Publications by authors named "Michael Bolte"

396 Publications

Nucleophilic borylation of fluorobenzenes with reduced arylboranes.

Chem Commun (Camb) 2021 Dec 23;58(2):254-257. Epub 2021 Dec 23.

Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Straße 7, Frankfurt (Main) D-60438, Germany.

Two challenging but rewarding topics in chemical synthesis are C-F-bond activation and the development of B-centered nucleophiles. We have now tackled both subjects simultaneously by forming aryl-B bonds SAr-type reactions on fluorobenzenes under mild conditions using Na[FluBBFlu], Li[HBFlu], and Li[MeDBA] (BFlu = 9-borafluorenyl, MeDBA = 9,10-dimethyl-9,10-dihydro-9,10-diboraanthracene).
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http://dx.doi.org/10.1039/d1cc06225eDOI Listing
December 2021

Subvalent mixed SiGe oligomers: (ClSi)Ge and Cl(MeEtN)SiGe(SiCl).

Chem Commun (Camb) 2021 Nov 11;57(90):12028-12031. Epub 2021 Nov 11.

Institut für Anorganische Chemie, Goethe-Universität Frankfurt am Main, Max-von-Laue-Straße 7, 60438 Frankfurt am Main, Germany.

(ClSi)Ge (1; 91%) is accessible from GeCl, the SiCl/[BuN]Cl silylation system, and excess SiCl. A key intermediate step involves Cl sequestration with AlCl in the course of the reaction between the first-formed germanide [(ClSi)Ge] and SiCl. The related adduct Cl(MeEtN)SiGe(SiCl) (2; quantitative conversion) was prepared either by amine-induced cleavage of 1 or by a bottom-up synthesis starting from GeCl and SiCl.
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http://dx.doi.org/10.1039/d1cc05604bDOI Listing
November 2021

Synthesis of γ-Hydroxy-α-amino Acid Derivatives by Enzymatic Tandem Aldol Addition-Transamination Reactions.

ACS Catal 2021 Apr 2;11(8):4660-4669. Epub 2021 Apr 2.

Institute for Advanced Chemistry of Catalonia, Department of Biological Chemistry, IQAC-CSIC, Jordi Girona 18-24, Barcelona 08034, Spain.

Three enzymatic routes toward γ-hydroxy-α-amino acids by tandem aldol addition-transamination one-pot two-step reactions are reported. The approaches feature an enantioselective aldol addition of pyruvate to various nonaromatic aldehydes catalyzed by --hydroxybenzylidene pyruvate hydratase-aldolase (HBPA) from . This affords chiral 4-hydroxy-2-oxo acids, which were subsequently enantioselectively aminated using -selective transaminases. Three transamination processes were investigated involving different amine donors and transaminases: (i) l-Ala as an amine donor with pyruvate recycling, (ii) a benzylamine donor using benzaldehyde lyase from Biovar I (BAL) to transform the benzaldehyde formed into benzoin, minimizing equilibrium limitations, and (iii) l-Glu as an amine donor with a double cascade comprising branched-chain α-amino acid aminotransferase (BCAT) and aspartate amino transferase (AspAT), both from , using l-Asp as a substrate to regenerate l-Glu. The γ-hydroxy-α-amino acids thus obtained were transformed into chiral α-amino-γ-butyrolactones, structural motifs found in many biologically active compounds and valuable intermediates for the synthesis of pharmaceutical agents.
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http://dx.doi.org/10.1021/acscatal.1c00210DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8482765PMC
April 2021

The power of trichlorosilylation: isolable trisilylated allyl anions, allyl radicals, and allenyl anions.

Chem Sci 2021 Sep 13;12(37):12419-12428. Epub 2021 Aug 13.

Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt Max-von-Laue-Straße 7 D-60438 Frankfurt (Main) Germany

Treatment of hexachloropropene (ClC[double bond, length as m-dash]C(Cl)-CCl) with SiCl and [BuN]Cl (1 : 4 : 1) in CHCl results in a quantitative conversion to the trisilylated, dichlorinated allyl anion salt [BuN][ClC[double bond, length as m-dash]C(SiCl)-C(SiCl)] ([BuN][]). Tetrachloroallene ClC[double bond, length as m-dash]C[double bond, length as m-dash]CCl was identified as the first intermediate of the reaction cascade. In the solid state, [] adopts approximate symmetry with a dihedral angle between the planes running through the olefinic and carbanionic fragments of [] of C[double bond, length as m-dash]C-Si//Si-C-Si = 78.3(1)°. One-electron oxidation of [BuN][] with SbCl furnishes the distillable blue radical ˙. The neutral propene ClC[double bond, length as m-dash]C(SiCl)-C(SiCl)H () was obtained by (i) protonation of [] with HOSOCF (HOTf) or (ii) H-atom transfer to ˙ from 1,4-cyclohexadiene. Quantitative transformation of all three SiCl substituents in to Si(OMe) ( ) or SiMe ( ) substituents was achieved by using MeOH/NMeEt or MeMgBr in CHCl or THF, respectively. Upon addition of 2 equiv. of BuLi, underwent deprotonation with subsequent LiCl elimination, 1,2-SiMe migration and Cl/Li exchange to afford the allenyl lithium compound MeSi(Li)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiMe) (Li[]), which is an efficient building block for the introduction of Me, SiMe, or SnMe () groups. The trisilylated, monochlorinated allene ClSi(Cl)C[double bond, length as m-dash]C[double bond, length as m-dash]C(SiCl) (), was obtained from [BuN][] through Cl-ion abstraction with AlCl and rearrangement in CHCl (˙ forms as a minor side product, likely because the system AlCl/CHCl can also act as a one-electron oxidant).
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http://dx.doi.org/10.1039/d1sc03958jDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8480423PMC
September 2021

Oxyenamides as Versatile Building Blocks for a Highly Stereoselective One-Pot Synthesis of the 1,3-Diamino-2-ol-Scaffold Containing Three Continuous Stereocenters.

