Chalcogen bonding is a type of noncovalent interaction in which a covalently bonded chalcogen atom (O, S, Se or Te) acts as an electrophilic species towards a nucleophilic (negative) region(s) in another or in the same molecule. In general, this interaction is strengthened by the presence of an electron-withdrawing group on the electron-acceptor chalcogen atom and upon moving down in the periodic table of elements, from O to Te. Following a short discussion of the phenomenon of chalcogen bonding, this Perspective presents some demonstrative experimental observations in which this bonding is crucial for synthetic transformations, crystal engineering, catalysis and design of materials as synthons/tectons.

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Copper species are widely found in nature and are present in many enzymes as di-, tri-or polynuclear Cu centers that catalyze selectively various oxidation reactions.[1] These reactions include the poorly characterized particulate methane monooxygenase (pMMO), which is present in methanotrophs, wherein a tri-or multinuclear Cu cluster catalyzes alkane hydroxylation and alkene epoxidation.[1f-i] Although increasing attention has been paid to the design of Cu complexes with polydentate ligands as models of copper oxidases [1a,b, 2] and some mononuclear compounds have been

Abstract:The mono-, di-, tri-, tetra-and polynuclear copper (II) (5), respectively, are highly active and selective catalysts or catalyst precursors for the peroxidative oxidation of cyclohexane, in acetonitrile, to a cyclohexanol and cyclohexanone mixture, by aqueous hydrogen peroxide in acidic medium (liquid biphasic catalysis) at room temperature and atmospheric pressure. The effects on the catalytic activity of various factors, e.g., the relative amounts of cyclohexane, oxidant, catalyst, solvent and nitric acid, reaction time, catalyst recycling and impact of both carbon-and oxygen-centred radical traps (supporting mainly radical mechanisms) were investigated and allowed us to achieve yields and TONs up to ca. 39% and 380, respectively, corresponding to the most active copper systems so far reported for the oxidation of cyclohexane under mild conditions. The catalysts can be reused for recycling and, at least complex 4 maintains almost the same level of activity even after five reaction cycles. The preparation of the new complexes 1, 2b and 2c by self-assembly at room temperature, and their full characterization by IR spectroscopy, FAB-MS þ , elemental and X-ray diffraction structural (for 1 and 2c) analyses are also reported.

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