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- ItemIron-Based Binary Catalytic System for the Valorization of CO2 into Biobased Cyclic Carbonates(Washington, DC : ACS Publ., 2016) Büttner, Hendrik; Grimmer, Christoph; Steinbauer, Johannes; Werner, ThomasThe atom economic conversion of epoxidized vegetable oils and fatty acid derivatives with CO2 into cyclic carbonates permits the synthesis of novel oleo compounds from renewable resources as well as the valorization of CO2 as a C1-building block. Organic phosphorus salts proved to be selective catalysts for this reaction. In a widespread screening 11 inexpensive and nontoxic iron salts were evaluated as cocatalysts to enhance the reaction rate. In the presence of 0.25 mol % iron chloride the selectivity and conversion were significantly improved. The reaction parameters were optimized under solvent-free conditions, and the scope and limitation were evaluated for 9 epoxidized fatty acid esters and 4 epoxidized vegetable oils. The biobased carbonates were isolated in excellent yields up to 95% and can be considered to be based on 100% CO2 in respect to carbon. This binary catalyst system features high efficiency and plain simplicity while valorizing CO2 into cyclic carbonates based on renewable feedstocks.
- ItemOn the Reactivity of Phosphaalumenes towards C−C Multiple Bonds(Weinheim : Wiley-VCH, 2023) Nees, Samuel; Wellnitz, Tim; Dankert, Fabian; Härterich, Marcel; Dotzauer, Simon; Feldt, Milica; Braunschweig, Holger; Hering‐Junghans, ChristianHeterocycles containing group 13 and 15 elements such as borazines are an integral part of organic, biomedical and materials chemistry. Surprisingly, heterocycles containing P and Al are rare. We have now utilized phosphaalumenes in reactions with alkynes, alkenes and conjugated double bond systems. With sterically demanding alkynes 1,2-phosphaalumetes were afforded, whereas the reaction with HCCH or HCCSiMe3 gave 1,4-phosphaaluminabarrelenes. Using styrene saturated 1,2-phosphaalumates were formed, which reacted further with additional styrene to give different regio-isomers of 1,4-aluminaphosphorinanes. Using ethylene, a 1,4-aluminaphosphorinane is obtained, while with 1,3-butadiene a bicyclic system containing an aluminacyclopentane and a phosphirane unit was synthesized. The experimental work is supported by theoretical studies to shed light on the mechanism governing the formation of these heterocycles.
- ItemA selective route to aryl-triphosphiranes and their titanocene-induced fragmentation(Cambridge : RSC, 2019) Schumann, André; Reiß, Fabian; Jiao, Haijun; Rabeah, Jabor; Siewert, Jan-Erik; Krummenacher, Ivo; Braunschweig, Holger; Hering-Junghans, ChristianTriphosphiranes are three-membered phosphorus cycles and their fundamental reactivity has been studied in recent decades. We recently developed a high-yielding, selective synthesis for various aryl-substituted triphosphiranes. Variation of the reaction conditions in combination with theoretical studies helped to rationalize the formation of these homoleptic phosphorus ring systems and highly reactive intermediates could be isolated. In addition we showed that a titanocene synthon [Cp2Ti(btmsa)] facilitates the selective conversion of these triphosphiranes into titanocene diphosphene complexes. This unexpected reactivity mode was further studied theoretically and experimental evidence is presented for the proposed reaction mechanism. This journal is © The Royal Society of Chemistry.
- ItemNanoscopic tip sensors fabricated by gas phase etching of optical glass fibers(Heidelberg : Springer, 2012) Bierlich, J.; Kobelke, J.; Brand, D.; Kirsch, K.; Dellith, J.; Bartelt, H.Silica-based fiber tips are used in a variety of spectroscopic, micro- or nano-scopic optical sensor applications and photonic micro-devices. The miniaturization of optical sensor systems and the technical implementation using optical fibers can provide new sensor designs with improved properties and functionality for new applications. The selective-etching of specifically doped silica fibers is a promising method in order to form complex photonic micro structures at the end or within fibers such as tips and cavities in various shapes useful for the all-fiber sensor and imaging applications. In the present study, we investigated the preparation of geometrically predefined, nanoscaled fiber tips by taking advantage of the dopant concentration profiles of highly doped step-index fibers. For this purpose, a gas phase etching process using hydrofluoric acid (HF) vapor was applied. The shaping of the fiber tips was based on very different etching rates as a result of the doping characteristics of specific optical fibers. Technological studies on the influence of the etching gas atmosphere on the temporal tip shaping and the final geometry were performed using undoped and doped silica fibers. The influence of the doping characteristics was investigated in phosphorus-, germanium-, fluorine- and boron-doped glass fibers. Narrow exposed as well as protected internal fiber tips in various shapes and tip radiuses down to less than 15 nm were achieved and characterized geometrically and topologically. For investigations into surface plasmon resonance effects, the fiber tips were coated with nanometer-sized silver layers by means of vapour deposition and finally subjected to an annealing treatment.
- ItemSynthesis and Reactivity of Monocyclic Homoleptic Oligophosphanes(Weinheim : Wiley-VCH, 2021) Wellnitz, Tim; Hering‐Junghans, ChristianThis Minireview outlines the synthesis and reactivity of homoleptic, cyclic oligophosphanes, which have been known for more than 150 years. We will discuss a variety of (PR)n (n = 3,4,5,6) species and outline approaches towards their syntheses in the first part of this review. Then the unique reactivity of these inorganic ring systems will be discussed in detail with a focus on recent findings within the last 20 years. First ring expansion reactions will be described, which are mainly restricted to cyclotriphosphanes. Secondly, ring fragmentation will be highlighted, including phosphinidene transfer reactions. Furthermore, cyclooligophosphanes can be functionalized while retaining the parent ring structures. As oligophosphanes offer multiple donor sites, in a last part the coordination chemistry of these species is highlighted. We hope that this Minireview will spark further interest in this underexplored class of compounds as reagents in inorganic and organic synthesis, as well as the design of new P-containing materials.
- ItemOn New Staudinger Type Reactions of Phosphorus Centered Biradicaloids, [P(μ-NR)]2 (R = Ter, Hyp), with Ionic and Covalent Azides(Weinheim : Wiley-VCH, 2020) Schulz, Axel; Hinz, Alexander; Rölke, Anne; Villinger, Alexander; Wustrack, RonaldPhosphorus centered biradicaloids of the type [P(μ-NTer)]2 [R = Ter = terphenyl = 2,6-bis(2,4,6-trimethylphenyl)phenyl, Hyp = tris(trimethylsilyl)silyl] were treated with covalent (R-N3) and ionic azides (AgN3 and Hg(N3)2). While the reaction with the ionic azides led exclusively to the formation of diazides, [N3P(μ-NTer)]2, triaza-diphospha-pentadienes, RN=P–N(R')–P=NR, were observed in the reaction with covalent azides featuring a Staudinger type reaction followed by PN bond rearrangement reactions. This new Staudinger type mechanism as well as the structure, bonding and thermodynamics along different reaction paths are discussed based on DFT computations.