Angew Chem Int Ed Engl 2021 10 28;60(44):23667-23671. Epub 2021 Sep 28.

Department of Chemistry, Technical University Kaiserslautern, Erwin-Schrödinger-Strasse Geb. 54, 67663, Kaiserslautern, Germany.

A highly diastereoselective one-pot synthesis of the 1,3-diamino-2-alcohol unit bearing three continuous stereocenters is described. This method utilizes 2-oxyenamides as a novel type of building block for the rapid assembly of the 1,3-diamine scaffold containing an additional stereogenic oxygen functionality at the C2 position. A stereoselective preparation of the required (Z)-oxyenamides is reported as well.
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http://dx.doi.org/10.1002/anie.202109752DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8597051PMC
October 2021

Selective One-Pot Syntheses of Mixed Silicon-Germanium Heteroadamantane Clusters.

Chemistry 2021 Oct 15;27(58):14401-14404. Epub 2021 Sep 15.

Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Straße 7, 60438, Frankfurt am Main, Germany.

Si Ge alloys are emerging materials for modern semiconductor technology. Well-defined model systems of the bulk structures aid in understanding their intrinsic characteristics. Three such model clusters have now been realized in the form of the Si Ge heteroadamantanes [0], [1], and [2] through selective one-pot syntheses starting from Me GeCl , Si Cl , and [nBu N]Cl. Compound [0] contains six GeMe and four SiSiCl vertices, whereas one and two of the GeMe groups are replaced by SiCl moieties in compounds [1] and [2], respectively. Chloride-ion-mediated rearrangement quantitatively converts [2] into [1] at room temperature and finally into [0] at 60 °C, which is not only remarkable in view of the rigidity of these cage structures but also sheds light on the assembly mechanism.
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http://dx.doi.org/10.1002/chem.202102732DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8596519PMC
October 2021

[[email protected]]: Parent Siladodecahedrane with Endohedral Chloride Ion.

J Am Chem Soc 2021 07 13;143(29):10865-10871. Epub 2021 Jul 13.

Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt am Main, Max-von-Laue-Straße 7, 60438 Frankfurt am Main, Germany.

Fullerenes and diamondoids are at the core of nanoscience. Comparable monodisperse silicon analogues are scarce. Herein, we report the synthesis of the parent siladodecahedrane, which represents the largest Platonic solid. It shares its pattern of pentagonal faces with the smallest fullerene, C, and its saturated, H-terminated skeleton with diamondoids. Similar to endofullerenes, the silicon cage encapsulates a chloride ion ([[email protected]]); similar to diamondoids, its Si-H termini offer a wealth of opportunities for further functionalization. Mere treatment with chloromethanes leads to the perchlorinated cluster [[email protected]]. Both compounds were characterized by mass spectrometry, X-ray crystallography, NMR spectroscopy, and quantum-chemical calculations. The experimentally determined Cl resonances of the endohedral chloride ions are particularly diagnostic to probe the Cl → Si interaction strength as a function of the different surface substituents, as we have proven by high-level computational analyses.
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http://dx.doi.org/10.1021/jacs.1c05598DOI Listing
July 2021

One tool to bring them all: Au-catalyzed synthesis of B,O- and B,N-doped PAHs from boronic and borinic acids.

Chem Sci 2021 Mar 17;12(16):5898-5909. Epub 2021 Mar 17.

Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt Max-von-Laue-Straße 7 D-60438 Frankfurt (Main) Germany

The isoelectronic replacement of C[double bond, length as m-dash]C bonds with B[double bond, length as m-dash]N bonds in polycyclic aromatic hydrocarbons (PAHs) is a widely used tool to prepare novel optoelectronic materials. Far less well explored are corresponding B,O-doped PAHs, although they have a similarly high application potential. We herein report on the modular synthesis of B,N- and B,O-doped PAHs through the [Au(PPh)NTf]-catalyzed 6--dig cyclization of BN-H and BO-H bonds across suitably positioned C[triple bond, length as m-dash]C bonds in the key step. Readily available, easy-to-handle -alkynylaryl boronic and borinic acids serve as starting materials, which are either cyclized directly or first converted into the corresponding aminoboranes and then cyclized. The reaction even tolerates bulky mesityl substituents on boron, which later kinetically protect the formed B,N/O-PAHs from hydrolysis or oxidation. Our approach is also applicable for the synthesis of rare doubly B,N/O-doped PAHs. Specifically, we prepared 1,2-B,E-naphthalenes and -anthracenes, 1,5-B-2,6-E-anthracenes (E = N, O) as well as B,O-containing and unprecedented B,N,O-containing phenalenyls. Selected examples of these compounds have been structurally characterized by X-ray crystallography; their optoelectronic properties have been studied by cyclic voltammetry, electron spectroscopy, and quantum-chemical calculations. Using a new unsubstituted (B,O)-perylene as the substrate for late-stage functionalization, we finally show that the introduction of two pinacolatoboryl (Bpin) substituents is possible in high yield and with perfect regioselectivity an Ir-catalyzed C-H borylation approach.
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http://dx.doi.org/10.1039/d1sc00543jDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8179653PMC
March 2021

A Chemiluminescent Tetraaryl Diborane(4) Tetraanion.

