The activation of dioxygen by dopamine β-monooxygenase (DβM) and peptidylglycine α-hydroxylating monooxygenase (PHM) is postulated to occur at a copper site ligated by two histidine imidazoles and a methionine thioether, which is unusual since such thioether ligation is not present in other O 2 -activating copper proteins. In order to assess the possible role of the thioether ligand in O 2 activation by DβM and PHM, two new ligands comprising β-diketiminates with thioether substituents were synthesized and Cu(I) and Cu(II) complexes isolated. The Cu(II) compounds are monomeric and exhibit intramolecular thioether coordination. While the Cu(I) complexes exhibit a multinuclear topology in the solid state, variable temperature 1 H NMR studies implicate equilibria in solution, possibly including monomers with intramolecular thioether coordination that are structurally defined by DFT calculations. Low temperature oxygenation of solutions of the Cu(I) complexes generates stable 1:1 Cu/O 2 adducts, which on the basis of combined experimental and theoretical studies adopt side-on "η 2 " structures with negligible Cu-thioether bonding and significant peroxo-Cu(III) character. In contrast to previously reported findings with related ligands lacking the thioether group, however, purging the solutions of the thioether-containing adducts with argon results in conversion to bis(μ-oxo)dicopper(III) species. A role for the thioether in promoting loss of O 2 from the 1:1 Cu/O 2 adduct and facilitating trapping of the resulting Cu(I) complex to yield the bis (μ-oxo) species is proposed and the possible relevance of this role to that of the methionine in the active sites of DβM and PHM is discussed.

Copper(i) complexes with the beta-diketiminate ligands HC{C(R)N(Dipp)}{C(R')N(Dipp)}(-) (Dipp = C(6)H(3)(i)Pr(2-)2,6; L(1), R = CF(3), R' = CH(3); L(2), R = R' = CF(3)) have been isolated and fully characterized. On the basis of X-ray structural comparisons with the previously reported complex LCu(CH(3)CN) (L = HC{C(CH(3))N(Dipp)}(2)(-)), the ligand environments at the copper centers in the analogous nitrile adducts with L(1) and L(2) impose similar steric demands. L(1)Cu(CH(3)CN) reacts instantaneously at low temperature with O(2) to form a thermally-unstable intermediate with an isotope-sensitive vibration at 977 cm(-1) (928 cm(-1) with (18)O(2)), in accord with the peroxo O-O stretch associated with side-on coordination for LCu(O(2)). However, L(2)Cu(CH(3)CN) is unreactive toward O(2) even at room temperature. Evaluation of the redox potentials of the nitrile adducts and the CO stretching frequencies of the carbon monoxide adducts revealed an incremental adjustment of the electronic environment at the copper center that correlated with the extent of ligand fluorination. Furthermore, theoretical calculations (DFT, CASPT2) predicted that an increasing extent of Cu(ii)-superoxo character and end-on coordination of the O(2) moiety in the Cu/O(2) product (L(2) > L(1) > L) are accompanied by increases in the free energy for the oxygenation reaction, with L(2) unable to support a Cu/O(2) intermediate. Calculations also predict the 1 : 1 Cu/O(2) adducts to be unreactive with respect to hydrogen atom abstraction from hydrocarbon substrates on the basis of their stability towards both reduction and protonation.

Copper(I) complexes of a diketiminate featuring CF 3 groups on the backbone and dimethylphenyl substituents (4) and a nitroformazan (5) were synthesized and shown by spectroscopy, X-ray crystallography, cyclic voltammetry, and theory to contain Cu(I) sites electron deficient relative to those supported by previously studied diketiminate complexes comprising alkyl or aryl backbone substituents. Despite their electron poor nature, oxygenation of LCu(CH 3 CN) (L = 4 or 5) at room temperature yielded bis(hydroxo)dicopper(II) compounds and at − 80 °C yielded bis(μ-oxo)dicopper complexes that were identified on the basis of UV-vis and resonance Raman spectroscopy, spectrophotometric titration results (2:1 Cu/O 2 ratio), EPR silence, and DFT calculations. The bis (μ-oxo)dicopper complex supported by 5 exhibited unusual spectroscopic properties and decayed via a novel intermediate proposed to be a metallaverdazyl radical complex, findings which highlight the potential for the formazan ligand to exhibit 'non-innocent' behavior.

The syntheses, characterization, epsilon-caprolactone (CL) polymerization activity, and kinetics investigation of two zinc(II) bis(phenolato)amine complexes L2Zn2 are reported (L = methylamino-N,N-bis(2-methylene-4,6-di-tert-butylphenolato) and/or methylamino-N,N-bis(2-methylene-4-adamantyl-6-tert-butylphenolato)). X-ray crystallographic and 1H NMR studies, including NOESY and PGSE experiments, provided insight into the solid and solution state structures, respectively, as well as evidence for the catalytically active species responsible for the ring-opening polymerization of CL. Additionally, solution polymerizations and kinetic experiments involving (L1)2Zn2 in the presence of benzyl alcohol (BnOH) were performed to elucidate the influence of catalyst structure, solvent, and the concentration dependence of the catalytically active species, CL, and BnOH on the rate and control of poly-epsilon-caprolactone (PCL) formation. The structural, polymerization, and kinetic data support equilibria involving both mononuclear and dinuclear forms of (L1)2Zn2 as well as a monomer-activated route to PCL.

