@article{BruneckerMuessigArrowsmithetal.2020,
author = {Brunecker, Carina and M{\"u}ssig, Jonas H. and Arrowsmith, Merle and Fantuzzi, Felipe and Stoy, Andreas and B{\"o}hnke, Julian and Hofmann, Alexander and Bertermann, R{\"u}diger and Engels, Bernd and Braunschweig, Holger},
title = {Boranediyl- and Diborane(4)-1,2-diyl-Bridged Platinum A-Frame Complexes},
series = {Chemistry - A European Journal},
volume = {26},
journal = {Chemistry - A European Journal},
number = {39},
doi = {10.1002/chem.202001168},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214707},
pages = {8518 -- 8523},
year = {2020},
abstract = {Diplatinum A-frame complexes with a bridging (di)boron unit in the apex position were synthesized in a single step by the double oxidative addition of dihalo(di)borane precursors at a bis(diphosphine)-bridged Pt\(^{0}\)\(_{2}\) complex. While structurally analogous to well-known μ-borylene complexes, in which delocalized dative three-center-two-electron M-B-M bonding prevails, theoretical investigations into the nature of Pt-B bonding in these A-frame complexes show them to be rare dimetalla(di)boranes displaying two electron-sharing Pt-B σ-bonds. This is experimentally reflected in the low kinetic stability of these compounds, which are prone to loss of the (di)boron bridgehead unit.},
language = {en}
}
@article{BruecknerFantuzziStennettetal.2021,
author = {Br{\"u}ckner, Tobias and Fantuzzi, Felipe and Stennett, Tom E. and Krummenacher, Ivo and Dewhurst, Rian D. and Engels, Bernd and Braunschweig, Holger},
title = {Isolation of neutral, mono-, and dicationic B\(_2\)P\(_2\) rings by diphosphorus addition to a boron-boron triple bond},
series = {Angewandte Chemie International Edition},
volume = {60},
journal = {Angewandte Chemie International Edition},
number = {24},
doi = {10.1002/anie.202102218},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256451},
pages = {13661-13665},
year = {2021},
abstract = {The NHC-stabilised diboryne (B\(_2\)(SIDep)\(_2\); SIDep=1,3-bis(2,6-diethylphenyl)imidazolin-2-ylidene) undergoes a high-yielding P-P bond activation with tetraethyldiphosphine at room temperature to form a B\(_2\)P\(_2\) heterocycle via a diphosphoryldiborene by 1,2-diphosphination. The heterocycle can be oxidised to a radical cation and a dication, respectively, depending on the oxidant used and its counterion. Starting from the planar, neutral 1,3-bis(alkylidene)-1,3-diborata-2,4-diphosphoniocyclobutane, each oxidation step leads to decreased B-B distances and loss of planarity by cationisation. X-ray analyses in conjunction with DFT and CASSCF/NEVPT2 calculations reveal closed-shell singlet, butterfly-shaped structures for the NHC-stabilised dicationic B\(_2\)P\(_2\) rings, with their diradicaloid, planar-ring isomers lying close in energy.},
language = {en}
}
@unpublished{BoehnkeDellermannCeliketal.2018,
author = {B{\"o}hnke, Julian and Dellermann, Theresa and Celik, Mehmet Ali and Krummenacher, Ivo and Dewhurst, Rian D. and Demeshko, Serhiy and Ewing, William C. and Hammond, Kai and Heß, Merlin and Bill, Eckhard and Welz, Eileen and R{\"o}hr, Merle I. S. and Mitric, Roland and Engels, Bernd and Meyer, Franc and Braunschweig, Holger},
title = {Isolation of diradical products of twisted double bonds},
series = {Nature Communications},
journal = {Nature Communications},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160248},
year = {2018},
abstract = {Molecules containing multiple bonds between atoms—most often in the form of olefins—are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond. Here, we present the isolation of double-bond-containing species based on boron, as well as their fully twisted diradical congeners, by the incorporation of attached groups with different electronic properties. The compounds comprise a structurally authenticated set of diamagnetic multiply-bound and diradical singly-bound congeners of the same class of compound.},
language = {en}
}
@article{BoehnkeDellermannCeliketal.2018,
author = {B{\"o}hnke, Julian and Dellermann, Theresa and Celik, Mehmet Ali and Krummenacher, Ivo and Dewhurst, Rian D. and Demeshko, Serhiy and Ewing, William C. and Hammond, Kai and Heß, Merlin and Bill, Eckhard and Welz, Eileen and R{\"o}hr, Merle I. S. and Mitric, Roland and Engels, Bernd and Meyer, Franc and Braunschweig, Holger},
title = {Isolation of diborenes and their 90°-twisted diradical congeners},
series = {Nature Communications},
volume = {9},
journal = {Nature Communications},
number = {Article number: 1197},
doi = {10.1038/s41467-018-02998-3},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160431},
year = {2018},
