Monolayers of 4-(2,6-di(1 H-pyrazol-1-yl)pyridine-4-yl)benzoic acid (DPP-BA) on Au substrates modified by an underpotential-deposited bilayer of Ag were studied by X-ray photoelectron spectroscopy (XPS), near edge X-ray absorption fine structure spectroscopy, and scanning tunneling microscopy. Highly crystalline layers are formed with molecules coordinatively bonding to the surface through the carboxylate moiety in a bidentate configuration. The molecules assemble to rows characterized by densely packed upright-orientated DPP units occupying an area of 41 Å. The DPP units adopt a trans-trans conformation as inferred from the N 1s XPS spectra taken at different photon energies. Their alignment alternates between adjacent rows, giving rise to a herringbone pattern. The pronouncedly different structure of the weakly commensurate self-assembled monolayer (SAM) of DPP-BA on Ag compared to the commensurate SAM of a DPP thiol on Au is a manifestation of the shift from substrate-directed assembly in the latter case to assembly dominated by intermolecular interactions in the former case.

The straightforward large-scale synthesis and the ability to adjust the properties of polymers make polymers very attractive materials. Polymers have been used in numerous applications and an increased demand is foreseeable. However, a serious issue is the accumulation of enormous amounts of end-of-life polymers, which are currently recycled by thermal degradation, undergo downcycling, or buried in landfills. In contrast, only a minor fraction of polymers is recycled by selective depolymerization processes to produce low molecular weight chemicals that can be polymerized to new polymers. Polysiloxanes (silicones) are widely used polymers, and recycling is challenging due to their intrinsic properties. A few high temperature or less environmentally friendly protocols have been reported for recycling silicones. To circumvent these problems, a lowtemperature process was developed for the depolymerization of polysiloxanes using catalytic amounts of cheap, iron salts as a precatalyst and benzoyl fluoride as a depolymerization reagent. Low molecular weight products (difluorodimethylsilane and 1,3-difluoro-1,1,3,3-tetramethyldisiloxane) are used for the synthesis of new polysiloxanes; hence, overall a recycling process is feasible. This inorganic chemistry experiment introduces second-year undergraduate students to the concept of feedstock recycling via depolymerization/polymerization processes and exemplifies modern advances in sustainable chemistry.Every year, large amounts of end-of-life plastics are produced on a multiton scale by our consumer society. 1−4 State-of-the-art waste management is composed of landfill storage, thermal recycling (decomposition for energy purposes), and downcycling to produce low-quality materials. In contrast, the selective degradation to valuable synthons (feedstock recycling) is only performed for a minor fraction of the waste. 5 Noteworthy, low molecular weight chemicals can be applied as feedstock for new high-performance polymers, and therefore, a recycling of polymers is feasible. The development of efficient recycling technologies can be an opportunity to save steadily decreasing natural resources and to contribute to a greener society. 5 The advantages of feedstock recycling are apparent; however, several issues hamper implementation, for example, high energy demand for depolymerizations, copolymers, and selectivity. The application of catalysis can be a useful tool to overcome these issues and to make the whole process more valuable. 6,7 Widely used polymeric materials are polysiloxanes/ silicones (e.g., silicone-oil, -rubber, -grease, -resin) with outstanding properties, for example, thermal stability, low chemical reactivity, low toxicity, stability to UV radiation, and electrical insulation. With these properties, a broad range of applications spanning from medicine, electronics, cookware, and coatings to the construction industry has been established. Moreover, the straightforward availability of polysiloxanes on a large scale by the Muller−Rochow Process and subsequent hydro...

Dedicated to Professor Hansgeorg Schnöckel on occasion of his 80 th birthday L-Nτ-methylhistidine methyl ester, MeHisOMe, has been employed as a potential ligand to mimic the histidine brace-type coordination of copper ions in enzymes such as the particulate methane monoxygenase or lytic polysaccharide monooxygenases. MeHisOMe was prepared by double-methylation of histidine methyl ester. Subsequently, its complexation by diphosphine copper(I) precursors [Cu(P^P)(MeCN) 2 ]BF 4 was tested, which led to the complexes [Cu(P^P)(MeHisOMe)]BF 4 (P^P = dpePhos: 1, P^P = XantPhos: 2, P^P = dppf: 3). 1-3 were fully characterized, also by single crystal X-ray analysis, thus providing first structural data for copper complexes with a synthetic, authentic histidine brace. The complexes proved inert in contact with dioxygen. To improve the biomimetic character attempts were made to formally replace the diphosphine ligands by bis(pyrazolyl)methanes, Bpm. Correspondingly, [BpmCu(NCMe) x ]BF 4 precursors were synthesized, with different substituents at the 3-positions of the pyrazolyl (i. e. Bpm = di(3-(phenyl)-1H-pyrazol-1-yl)diphenylmethane, di(3-(mesityl)-1Hpyrazol-1-yl)methane and di(3-(tert-butyl)-1H-pyrazol-1-yl) diphenylmethane). Addition of MeHisOMe to these complexes led to products that were so sensitive towards oxidation by the environment that they eluded isolation. One experiment provided blue crystals as a product of such a reaction. They belonged to a salt with a complex cation consisting of a Cu(μ-OH) 2 Cu core ligated by two MeHisOMe ligands, which dimerises in the solid state to give [Cu 4 (OH) 4 (MeHisOMe) 4 ] 4 + .