A series of copper(I) complexes with a sterically hindered, bidentate ligand, BL iPr, derived from an N-heterocyclic carbene precursor have been isolated, characterized and their reactivity studied. The ethylene-bridged bis(imidazolin-2-imine) ligand (BL iPr) provides strongly donating N-donor atoms for the stabilization of a copper(I) metal center, priming it for reactivity. The complexes [(BL iPr)Cu(XyNC)]PF6 (4) and [(BL iPr)CuCl] (5) were characterized by X-ray crystallography and exhibit trigonal coordination at the copper centers. The reactivity of [(BL iPr)Cu]SbF6 toward dioxygen was studied at low temperature, indicating formation of a thermally sensitive intermediate with intense UV/Vis features and an isotope-sensitive vibration at 625 cm(-1) (599 cm(-1) with 18 O2). The intermediate is assigned as containing the bis(mu-oxo)dicopper(III) core, [2](PF6)2, and the related, stable hydroxo form was crystallized as [{(BL iPr)Cu}2(mu-OH)2](PF6)2, [3](PF6)2. The reactivity of 5 as a catalyst for the ATR polymerization of styrene was assessed in terms of reaction kinetics and polymer properties, with low PDI values achieved for polymers with molecular weights up to 30 000 g mol(-1).

The complexes cis-TpiPrMoVIO2(OAr-R) (TpiPr=hydrotris(3-isopropylpyrazol-1-yl)borate, -OAr-R=hydrogen-bonding phenolate derivative) are formed upon reaction of TpiPrMoO2Cl, HOAr-R, and NEt3 in dichloromethane. The orange, diamagnetic, dioxo-Mo(VI) complexes exhibit strong nu(MoO2) IR bands at ca. 935 and 900 cm(-1) and NMR spectra indicative of Cs symmetry. They undergo electrochemically reversible, one-electron reductions at potentials in the range -0.836 to -0.598 V vs SCE; the only exception is the 2-CO2Ph derivative, which exhibits an irreversible reduction at -0.924 V. The complexes display distorted octahedral geometries, with a cis arrangement of terminal oxo ligands and with d(Mo=O)av=1.695 A and angle(MoO2)av=103.2 degrees. The R groups of the 2-CHO and 2-NHCOMe derivatives are directed away from the oxo groups and into a cleft in the TpiPr ligand; these derivatives are characterized by Mo-O-Cipso angles of ca. 131 degrees (conformation 1). The R group(s) in the 2-CO2Me and 2,3-(OMe)2 derivatives lie above the face of the three O-donor atoms (directed away from the TpiPr ligand) and the complexes display Mo-O-Cipso angles of 153.1(2) and 149.7(2) degrees, respectively (conformation 2). Conformations 1 and 2 are both observed in the positionally disordered 2-COMe and 2-COEt derivatives, the two conformers having Mo-O-Cipso angles of 130-140 and >150 degrees, respectively. The 3-COMe and 3-NEt2 derivatives have substituents that project away from the TpiPr ligand and Mo-O-Cipso angles of 134.2(2) and 147.7(2) degrees, respectively. Many of the complexes exhibit fluxional behavior on the NMR time scale, consistent with the rapid interconversion of two conformers in solution.

No abstract

The gold surface of a quartz crystal microbalance was modified by the attachment of silica particles derivatised with N- [(3-trimethoxysilyl)propyl]ethylenediaminetriacetic acid. The device was employed to study the kinetics of the interaction of aqueous solutions of lead(ii) nitrate and silver(i) nitrate with the surface and for the selective separation of the metal ions.The quartz crystal microbalance (QCM) consists of a thin, circular, quartz crystal with circular gold electrodes placed centrosymmetrically on opposite faces. 1-5 Application of an electric field across the crystal, using an electronic oscillator, results in vibration of the crystal at its resonant frequency. The frequency of the oscillating crystal is decreased by deposition of mass on its surface and it has been shown that in the gas phase the change in frequency for a quartz crystal is related to change in mass by the Sauerbrey equation. 6 These devices are radially sensitive, i.e., it is the area under the gold electrode surface which is the most sensitive part, and the quartz surface projecting radially from the centre becomes less sensitive to mass deposited. 7 The mass sensitivity of the QCM has been exploited in both the vapour phase and in liquids, and there are numerous reported applications. [1][2][3][4][5][8][9][10][11][12][13][14][15][16] Two areas of the application of QCM devices are of immediate interest. The first involves the monitoring of biomolecular reactions in the liquid phase, in particular kinetic immunoassays which can be followed by the change in frequency as the mass on the surface of the crystal increases. 17 The piezoelectric device offers an alternative to the measurement of reaction kinetics of heterogeneous systems involving biomacromolecular interactions using the BIAcore TM instrument, although in the latter case the kinetic analyses have been more extensively investigated and developed. 18-20 Second, we are interested in the development of piezoelectric devices for the detection and determination of metal ions in solution, 14,[21][22][23][24][25][26][27] where sorbents chemically attached to the crystal are employed in order to obtain the selectivity required to determine one metal ion in the presence of others.We describe an application of the QCM which combines the two areas. The QCM device described in this work is not employed specifically as a mass sensor, in line with recent studies which question this aspect of their use, 28,29 but more so as an event sensor. A QCM device, derivatised with an aminopolycarboxylate ligand covalently attached to spherical silica particles, is employed in the search for selective substrates and/or conditions under which it would be possible to separate metal ions under flow conditions. A combination of the determination of an adsorption isotherm and investigation of association and dissociation phase kinetic parameters has been employed to permit the prediction of the behaviour of two metal ions on the derivatised silica substrate.