Bernt Krebs

Bio: Bernt Krebs is an academic researcher from University of Münster. The author has contributed to research in topics: Crystal structure & Ligand. The author has an hindex of 56, co-authored 729 publications receiving 16336 citations. Previous affiliations of Bernt Krebs include Leiden University & Clariant.

Reactive EC [p‐p] π Systems, 46 Syntheses and X‐ray Crystal‐Structure Analyses of Trifluoromethyl‐Substituted Ketiminodiselanes, Selenoamides and Selenoacrylamides

Abstract: Bis(trifluoromethylketiminoalkyl)diselanes [SeC(=NR)CF3]2 (6) [R = Me (a), iPr (b), tBu (c)] have been prepared in high yields (55-70%) by reaction of the diselane (SeC2F5)2 (2) with RNH2. However, the analogous reaction of 2 with secondary amines, R2NH, results in the cleavage of the Se-Se bond and leads to the N,N-dialkyl-2,2,2-trifluoroselenoacetamides Se=C(NR2)CF3 (7) [R = Me (a), iPr (b)]. Cleavage of 6a-6c with Me3SnH affords the selenoamides Se=C(NHR)CF3 (9) and the corresponding stannylselanes Me3SnSeC(=NR)CF3 (10) [R = Me(a), iPr (b), tBu (c)]. Selenoamides 7 and 9 can also be prepared from pentafluoroethylselenol HSeC2F5 (3), Se=C(F)CF3, (1) or its polymer [SeC(F)CF3]n (4) and primary or secondary amines. N,N-dialkyl-2-methyl-3-fluoro-4,4,4-trifluoroselenoacrylamides Se=C(NR2)C(Me)=C(F)CF3[R = Et (13a), iPr (13b)] are prepared in moderate yields under mild conditions by treating either trifluoromethylselenocarbonyl fluoride (1) or its polymer [SeC(F)CF3]n with 1-dialkylamino-1-propynes. The reaction proceeds by [2 + 2] cycloaddition and stereospecific electrocyclic ring-opening, yielding, with respect to the resulting CC double bond, the E isomer as the only product. The molecular structures of 7b, 9a and 13b show the typical features of selenoamides with C(Se)-N bond shortening and C-Se bond elongation due to π interaction of the N lone pair with the CSe double bond. The observed perpendicular orientation of the selenoamide and the alkene units of 13b prevents π delocalization.

Umlagerung von azabicyclischen Hydroxylamin‐Derivaten unter Sauerstoff‐Insertion

Abstract: N-Hydroxy-2-azabicyclo[2.2.1]hept-5-en (1) wird bei der Umsetzung mit Tosyl- und Benzoylchlorid umgelagert zu den Oxaazabicyclen 3, 4 und 8. Die Struktur von 3 wurde durch Rontgenstrukturanalyse bewiesen. Versuche mit [18O]Tosylchlorid sowie die Abfangprodukte mit Methanol sprechen fur eine ionische Spaltung in dem durch N-Tosylierung gebildeten Intermediaren 11, im Gegensatz zum radikalischen Ablauf der sonst analogen Meisenheimer-Umlagerung. Rearrangement with Oxygen-Insertion in Azabicyclic Hydroxylamine Derivatives N-Hydroxy-2-azabicyclo[2.2.1]hept-5-ene (1) is rearranged to the oxaazabicyclic compounds 3, 4, and 8 by the reaction with either tosyl or benzoyl chloride. The structure of 3 was proved by X-ray analysis. Experiments with [18O]tosyl chloride as well as products of the intermediate 12 with methanol are consistent with a heterolysis in the intermediate 11 formed by N-tosylation — in contrast to the homolytic1) Meisenheimer rearrangement.

Hafniumtetrajodid HfI4: Struktur und eigenschaften. Ein neuer AB4-strukturtyp

Abstract: Zusammenfassung HfI4, das aus den Elementen in geschlossenem System mit anschliessender Sublimation in Form orangeroter Einkristalle dargestellt wurde, bildet einen neuen AB4-Strukturtyp. Die Rontgenstrukturanalyse zeigt gewinkelte unendliche Ketten aus kantenverknupften HfI6-Oktaedern mit einer Identitatsperiode von vier Formeleinheiten (keine trans-Verknupfung), die sich grundsatzlich von den Kettenstrukturen des α-NbI4, ZrCl4 und ZrI4 unterscheiden. Die Hf-I-Bindungslangenliegen zwischen 2,678(2) und 3,007(2) A, die Hf…Hf-Abstande (4,377(2) A) schliessen erwartungsgemass Hf-HfBindungsanteile aus. Die Kristalldaten sind wie folgt: monoklin, Raumgruppe C2 c , a = 11,787(4) A , b = 11,801 (3) A , c = 12,905(4) A , β = 116,30(3)°, Z = 8 HfI 4 . Massenspektren zeigen, dass die Sublimation uber HfI4-Molekule erfolgt und dass sich keine Gaskomplexe zwischen AlI3 und HfI4 bilden. Die IR- und Ramanspektren von kristallinem HfI4 werden mitgeteilt.