Angew Chem Int Ed Engl 2021 Aug 20;60(35):19397-19405. Epub 2021 Jul 20.

Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt (Main), Germany.

Two subvalent, redox-active diborane(4) anions, [3] and [3] , carrying exceptionally high negative charge densities are reported: Reduction of 9-methoxy-9-borafluorene with Li granules without stirring leads to the crystallization of the B(sp )-B(sp ) diborane(5) anion salt Li[5]. [5] contains a 2,2'-biphenyldiyl-bridged B-B core, a chelating 2,2'-biphenyldiyl moiety, and a MeO substituent. Reduction of Li[5] with Na metal gives the Na salt of the tetraanion [3] in which two doubly reduced 9-borafluorenyl fragments are linked via a B-B single bond. Comproportionation of Li[5] and Na [3] quantitatively furnishes the diborane(4) dianion salt Na [3], the doubly boron-doped congener of 9,9'-bis(fluorenylidene). Under acid catalysis, Na [3] undergoes a formal Stone-Wales rearrangement to yield a dibenzo[g,p]chrysene derivative with B=B core. Na [3] shows boron-centered nucleophilicity toward n-butyl chloride. Na [3] produces bright blue chemiluminescence when exposed to air.
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http://dx.doi.org/10.1002/anie.202106980DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8456833PMC
August 2021

Supramolecular structures of Ni and Cu with the sterically demanding Schiff base dyes driven by cooperative action of preagostic and other non-covalent interactions.

IUCrJ 2021 May 1;8(Pt 3):351-361. Epub 2021 May 1.

University of Tyumen, Volodarskogo Street 6, Tyumen, 625003, Russian Federation.

This work reports on synthesis and extensive experimental and theoretical investigations on photophysical, structural and thermal properties of the Ni and Cu discrete mononuclear homoleptic complexes [Ni( )] and [Cu( )] fabricated from the Schiff base dyes -HOCH-CH=N--CH (H ) and -HOCH-CH=N--CH (H ), containing the sterically crowding cyclo-hexyl units. The six-membered metallocycles adopt a clearly defined envelope conformation in [Ni( )], while they are much more planar in the structures of [Ni( )] and [Cu( )]. It has been demonstrated by in-depth bonding analyses based on the ETS-NOCV and Interacting Quantum Atoms energy-decomposition schemes that application of the bulky substituents, containing several C-H groups, has led to the formation of a set of classical and unintuitive intra- and inter-molecular interactions. All together they are responsible for the high stability of [Ni( )] and [Cu( )]. More specifically, London dispersion dominated intramolecular C-H⋯O, C-H⋯N and C-H⋯H-C hydrogen bonds are recognized and, importantly, the attractive, chiefly the Coulomb driven, preagostic (not repulsive anagostic) C-H⋯Ni/Cu interactions have been discovered despite their relatively long distances (∼2.8-3.1 Å). All the complexes are further stabilized by the extremely efficient intermolecular C-H⋯π(benzene) and C-H⋯π(chelate) interactions, where both the charge-delocalization and London dispersion constituents appear to be crucial for the crystal packing of the obtained complexes. All the complexes were found to be photoluminescent in CHCl, with [Cu( )] exhibiting the most pronounced emission - the time-dependent density-functional-theory computations revealed that it is mostly caused by metal-to-ligand charge-transfer transitions.
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http://dx.doi.org/10.1107/S2052252521000610DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8086159PMC
May 2021

First crystal structure of a Pigment Red 52 compound: DMSO solvate hydrate of the monosodium salt.

Acta Crystallogr E Crystallogr Commun 2021 Apr 19;77(Pt 4):402-405. Epub 2021 Mar 19.

Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany.

Pigment Red 52, Na[CHClNOS], is an industrially produced hydrazone-laked pigment. It serves as an inter-mediate in the synthesis of the corresponding Ca and Mn salts, which are used commercially for printing inks and lacquers. Hitherto, no crystal structure of any salt of Pigment Red 52 is known. Now, single crystals have been obtained of a dimethyl sulfoxide solvate hydrate of the monosodium salt of Pigment Red 52, namely, monosodium 2-[2-(3-carb-oxy-2-oxo-1,2-di-hydro-naphthalen-1-yl-idene)hydrazin-1-yl]-5-chloro-4-methyl-benz-ene-sulfonate dimethyl sulfoxide monosolvate monohydrate, Na·CHClNOS·HO·CHOS, obtained from in-house synthesized Pigment Red 52. The crystal structure was determined by single-crystal X-ray diffraction at 173 K. In this monosodium salt, the SO group is deprotonated, whereas the COOH group is protonated. The residues form chains ionic inter-actions and hydrogen bonds. The chains are arranged in polar/non-polar double layers.
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http://dx.doi.org/10.1107/S2056989021002577DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8025858PMC
April 2021

B-B vs. B-H Bond Activation in a (μ-Hydrido)diborane(4) Anion upon Cycloaddition with CO , Isocyanates, or Carbodiimides.

Angew Chem Int Ed Engl 2021 Jun 7;60(24):13500-13506. Epub 2021 May 7.

Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt (Main), Germany.