abstract = {Molecules containing multiple bonds between atoms—most often in the form of olefins—are ubiquitous in nature, commerce, and science, and as such have a huge impact on everyday life. Given their prominence, over the last few decades, frequent attempts have been made to perturb the structure and reactivity of multiply-bound species through bending and twisting. However, only modest success has been achieved in the quest to completely twist double bonds in order to homolytically cleave the associated π bond. Here, we present the isolation of double-bond-containing species based on boron, as well as their fully twisted diradical congeners, by the incorporation of attached groups with different electronic properties. The compounds comprise a structurally authenticated set of diamagnetic multiply-bound and diradical singly-bound congeners of the same class of compound.},
language = {en}
}
@article{BuendgenEngelsPeyerimhoff1991,
author = {B{\"u}ndgen, P. and Engels, Bernd and Peyerimhoff, S.D.},
title = {An MRD-CI study of low-lying electronic states in CaF},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58880},
year = {1991},
abstract = {Dipole moments and various spectroscopic constants of some low-lying electronic states of the CaF molecule have been calculated using the multireference single· and double-excitation configuration-interaction (MRD-CI) method. The electronic structure of the highly ionic molecule in various excited states can be explained in tenns of different polarisations of the mainly Cacentered valence electron in the field of the F\(^-\) anion. Plots of natural orbitals occupied by the valence electron in the different states give a qualitative picture of the charge distribution and provide a visualisation of the different polarisations of the valence electron in the various states. Comparisons with the electrostatic polarisation model ofT{\"o}rring, Ernstand K{\"a}ndler (TEK model) are made. The unknown A' \(^2 \Delta\) state is predicted to lie about 21200 cm\(^{-1}\) above the ground state.},
subject = {Organische Chemie},
language = {en}
}
@article{DietschreitWagnerLeetal.2020,
author = {Dietschreit, Johannes C. B. and Wagner, Annika and Le, T. Anh and Klein, Philipp and Schindelin, Hermann and Opatz, Till and Engels, Bernd and Hellmich, Ute A. and Ochsenfeld, Christian},
title = {Predicting \(^{19}\)F NMR Chemical Shifts: A Combined Computational and Experimental Study of a Trypanosomal Oxidoreductase-Inhibitor Complex},
series = {Angewandte Chemie International Edition},
volume = {59},
journal = {Angewandte Chemie International Edition},
number = {31},
doi = {10.1002/anie.202000539},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-214879},
pages = {12669 -- 12673},
year = {2020},
abstract = {The absence of fluorine from most biomolecules renders it an excellent probe for NMR spectroscopy to monitor inhibitor-protein interactions. However, predicting the binding mode of a fluorinated ligand from a chemical shift (or vice versa) has been challenging due to the high electron density of the fluorine atom. Nonetheless, reliable \(^{19}\)F chemical-shift predictions to deduce ligand-binding modes hold great potential for in silico drug design. Herein, we present a systematic QM/MM study to predict the \(^{19}\)F NMR chemical shifts of a covalently bound fluorinated inhibitor to the essential oxidoreductase tryparedoxin (Tpx) from African trypanosomes, the causative agent of African sleeping sickness. We include many protein-inhibitor conformations as well as monomeric and dimeric inhibitor-protein complexes, thus rendering it the largest computational study on chemical shifts of \(^{19}\)F nuclei in a biological context to date. Our predicted shifts agree well with those obtained experimentally and pave the way for future work in this area.},
language = {en}
}
@article{Engels1993,
author = {Engels, Bernd},
title = {Study of influences of various excitation classes on ab initio calculated isotropic hyperfine coupling constants},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58973},
year = {1993},
abstract = {Reliable prediction of the isotropic hyperfine coupling constant A\(_{iso}\) is still a difficult task for ab initio calculations. Strang dependence on the method employed for its ca1culation has been found. Within a CI ansatz A\(_{iso}\) is considerably affected by the excitation classes taken into account within the CI calculation. In the present work the influence of various excitation classes on A\(_{iso}\) is examined. Calculations including all single, double, triple and a large part of the quadruple excitations are performed and the individual effects of the excitation classes are studied. It is found that the surprisingly good agreement found for S-CI treatments is due to large error cancellations. The importance of higher than double excitations arises from their indirect influence on the single excitations.},
subject = {Organische Chemie},
language = {en}
}
@article{Engels1994,
author = {Engels, Bernd},
title = {Detailed study of the configuration selected multi-reference configuration interaction method combined with perturbation theory to correct the wave function},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59019},
year = {1994},
