Both global warming and limited fossil resources make the transition from fossil to solar fuels an urgent matter. In this regard, the splitting of water activated by sunlight is a sustainable and carbon‐free new energy conversion scheme able to produce efficient technological devices. The availability of appropriate catalysts is essential for the proper kinetics of the two key processes involved, namely, the oxygen evolution reaction (OER) and the hydrogen evolution reaction (HER). During the last decade, ruthenium nanoparticle derivatives have emerged as true potential substitutes for the state‐of‐the‐art platinum and iridium oxide species for the HER and OER, respectively. Thus, after a summary of the most common methods for catalyst benchmarking, this review covers the most significant developments of ruthenium‐based nanoparticles used as catalysts for the water‐splitting process. Furthermore, the key factors that govern the catalytic performance of these nanocatalysts are discussed in view of future research directions.

This article describes the generalization of an overlooked mechanism for CH bond activation at early transition metal centers, namely 1,3-CH bond addition at an η 2 -alkene intermediate. The X-ray-characterized [Cp 2 Zr(c-C 3 H 5 ) 2 ] eliminates cyclopropane by a β-H abstraction reaction to generate the transientA rapidly cleaves the CH bond of furan and thiophene to give the furyl and thienyl complexes [Cp 2 Zr(c-C 3 H 5 )(2-C 4 H 3 X)] (X = O, S), respectively. Benzene is less cleanly activated. Mechanistic investigations including kinetic studies, isotope labeling, and DFT computation of the reaction profile all confirm that rapid stereospecific 1,3-CH bond addition across the Zr(η 2 -alkene) bond of A follows the rate-determining β-H abstraction reaction. DFT computations also suggest that an α-CC agostic rotamer of [Cp 2 Zr(c-C 3 H 5 ) 2 ] assists the β-H abstraction of cyclopropane. The nature of the α-CC agostic interaction is discussed in the light of an NBO analysis.

Cobalt nanoparticles (NPs) have been prepared by hydrogenation of the organometallic complex [Co( 3-C8H13)( 4-C8H12)] in 1-heptanol in the absence of any other stabilizer and then transformed to Co3O4 NPs using mild oxidative reaction conditions. After deposition onto glassy carbon rotating disk electrodes, the electrocatalytic performance of the Co3O4 NPs in water oxidation has been tested in 1M NaOH. The activity has been benchmarked with that of state-of-the-art Co3O4 NPs through electrochemically-active surface area (ECSA) and specific current density measurements. Furthermore, the covalent grafting of photosensitive polypyridyl-based Ru II complexes onto the surface of Co3O4 NPs afforded hybrid nanostructured materials able to photo-oxidize water into O2, while steady-state and time-resolved spectroscopic measurements gave some further insight into kinetics and pertinent reaction steps following excitation. These first-row transition metal oxide hybrid nanocatalysts display better catalytic performance than simple mixtures of non-grafted photosensitizers and Co3O4 NPs, thus evidencing the advantage of the direct coupling between the two entities for the photo-induced water oxidation reaction.

Heteroleptic silylamido complexes of the heavier alkaline earth elements calcium and strontium containing the highly fluorinated 3-phenyl hydrotris(indazolyl)borate {F12-Tp(4Bo, 3Ph)}(-) ligand have been synthesized by using salt metathesis reactions. The homoleptic precursors [Ae{N(SiMe3)2}2] (Ae = Ca, Sr) were treated with [Tl(F12-Tp(4Bo, 3Ph))] in pentane to form the corresponding heteroleptic complexes [(F12-Tp(4Bo, 3Ph))Ae{N(SiMe3)2}] (Ae = Ca (1); Sr (3)). Compounds 1 and 3 are inert towards intermolecular redistribution. The molecular structures of 1 and 3 have been determined by using X-ray diffraction. Compound 3 exhibits a Sr⋅⋅⋅MeSi agostic distortion. The synthesis of the homoleptic THF-free compound [Ca{N(SiMe2H)2}2] (4) by transamination reaction between [Ca{N(SiMe3)2}2] and HN(SiMe2H)2 is also reported. This precursor constitutes a convenient starting material for the subsequent preparation of the THF-free complex [(F12-Tp(4Bo, 3Ph))Ca{N(SiMe2H)2}] (5). Compound 5 is stabilized in the solid state by a Ca⋅⋅⋅β-Si-H agostic interaction. Complexes 1 and 3 have been used as precatalysts for the intramolecular hydroamination of 2,2-dimethylpent-4-en-1-amine. Compound 1 is highly active, converting completely 200 equivalents of aminoalkene in 16 min with 0.50 mol % catalyst loading at 25 °C.