The intriguing (μ-hydrido)diboranes(4) with their prominent pristine representative [B H ] have mainly been studied theoretically. We now describe the behavior of the planarized tetraaryl (μ-hydrido)diborane(4) anion [1H] in cycloaddition reactions with the homologous series of heterocumulenes CO , iPrNCO, and iPrNCNiPr. We show that a C=O bond of CO selectively activates the B-B bond of [1H] , while the μ-H ligand is left untouched ([2H] ). The carbodiimide iPrNCNiPr, in contrast, neglects the B-B bond and rather adds the B-bonded H ion to its central C atom to generate a formamidinate bridge across the B pair ([3] ). As a hybrid, the isocyanate iPrNCO combines the reactivity patterns of both its congeners and gives two products: one of them ([4H] ) is related to [2H] , the other ([5] ) is an analog of [3] . We finally propose a mechanistic scenario that rationalizes the individual reaction outcomes and combines them to a coherent picture of B-B vs. B-H bond activation.
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http://dx.doi.org/10.1002/anie.202103427DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC8252796PMC
June 2021

Synthesis, X-ray, Hirshfeld surface analysis, exploration of DNA binding, urease enzyme inhibition and anticancer activities of novel adamantane-naphthyl thiourea conjugate.

Bioorg Chem 2021 04 9;109:104707. Epub 2021 Feb 9.

Hacettepe University, Department of Physics, 06800 Beytepe-Ankara, Turkey.

1-(adamantane-1-carbonyl-3-(1-naphthyl)) thiourea (CHNOS (4), was synthesized by the reaction of freshly prepared adamantane-1-carbonyl chloride from corresponding acid (3) with ammonium thiocyanate in 1:1 M ratio in dry acetone to afford the adamantane-1-carbonyl isothiocyanate (2) in situ followed by treatment with 1-naphthyl amine (3). The structure was established by elemental analyses, FTIR, H, C NMR and mass spectroscopy. The molecular and crystal structure were determined by single crystal X-ray analysis. It belongs to triclinic system P - 1 space group with a = 6.7832(5) Å, b = 11.1810(8) Å, c = 13.6660(10) Å, α = 105.941(6)°, β = 103.730(6)°, γ = 104.562(6)°, Z = 2, V = 910.82(11) Å. The naphthyl group is almost planar. In the crystal structure, intermolecular CH···O hydrogen bonds link the molecules into centrosymmetric dimers, enclosing R(14) ring motifs, while the intramolecular NH···O hydrogen bonds enclose S(6) ring motifs, in which they may be effective in the stabilization of the structure. The Hirshfeld surface analysis of the crystal structure indicates that the most important contributions for the crystal packing are from H … H (59.3%), H … C/C … H (19.8%) and H … S/S … H (10.1%) interactions. Hydrogen bonding and van der Waals interactions are the dominant interactions in the crystal packing. DFT, molecular docking and urease inhibition studies revealed stability and electron withdrawing nature of 4 as compared to DNA base pairs and residues of urease. The DNA binding results from docking, UV- visible spectroscopy, and viscosity studies indicated significant binding of 4 with the DNA via intercalation and groove binding. Further investigation of the compound was done on hepatocellular carcinoma; Huh-7 cell line as well as normal human embryonic kidney; Hek-293 cell line. The compound showed significant cytotoxic activity against Huh-7 cells in comparison to normal Hek-293 cells indicating selective cytotoxicity towards cancer cells.
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http://dx.doi.org/10.1016/j.bioorg.2021.104707DOI Listing
April 2021

Two salts of the 6,6-di-fluoro-6-dibenzo[,][1,2]oxaborinin-6-ide anion with different cations.

Acta Crystallogr E Crystallogr Commun 2020 Dec 17;76(Pt 12):1837-1840. Epub 2020 Nov 17.

Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany.

The crystal structures are reported of the 6,6-di-fluoro-6-dibenzo[,][1,2]oxaborinin-6-ide (or 9,9-di-fluoro-10-oxa-9-boraphenanthren-9-ide) anion with two different cations, namely, potassium 6,6-di-fluoro-6-dibenzo[,][1,2]oxaborinin-6-ide, K·CHBFO, (), featuring a polymeric structure, and bis-(tetra-phenyl-phospho-nium) bis-(6,6-di-fluoro-6-dibenzo[,][1,2]oxaborinin-6-ide) aceto-nitrile tris-olvate, 2CHP·2CHBFO·3CHCN, (), which is composed of discrete cations, anions and aceto-nitrile solvent mol-ecules linked by C-H⋯O, C-H⋯N and C-H⋯F hydrogen bonds. There are only minor differences in the geometrical parameters of the anions in these structures.
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http://dx.doi.org/10.1107/S2056989020015066DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7784652PMC
December 2020

Biocatalytic Construction of Quaternary Centers by Aldol Addition of 3,3-Disubstituted 2-Oxoacid Derivatives to Aldehydes.

J Am Chem Soc 2020 11 4;142(46):19754-19762. Epub 2020 Nov 4.

Biological Chemistry Department, Instituto de Química Avanzada de Cataluña, IQAC-CSIC, Jordi Girona 18-26, 08034 Barcelona, Spain.

The congested nature of quaternary carbons hinders their preparation, most notably when stereocontrol is required. Here we report a biocatalytic method for the creation of quaternary carbon centers with broad substrate scope, leading to different compound classes bearing this structural feature. The key step comprises the aldol addition of 3,3-disubstituted 2-oxoacids to aldehydes catalyzed by metal dependent 3-methyl-2-oxobutanoate hydroxymethyltransferase from (KPHMT) and variants thereof. The 3,3,3-trisubstituted 2-oxoacids thus produced were converted into 2-oxolactones and 3-hydroxy acids and directly to ulosonic acid derivatives, all bearing -dialkyl, -cycloalkyl, and spirocyclic quaternary centers. In addition, some of these reactions use a single enantiomer from racemic nucleophiles to afford stereopure quaternary carbons. The notable substrate tolerance and stereocontrol of these enzymes are indicative of their potential for the synthesis of structurally intricate molecules.
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http://dx.doi.org/10.1021/jacs.0c09994DOI Listing
November 2020

Electron Transfer Dynamics and Structural Effects in Benzonitrile Monolayers with Tuned Dipole Moments by Differently Positioned Fluorine Atoms.