abstract = {A reliable prediction of the isotropic hyperfine coupling constant A\(_{iso}\) is still a difficult task for ab initio calculations. In previous studies, the configuration selected multireference configuration interaction method in combination with perturbation theory to correct the wave function (MRCI/ B\(_K\)) yielded accurate isotropic hyperfine coupling constants very economically. The present study gives a detailed analysis of the MRCI/ B\(_K\) method based on the X\(^2 \pi\) state of CH as a test case. Furthermore, a comparison to various other methods such as Maller-Ptesset perturbation theory and the coupled cluster approach is made. The success of the MRCI/ B\(_K\) method in predicting isotropic hyperfine coupling constants is explained in terms of the inßuence of higher than double excitations.},
subject = {Organische Chemie},
language = {en}
}
@article{Engels1991,
author = {Engels, Bernd},
title = {Estimation of the influence of the configurations neglected within truncated MR-CI wavefunctions on molecular properties},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58890},
year = {1991},
abstract = {Reliable prediction of the isotropic hyperfine coupling constant, a\(_{iso}\), is still a difficult task for ab initio calculations. Strong dependence on the method used for its calculation is found. Within a truncated multi-referencc ansatz a\(_{iso}\) is strongly affected by the size ofthe reference space and the nurober of terms in the truncated Cl expansion. In the present paperdifferent effects of the neglected Cl space are discussed. Modified B\(_K\) and A\(_K\) methods are used to estimate the contributions ofthe neglected configurations. lt can be shown that a combination of both methods is able to recover about 90-9 S\% of the total error in a\(_{iso}\)· Furthermore, it was found that to obtain about 90\% of the B\(_K\) correction only about I 0-20\% ofthe configurations within H0 have to be corrected.},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPericReuteretal.1992,
author = {Engels, Bernd and Peric, M. and Reuter, W. and Peyerimhoff, S.D. and Grein, F.},
title = {Study of the hyperfine coupling constants \(^{14}\)N and \(^1\)H) of the NH\(_2\) molecule in the X\(^2\)B\(_1\) ground state and the A\(^2\)A\(_1\) excited state},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58937},
year = {1992},
abstract = {The hyperfine coupling constants (hfcc) A\(_{iso}\) and A\(_{ij}\) are calculated for the atoms of NH\(_2\) in its, two lowest-lying electronk states at various molecular geometries by means of the ab initio multireference configuration interaction .method. The vibronically averaged values of the hfccs for the K = 0 and 1 levels in \(^{14}\)N \(^1\)H\(_2\) in the energy range up to 20 000 cm\(^{-1}\) are computed. Polarization elfects which determine A\(_{iso}\) as well as a simple model to describe the dipolar hfccs are discussed. All resrilts are in excellent agreement with experimental data.},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPeyerimhoff1986,
author = {Engels, Bernd and Peyerimhoff, S. D.},
title = {Theoretical study of the bridging in β-Halo Ethyl},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58779},
year = {1986},
abstract = {Large-acale multi-reference configuration interaction (MRD-CI) calculations in a quite flexible AO basis are employed to study the energy hypersurface for the reaction intermediates XC\(_3\)H\(_4\) with X = Cl, Br and F. Particular emphasis is therby placed on determining the equilibrium conformations, the CH\(_2\) rotation barrier and the energy surface for a possible bridging (shuttling motion (1a] of X between the two carbon centers). The absolute minimum in the potential energy surface is found in all three cases for the asymmetric ß-halo radical in general agreement with ESR data at an XCC angle of ca. 110°, a c-c separation somewhat shorter than a single bond and an approximate sp3 type hybridization (\(\alpha _2 \approx \) 135-140°). In FC\(_2\)H\(_4\) the energy difference between the minimum in the symmetric conformation and the absolute minimum is found to be more than 30 kcal so that shuttling seems impossible in agreement with experimental findings. In BrC\(_2\)H\(_4\) the difference between these two potential minima is only between 1-2 kcal, i.e., smaller than the barrier to CH\(_2\), rotation, so that· shuttling is favored, while ClC\(_2\)H\(_4\) takes an intermediate position between these extremes. The use of correlated wavefunctions is found to be quite important for such a study; the results are related to various kinetic studies of these radicals.},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPeyerimhoff1989,
author = {Engels, Bernd and Peyerimhoff, S.D.},
title = {Theoretical study of FC\(_2\)H\(_4\)},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58824},
year = {1989},
