Electron-rich triarylphosphines, namely 4-(methoxyphenyl)diphenylphosphine (MMTPP) and tris(4-trimethoxyphenyl)phosphine (TMTPP), outperform commonly used triphenylphosphine (TPP) in catalyzing oxa-Michael additions. A matrix consisting of three differently strong Michael acceptors and four alcohols of varying acidity was used to assess the activity of the three catalysts. All test reactions were performed with 1 mol % catalyst loading, under solvent-free conditions and at room temperature. The results reveal a decisive superiority of TMTPP for converting poor and intermediate Michael acceptors such as acrylamide and acrylonitrile and for converting less acidic alcohols like isopropanol. With stronger Michael acceptors and more acidic alcohols, the impact of the more electron-rich catalysts is less pronounced. The experimental activity trend was rationalized by calculating the Michael acceptor affinities of all phosphine–Michael acceptor combinations. Besides this parameter, the acidity of the alcohol has a strong impact on the reaction speed. The oxidation stability of the phosphines was also evaluated and the most electron-rich TMTPP was found to be only slightly more sensitive to oxidation than TPP. Finally, the catalysts were employed in the oxa-Michael polymerization of 2-hydroxyethyl acrylate. With TMTPP polymers characterized by number average molar masses of about 1200 g/mol at room temperature are accessible. Polymerizations carried out at 80 °C resulted in macromolecules containing a considerable share of Rauhut–Currier-type repeat units and consequently lower molar masses were obtained.
The performance of the strong Lewis base tris(2,4,6-trimethoxyphenyl)phosphine (TTMPP) in catalysing oxa-Michael reactions is assessed and compared with other electron-rich tertiary arylphosphines and, as the benchmark, with the Brønsted base...
The terminal zinc hydride complex [Tntm]ZnH (2; Tntm=tris(6-tert-butyl-3-thiopyridazinyl)methanide) is an efficient hydrosilylation catalyst of CO at room temperature without the need of Lewis acidic additives. The inherent electrophilicity of the system leads to selective formation of the monosilylated product (MeO) SiO CH (at room temperature with a TOF of 22.2 h and at 45 °C with a TOF of 66.7 h ). In absence of silanes, the intermediate formate complex [Tntm]Zn(O CH) (3) is quantitatively formed within 5 min. All complexes were fully characterized by H and C NMR spectroscopy and single-crystal X-ray diffraction analyses. Density functional theory (DFT) calculations reveal a high positive charge on zinc and the increased preference of the ligand to adopt a κ -coordination mode.
Polymer electrolytes containing Li-ion conducting fillers are among the extensively investigated materials for the development of solid-state Li metal batteries. The practical realization of these electrolytes is, however, impeded by their low Li-ion conductivity, which is related to the filler and the interplay between the filler and the polymer. Therefore, we performed an in-depth analysis on the influence of the filler content (0, 10, and 20 wt%) and filler morphology (particles and nanowires) on the electrical and electrochemical properties of the PEO-based composite electrolyte using a wide spectrum of characterization techniques, such as 3D micro-X-ray computed tomography, cross-sectional scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry, impedance spectroscopy, and galvanostatic cycling. The studies reveal that the filler materials are well distributed within the membranes, without any indications for the formation of agglomerates. For 10 wt% filler, a decrease in the crystallinity compared to PEO was observed, in contrast to 20 wt% filler showing an increase in crystallinity. Impedance spectroscopic studies on the Li-ion conductivity of the membranes have shown that the change in the Li-ion conductivity is solely related to the change in the crystallinity, rather than to the participation of LLZO as an active transport mediator. The PEO membranes containing 10 wt% LLZO have been tested in terms of their rate capability in symmetrical Li cells by galvanostatic cycling. A critical current density of up to 1 mA cm−2 at 60°C was observed.
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