ACS Appl Mater Interfaces 2020 Sep 20;12(35):39859-39869. Epub 2020 Aug 20.

Angewandte Physikalische Chemie, Universität Heidelberg, Im Neuenheimer Feld 253, D-69120 Heidelberg, Germany.

To understand the influence of the molecular dipole moment on the electron transfer (ET) dynamics across the molecular framework, two series of differently fluorinated, benzonitrile-based self-assembled monolayers (SAMs) bound to Au(111) by either thiolate or selenolate anchoring groups were investigated. Within each series, the molecular structures were the same with the exception of the positions of two fluorine atoms affecting the dipole moment of the SAM-forming molecules. The SAMs exhibited a homogeneous anchoring to the substrate, nearly upright molecular orientations, and the outer interface comprised of the terminal nitrile groups. The ET dynamics was studied by resonant Auger electron spectroscopy in the framework of the core-hole clock method. Resonance excitation of the nitrile group unequivocally ensured an ET pathway from the tail group to the substrate. As only one of the π* orbitals of this group is hybridized with the π* system of the adjacent phenyl ring, two different ET times could be determined depending on the primary excited orbital being either localized at the nitrile group or delocalized over the entire benzonitrile moiety. The latter pathway turned out to be much more efficient, with the characteristic ET times being a factor 2.5-3 shorter than those for the localized orbital. The dynamic ET properties of the analogous thiolate- and selenolate-based adsorbates were found to be nearly identical. Finally and most importantly, these properties were found to be unaffected by the different patterns of the fluorine substitution used in the present study, thus showing no influence of the molecular dipole moment.
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http://dx.doi.org/10.1021/acsami.0c10513DOI Listing
September 2020

Two monosodium salt hydrates of Colour Index Pigment Red 48.

Acta Crystallogr C Struct Chem 2020 Aug 6;76(Pt 8):716-722. Epub 2020 Jul 6.

Institut für Organische Chemie und Chemische und Chemische Biologie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany.

We report herein the crystal structures of a monohydrate of Colour Index Pigment Red 48 (P.R.48) (systematic name: monosodium 2-{2-[3-carboxy-2-oxo-1,2-dihydronaphthalen-1-ylidene]hydrazin-1-yl}-4-chloro-5-methylbenzenesulfonate monohydrate), Na·CHClOS·HO, and a dihydrate, Na·CHClOS·2HO. The two monosodium salt hydrates of P.R.48 were obtained from in-house synthesized P.R.48. Both have monoclinic (P2/c) symmetry at 173 K. The crystal packing of both crystal structures shows a layer arrangement whereby N-H...O and O-H...O hydrogen bonds are formed.
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http://dx.doi.org/10.1107/S2053229620008530DOI Listing
August 2020

Building up Strain in One Step: Synthesis of an Edge-Fused Double Silacyclobutene from an Extensively Trichlorosilylated Butadiene Dianion.

Angew Chem Int Ed Engl 2020 Sep 29;59(37):16181-16187. Epub 2020 Jun 29.

Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Straße 7, 60438, Frankfurt (Main), Germany.

The exhaustive trichlorosilylation of hexachloro-1,3-butadiene was achieved in one step by using a mixture of Si Cl and [nBu N]Cl (7:2 equiv) as the silylation reagent. The corresponding butadiene dianion salt [nBu N] [1] was isolated in 36 % yield after recrystallization. The negative charges of [1] are mainly delocalized across its two carbanionic (Cl Si) C termini (α-effect of silicon) such that the central bond possesses largely C=C double-bond character. Upon treatment with 4 equiv of HCl, [1] is converted into neutral 1,2,3,4-tetrakis(trichlorosilyl)but-2-ene, 3. The Cl acceptor AlCl , induces a twofold ring-closure reaction of [1] to form a six-membered bicycle 4 in which two silacyclobutene rings are fused along a shared C=C double bond (84 %). Compound 4, which was structurally characterized by X-ray crystallography, undergoes partial ring opening to a monocyclic silacyclobutene 2 in the presence of HCl, but is thermally stable up to at least 180 °C.
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http://dx.doi.org/10.1002/anie.202006463DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7540532PMC
September 2020

BNB-Doped Phenalenyls: Modular Synthesis, Optoelectronic Properties, and One-Electron Reduction.

J Am Chem Soc 2020 06 15;142(25):11072-11083. Epub 2020 Jun 15.

Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt am Main, Max-von-Laue-Straße 7, 60438 Frankfurt am Main, Germany.

A highly modular synthesis of BNB- and BOB-doped phenalenyls is presented. Treatment of the 1,8-naphthalenediyl-bridged boronic acid anhydride with LiAlH/MeSiCl afforded the corresponding 1,8-naphthalenediyl-supported diborane(6) , which served as the starting material for all subsequent transformations. Upon addition of MesMgBr/MeSiCl, was readily converted to the tetraorganyl diborane(6) . The further heteroatoms were finally introduced through the reaction of with (MeSi)NR' or with HNR' or HO (R' = H, Me, -Tol). A helically twisted, fully BNB-embedded PAH was prepared by combining with a dibrominated -terphenylamine, followed by a Grignard-mediated double ring-closure reaction. All compounds devoid of B-H bonds show favorable optoelectronic properties, such as luminescence and reversible reduction behavior. In the case of the BNB-phenalenyl (BMes, NMe), the radical-anion salt K[] was generated through chemical reduction with K metal and characterized by EPR spectroscopy. K[] is not long-term stable in a THF/-hexane solution, but abstracts an H atom with formation of the diamagnetic BNB-doped 1-phenalene K[H].
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http://dx.doi.org/10.1021/jacs.0c03118DOI Listing
June 2020

Resonance Assisted Hydrogen Bonding Phenomenon Unveiled through Both Experiments and Theory: A New Family of Ethyl N-Salicylideneglycinate Dyes.