abstract = {Large-scale multireference configuration interaction (MRD-CI) calculations in a quite flexible AO basis are employed to study the energy hypersurface for the reaction intermediate FC\(_2\)H\(_4\) • The reaction F + C\(_2\)H\(_4\) -> FC\(_2\)H\(_4\) as weil as the 1,2 migration of the fluorine atom in FC\(_2\)H\(_4\) is investigated. In addition the rotation around the CC bond in the optimum conformation is studied. The absolute minimum in the potential energy is found for the asymmetric structure but the symmetric structure is also found to be stable with respect to the dissociation, so that a shuttling of the fluorine atom is in principle possible but highly unlikely because ( l) the activation energy is high ( II 5-130 kJ fmol) and the saddle point lies only 4(}-50 kJ jmol below the dissociation Iimit of F + C\(_2\)H\(_4\) and (2) the competitive motion, i.e., rotation around the CC axis, is nearly free (I 1-17 kJ/mol).},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPeyerimhoff1989,
author = {Engels, Bernd and Peyerimhoff, S.D.},
title = {The hyperfine coupling constants of the X\(^3\)Σ\(^-\) state of NH : Influence of polarization functions and configuration space on the description of spin polarization},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58832},
year = {1989},
abstract = {The hyperfine coupling constants for the \(^3\)Σ\(-\) ground state of the NH molecule are determined by configuration interaction calculations whereby the infl.uence of polarization functions as weil as of the configuration space on the spin polarization mechanism is analysed. The dipolar part Au(N) and Au(H) can be obtained very reliably without much computational effort (A .. (N) == -45·3 MHz and A"(H) = -62·3 MHz). The value for the isotropic contribution a1.., in the best AO basis and MRD-CI treatment is - 64·5 MHz for H and 16·6 MHz for nitrogen compared to the corresponding experimental quantities of -66 MHz and 19 MHz respectively. Their determination depends on a subtle balance of the lu, 2u and 3u shell correlation description, whereby the dominant contribution to a1..,(H) results from the 2u shell. It is shown that the often good agreement of a110 values with experiment in a small basis singledouble configuration interaction treatment results from a cancellation of two errors.},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPeyerimhoff1989,
author = {Engels, Bernd and Peyerimhoff, S.D.},
title = {Study of orbital transformations in configurational interaction calculation of hyperfine coupling in nitrogen and CH molecule},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58847},
year = {1989},
abstract = {Multi-reference configuration interaction calculations employing various orbital transformations are undertaken to obtain the isotropic hyperfine coupling constant a\(_{iso\) in nitrogen and a\(_{iso\) (H) in the CH molecule. The natural orbital (NO) basis is found to be more effective than the simple RHF-MO basis; the most obvious is a basis of spin natural orbitals (SNO). It is found that a\(_{iso\) is approached from opposite sides in the NO and 2s shell SNO basis if the CI expansion is increased. Both results are within a few percent of the full CI Iimit for the nitrogen atorn (in the given AO basis) and the experimental value for Hin the CH radical. Various features ofthe SNO are discussed.},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPeyerimhoff1988,
author = {Engels, Bernd and Peyerimhoff, S.D.},
title = {Study of the 1s and 2s shell contributions to the isotropic hyperfine coupling constant in nitrogen},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58793},
year = {1988},
abstract = {The istropic part of the hyperfine coupling constant is investigated by means of multireference configuration interaction calculations employing Gaussian basis sets. A detailed study of the 1s and 2s spin polarisation in the nitrogen atom and the NH molecule shows that the structure of the lower-energy space of the unoccupied orbitals is essential for the results. A contraction of the Gaussian basis is possible without loss of accuracy if enough flexibility is retained to describe the main features of the original space of unoccupied functions. Higher than double excitations are found to be non-negligible for the description of α\(_{iso}\).},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPeyerimhoffDavidson1987,
author = {Engels, Bernd and Peyerimhoff, S.D. and Davidson, E.R.},
title = {Calculation of hyperfine coupling constants : An ab initio MRD-CI study for nitrogen to analyse the effects of the basis sets and CI parameter},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58784},
year = {1987},
abstract = {The hyperfine coupling constant for the nitrogen atom is evaluated by large-scale MRD-CI calculations. A detailed analysis of the charge density at the nucleus and the spin polarization in the ls and 2s shell as a function of various technical parameters is undertaken. Various (s, p) AO basis sets and the inftuence of correlation orbitals is investigated as weil as selection threshold and other properlies in CI calculations. The best value, obtained for the isotropic hyperfine coupling constant in an s, p, d basis, based on theoretical judgment of' best' quantities, is 9·9 MHz compared to 10·4509 MHz.},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPeyerimhoffKarnaetal.1988,
