Fresh Impetus in the Chemistry of Calcium Peroxides.

Redox-inactive metal ions are essential in modulating the reactivity of various oxygen-containing metal complexes and metalloenzymes, including photosystem II (PSII). The heart of this unique membrane-protein complex comprises the Mn4CaO5 cluster, in which the Ca2+ ion acts as a critical cofactor in the splitting of water in PSII. However, there is still a lack of studies involving Ca-based reactive oxygen species (ROS) systems, and the exact nature of the interaction between the Ca2+ center and ROS in PSII still generates intense debate. Here, harnessing a novel Ca-TEMPO complex supported by the ß-diketiminate ligand to control the activation of O2, we report the isolation and structural characterization of hitherto elusive Ca peroxides, a homometallic Ca hydroperoxide and a heterometallic Ca/K peroxide. Our studies indicate that the presence of K+ cations is a key factor controlling the outcome of the oxygenation reaction of the model Ca-TEMPO complex. Combining experimental observations with computational investigations, we also propose a mechanistic rationalization for the reaction outcomes. The designed approach demonstrates metal-TEMPO complexes as a versatile platform for O2 activation and advances the understanding of Ca/ROS systems.

A New Look at Molecular and Electronic Structure of Homoleptic Diiron(II,II) Complexes with N,N-Bidentate Ligands: Combined Experimental and Theoretical Study.

Paddlewheel-type binuclear complexes featuring metal-metal bonding have been the subject of widespread interest due to fundamental concern in their electronic structures and potential applications. Here, we explore the molecular and electronic structures of diiron(II,II) complexes with N,N'-diarylformamidinate ligands. While a paddlewheel-type diiron(II,II) complex with N,N'-diphenylformamidinate ligands (DPhF) exhibits the centrosymmetric [Fe2 (µ-DPhF)4 ] structure, a minor alteration in the ligand system, i. e., switching from phenyl to p-tolyl N-substituted formamidinate ligand (DTolF), resulted in the isolation of an unprecedented non-centrosymmetric [Fe(µ-DTolF)3 Fe(κ2 -DTolF)] complex. Both complexes were characterized using single-crystal X-ray diffraction, magnetic measurements, 57 Fe Mössbauer spectroscopy, and cyclic voltammetry along with high-level ab-initio calculations. The results provide a new view on a range of factors controlling the ground-state electronic configuration and structural diversity of homoleptic diiron(II,II) complexes. Model calculations determined that the Mayer bond orders for Fe-Fe interactions are significantly lower than 1 and equal to 0.15 and 0.28 for [Fe2 (µ-DPhF)4 ] and [Fe(µ-DTolF)3 Fe(κ2 -DTolF)], respectively.

Controlled hydrolysis of AlMe3 to tetramethylalumoxane and a new look at incipient adducts with water.

We present an efficient route to tetramethylalumoxane by the controlled hydrolysis of AlMe3 in the presence of pyridine. The AlMe3(pyr) hydrolysis by 0.5 and 1 equiv. of H2O has been followed with real-time 1H NMR. Based on high-level quantum-chemical calculations, we conclude that hypervalent, pentacoordinate aluminium species are critical in the first steps of hydrolysis.

Non-redox reactivity of V(II) and Fe(II) formamidinates towards CO2 resulting in the formation of novel M(II) carbamates.

Chemical fixation of CO2 is a powerful tool for the preparation of novel multinuclear metal complexes and functional materials. Particularly, the insertion of CO2 into a metal-X bond (X = H, C, N, O) often is a key elementary step in the various processes transforming this greenhouse gas into valuable products. Herein, we report on the reactivity between CO2 and V(II) and Fe(II) complexes supported by N,N'-bis(2,6-diisopropylphenyl)formamidinate ligands (DippF). The reactions proceeded with multiple insertions of CO2 into the M-N bonds leading to the isolation of three novel complexes: [(κ2-DippFCO2)(THF)V(µ-DippFCO2)3V(THF)], [(κ2-DippFCO2)Fe(µ-DippFCO2)2(µ-DippF)Fe(THF)] and [(κ2-DippFCO2)Fe(µ-DippFCO2)3Fe(κ1-DippFH)], which were characterised using single-crystal X-ray diffraction, FTIR and 57Fe Mössbauer spectroscopy (for the diiron compounds). We provide the first well-documented studies of the CO2 reactivity towards the V-N bond and broaden the state-of-the-art of the undeveloped area of the reactivity of low-valent V(II) complexes. Moreover, we showed that the effectivity of the examined CO2 insertion processes strongly depends on the used solvent's characteristics (for the Fe(II) system) and the metal centre's coordination sphere geometry (for the V(II) system).