Chemistry 2020 Oct 3;26(57):12987-12995. Epub 2020 Sep 3.

University of Tyumen, Volodarskogo Str.6, 625003, Tyumen, Russian Federation.

Extensive experimental and theoretical investigations are reported on the nature of resonance-assisted hydrogen bonding phenomenon (RAHB) and its influence on photophysical properties of the newly designed dyes differing in donor-acceptor properties, namely ethyl N-salicylideneglycinate (1), ethyl N-(5-methoxysalicylidene)glycinate (2), ethyl N-(5-bromosalicylidene)glycinate (3) and ethyl N-(5-nitrosalicylidene)glycinate (4). All compounds are thermochromic in the solid state and they contain a typical intramolecular O-H⋅⋅⋅N hydrogen bond formed between the hydroxyl hydrogen atom and the imine nitrogen atom, yielding the enol form in the solid state. It is unveiled, that the magnitude of RAHB effect fine tunes the strength of the O-H⋅⋅⋅N bonding and accordingly the relative populations of the enol, cis-keto and trans-keto forms leading to variation of the photophysical properties of 1-4. It is determined, that the electron-withdrawing NO in 4 amplifies the most RAHB effect causing the breaking of the O-H⋅⋅⋅N hydrogen bond and accordingly formation of the dominant cis-keto isomer in both the solid state and EtOH. To this end, the UV/Vis spectra of 1-3 in EtOH revealed the exclusive presence of the enol form, while the prevalent contribution of the cis-keto form was found for 4. Furthermore, only compound 4 is emissive in the solid state in ambient condition due to dual emission arising from the cis-keto* and trans-keto* forms, while 2 was found to be highly emissive in EtOH. It is revealed qualitatively and quantitatively, based on the ETS-NOCV charge and energy decomposition scheme and the EDDB population-based method, that RAHB is strongly a non-local phenomenon based on electrons pumping or sucking through both the π- and σ-channels, which accordingly exerts chemical bonding changes at both the phenyl ring and predominantly a distant O-H⋅⋅⋅N area.
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http://dx.doi.org/10.1002/chem.202001551DOI Listing
October 2020

Synthesis and Biological Screening of New Lawson Derivatives as Selective Substrate-Based Inhibitors of Cytochrome bo Ubiquinol Oxidase from Escherichia coli.

ChemMedChem 2020 07 14;15(14):1262-1271. Epub 2020 Apr 14.

Center for Biomolecular Magnetic Resonance Institute of Organic Chemistry and Chemical Biology, Goethe-Universität Frankfurt am Main, Max-von Laue-Straße 7, 60438, Frankfurt am Main, Germany.

The respiratory chain of Escherichia coli contains two different types of terminal oxidase that are differentially regulated as a response to changing environmental conditions. These oxidoreductases catalyze the reduction of molecular oxygen to water and contribute to the proton motive force. The cytochrome bo oxidase (cyt bo ) acts as the primary terminal oxidase under atmospheric oxygen levels, whereas the bd-type oxidase is most abundant under microaerobic conditions. In E. coli, both types of respiratory terminal oxidase (HCO and bd-type) use ubiquinol-8 as electron donor. Here, we assess the inhibitory potential of newly designed and synthesized 3-alkylated Lawson derivatives through L-proline-catalyzed three-component reductive alkylation (TCRA). The inhibitory effects of these Lawson derivatives on the terminal oxidases of E. coli (cyt bo and cyt bd-I) were tested potentiometrically. Four compounds were able to reduce the oxidoreductase activity of cyt bo by more than 50 % without affecting the cyt bd-I activity. Moreover, two inhibitors for both cyt bo and cyt bd-I oxidase could be identified. Based on molecular-docking simulations, we propose binding modes of the new Lawson inhibitors. The molecular fragment benzyl enhances the inhibitory potential and selectivity for cyt bo , whereas heterocycles reduce this effect. This work extends the library of 3-alkylated Lawson derivatives as selective inhibitors for respiratory oxidases and provides molecular probes for detailed investigations of the mechanisms of respiratory-chain enzymes of E. coli.
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http://dx.doi.org/10.1002/cmdc.201900707DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7497249PMC
July 2020

A new pseudopolymorph of perchlorinated neo-penta-silane: the benzene monosolvate Si(SiCl)·CH.

Acta Crystallogr E Crystallogr Commun 2020 Feb 31;76(Pt 2):261-263. Epub 2020 Jan 31.

Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438 Frankfurt am Main, Germany.

A new pseudopolymorph of dodeca-chloro-penta-silane, namely a benzene monosolvate, SiCl·CH, is described. There are two half mol-ecules of each kind in the asymmetric unit. Both SiCl mol-ecules are completed by crystallographic twofold symmetry. One of the benzene mol-ecules is located on a twofold rotation axis with two C-H groups located on this rotation axis. The second benzene mol-ecule has all atoms on a general position: it is disordered over two equally occupied orientations. No directional inter-actions beyond normal van der Waals contacts occur in the crystal.
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http://dx.doi.org/10.1107/S2056989020000900DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7001847PMC
February 2020

B-B Bond Nucleophilicity in a Tetraaryl μ-Hydridodiborane(4) Anion.