author = {Engels, Bernd and Peyerimhoff, S.D. and Karna, S.P. and Grein, F.},
title = {The hyperfine coupling constants of the five lowest states of CH : An ab initio MRD-CI study},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58807},
year = {1988},
abstract = {No abstract available},
subject = {Organische Chemie},
language = {en}
}
@article{EngelsPeyerimhoffSkell1990,
author = {Engels, Bernd and Peyerimhoff, S.D. and Skell, P.S.},
title = {Theoretical study of the potential energy surface governing the stereochemistry in ClC\(_2\)H\(_4\) reactions},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58851},
year = {1990},
abstract = {Large-scale multireference configuration interaction calculations in a double·t·type AO basis including polarization functions are carried out for the potential surface of the ClC\(_2\)H\(_4\9 system. The charge distribution for various extreme points of the surface is discussed. The absolute minimum is found for an asymmetric ClC2H4 structure. The symmetrical bridged nuclear conformation is also found to be stable with respect to dissociation into Cl + C\(_2\)H\(_4\)• The activation energy for rotation about the C-C axis is calculated tobe around 18 kJ/mol, which is comparable tothat for the 1,2 migration {around 26 kJ/mol). The stereochemistry is governed by the fact that addition of CI to C\(_2\)H\(_4\) (or dissociation) is a two-step reaction proceeding through a symmetrica1 intermediate. The direct addition pathway possesses a small barrier of about 8 kJ jmol.},
subject = {Organische Chemie},
language = {en}
}
@article{FranzsicoFantuzziCardozoetal.2021,
author = {Franzsico, Marcos A. S. and Fantuzzi, Felipe and Cardozo, Thiago M. and Esteves, Pierre M. and Engels, Bernd and Oliveira, Ricardo R.},
title = {Taming the Antiferromagnetic Beast: Computational Design of Ultrashort Mn-Mn Bonds Stabilized by N-Heterocyclic Carbenes},
series = {Chemistry—A European Journal},
volume = {27},
journal = {Chemistry—A European Journal},
number = {47},
doi = {10.1002/chem.202101116},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256874},
pages = {12126-12136},
year = {2021},
abstract = {The development of complexes featuring low-valent, multiply bonded metal centers is an exciting field with several potential applications. In this work, we describe the design principles and extensive computational investigation of new organometallic platforms featuring the elusive manganese-manganese bond stabilized by experimentally realized N-heterocyclic carbenes (NHCs). By using DFT computations benchmarked against multireference calculations, as well as MO- and VB-based bonding analyses, we could disentangle the various electronic and structural effects contributing to the thermodynamic and kinetic stability, as well as the experimental feasibility, of the systems. In particular, we explored the nature of the metal-carbene interaction and the role of the ancillary η\(^{6}\) coordination to the generation of Mn\(_{2}\) systems featuring ultrashort metal-metal bonds, closed-shell singlet multiplicities, and positive adiabatic singlet-triplet gaps. Our analysis identifies two distinct classes of viable synthetic targets, whose electrostructural properties are thoroughly investigated.},
language = {en}
}
@article{FroudakisZdetsisMuehlhaeuseretal.1994,
author = {Froudakis, G. and Zdetsis, A. and M{\"u}hlh{\"a}user, M. and Engels, Bernd and Peyerimhoff, S. D.},
title = {A comparative ab initio study of the Si\(_2\)C\(_4\), Si\(_3\)C\(_3\), Si\(_4\)C\(_2\) clusters},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59097},
year = {1994},
abstract = {Various structural possibilities for the Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters are investigated by employing a basis set of triple-zeta plus polarization quality; electron correlation is generally accounted for by second-order M0ller-Plesset and, in certain instances, by higher-order perturbation (CASPT2) approaches. The building-up principle recently suggested from an analysis of Si\(_3\)C\(_3\) clusters is found to be fully operative for Si\(_2\)C\(_4\) and Si\(_4\)C\(_2\) clusters. A comparison of the structure and stability of various geometrical arrangements in the series C\(_6\) , Si\(_2\)C\(_4\) , Si\(_3\)C\(_3\) , Si\(_4\)C\(_2\), and Si\(_6\) shows that linear and planar structures become rapidly less stable if carbons are replaced by silicons and that the three-dimensional bipyramidal forms become less favorable as soon as silicons are exchanged by carbons in the parent Si\(_6\) structure. The effects can be rationalized in qualitative terms based on differences in silicon and carbon bonding.},
subject = {Organische Chemie},
language = {en}
}
@article{FunkenEngelsPeyerimhoffetal.1990,
author = {Funken, K. and Engels, Bernd and Peyerimhoff, S.D. and Grein, F.},
title = {Study of the hyperfine coupling constants of the moleculs NH2, NHD and ND2},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58875},
year = {1990},
