Strategies for the conversion of CO2 to valuable products are paramount for reducing the environmental risks associated with high levels of this greenhouse gas and offer unique opportunities for transforming...

Vanadyl N,N′-bis(salicylidene)-o-phenylenediamine (salophen) complexes have been extensively investigated by cyclic voltammetry, UV-visible spectroscopy and theoretical calculations in MeCN, THF (tetrahydrofuran) and DMF (N,N-dimethylformamide), in order to elucidate the overall factors that influence the electronic density of the metal and therefore the properties of these complexes in various applications. Different substituents were introduced into the salophen skeleton to change the vanadium electron density. Results obtained and here presented showed that the substituents influence the metal electronic character in a way that cannot be easily predicted by considering only the electronic effect. Similarly, the solvent polarity or coordination ability affects the metal complex properties in an unpredictable way. Therefore, experimental and theoretical data here collected are a powerful tool to a priori design salophen ligands to obtain vanadyl complexes having the specific electronic properties suitable for desired applications.

A novel class of dicationic homodimetallic nickel(II) NHC complexes [(NHC)2Ni(µ-OH)2Ni(NHC)2] 2+ was synthesized starting from nickel acetate as metal precursor. Symmetrically substituted N-alkyl (methyl, isopropyl and isobutyl) imidazolylidene (imi) as well as N1-methyl, phenyl, mesityl and butyl substituted triazolylidene (trz) ligands were coordinated to the metal center through NaH-mediated metalation. Reaction of these bimetallic complexes with CH3 + as electrophile (MeOTf) induced alkylation of the bridging hydroxid ligands and afforded new alkoxy-bridged complexes [(NHC)2Ni(µ-OMe)2Ni(NHC)2] 2+ . In contrast, reactions of [(imi)2Ni(µ-OH)2Ni(imi)2] 2+ with H + as electrophile (mild acids with pKa >6) lead to cleavage of the dimeric structure and formation of mononuclear complexes [Ni(X)2(imi)2]. Conversely, no reaction occurs for the triazolylidene analogues [(trz)2Ni(µ-OH)2Ni(trz)2] 2+ , indicating different robustness of the dimetallic core to acidic media. Only exposure to stronger acids (pKa <5) induced dimer cleavage for the trz complexes and gave either the corresponding triazolium salt, or in the presence of a coordinating anion, monomeric species [Ni(X)2(trz)2] with X = I, OAc or (X)2 = CO3. All complexes were inert towards Lewis and Brønsted bases such as NEt3 or NaOMe. These results reveal a remarkable robustness of the acidic Ni centers and the OH protons towards bases, and contrast the distinct reactivity of the Lewis basic oxygen donor sites, which are more reactive than the carbene towards electrophiles.

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A novel complex featuring a mesoionic carbene [Fe2(CO)5(trz)(μ-pdt)] (1) (trz = 1-phenyl-l,3-methyl,4-butyl-1,2,3-triazol-5-ylidene), was synthesized and spectroscopically and structurally characterized. The reductive behaviour of this compound in the presence and in the absence of acid (CH3CO2H) was examined by cyclic voltammetry (CV) that revealed the lack of efficient activity towards proton reduction.