Angew Chem Int Ed Engl 2020 May 19;59(20):7726-7731. Epub 2020 Mar 19.

Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt (Main), Germany.

The tetraaryl μ-hydridodiborane(4) anion [2H] possesses nucleophilic B-B and B-H bonds. Treatment of K[2H] with the electrophilic 9-H-9-borafluorene (HBFlu) furnishes the B cluster K[3], with a triangular boron core linked through two BHB two-electron, three-center bonds and one electron-precise B-B bond, reminiscent of the prominent [B H ] anion. Upon heating or prolonged stirring at room temperature, K[3] rearranges to a slightly more stable isomer K[3 a]. The reaction of M[2H] (M =Li , K ) with MeI or Me SiCl leads to equimolar amounts of 9-R-9-borafluorene and HBFlu (R=Me or Me Si). Thus, [2H] behaves as a masked [:BFlu] nucleophile. The HBFlu by-product was used in situ to establish a tandem substitution-hydroboration reaction: a 1:1 mixture of M[2H] and allyl bromide gave the 1,3-propylene-linked ditopic 9-borafluorene 5 as sole product. M[2H] also participates in unprecedented [4+1] cycloadditions with dienes to furnish dialkyl diaryl spiroborates, M[R BFlu].
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http://dx.doi.org/10.1002/anie.202000292DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7317828PMC
May 2020

Highly Selective Anion Template Effect in the Synthesis of Constrained Pseudopeptidic Macrocyclic Cyclophanes.

J Org Chem 2020 01 3;85(2):1138-1145. Epub 2020 Jan 3.

Departamento de Química Inorgánica y Orgánica , Universitat JaumeI , Av. Sos Baynat s/n , 12071 Castellón , Spain.

Herein, we report the synthesis of a novel family of constrained pseudopeptidic macrocyclic compounds containing the hexahydropyrrolo[3,4-]isoindolocyclophane scaffold and involving four coupled substitution reactions in the macrocyclization process. Although the increase in the number of steps involved in the macrocyclization could lead to a larger number of possible side products, the optimization of the methodology and the study of the driving forces have made it possible to obtain the desired macrocycles in excellent yields. A thorough computational study has been carried out to understand the macrocyclization process, and the results obtained nicely agree with experimental data. Moreover, the bromide anion had a clear catalytic template effect in the macrocyclization reaction, and surprisingly, the chloride anion had a negative template effect in opposition to the results obtained for analogous macrocycles. The parameters responsible for the specific kinetic template effect observed have been studied in detail.
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http://dx.doi.org/10.1021/acs.joc.9b03048DOI Listing
January 2020

The 9H-9-Borafluorene Dianion: A Surrogate for Elusive Diarylboryl Anion Nucleophiles.

Angew Chem Int Ed Engl 2020 Mar 22;59(14):5621-5625. Epub 2020 Jan 22.

Institut für Anorganische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, 60438, Frankfurt (Main), Germany.

Double reduction of the THF adduct of 9H-9-borafluorene (1⋅THF) with excess alkali metal affords the dianion salts M [1] in essentially quantitative yields (M=Li-K). Even though the added charge is stabilized through π delocalization, [1] acts as a formal boron nucleophile toward organoboron (1⋅THF) and tetrel halide electrophiles (MeCl, Et SiCl, Me SnCl) to form B-B/C/Si/Sn bonds. The substrate dependence of open-shell versus closed-shell pathways has been investigated.
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http://dx.doi.org/10.1002/anie.201914219DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7155136PMC
March 2020

Mechanochemical synthesis and X-ray structural characterization of three 3-nitrophenol cocrystals with three aminal cage azaadamantanes: the role of the stereoelectronic effect on intermolecular hydrogen-bonding patterns.

Acta Crystallogr C Struct Chem 2019 12 22;75(Pt 12):1635-1643. Epub 2019 Nov 22.

Institut für Anorganische Chemie, J. W. Goethe-Universität Frankfurt, Max-von Laue-Strasse 7, 60438 Frankfurt/Main, Germany.

The structures of the cocrystalline adducts of 3-nitrophenol (3-NP) with 1,3,5,7-tetraazatricyclo[3.3.1.1]decane [HMTA, (1)] as the 2:1:1 hydrate, 2CHNO·CHN·HO, (1a), with 1,3,6,8-tetraazatricyclo[4.3.1.1]undecane [TATU (2)] as the 2:1 cocrystal, 2CHNO·CHN, (2a), and with 1,3,6,8-tetraazatricyclo[4.4.1.1]dodecane [TATD, (3)] as the 2:1 cocrystal, 2CHNO·CHN, (3a), are reported. In the binary crystals (2a) and (3a), the 3-nitrophenol molecules are linked via O-H...N hydrogen bonds into aminal cage azaadamantanes. In (1a), the structure is stabilized by O-H...N and O-H...O hydrogen bonds, and generates ternary cocrystals. There are C-H...O hydrogen bonds present in all three cocrystals, and in (1a), there are also C-H...O and C-H...π interactions present. The presence of an ethylene bridge in the structures of (2) and (3) defines the formation of a hydrogen-bonded motif in the supramolecular architectures of (2a) and (3a). The differences in the C-N bond lengths of the aminal cage structures, as a result of hyperconjugative interactions and electron delocalization, were analysed. These three cocrystals were obtained by the solvent-free assisted grinding method. Crystals suitable for single-crystal X-ray diffraction were grown by slow evaporation from a mixture of hexanes.
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http://dx.doi.org/10.1107/S205322961901516XDOI Listing
December 2019

Remote Control of the Synthesis of a [2]Rotaxane and its Shuttling via Metal-Ion Translocation.

