Very high activities were observed in the redox-induced hydroamination of alkynes by employing a redox-active gold(i) complex featuring an electron-deficient, terphenyl-substituted phosphonite-based ligand.
The
preparation of a novel class of ε-caprolactone (CL) monomers,
modified at the β-position of the ester function, is described.
The efficient thia-Michael addition to cyclohex-2-en-1-one and subsequent
Baeyer–Villiger oxidation provided the regioselectively modified
CL monomers. To enable a sustainable Baeyer–Villiger oxidation,
several reaction procedures were investigated. In order to test a
controlled ring-opening polymerization of the prepared monomers, the
kinetics were studied and the monomer to initiator ratios were varied
in order to prepare poly(ε-caprolactone)s with different molecular
weights and different side groups.
Reaction of [Si(3,5-Me2 pz)4 ] (1) with [Cu(MeCN)4 ][BF4 ] (2) gave the mono- and dinuclear copper complexes [Cu2 ((F) Tp*)2 ] (3) and [Cu((F) Tp*)2 ] (4). Both complexes contain the so-far unprecedented boron-fluorinated (F) Tp* ligand ([FB(3,5-Me2 pz)3 ](-) with pz=pyrazolyl) originating from 1, acting as a pyrazolyl transfer reagent, and the [BF4 ](-) counter anion of 2, serving as the source of the {BF} entity. The solid-state structures as well as the NMR and EPR spectroscopic characteristics of the complexes were elaborated. Pulsed gradient spin echo (PGSE) experiments revealed that 3 retains (almost entirely) its dimeric structure in benzene, whereas dimer cleavage and formation of acetonitrile adducts, presumably [Cu((F) Tp*)(MeCN)], is observed in acetonitrile. The short Cu⋅⋅⋅Cu distance of 269.16 pm in the solid-state is predicted by DFT calculations to be dictated by dispersion interactions between all atoms in the complex (the Cu-Cu dispersion contribution itself is only very small). As revealed by cyclic voltammetry studies, 3 shows an irreversible (almost quasi-reversible at higher scan rates) oxidation process centred at E(pa) =-0.23 V (E(0) 1/2 =-0.27 V) (vs. Fc/Fc(+) ). Oxidation reactions on a preparative scale with one equivalent of the ferrocenium salt [Fc][BF4 ] (very slow reaction) or air (fast reaction) furnished blue crystals of the mononuclear copper(II) complex [Cu((F) Tp*)2 ] (4). As expected for a Jahn-Teller-active system, the coordination sphere around copper(II) is strongly distorted towards a stretched octahedron, in accordance with EPR spectroscopic findings.
The mechanical behavior of Fe-Cr-Al-alloys was investigated at different temperatures and after several heat-treatments in order to determine critical conditions for the ductility of the material. It was found that a significant embrittlement takes place during deformation at higher temperatures around 400 °C as well as after heat-treatments at temperatures above 1000 °C in combination with very high or very low cooling rates. Possible reasons for this behavior are discussed with respect to the results of transmission electron microscopy (TEM), Auger spectroscopy (AES), positron annihilation spectroscopy (PAS) and measurements of the electrical resistivity.
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