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Electrochemical water reduction by employing first-row transition-metal nanoparticles (NPs) constitutes a sustainable way for the generation of H-2. We have synthesized Co-based NPs from a molecular Co-II/Co-III precursor after its reductive decomposition at -1.86 V versus NHE in different organic solvents. These NPs are able to electrochemically reduce water at pH 14. SEM, EDX and XPS analyses have allowed the determination of the chemical nature of the as-deposited NPs: CoO when using MeCN as the solvent and CoO(OH) when employing either dichloromethane (DCM) or MeOH. After 2 h of constant polarization at 10 mAcm(-2), the electrocatalytic activity of the NPs obtained in MeCN and DCM decreases, whereas it increases for those obtained in MeOH. In this solvent, the overpotential is reduced by 215-220 mV and the specific current density is tripled. Interestingly, during this activation process in MeOH, the precursor CoO(OH) NPs are converted into Co(OH)(2). The implications of these results in the context of the current research in the field are also discussed.

Five new tetradentate N-donor ligands with the spirobi(chroman) skeleton (either chiral or racemic) have been synthesized and fully characterized by NMR, EST-MS, and optical polarimetry. These ligands have been coordinated to a series of manganese salts, affording a family of new chiral and racemic Mn-II complexes, which have also been characterized through analytical and spectroscopic techniques. The crystallographic structures of five of them have been obtained by X-ray diffraction; all show a distorted octahedral geometry with the ligand adopting a cis-alpha conformation over the Mn ion. All the complexes have been tested in the catalytic epoxidation of styrene, showing that both conversion and selectivity values increase in the presence of additives in the catalytic media. Experimental results and computational calculations explain the stereospecificity for the cis epoxide in the epoxidation of cis-beta-methylstyrene mediated by one of the complexes synthesized This research has been financed by the Spanish Ministerio de Economia y Competitividad (MINECO) through projects CTQ2010-21532-C02-01, CTQ2011-23156/BQU, CTQ2008-00683, and Consolider Ingenio 2010 (CSD2006_0003). J. R. thanks the Universitat of Girona for a BR predoctoral grant. A. P. thanks MINECO for a Ramon y Cajal contract (reference number RYC-2009-05226) and the European Commission for a Career Integration Grant (CIG09-GA-2011-293900). Z. F. thanks MINECO for a Ramon y Cajal contract. M. S. thanks the Catalan DIUE of the Generalitat de Catalunya (grant number 2009SGR637) and ICREA-Academia for an award

A large diversity of transition-metal complexes bearing the dinucleating tetra-N-dentate ligand 3,5-bis(2-pyridyl)pyrazole (Hbpp) is described. Hbpp is a compartamental ligand and can allow the formation of both mononuclear and dinuclear complexes bridged by the pyrazolate unit of the Hbpp. Furthermore, a slightly related ligand even allows the preparation of tetranuclear complexes. This large family of complexes has been shown to have multiple applications in diverse areas of science, from basic coordination properties to catalysis. From the former perspective phenomena such as linkage isomerization, intrasupramolecular interactions, and exciting magnetic properties have been described. In the field of catalyis it has been shown that this family of complexes is active in a range of reactions, including alcohol oxidation, epoxidation, hydrogen transfer, and water oxidation.

The structural, spectroscopic, and electrochemical characterization and a preliminary catalytic investigation of a family of RuII complexes with general formula [Ru(Y)(terpy)(phbox-R)]n+ [where terpy is 2,2′:6′,2″-terpyridine, phbox-R is a C2-symmetric bidentate oxazoline ligand (R = Et or iPr), and Y is a monodentate ligand], are discussed. The X-ray structure of [RuCl(terpy)(phbox-iPr)]2+ has been solved and confirms, as we described recently, the predicted generation of the less hindered atropisomer, which is determined by the conformation of the stereogenic centers in the bidentate ligand. The catalytic properties of the aquo complexes have been tested in epoxidation reactions, and moderate selectivity for the epoxides is obtained for styrene and trans-stilbene when using PhI(OAc)2 as co-oxidant. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

The synthesis of a new Ru−H2O complex [Ru(phen)(H2O)([9]aneS3)](ClO4)2, 2, (phen = 1,10-phenanthroline, [9]aneS3 = 1,4,7-trithiacyclononane) is described. The complex is characterized by UV/Vis and 1-D and 2-D NMR spectroscopy in solution. The complex has been further characterized in the solid-state by X-ray diffraction analysis which displays a distorted octahedral coordination geometry around the Ru metal center. The cyclic voltammetric experiments of the complex show a pH-dependent chemically irreversible wave at Ep,a = 0.82 V, at pH = 7.0, indicating the low stability of the higher oxidation states. Nevertheless, before the complex decomposes, it is capable of electrocatalytically oxidizing benzyl alcohol (BzOH) to benzaldehyde with a second-order rate constant of 19.8 M−1s−1. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)