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.

Organische Synthesen mit Übergangsmetall‐Komplexen, 54 Cyclopentadiene aus 1‐Metalla‐1,3‐dienen und Alkinen durch Cyclisierung intermediärer 1‐Metalla‐1,3,5‐triene (Metall = Wolfram)

Abstract: Organic Syntheses via Transition Metal Complexes, 54. — Cyclopentadienes from 1-Metalla-1,3-dienes and Alkynes by Cyclization of Intermediate 1-Metalla-1,3,5-trienes (Metal = Tungsten) We report on first examples of the formation of cyclopentadienes from a 1-metalla-1,3-diene LnM=C-C=C [LnM = W(CO)5] and an alkyne in [3 + 2] cycloaddition multistep reactions. In a first step the alkyne Et2N-C=C-Me (2) adds to the 1-metalla-1,3-diene (CO)5W = C(OEt)-CH=CHPh (1b) to give 1-metalla-1,3,5-trienes (CO)5W=C(NEt2)-CMe=C(OEt)-CH=CHPh (3b) and (CO)5W=C(OEt)-CH=C(NEt2)-CMe=CHPh (4b). In a second step 3b cyclizes to thecyclopentadiene complex 5, which has an η1 ylide-type structure as established by an X-ray analysis. Hydrolysis of 5 leads to the formation of a 3-aminocyclopentenone 7. The 1-metalla-1,3,5-triene 4b yields a cyclopentadiene complex 8. In contrast to 5 the carbon skeleton of 8 has a connectivity different from that of the C3 unit of the 1-metalla-1,3-diene 1.

Reaktive EC (p ? p) π‐Systeme, XIV. Synthese und Struktur von Phosphaalkenen des Typs F3CPC(F)NR2

Abstract: Perfluor-2-phosphapropen 1reagiert mit sekundaren Aminen R2NH im Molverhaltnis 1:2 bei Temperaturen zwischen −120 und −40°C quantitativ zu (Trifluormethyl) phosphaalkenen des typs F3CPC(F)NR2 [R = me(2), Et (3), i-Pr (4); NR2 = Pyrrolidino (5), Piperidino (6), 2-methylpiperidino (7), 3-Methylpiperidino (8), N-Methylanilino (9)]. diphenylamin Setzt sich selbst bei Raumtemperatur nicht in analoger Weise um. Zu den Gleichen Produkten gelangt man durch Umsetzung von (CF3)2PH mit R2NH bzw. R2NH/NEt3 im Molverhaltnis 1:3 bzw. 1:1 bzw. 1:1:2. Die neuen Verbindungen 4–9 sind wie 2 und 3 bei Raumtemperatur bestandig and besitzen ausnahmslos die Z-Konfiguration. Die Rontgenbeugungsanalyse des 1-(Dimethylamino)-1,3,3,3-tetrafluor-2-phospha-1-propens (2) beweist die beteiligung des freien Elektronenpaars am Stickstoff an der Stabilisierung des Systems. Das Gitter von 2. enthalt C4H6F4NP-Molekule mit fast planarem CPC(F)NC2-Gerust. Der PC-Bindungsabstand betragt 1.744 (2) A, der CN-Abstand ist mit 1.311(2)A 0.16A Kurzer als die CN Einfachbindungen in Aminen und zeigt eine Bindungsordnung nahe 2 an. Die Umsetzung von 2Mit Cr(CO)5(THF) liefert den Komplex CR(CO)5[F3PCC(F)NMe2] (10) mit P-Koordination. IN der Kristallstruktur von 10ist der CN-abstand des Koordinierten Liganden Geringfugig uber (1.29 A), der PC-Abstand deutlich groβer (1.80A) als in 2.10 wandelt sich bei 25°C unter Freisetzung von 2 langsam in den Zweikernkomplex [cr(CO)5]2F3CPC(F)NMe2 (11) um. Reactive EC (pp) π Systems, XIV. — Synthesis and Structure of Phosphaalkenes of the Type F3CPC(F)NR2 Perfluoro-2-phosphapropene 1reacts quantitatively with secondary amines R2NH in the molar ratio of 1:2 at temperatures between −120 and −40°C to give (trifluoromethyl)phosphaalkenes of the type F3CPC(F)NR2 R = Me (2), Et (3), i-pr (4); NR2 = pyrrolidino (5), piperidino (6), 2-methylpiperidino (7, 3-methylpiperidino (8), N-methylanilino (9). Diphenylamine does not react in the same way even at room temperature. The same products are obtained by teh reaction of (CF3)2PH with R2NH and R2NH/NEt3, respectively, in molar rations of 1:3 or 1:1:2. The new compounds 4–9 just as 2 and 3 are stable at room temperature and without exception have Z configuration. The X-ray structure analysis of 1-(dimethylamino)- 1,3,3,3-tetrafluoro-2-phospha-1propene (2) proves the participation of the lone pair on nitrogen in stabilizing the system. The lattice of 2 contains C4H6F4NP molecules with an almost planar CPC(F)NC2 skeleton. The PC bond distance amounts 1.744(2) A, the CN bond [1.311(2)A] is 0.16A shorter than CN single bonds in amines suggesting a bond order near 2. The reaction of 2With Cr(CO)5(THF) yields the complex Cr(CO)5[F3CPC(F)NMe2] (10) with P-coordination. In the crystal structure of 10 the CN distance of the coordination. In teh crystal structure of 10 the CN distance of the coordinated ligand is somewhat smaller (1.29 A) and is slowly transformed to give 2 and the binuclear complex [Cr(CO)5]2F3CPC(F)NMe2 (11)

Chelate ring size variations and their effects on coordination chemistry and catechol dioxygenase reactivity of iron(III) complexes.

Abstract: The catechol dioxygenase reactivity of iron(III) complexes using tripodal ligands was investigated. Increasing, as well as decreasing, chelate ring sizes in the highly active complex [Fe(tmpa)(dbc)]B(C6H5)4 (tmpa = tris[(2-pyridyl)methyl]amine; dbc = 3,5-di-tert-butylcatecholate dianion), using related ligands, only resulted in decreased reactivity of the investigated compounds. A detailed low-temperature stopped-flow investigation of the reaction of dioxygen with [Fe(tmpa)(dbc)]B(C6H5)4 was performed, and activation parameters of DeltaH++ = 23 +/- 1 kJ mol(-1) and DeltaS++ = -199 +/- 4 J mol(-1) K(-1) were obtained. Crystal structures of bromo-(tetrachlorocatecholato-O,O')(bis((2-pyridyl)methyl)-2-pyridylamine-N,N',N'')-iron(III), (mu-oxo)-bis(bromo)(bis((2-pyridyl)methyl)-2-pyridylamine-N,N',N' ',N''')-diiron(III), dichloro-((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N' ',N''')-iron(III) and (tetrachlorocatecholato-O,O')((2-(2-pyridyl)ethyl)bis((2-pyridyl)methyl)amine-N,N',N' ',N''')-iron(III) are reported.

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.