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A new mononuclear nickel(II) complex, [Ni (dpaq)Cl] (1), containing a tetradentate monoamido ligand, dpaq (dpaq=2-[bis(pyridin-2-ylmethyl)amino]-N-(quinolin-8-yl)acetamide), has been synthesized and characterized by IR spectroscopy, elemental analysis, and UV/Vis spectroscopy. The structure of the nickel complex has been determined by X-ray crystallography. This nonheme Ni complex 1 catalyzed the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (m-CPBA) under mild conditions. Olefin epoxidation using this catalytic system has been proposed to involve a new reactive Ni -oxo (4) species, based on the evidence from a PPAA (peroxyphenylacetic acid) probe, Hammett studies, H O exchange experiments, and ESI mass spectroscopic analysis. Moreover, the nature of solvent significantly influenced partitioning between heterolytic and homolytic O-O bond cleavage of the Ni-acylperoxo intermediate (2). The O-O bond of 2 proceeded predominantly through heterolytic cleavage in a protic solvent, such as CH OH. These results suggest that possibly a Ni -oxo species is a common reactive intermediate in protic solvents. The two active oxidants, namely Ni -oxo (3) and Ni -oxo (4), which are responsible for stereospecific olefin epoxidation and radical-type oxidations, respectively, operate in aprotic solvents.

A new bi-functional chemosensor 1 based on 3,5-dichlorosalicylaldehyde and 2-(methylthio)aniline has been synthesized. It can detect Cu with a color change from pale yellow to dark yellow in aqueous solution. The selective mechanism of 1 for Cu was proposed to be the enhancement of the intramolecular charge transfer (ICT) band, which was explained by theoretical calculations. The sensor 1 could be used to detect and quantify Cu in water samples. In addition, the sensor 1 displayed "turn-on" fluorescence response only to Zn, based on an effect of chelation-enhanced fluorescence (CHEF). Therefore, 1 can serve as a 'single sensor for two different targets' with dual modes.

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A new nickel(II) porphyrin complex, [Ni (porp)] (1), has been synthesized and characterized by H NMR, C NMR and mass spectrometry analysis. This Ni porphyrin complex 1 quantitatively catalyzed the epoxidation reaction of a wide range of olefins with meta-chloroperoxybenzoic acid (m-CPBA) under mild conditions. Reactivity and Hammett studies, H O-exchange experiments, and the use of PPAA (peroxyphenylacetic acid) as a mechanistic probe suggested that participation of multiple active oxidants Ni -OOC(O)R 2, Ni -Oxo 3, and Ni -Oxo 4 within olefin epoxidation reactions by the nickel porphyrin complex is markedly affected by solvent polarity, concentration, and type of substrate. In aprotic solvent systems, such as toluene, CH Cl , and CH CN, multiple oxidants, Ni -(O)R 2, Ni -Oxo 3, and Ni -Oxo 4, operate simultaneously as the key active intermediates responsible for epoxidation reactions of easy-to-oxidize substrate cyclohexene, whereas Ni -Oxo 3 and Ni -Oxo 4 species become the common reactive oxidant for the difficult-to-oxidize substrate 1-octene. In a protic solvent system, a mixture of CH CN and H O (95:5), the Ni -OOC(O)R 2 undergoes heterolytic or homolytic O-O bond cleavage to afford Ni -Oxo 3 and Ni -Oxo 4 species by general acid catalysis prior to direct interaction between 2 and olefin, regardless of the type of substrate. In this case, only Ni -Oxo 3 and Ni -Oxo 4 species were the common reactive oxidant responsible for olefin epoxidation reactions.

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Atom-transfer chemistry represents an important class of reactions catalyzed by metalloenzymes. As a functional mimic of non-heme iron enzymes that deliver oxygen atoms to olefins, we have designed monoiron complexes supported by new N-donor chelates. These ligands take advantage of heme-like conformational rigidity of the π-conjugated molecular backbone, and synthetic flexibility of tethering non-heme donor groups for additional steric and electronic control. Iron complexes generated in situ can be used to carry out catalytic epoxidation of a wide range of olefin substrates by using mCPBA as a terminal oxidant. The fate of initial iron-peracid adduct and the involvement of iron-oxo species in this process were investigated further by mechanistic probes and isotope exchange studies. Our findings suggest that anilidopyridyl-derived [N,N]-bidentate motif could serve as a versatile structural platform to build non-heme ligands for catalytic oxidation chemistry.