ChemistryOpen 2019 Nov 19;8(11):1355-1360. Epub 2019 Nov 19.

Center of Micro and Nanochemistry and Engineering, Organische Chemie I Universität Siegen Adolf-Reichwein-Str. 2 D-57068 Siegen Germany.

Remote control in an eight-component network commanded both the synthesis and shuttling of a [2]rotaxane via metal-ion translocation, the latter being easily monitored by distinct colorimetric and fluorimetric signals. Addition of zinc(II) ions to the red colored copper-ion relay station rapidly liberated copper(I) ions and afforded the corresponding zinc complex that was visualized by a bright sky blue fluorescence at 460 nm. In a mixture of all eight components of the network, the liberated copper(I) ions were translocated to a macrocycle that catalyzed formation of a rotaxane by a double-click reaction of acetylenic and diazide compounds. The shuttling frequency in the copper-loaded [2]rotaxane was determined to =30 kHz (Δ =62.3±0.6 kJ mol, Δ =50.1±5.1 J mol K, Δ =47.4 kJ mol). Removal of zinc(II) ions from the mixture reversed the system back generating the metal-free rotaxane. Further alternate addition and removal of Zn reversibly controlled the shuttling mode of the rotaxane in this eight-component network where the ion translocation status was monitored by the naked eye.
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http://dx.doi.org/10.1002/open.201900293DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6863578PMC
November 2019

Selective access to either a doubly boron-doped tetrabenzopentacene or an oxadiborepin from the same precursor.

Chem Sci 2019 Oct 31;10(39):9017-9027. Epub 2019 Jul 31.

Institut für Anorganische Chemie , Goethe-Universität Frankfurt , Max-von-Laue-Strasse 7 , D-60438 Frankfurt (Main) , Germany . Email:

The well-known red emitter tetrabenzo[,,,]pentacene () has been transformed into a bright blue emitter (; λ = 472 nm; c-hexane) substitutional doping with two boron atoms. In contrast to the electron-rich , which forms -peroxides with O under daylight, the benchtop-stable is a good electron acceptor and undergoes reversible reduction at a moderate half-wave potential of = -1.73 V ( FcH/FcH; THF). Although the size of falls within the nanoscale, the helically twisted compound readily dissolves in c-hexane and does not require solubilizing substituents. The synthesis of is based on the nickel-mediated Yamamoto-type dehalogenation of tetrabrominated 9,10-di(naphth-1-yl)-9,10-dihydro-9,10-diboraanthracene. This intramolecular C-C heterocoupling reaction shows a remarkable solvent dependence: forms only in pyridine (79% yield), whereas an oxadiborepin is obtained from THF solutions (, 81%; the reaction mixture is quenched with air in both cases). Insight into the corresponding reaction mechanism was gained from the isolation of intermediates and an investigation of their chemical properties. is an interesting blue emitter in its own right. Furthermore, it can be ring-opened with excess BBr at the B-O-B moiety to afford a dimeric borabenzo[]anthracene.
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http://dx.doi.org/10.1039/c9sc03115dDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7442282PMC
October 2019

An Enamide-Based Domino Reaction for a Highly Stereoselective Synthesis of Tetrahydropyrans.

Angew Chem Int Ed Engl 2019 Sep 7;58(37):13056-13059. Epub 2019 Aug 7.

Department of Organic Chemistry, Technical University Kaiserslautern, Erwin-Schrödinger-Strasse Geb. 54, 67663, Kaiserslautern, Germany.

A novel method for the highly stereoselective synthesis of tetrahydropyrans is reported. This domino reaction is based on a twofold addition of enamides to aldehydes followed by a subsequent cyclization and furnishes fully substituted tetrahydropyrans in high yields. Three new σ-bonds and five continuous stereogenic centers are formed in this one-pot process with a remarkable degree of diastereoselectivity. In most cases, the formation of only one out of 16 possible diastereomers is observed. Two different stereoisomers can be accessed in a controlled fashion starting either from an E- or a Z-configured enamide.
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http://dx.doi.org/10.1002/anie.201907565DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6772187PMC
September 2019

pH-Dependent Chloride Transport by Pseudopeptidic Cages for the Selective Killing of Cancer Cells in Acidic Microenvironments.

Angew Chem Int Ed Engl 2019 09 1;58(36):12465-12468. Epub 2019 Aug 1.

Department of Biological Chemistry, IQAC-CSIC, Jordi Girona, 18-26, 08034, Barcelona, Spain.

Acidic microenvironments in solid tumors are a hallmark of cancer. Inspired by that, we designed a family of pseudopeptidic cage-like anionophores displaying pH-dependent activity. When protonated, they efficiently bind chloride anions. They also transport chloride through lipid bilayers, with their anionophoric properties improving at acidic pH, suggesting an H /Cl symport mechanism. NMR studies in DPC micelles demonstrate that the cages bind chloride within the lipid phase. The chloride affinity and the chloride-exchange rate with the aqueous bulk solution are improved when the pH is lowered. This increases cytotoxicity towards lung adenocarcinoma cells at the pH of the microenvironment of a solid tumor. These properties depend on the nature of the amino-acid side chains of the cages, which modulate their lipophilicity and interactions with the cell membrane. This paves the way towards using pH as a parameter to control the selectivity of cytotoxic ionophores as anticancer drugs.
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http://dx.doi.org/10.1002/anie.201905965DOI Listing
September 2019
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