of [(LCu)2(μ-η2:η2-O2) (L = 1,4,7-triisopropyl-1,4,7-triazacyclononane) with 2,4-di-tert-butylphenol at −78 °C during purging with O2. Confirmation of this unexpected regioselectivity was obtained from the X-ray structure of the shown bis(μ-alkoxo)dicopper(II) compound, which was derived from the initial reaction product, a unique bis(μ-alkylperoxo)dicopper(II) species.

The first examples of mononuclear nitrogen/sulfur-ligated Co(II) alkoxide complexes, species of relevance to a reactive intermediate observed for Co(II)-substituted liver alcohol dehydrogenase, have been isolated and characterized by multiple methods including X-ray crystallography, EPR, paramagnetic 1H NMR, and cyclic voltammetry.

Despite its prevalence in transition metal chemistry in general, to our knowledge the doubly-bridged M{sub 2}({mu}-SR){sub 2} motif is unknown for M = Cu(II), presumably because of the tendency for operation of eq 2Cu(II) + 2SR{sup -1} {yields} 2Cu(I) + RSSR, for which the appropriate stoichiometry would be provided in attempted assembly reactions. Herein we report the use of a new, sterically hindered ligand for the isolation of the first example of such a complex, which has been subjected to structural investigations oriented toward relating its properties to those of the CcO and N{sub 2}OR electron transfer sites. 21 refs., 2 figs.

This paper reports the isolation, spectroscopic and theoretical characterization, and C-H bond activation chemistry of a new species derived from the reaction of a Cu(I) complex with dioxygen. The proposed [Cu{sub 2}({mu}-O){sub 2}]C{sup 2+} core of this molecule is unprecedented in copper chemistry and may be viewed as a possible intermediate in oxidation reactions catalyzed by multicopper enzymes and small-molecule catalysts. 18 refs., 2 figs.

The central role of the binding and/or activation of dioxygen by copper(1) ions in a wide rangeof important processes in biology and catalysis has led to intense interest in the synthesis, characterization, and examination of the reactivity of Cu,02 complexes.' Relatively few such complexes have been definitively identified, however, and only two, [((TMPA)Cu)2(02)] (PF&233 and [ (TpiPr2Cu)2(O,)] ,2v4 have been characterized structurally by X-ray crystallography. The former complex contains a transp-1,2-peroxo ligand, while the latter has a planar dicopper(I1)p-$$-peroxo core that accurately models the dioxygen adduct of hemocyanin ( H c ) . ~ Despite extensive studies of the reaction pathways followed by these and other less well-defined Cu/02 adducts in synthetic and biological systems, our understanding of the relationship between their structural features and their reactivity with substrates remains rudimentary.Iv6 In particular, insight into the mechanistic details of aliphatic hydrocarbon oxidations that involve Cu/02 species in proteins, such as those catalyzed by dopamine 6-monooxygenase (DPM),7 peptidylglycine a-amidating enzyme (PAM)! and particulate methane monooxygenase (pMM0),9 has been limited by the relatively small number of synthetic copper-dioxygen complexes available for study and their general lack of reactivity with aliphatic C-H bonds. Here we report the preparation of a new dicopper(I1)p-g2:q2-peroxo complex and demonstrate unequivocally the cleavage of an sp3 C-H(D)bond by the Cu202 unit.1° Treatment of solutionsof [ L C U ( C H ~ C N ) ] C F ~ S O ~ (L = 1,4,7triisopropyl1,4,7-tria~acyclononane)~~J~ in CH2Cl2 or acetone with dry O2 at -78 OC resulted in the formation of red-brown [ ( L C U ) ~ ( O ~ ) ] (CF3S03)2 (Scheme 1). The adduct was not perturbed by an N2 purge or application of vacuum at -78 OC, suggesting that 0 2 binding is essentially irreversible a t this temperature. Assignment of a dicopper(II)-p-$:q2-peroxo structure to the product is based on (i) manometric data [Cu:02 = 2.2(2):1]; (ii) its UV-vis spectrum, which contains 0z2+ Cu(11) charge transfer bands [Figure 1; A, , = 365 (t l l 000 M-i

In a reaction relevant to environmetally important processes carried out by copper-containing enzymes and heterogeneous catalysts, copper(I) complexes of 1,4,7-triisopropyl-1,4,7-triazacyclononane dissolved in alcohols (e.g. benzyl alcohol) efficiently promote the reduction of NO to N2O by the solvent at room temperature, yielding the respective carbonyl compounds (e.g. benzaldehyde).