TY - JOUR A1 - Zhang, Xiaolei A1 - Friedrich, Alexandra A1 - Marder, Todd B. T1 - Copper-Catalyzed Borylation of Acyl Chlorides with an Alkoxy Diboron Reagent: A Facile Route to Acylboron Compounds JF - Chemistry—A European Journal N2 - Herein, the copper-catalyzed borylation of readily available acyl chlorides with bis(pinacolato)diboron, (B\(_{2}\)pin\(_{2}\)) or bis(neopentane glycolato)diboron (B\(_{2}\)neop\(_{2}\)) is reported, which provides stable potassium acyltrifluoroborates (KATs) in good yields from the acylboronate esters. A variety of functional groups are tolerated under the mild reaction conditions (room temperature) and substrates containing different carbon-skeletons, such as aryl, heteroaryl and primary, secondary, tertiary alkyl are applicable. Acyl N-methyliminodiacetic acid (MIDA) boronates can also been accessed by modification of the workup procedures. This process is scalable and also amenable to the late-stage conversion of carboxylic acid-containing drugs into their acylboron analogues, which have been challenging to prepare previously. A catalytic mechanism is proposed based on in situ monitoring of the reaction between p-toluoyl chloride and an NHC-copper(I) boryl complex as well as the isolation of an unusual lithium acylBpinOBpin compound as a key intermediate. KW - boronate KW - catalysis KW - borylation KW - carbonyl KW - copper Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318318 VL - 28 IS - 42 ER - TY - JOUR A1 - Wu, Zhu A1 - Roldao, Juan Carlos A1 - Rauch, Florian A1 - Friedrich, Alexandra A1 - Ferger, Matthias A1 - Würthner, Frank A1 - Gierschner, Johannes A1 - Marder, Todd B. T1 - Pure Boric Acid Does Not Show Room-Temperature Phosphorescence (RTP) JF - Angewandte Chemie N2 - Boric acid (BA) has been used as a transparent glass matrix for optical materials for over 100 years. However, recently, apparent room-temperature phosphorescence (RTP) from BA (crystalline and powder states) was reported (Zheng et al., Angew. Chem. Int. Ed. 2021, 60, 9500) when irradiated at 280 nm under ambient conditions. We suspected that RTP from their BA sample was induced by an unidentified impurity. Our experimental results show that pure BA synthesized from B(OMe)\(_{3}\) does not luminesce in the solid state when irradiated at 250–400 nm, while commercial BA indeed (faintly) luminesces. Our theoretical calculations show that neither individual BA molecules nor aggregates would absorb light at >175 nm, and we observe no absorption of solid pure BA experimentally at >200 nm. Therefore, it is not possible for pure BA to be excited at >250 nm even in the solid state. Thus, pure BA does not display RTP, whereas trace impurities can induce RTP. KW - boric acid KW - room-temperature phosphorescence (RTP) KW - optical materials Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318308 VL - 61 IS - 15 ER - TY - JOUR A1 - Wu, Zhu A1 - Dinkelbach, Fabian A1 - Kerner, Florian A1 - Friedrich, Alexandra A1 - Ji, Lei A1 - Stepanenko, Vladimir A1 - Würthner, Frank A1 - Marian, Christel M. A1 - Marder, Todd B. T1 - Aggregation-Induced Dual Phosphorescence from (o-Bromophenyl)-Bis(2,6-Dimethylphenyl)Borane at Room Temperature JF - Chemistry—A European Journal N2 - Designing highly efficient purely organic phosphors at room temperature remains a challenge because of fast non-radiative processes and slow intersystem crossing (ISC) rates. The majority of them emit only single component phosphorescence. Herein, we have prepared 3 isomers (o, m, p-bromophenyl)-bis(2,6-dimethylphenyl)boranes. Among the 3 isomers (o-, m- and p-BrTAB) synthesized, the ortho-one is the only one which shows dual phosphorescence, with a short lifetime of 0.8 ms and a long lifetime of 234 ms in the crystalline state at room temperature. Based on theoretical calculations and