Nickel­(II) complexes with 15-membered (1–5) and 14-membered (6) octaazamacrocyclic ligands derived from 1,2- and 1,3-diketones and S-methylisothiocarbohydrazide were prepared by template synthesis. The compounds were characterized by elemental analysis, electrospray ionization mass spectrometry, IR, UV–vis, 1H NMR spectroscopies, and X-ray diffraction. The complexes contain a low-spin nickel­(II) ion in a square-planar coordination environment. The electrochemical behavior of 1–6 was investigated in detail, and the electronic structure of 1e-oxidized and 1e-reduced species was studied by electron paramagnetic resonance, UV–vis–near-IR spectroelectrochemistry, and density functional theory calculations indicating redox noninnocent behavior of the ligands. Compounds 1–6 were tested in the microwave-assisted solvent-free oxidation of cyclohexane by tert-butyl hydroperoxide to produce the industrially significant mixture of cyclohexanol and cyclohexanone (i.e., A/K oil). The results showed that the catalytic activity was affected by several factors, namely, reaction time and temperature or amount and type of catalyst. The best values for A/K oil yield (23%, turnover number of 1.1 × 102) were obtained with compound 6 after 2 h of microwave irradiation at 100 °C.

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Geometry optimization, energetics, electronic structure, and topology of electron density of dicopper (I) and dichromium (II) tetrakis(μ‐acetato)‐diaqua complexes are studied focusing on the metal–metal interactions. The performance of broken symmetry (BS) single‐determinant ab initio (Hartree–Fock, Møller–Plesset perturbation theory to the second and third orders, coupled clusters singles and doubles) and density functional theory (BLYP, B3LYP, B3LYP‐D3, B2PLYP, MPW2PLYP) methods is compared to multideterminant ab initio (CASSCF, NEVPT2) methods as well as to the multipole model of charge density from a single‐crystal X‐ray diffraction experiment (Herich et al., Acta Cryst. 2018, B74, 681–692). In vacuo DFT geometry optimizations (improper axial water ligand orientation) are compared against the periodic ones. The singlet state is found to be energetically preferred. J coupling of (I) becomes underestimated for all ab initio methods used, when compared to experiment. It is concluded that the strength of the direct M─M interactions correlates closely with the J coupling magnitude at a given level of theory. The double potential well character of (II) and of the dehydrated form of (II) are considered with respect to the Cr─Cr distance. The physical effective bond order of the metal–metal interaction is small (below 0.1 e) in (I) and moderate (0.4 e) in (II). The CASSCF results overestimate the electron density of the metal–metal bond critical point by 20% and 50% in (I) and (II), respectively, when compared to the multipole model. © 2019 Wiley Periodicals, Inc.

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NMR shifts of N-phenyl-N'-alkyl-p-phenylenediamines (PPD) in vacuum were evaluated by B3LYP calculations using GIAO method. According to our previous studies, the Molar Antioxidant Effectiveness (AEM) of PPD antioxidants correlates with NMR chemical shifts of the amine nitrogen between aromatic rings (N A ), the side aliphatic chain nitrogen (N B ) and its neighboring tertiary carbon atom (C T ) as well as of the hydrogens bonded to them. Our results indicate that the above mentioned chemical shifts correlate with increasing reactivity of dehydrogenated PPD antioxidants at these sites as well.