abstract = {In the present paper we c:alculate tbe magnetic hyperfine couplina constants (hfcc) ai.ID and A11 of the ground states of the isotopes NH2, NHD and ND2 using truncated MR..CI methods. Differences from other theoretical methocls and shortoominp of the truncated Cl approach in calculating tlj10 are studied. Polarization effects wbich detennirae ailo. as weU as a simple model to describe the dipolar hfcc's, are discussed. All results are in. excellent aareement with experimental data. lt is shown that ab initio methods are able to obtain reliable values for otf-diaaonal values of A41 which are difficult to measure experimentaDy.},
subject = {Organische Chemie},
language = {en}
}
@article{GittinsHarrisFieldetal.1993,
author = {Gittins, C. M. and Harris, N. A. and Field, R. W. and Verges, J. and Ernst, W. E. and B{\"u}ndgen, P. and Engels, Bernd},
title = {Analysis and Depertubation of the C\(^2\)Π and D\(^2\)Σ\(^+\) states of CaF},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58980},
year = {1993},
abstract = {No abstract available},
subject = {Organische Chemie},
language = {en}
}
@article{HermannFantuzziArrowsmithetal.2020,
author = {Hermann, Alexander and Fantuzzi, Felipe and Arrowsmith, Merle and Zorn, Theresa and Krummenacher, Ivo and Ritschel, Benedikt and Radacki, Krzysztof and Engels, Bernd and Braunschweig, Holger},
title = {Oxidation, Coordination, and Nickel-Mediated Deconstruction of a Highly Electron-Rich Diboron Analogue of 1,3,5-Hexatriene},
series = {Angewandte Chemie, International Edition},
volume = {59},
journal = {Angewandte Chemie, International Edition},
number = {36},
doi = {10.1002/anie.202006131},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-240652},
pages = {15717-15725},
year = {2020},
abstract = {The reductive coupling of an N-heterocyclic carbene (NHC) stabilized (dibromo)vinylborane yields a 1,2-divinyl- diborene, which, although isoelectronic to a 1,3,5-triene, displays no extended p conjugation because of twisting of the C\(_2\)B\(_2\)C\(_2\) chain. While this divinyldiborene coordinates to copper(I) and platinum(0) in an η\(^2\)-B\(_2\) and η\(^4\)-C\(_2\)B\(_2\) fashion, respectively, it undergoes a complex rearrangement to an η\(^4\)-1,3-diborete upon complexation with nickel(0).},
language = {en}
}
@article{HuangSuterEngels1994,
author = {Huang, M.-B. and Suter, H. U. and Engels, Bernd},
title = {Theoretical Study of the Dimethylamino Radical (CH\(_3\))\(_2\)N and its protonated cation (CH\(_3\))\(_2\)NH\(^+\)},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59047},
year = {1994},
abstract = {In the present work the dimethylamino radical ( ( CH\(_3\)) \(_2\)N) and its protonated cation ( ( CH\(_3\))\(_2\)NH\(^+\)) are investigated by means of ab initio methods. The geometries of various conformations of both compounds are obtained with UMP2/6·31 G** calculations, while the hyperfine structure and its dependence on the geometry is studied using the MRD-Cl/B\(_K\) method. The two molecules are compared to study the inftuence of the protonation on geometry and hyperfine structure. The effects of the rotational barriers on the hyperfine structures of (CH\(_3\))\(_2\)N, (CH\(_3\)CH\(_2\))\(_2\)N and ( (CH\(_3\))\(_2\)CH)\(_2\)N will be discussed.},
subject = {Organische Chemie},
language = {en}
}
@article{KarnaGreinEngelsetal.1989,
author = {Karna, S. and Grein, F. and Engels, Bernd and Peyerimhoff, S.D.},
title = {The hyperfine coupling constants of \(^{19}\)F\(_2\)},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58817},
year = {1989},
abstract = {The isotropic (a\(_{iso}\)) and dipolar (A\(_{dip}\)) hyperfine coupling constants of 19F2 were obtained from MRD-CI wave functions using a variety of basis sets. In series I, increasing numbers of d functions were added to a 5s4p contracted Huzinaga!Dunning basis. In series II, the 5s3p basis set was uncontracted in several steps until 9s5p was reached, to which were added from one to three d-polarization functions. Cl parameters (selectioo threshoids and the number of reference coofiguratioos) were also varied. A study of the R dependence of aiso and Adip was perfonned. The best values obtained at R\(_e\) are 260 G for a\(_{iso}\) and 308 G for A\(_{dip}\)• compared with experimental values of about 280 G for a;10 and 320 G for A\(_{dip}\)·},
subject = {Organische Chemie},
language = {en}
}
@article{KarnaGreinEngelsetal.1990,
author = {Karna, S.P. and Grein, F. and Engels, Bernd and Peyerimhoff, S.D.},
title = {Ab initio configuration-interaction studies of the ground state potential energy and hyperfine coupling constants of \(^{35}\)Cl\(_2^-\)},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58869},
year = {1990},