crystal structure analysis of o-BrTAB, the short lifetime component is ascribed to the T\(^M_1\) state of the monomer which emits the higher energy phosphorescence. The long-lived, lower energy phosphorescence emission is attributed to the T\(^A_1\) state of an aggregate, with multiple intermolecular interactions existing in crystalline o-BrTAB inhibiting nonradiative decay and stabilizing the triplet states efficiently. KW - AIE KW - luminescence KW - phosphorescence KW - triarylborane KW - triplet Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318297 VL - 28 IS - 30 ER - TY - JOUR A1 - Schulz, Ellina A1 - Mawamba, Viviane A1 - Löhr, Mario A1 - Hagemann, Carsten A1 - Friedrich, Alexandra A1 - Schatzschneider, Ulrich T1 - Structure–activity relations of Pd(II) and Pt(II) thiosemicarbazone complexes on different human glioblastoma cell lines JF - Zeitschrift für Anorganische und Allgemeine Chemie N2 - Ten thiosemicarbazone ligands obtained by condensation of pyridine-2-carbaldehyde, quinoline-2-carbaldehyde, 2-acetylpyridine, 2-acetylquinoline, or corresponding 2-pyridyl ketones with thiosemicarbazides RNHC(S)NHNH\(_{2}\) and R=CH\(_{3}\), C\(_{6}\)H\(_{5}\) were prepared in good yield. The reaction of [PdCl\(_{2}\)(cod)] with cod=1,5-cyclooctadiene or K\(_{2}\)[PtCl\(_{4}\)] resulted in a total of 17 Pd(II) and Pt(II) complexes isolated in excellent purity, as demonstrated by \(^{1}\)H, \(^{13}\)C, and, where applicable, \(^{195\)Pt NMR spectroscopy combined with CHNS analysis. The cytotoxicity of the title compounds was studied on four human glioblastoma cell lines (GaMG, U87, U138, and U343). The most active compound, with a Pd(II) metal centre, a 2-quinolinyl ring, and methyl groups on both the proximal C and distal N atoms exhibited an EC\(_{50}\) value of 2.1 μM on the GaMG cell lines, thus being slightly more active than cisplatin (EC\(_{50}\) 3.4 μM) and significantly more potent than temozolomide (EC\(_{50}\) 67.1 μM). Surprisingly, the EC\(_{50}\) values were inversely correlated with the lipophilicity, as determined with the “shake-flask method”, and decreased with the length of the alkyl substituents (C\(_{1}\)>C\(_{8}\)>C\(_{10}\)). Correlation with the different structural motifs showed that for the most promising anticancer activity, a maximum of two aromatic rings (either quinolinyl or pyridyl plus phenyl) combined with one methyl group are favoured and the Pd(II) complexes are slightly more potent than their Pt(II) analogues. KW - glioblastoma KW - platinum KW - palladium KW - thiosemicarbazone KW - anticancer activity Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318281 SN - 0044-2313 VL - 648 IS - 12 ER - TY - JOUR A1 - Rauch, Florian A1 - Fuchs, Sonja A1 - Friedrich, Alexandra A1 - Sieh, Daniel A1 - Krummenacher, Ivo A1 - Braunschweig, Holger A1 - Finze, Maik A1 - Marder, Todd B. T1 - Highly Stable, Readily Reducible, Fluorescent, Trifluoromethylated 9‐Borafluorenes JF - Chemistry – A European Journal N2 - Three different perfluoroalkylated borafluorenes (\(^{F}\)Bf) were prepared and their electronic and photophysical properties were investigated. The systems have four trifluoromethyl moieties on the borafluorene moiety as well as two trifluoromethyl groups at the ortho positions of their exo‐aryl moieties. They differ with regard to the para substituents on their exo‐aryl moieties, being a proton \(^{F}\)Xyl\(^{F}\)Bf, \(^{F}\)Xyl: 2,6‐bis(trifluoromethyl)phenyl), a trifluoromethyl group (\(^{F}\)Mes\(^{F}\)Bf, \(^{F}\)Mes: 2,4,6‐tris(trifluoromethyl)phenyl) or a dimethylamino group (p‐NMe\(_{2}\)‐\(^{F}\)Xyl\(^{F}\)Bf, p‐NMe\(_{2}\)‐\(^{F}\)Xyl: 4‐(dimethylamino)‐2,6‐bis(trifluoromethyl)phenyl), respectively. All derivatives exhibit extraordinarily low reduction potentials, comparable to those of perylenediimides. The most