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A salophen cobalt(II) complex enables water oxidation at neutral pH in photoactivated sacrificial cycles under visible light, thus confirming the high appeal of earth abundant single site catalysis for artificial photosynthesis.Inspired by the natural Mn 4 CaO x oxygen evolving centre in photosystem II, 1 remarkable efforts have been dedicated towards the development of multinuclear transition metal complexes enabling water oxidation for artificial photosynthesis. 2,3 Multimetallic catalysts could in principle distribute the oxidation equivalents necessary for water oxidation over several metal centres, thus lowering the energy barrier of the overall catalytic process. 3 However, the design of multi-metallic cores with oxygen evolving activity poses synthetic and stability hurdles. Noteworthily, single site metal complexes have been recently discovered, whose oxygen evolving activity offers a major opportunity to broaden the catalyst space within fundamental coordination chemistry. 4 Of particular interest are the earth-abundant cobalt complexes featuring polydentate organic ligands, such as corroles, polypyridines, porphyrins, and polyamines, which have been used under dark electrocatalysis conditions, 5 and in few cases also within photoactivated cycles. 6 Ligand diversity is expected to play a crucial role in tuning photocatalytic water oxidation, with the urgent quest to both optimize sequential photoinduced electron transfer and facilitate the dark-phase of the catalytic mechanism under a turnover regime.In this communication we present a cobalt(II) complex with a salophen ligand (N,N 0 -bis(salicylaldehyde)-1,2-phenylenediamine), ) as the sacrificial electron acceptor (Scheme 1). Combined UV-vis, dynamic light scattering (DLS) and Electron Paramagnetic Resonance (EPR) evidence identifies CoSlp as a competent oxygen evolving catalyst (OEC), enabling a two-fold photoinduced electron transfer in the ms time-frame. Our results confirm the ''privileged'' nature of the salophen ligand environment, readily available from simple condensation reactions, with wide applicability in different fields of catalysis, including bioinspired oxidations. CoSlp is obtained by direct reaction of cobalt acetate with the salophen ligand in methanol, followed by precipitation with diethyl ether and recrystallization.8 † Its solid state and solution identity was initially verified using FT-IR and UV-vis spectroscopy through comparison with literature data (Fig. S2 and S3, ESI †), 8 then confirmed using ESI-MS, where a base peak at m/z = 374 was observed, ascribed to the [CoSlpÁH] + ion (Fig. S4, ESI †). In the solid state, the cobalt ion in CoSlp displays a square planar geometry, 8c while in aqueous solution it extends the coordination sphere to square pyramidal, by ligation of a water molecule in the apical position. 8d Spectrophotometric titration yields a pK a = 6.40 for the aquo ligand (Fig. S5, ESI †), 9 which is therefore expected to be deprotonated at neutral pH, turning into a hydroxo moiety. Characterisation of CoSlp by...

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a b s t r a c tVanadium peroxides are known as very effective oxidants of different organic and inorganic substrates. In this short account reactivity, structural and mechanistic studies concerning the behaviour of peroxovanadates toward a number of different substrates are collected. Homogeneous and two-phase systems are presented, in addition, interesting synthetic results obtained with the use of ionic liquids as reaction media are also presented.

Catalysis by transition metal ions in oxidation reactions with hydrogen peroxide and alkyl hydroperoxides is a leading topic in the pursuit of more sustainable and selective processes, to obtain compounds with high added value. The most recent achievements concerning the synthesis and characterization, as well as the key aspects of reactivity, of V(V) and Mo(VI) peroxo complexes have been collected here.

[reaction: see text]. Room-temperature ionic liquids, 1-butyl-3-methylimidazolium hexafluorophosphate, 1-butyl-3-methylimidazolium tetrafluoroborate, 1-butyl-3-methylimidazolium bromide, and 1-butyl-3-methylimidazolium chloride, are used as "green" recyclable alternative to chlorinated solvents for the stereoselective halogenation of alkenes and alkynes.

The applicability of thianthrene 5-oxide as a mechanistic probe for distinguishing between the electrophilic and the nucleophilic character in oxygen-transfer processes from a series of Mo(V1) and W(V1) peroxo complexes has been investigated. In almost all the cases examined, the predominant formation of the corresponding sulfone has been observed. This would indicate a nucleophilic nature of the oxidants, which is, however, at odd with known chemistry of such species. In fact, competitive experiments performed by employing pchlorophenyl methyl sulfide and phenyl methyl sulfoxide together in equivalent amounts as substrates revealed the preferred oxidation of the former over the latter as expected for an electrophilic oxygen transfer. These apparently contrasting findings are interpreted in terms of an incursion of radical pathways in the oxidation reactions of thianthrene 5-oxide by these peroxo complexes.