abstract = {Potential energy and spectroscopic constants for the X\(^2 \sum^+ _\mu\) ground state of a;, were calculated by configuration-interaction (Cl) methods, using large basis sets with polarization and diffuse functions. From these CI wavefunctions, the isotropic (a\(_{iso}\)) and dipolar (A\(_{dip}\)) components of the hyperfine coupling constant were obtained. The effects of various s, p basis sets, polarization and diffuse functions, as well as the influence of reference configurations and configuration selection thresholds were investigated. The best values obtained are 35·31 G for a\(_{iso}\) and 29·440 for A\(_{dip}\)• tobe compared with experimental values of 37 ± 1 G and 32 ± 1 G, respectively. It is shown that the contributions to a1so of the K and L shells are opposite in sign, differing by about 4 G. Upon vibrational averaging, both a\(_{iso}\) and A\(_{dip}\) move towards smaller values as v increases. An adiabatic electron affinity of 2·46eV was obtained for CL\(_2\) , and a vertical electron detachment energy of 3·71 eV for Cl;.},
subject = {Organische Chemie},
language = {en}
}
@article{KleinBarthelsJoheetal.2020,
author = {Klein, Philipp and Barthels, Fabian and Johe, Patrick and Wagner, Annika and Tenzer, Stefan and Distler, Ute and Le, Thien Anh and Schmid, Paul and Engel, Volker and Engels, Bernd and Hellmich, Ute A. and Opatz, Till and Schirmeister, Tanja},
title = {Naphthoquinones as covalent reversible inhibitors of cysteine proteases — studies on inhibition mechanism and kinetics},
series = {Molecules},
volume = {25},
journal = {Molecules},
number = {9},
issn = {1420-3049},
doi = {10.3390/molecules25092064},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-203791},
year = {2020},
abstract = {The facile synthesis and detailed investigation of a class of highly potent protease inhibitors based on 1,4-naphthoquinones with a dipeptidic recognition motif (HN-l-Phe-l-Leu-OR) in the 2-position and an electron-withdrawing group (EWG) in the 3-position is presented. One of the compound representatives, namely the acid with EWG = CN and with R = H proved to be a highly potent rhodesain inhibitor with nanomolar affinity. The respective benzyl ester (R = Bn) was found to be hydrolyzed by the target enzyme itself yielding the free acid. Detailed kinetic and mass spectrometry studies revealed a reversible covalent binding mode. Theoretical calculations with different density functionals (DFT) as well as wavefunction-based approaches were performed to elucidate the mode of action.},
language = {en}
}
@article{KleinJoheWagneretal.2020,
author = {Klein, Philipp and Johe, Patrick and Wagner, Annika and Jung, Sascha and K{\"u}hlborn, Jonas and Barthels, Fabian and Tenzer, Stefan and Distler, Ute and Waigel, Waldemar and Engels, Bernd and Hellmich, Ute A. and Opatz, Till and Schirmeister, Tanja},
title = {New cysteine protease inhibitors: electrophilic (het)arenes and unexpected prodrug identification for the Trypanosoma protease rhodesain},
series = {Molecules},
volume = {25},
journal = {Molecules},
number = {6},
issn = {1420-3049},
doi = {10.3390/molecules25061451},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-203380},
year = {2020},
abstract = {Electrophilic (het)arenes can undergo reactions with nucleophiles yielding π- or Meisenheimer (σ-) complexes or the products of the S\(_N\)Ar addition/elimination reactions. Such building blocks have only rarely been employed for the design of enzyme inhibitors. Herein, we demonstrate the combination of a peptidic recognition sequence with such electrophilic (het)arenes to generate highly active inhibitors of disease-relevant proteases. We further elucidate an unexpected mode of action for the trypanosomal protease rhodesain using NMR spectroscopy and mass spectrometry, enzyme kinetics and various types of simulations. After hydrolysis of an ester function in the recognition sequence of a weakly active prodrug inhibitor, the liberated carboxylic acid represents a highly potent inhibitor of rhodesain (K\(_i\) = 4.0 nM). The simulations indicate that, after the cleavage of the ester, the carboxylic acid leaves the active site and re-binds to the enzyme in an orientation that allows the formation of a very stable π-complex between the catalytic dyad (Cys-25/His-162) of rhodesain and the electrophilic aromatic moiety. The reversible inhibition mode results because the S\(_N\)Ar reaction, which is found in an alkaline solvent containing a low molecular weight thiol, is hindered within the enzyme due to the presence of the positively charged imidazolium ring of His-162. Comparisons between measured and calculated NMR shifts support this interpretation},
language = {en}
}
@article{MetropoulosEngelsPeyerimhoff1993,
author = {Metropoulos, B. and Engels, Bernd and Peyerimhoff, S.D.},
title = {On the chemi-ionization reaction O + CH ----> HCO\(^+\)+ e\(^-\). Coollinear O-CH Approach},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58963},
year = {1993},
abstract = {We have investigated theoretically the importance of the O(\(^3\)P)+CH(a\(^4\sum^-\)) and the O(\(^3\)P)+CH(X\(^2\Pi\)) channels in the collinear chemi-ionization reaction O+CH->HCO\(^+\) +e\(^-\). We have found that both channels may lead to chemi-ionization via favorable Franck-Condon overlaps with the states ofthe ionic species.},
subject = {Organische Chemie},
language = {en}
}
@article{MukhopadhyaySchleierWirsingetal.2020,