electron‐deficient derivative \(^{F}\)Mes\(^{F}\)Bf was also chemically reduced and its radical anion isolated and characterized. Furthermore, all compounds exhibit very long fluorescent lifetimes of about 250 ns up to 1.6 μs; however, the underlying mechanisms responsible for this differ. The donor‐substituted derivative p‐NMe\(_{2}\)‐\(^{F}\)Xyl\(^{F}\)Bf exhibits thermally activated delayed fluorescence (TADF) from a charge‐transfer (CT) state, whereas the \(^{F}\)Mes\(^{F}\)Bf and FXylFBf borafluorenes exhibit only weakly allowed locally excited (LE) transitions due to their symmetry and low transition‐dipole moments. KW - borafluorenes KW - boron KW - EPR spectroscopy KW - fluorescence KW - heterocycles Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218390 VL - 26 IS - 56 SP - 12794 EP - 12808 ER - TY - JOUR A1 - Rauch, Florian A1 - Endres, Peter A1 - Friedrich, Alexandra A1 - Sieh, Daniel A1 - Hähnel, Martin A1 - Krummenacher, Ivo A1 - Braunschweig, Holger A1 - Finze, Maik A1 - Ji, Lei A1 - Marder, Todd B. T1 - An Iterative Divergent Approach to Conjugated Starburst Borane Dendrimers JF - Chemistry – A European Journal N2 - Using a new divergent approach, conjugated triarylborane dendrimers were synthesized up to the 2nd generation. The synthetic strategy consists of three steps: 1) functionalization, via iridium catalyzed C−H borylation; 2) activation, via fluorination of the generated boronate ester with K[HF\(_{2}\)] or [N(nBu\(_{4}\))][HF\(_{2}\)]; and 3) expansion, via reaction of the trifluoroborate salts with aryl Grignard reagents. The concept was also shown to be viable for a convergent approach. All but one of the conjugated borane dendrimers exhibit multiple, distinct and reversible reduction potentials, making them potentially interesting materials for applications in molecular accumulators. Based on their photophysical properties, the 1st generation dendrimers exhibit good conjugation over the whole system. However, the conjugation does not increase further upon expansion to the 2nd generation, but the molar extinction coefficients increase linearly with the number of triarylborane subunits, suggesting a potential application as photonic antennas. KW - density functional calculations KW - electron storage KW - luminescence KW - redox KW - triarylborane Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218345 VL - 26 IS - 57 SP - 12951 EP - 12963 ER - TY - JOUR A1 - Merz, Julia A1 - Dietz, Maximilian A1 - Vonhausen, Yvonne A1 - Wöber, Frederik A1 - Friedrich, Alexandra A1 - Sieh, Daniel A1 - Krummenacher, Ivo A1 - Braunschweig, Holger A1 - Moos, Michael A1 - Holzapfel, Marco A1 - Lambert, Christoph A1 - Marder, Todd B. T1 - Synthesis, Photophysical and Electronic Properties of New Red-to-NIR Emitting Donor-Acceptor Pyrene Derivatives JF - Chemistry - A European Journal N2 - We synthesized new pyrene derivatives with strong bis(para ‐methoxyphenyl)amine donors at the 2,7‐positions and n ‐azaacene acceptors at the K‐region of pyrene. The compounds possess a strong intramolecular charge transfer, leading to unusual properties such as emission in the red to NIR region (700 nm), which has not been reported before for monomeric pyrenes. Detailed photophysical studies reveal very long intrinsic lifetimes of >100 ns for the new compounds, which is typical for 2,7‐substituted pyrenes but not for K‐region substituted pyrenes. The incorporation of strong donors and acceptors leads to very low reduction and oxidation potentials, and spectroelectrochemical studies show that the compounds are on the borderline between localized Robin‐Day class‐II and delocalized Robin‐Day class‐III species. KW - orylation KW - K-region KW - luminescence KW - polycyclic aromatic hydrocarbons KW - redox Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-207486 VL - 26 IS - 2 ER - TY - JOUR A1 - Liu, Zhiqiang A1 - Kole, Goutam Kumar A1 - Budiman, Yudha P. A1 - Tian, Ya-Ming A1 - Friedrich, Alexandra A1 - Luo, Xiaoling A1 - Westcott, Stephen A. A1 - Radius, Udo A1 - Marder, Todd B. T1 - Transition metal catalyst-free, base-promoted 1,2-additions of polyfluorophenylboronates to aldehydes and ketones JF - Angewandte Chemie International Edition N2 - A novel protocol for the transition metal-free 1,2-addition of polyfluoroaryl boronate esters to aldehydes and ketones is reported, which provides secondary alcohols, tertiary alcohols, and ketones. Control experiments and DFT calculations indicate that both the ortho-F substituents on the polyfluorophenyl boronates and the counterion K\(^+\) in the carbonate base are critical. The distinguishing features of this procedure include the employment of commercially available starting materials and the broad scope of the reaction with a wide variety of carbonyl compounds giving moderate to excellent yields. Intriguing structural features involving O−H⋅⋅⋅O and O−H⋅⋅⋅N hydrogen bonding, as well as arene-perfluoroarene interactions, in this series of racemic polyfluoroaryl carbinols have also been addressed. KW - inorganic chemistry KW - transition metal-free KW - alcohol KW - 1,2-additionreaction KW - boronateesters KW - fluoroarene Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-256487 VL - 60 IS - 30 ER - TY - JOUR A1 - Liu, Zhiqiang A1 - Budiman, Yudha P. A1 - Tian, Ya‐Ming A1 - Friedrich, Alexandra A1 - Huang, Mingming A1 - Westcott, Stephen A. A1 - Radius, Udo A1 - Marder, Todd B. T1 - Copper‐Catalyzed Oxidative Cross‐Coupling of Electron‐Deficient Polyfluorophenylboronate Esters with Terminal Alkynes JF - Chemistry – A European Journal N2 - We report herein a mild procedure for the copper‐catalyzed oxidative cross‐coupling of electron‐deficient polyfluorophenylboronate esters with terminal alkynes. This method displays good functional group tolerance and broad substrate scope, generating cross‐coupled alkynyl(fluoro)arene products in moderate to excellent yields. Thus, it represents a simple alternative to the conventional Sonogashira reaction. KW - boronate esters KW - coupling reactions KW - fluorine KW - fluoroarenes KW - Sonogashira reaction Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-224362 VL - 26 IS - 71 SP - 17267 EP - 17274 ER - TY - JOUR A1 - Liu, Xiaocui A1 - Ming, Wenbo A1 - Zhang, Yixiao A1 - Friedrich, Alexandra A1 - Marder, Todd B. T1 - Kupferkatalysierte Triborierung: Einfache, atomökonomische Synthese von 1,1,1‐Triborylalkanen aus terminalen Alkinen und HBpin JF - Angewandte Chemie N2 - Eine effiziente, einstufige Synthese von 1,1,1‐Trialkylalkanen durch die sequenzielle, dehydrierende Borylierung und zweifache Hydroborierung von terminalen Alkinen mit Pinakolboran (HBpin) wurde unter Verwendung des kostengünstigen und einfach zugänglichen Kupfersalzes Cu(OAc)2 als Katalysator realisiert. Das Verfahren zeichnet sich durch ein breites Substratspektrum, eine außerordentliche Selektivität und eine hohe Toleranz gegenüber funktionellen Gruppen aus. Zudem kann die Reaktion ohne Ausbeuteverlust im Gramm‐Maßstab durchgeführt werden. Die somit erhaltenen 1,1,1‐Trialkylalkane können Anwendungen in der Herstellung von synthetisch wertvollen und bislang schwer zugänglichen α‐Vinylboronaten und zyklischen Boryl‐Verbindungen finden. Verschiedene Alkylgruppen können stufenweise über eine basenvermittelte deborylierende Alkylierung eingeführt werden, um racemische, tertiäre Alkylboronate herzustellen, die einfach in nützliche tertiäre Alkohole umgewandelt werden können. KW - Boronsäure KW - Dehydrierende Borylierung KW - Geminaler Bisboronat KW - Hydroborierung KW - Kreuzkupplung Y1 - 2019 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-212189 VL - 131 IS - 52 ER -