The molecular and supramolecular structures of new perfluorinated indazoles and hydrotris(indazolyl)borates reveal various types of intra- and intermolecular interactions and organizations.

Electrocatalytic Nitrobenzene Hydrogenation and competitive Hydrogen Evolution Reaction (HER) have been studied, using two catalytic systems: oxidized carbon fibers (organic) and Ruthenium nanoparticles supported on unaltered carbon fibers (inorganic).

Four different cathodes for the hydrogen evolution reaction (HER) have been developed by the decoration of commercial carbon microfibers with Ru nanoparticles (Ru NPs). Two types of carbon fibers have been used: pristine, as‐received, carbon fibers (pCF) and carbon fibers modified by an oxidative treatment that led to the functionalization of their surface with carboxylic groups (fCF). The decoration of these CFs with Ru NPs has been performed by two different methodologies based on the organometallic approach: direct synthesis of Ru NPs on top of the CFs (in‐situ Ru NPs) or impregnation of the CFs with a colloidal solution of preformed Ru NPs stabilized with 4‐phenylpyridine (RuPP NPs; ex‐situ Ru NPs). The electrocatalytic performance of these four cathodes (ex‐situ RuPP@pCF and RuPP@fCF; in‐situ Ru@pCF and Ru@fCF) for the HER has been studied in acidic conditions. The results obtained show that both the nature of the NPs and of the carbon fibers play a key role on the stability and activity of the hybrid electrodes: ex‐situ prepared Ru NPs afford better activities at lower overpotentials and better stabilities than those formed in‐situ. Among the two ex‐situ systems, an enhancement of the stability with pCF is observed, that may arise from more effective π‐interactions between 4‐phenylpyridine ligand and the surface of these carbon fibers. This interaction is somehow disfavored with fCF due to the presence of the surface carboxylic groups.

Heteroleptic phenylacetylide complexes [{F 12 -Tp 4Bo,3Ph }Ae(CCPh)] x of calcium (Ae = Ca, x = 2; 2) and magnesium (Ae = Mg, x = 1; 4) containing the highly fluorinated 3-phenyl hydrotris(indazolyl)borate {F 12 -Tp 4Bo,3Ph } − ligand have been synthesized by acid−base reactions between the corresponding silylamido derivatives [{F 12 -Tp 4Bo,3Ph }Ae{N(SiRMe 2 ) 2 }] (R = Me, Ae = Ca (1); R = H, Ae = Mg (3)) and PhCCH. Compounds 2 and 4 have been characterized by NMR spectroscopy and X-ray diffraction analysis. 2 crystallizes as a dinuclear complex, showing two nonsymmetrical "side-on" (π-type) interactions between the acetylide units and the Ca centers, whereas 4 crystallizes as a mononuclear complex, displaying a four-coordinate magnesium. The molecular structure of the complex [{F 12 -Tp 4Bo,3Ph }Mg-{N(SiMe 2 H) 2 }] (3), obtained by the salt metathesis reaction between [Mg{N(SiMe 2 H) 2 } 2 ] and [Tl{F 12 -Tp 4Bo,3Ph }], is also reported. 3 is also four-coordinate and exhibits a Mg•••β-Si−H agostic distortion. The synthesis and in situ characterization of the heteroleptic alkyl complex [{F 12 -Tp 4Bo,3Ph }Ca{CH(SiMe 3 ) 2 }(THF)] ( 5) is also reported, although attempts to isolate this compound failed due to its extreme sensitivity to temperature.