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In recent years, it has become clear that the presence of redox‐inactive Lewis acidic metal ions can decisively influence the reactivity of metal–dioxygen moieties that are formed in the course of O2 activation, in molecular complexes, and metalloenzymes. Superoxide species are often formed as the primary intermediates but they are mostly too unstable for a thorough investigation. We report here a series of chromium(III) superoxide complexes [L2Cr]M2O2(THF)y (L=−OSiPh2OSiPh2O−, M+=Li+, Na+, K+ and y=4, 5), which could be accessed, studied spectroscopically and partly crystallized at low temperatures. They only differ in the two incorporated Lewis acidic alkali metal counterions (M+) and it could thus be shown that the nature of M+ determines considerably its interaction with the superoxide ligand. This interaction, in turn, has a significant influence on the stability and reactivity of these complexes towards substrates with OH groups. Furthermore, we show that stability and reactivity are also highly solvent dependent (THF versus nitriles), as donor solvents coordinate to the alkali metal ions and thus also influence their interaction with the superoxide moiety. Altogether, these results provide a comprehensive and detailed picture concerning the correlation between spectroscopic properties, structure, and behavior of such superoxides, that may be exemplary for other systems. [ABSTRACT FROM AUTHOR]

Abstract: Reduced CO2 species are key intermediates in a variety of natural and synthetic processes. In the majority of systems, however, they elude isolation or characterisation owing to high reactivity or limited accessibility (heterogeneous systems), and their formulations thus often remain uncertain or are based on calculations only. We herein report on a Ni−CO22− complex that is unique in many ways. While its structural and electronic features help understand the CO2‐bound state in Ni,Fe carbon monoxide dehydrogenases, its reactivity sheds light on how CO2 can be converted into CO/CO32− by nickel complexes. In addition, the complex was generated by a rare example of formate β‐deprotonation, a mechanistic step relevant to the nickel‐catalysed conversion of HxCOyz− at electrodes and formate oxidation in formate dehydrogenases. [ABSTRACT FROM AUTHOR]

Abstract: Reduced CO2 species are key intermediates in a variety of natural and synthetic processes. In the majority of systems, however, they elude isolation or characterisation owing to high reactivity or limited accessibility (heterogeneous systems), and their formulations thus often remain uncertain or are based on calculations only. We herein report on a Ni−CO22− complex that is unique in many ways. While its structural and electronic features help understand the CO2‐bound state in Ni,Fe carbon monoxide dehydrogenases, its reactivity sheds light on how CO2 can be converted into CO/CO32− by nickel complexes. In addition, the complex was generated by a rare example of formate β‐deprotonation, a mechanistic step relevant to the nickel‐catalysed conversion of HxCOyz− at electrodes and formate oxidation in formate dehydrogenases. [ABSTRACT FROM AUTHOR]

The synthesis of two new unsymmetric dinucleating ligand systems, L1, combining a bidentate binding site with a tridentate binding site linked through a dibenzofuran spacer, and L2, with two tridentate binding sites bridged by an ethylene spacer, is reported. The ligands L1 and L2 were used for the preparation of the dicopper(I) complexes [Cu2(L1)(NCCH3)3](X)2, {[Cu2(L1)Cl2]} n and [Cu2(L2)(NCCH3)2](Y)2 (X = PF6, BF4, OTf; Y = ClO4, PF6, BF4), in which the two respective copper ions possess two different coordination environments. All complexes reacted with O2, but in the case of the L1 series, no primary O2 adduct could be identified by UV/Vis spectroscopy. Reaction of the [Cu2(L2)(NCCH3)2](Y)2 complexes with pure oxygen led to the formation of an O2 adduct that proved rather unstable. [ABSTRACT FROM AUTHOR]