[Fe2{o‐(SCH2)2C6H4}2{SC6H5}2]2− und [Fe2{o‐(SCH2)2C6H4}3]2−: Zweikernige Thiolatoeisen(II)‐Anionen mit tetraedrischer FeS4‐Koordination

Abstract: Das vollstandige Manuskript dieser Zuschrift erscheint in: Angew. Chem. Suppl. 1983, 323. DOI: 10.1002/ange.198303230

The chemistry of graphene oxide

Abstract: The chemistry of graphene oxide is discussed in this critical review Particular emphasis is directed toward the synthesis of graphene oxide, as well as its structure Graphene oxide as a substrate for a variety of chemical transformations, including its reduction to graphene-like materials, is also discussed This review will be of value to synthetic chemists interested in this emerging field of materials science, as well as those investigating applications of graphene who would find a more thorough treatment of the chemistry of graphene oxide useful in understanding the scope and limitations of current approaches which utilize this material (91 references)

Phd by thesis

Abstract: Deposits of clastic carbonate-dominated (calciclastic) sedimentary slope systems in the rock record have been identified mostly as linearly-consistent carbonate apron deposits, even though most ancient clastic carbonate slope deposits fit the submarine fan systems better. Calciclastic submarine fans are consequently rarely described and are poorly understood. Subsequently, very little is known especially in mud-dominated calciclastic submarine fan systems. Presented in this study are a sedimentological core and petrographic characterisation of samples from eleven boreholes from the Lower Carboniferous of Bowland Basin (Northwest England) that reveals a >250 m thick calciturbidite complex deposited in a calciclastic submarine fan setting. Seven facies are recognised from core and thin section characterisation and are grouped into three carbonate turbidite sequences. They include: 1) Calciturbidites, comprising mostly of highto low-density, wavy-laminated bioclast-rich facies; 2) low-density densite mudstones which are characterised by planar laminated and unlaminated muddominated facies; and 3) Calcidebrites which are muddy or hyper-concentrated debrisflow deposits occurring as poorly-sorted, chaotic, mud-supported floatstones. These

The hydrogen bond in the solid state.

Abstract: The hydrogen bond is the most important of all directional intermolecular interactions. It is operative in determining molecular conformation, molecular aggregation, and the function of a vast number of chemical systems ranging from inorganic to biological. Research into hydrogen bonds experienced a stagnant period in the 1980s, but re-opened around 1990, and has been in rapid development since then. In terms of modern concepts, the hydrogen bond is understood as a very broad phenomenon, and it is accepted that there are open borders to other effects. There are dozens of different types of X-H.A hydrogen bonds that occur commonly in the condensed phases, and in addition there are innumerable less common ones. Dissociation energies span more than two orders of magnitude (about 0.2-40 kcal mol(-1)). Within this range, the nature of the interaction is not constant, but its electrostatic, covalent, and dispersion contributions vary in their relative weights. The hydrogen bond has broad transition regions that merge continuously with the covalent bond, the van der Waals interaction, the ionic interaction, and also the cation-pi interaction. All hydrogen bonds can be considered as incipient proton transfer reactions, and for strong hydrogen bonds, this reaction can be in a very advanced state. In this review, a coherent survey is given on all these matters.

The transition metal dichalcogenides discussion and interpretation of the observed optical, electrical and structural properties

Abstract: The transition metal dichalcogenides are about 60 in number. Two-thirds of these assume layer structures. Crystals of such materials can be cleaved down to less than 1000 A and are then transparent in the region of direct band-to-band transitions. The transmission spectra of the family have been correlated group by group with the wide range of electrical and structural data available to yield useful working band models that are in accord with a molecular orbital approach. Several special topics have arisen; these include exciton screening, d-band formation, and the metal/insulator transition; also magnetism and superconductivity in such compounds. High pressure work seems to offer the possibility for testing the recent theory of excitonic insulators.

Multicopper Oxidases and Oxygenases

Abstract: Copper is an essential trace element in living systems, present in the parts per million concentration range. It is a key cofactor in a diverse array of biological oxidation-reduction reactions. These involve either outer-sphere electron transfer, as in the blue copper proteins and the Cu{sub A} site of cytochrome oxidase and nitrous oxide redutase, or inner-sphere electron transfer in the binding, activation, and reduction of dioxygen, superoxide, nitrite, and nitrous oxide. Copper sites have historically been divided into three classes based on their spectroscopic features, which reflect the geometric and electronic structure of the active site: type 1 (T1) or blue copper, type 2 (T2) or normal copper, and type 3 (T3) or coupled binuclear copper centers. 428 refs.