author = {Mukhopadhyay, Deb Pratim and Schleier, Domenik and Wirsing, Sara and Ramler, Jaqueline and Kaiser, Dustin and Reusch, Engelbert and Hemberger, Patrick and Preitschopf, Tobias and Krummenacher, Ivo and Engels, Bernd and Fischer, Ingo and Lichtenberg, Crispin},
title = {Methylbismuth: an organometallic bismuthinidene biradical},
series = {Chemical Science},
volume = {11},
journal = {Chemical Science},
number = {29},
doi = {10.1039/D0SC02410D},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-251657},
pages = {7562-7568},
year = {2020},
abstract = {We report the generation, spectroscopic characterization, and computational analysis of the first free (non-stabilized) organometallic bismuthinidene, BiMe. The title compound was generated in situ from BiMe\(_3\) by controlled homolytic Bi-C bond cleavage in the gas phase. Its electronic structure was characterized by a combination of photoion mass-selected threshold photoelectron spectroscopy and DFT as well as multi-reference computations. A triplet ground state was identified and an ionization energy (IE) of 7.88 eV was experimentally determined. Methyl abstraction from BiMe\(_3\) to give [BiMe(_2\)]• is a key step in the generation of BiMe. We reaveal a bond dissociation energy of 210 ± 7 kJ mol\(^{-1}\), which is substantially higher than the previously accepted value. Nevertheless, the homolytic cleavage of Me-BiMe\(_2\) bonds could be achieved at moderate temperatures (60-120 °C) in the condensed phase, suggesting that [BiMe\(_2\)]• and BiMe are accessible as reactive intermediates under these conditions.},
subject = {Photoelektronenspektroskopie},
language = {en}
}
@article{MuehlhaeuserEngelsMarianetal.1994,
author = {M{\"u}hlh{\"a}user, M. and Engels, Bernd and Marian, C. M. and Peyerimhoff, S. D. and Bruna, P. J. and Jansen, M.},
title = {Einfluß der Ladungsverteilung auf die Bindungsl{\"a}ngen im P\(_4\)O\(_6\) Ger{\"u}st bei Verbindungen des Typs P\(_4\)O\(_6\)X},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59034},
year = {1994},
abstract = {No abstract available},
subject = {Organische Chemie},
language = {de}
}
@article{MuehlhaeuserFroudakisZdetsisetal.1994,
author = {M{\"u}hlh{\"a}user, M. and Froudakis, G. and Zdetsis, A. and Engels, Bernd and Flytzanis, N. and Peyerimhoff, S. D.},
title = {Ab initio investigation of the stability of Si\(_3\)C<\(_3\) clusters and their structural and bonding features},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59060},
year = {1994},
abstract = {Various structural possibilities for Si\(_3\)C\(_3\) clusters are investigated by ab initio calculations employing basis sets of double- and triple-zeta quality augmented by d polarization functions. Correlation effects are included by a second-order Moeller Piesset perturbation treatment. For the two lowest-lying structures higher-order correlation corrections and multi-reference effects are also included. Bonding features are investigated by two different types of population analyses to obtain insight into the nature of chemical bonding. A total of 17 stationary points were investigated, 14 of which correspond to local minima and three being transition states. The energetically lowest-lying structures are: A "pyramidlike" structure with various multicenter bonds, followed by a es symmetric isomer closely related to the ground state Si6 structure. Planar structures, favoured in small carbon clusters, lie higher in energy and are transition states. The lowest-lying triplet system is found to be the linear nonsymmetric Si - C-C-C-Si -Si structure, which is calculated to lie about 38 kcalfmole above the singlet ground state. A building-up principle based on bonding criteria is suggested for the occurence of the various structural possibilities.},
subject = {Organische Chemie},
language = {en}
}
@article{MuellerMetaMeidneretal.2023,
author = {M{\"u}ller, Patrick and Meta, Mergim and Meidner, Jan Laurenz and Schwickert, Marvin and Meyr, Jessica and Schwickert, Kevin and Kersten, Christian and Zimmer, Collin and Hammerschmidt, Stefan Josef and Frey, Ariane and Lahu, Albin and de la Hoz-Rodr{\´i}guez, Sergio and Agost-Beltr{\´a}n, Laura and Rodr{\´i}guez, Santiago and Diemer, Kira and Neumann, Wilhelm and Gonz{\`a}lez, Florenci V. and Engels, Bernd and Schirmeister, Tanja},
title = {Investigation of the compatibility between warheads and peptidomimetic sequences of protease inhibitors — a comprehensive reactivity and selectivity study},
series = {International Journal of Molecular Sciences},
volume = {24},
journal = {International Journal of Molecular Sciences},
number = {8},
issn = {1422-0067},
doi = {10.3390/ijms24087226},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-313596},
year = {2023},
abstract = {Covalent peptidomimetic protease inhibitors have gained a lot of attention in drug development in recent years. They are designed to covalently bind the catalytically active amino acids through electrophilic groups called warheads. Covalent inhibition has an advantage in terms of pharmacodynamic properties but can also bear toxicity risks due to non-selective off-target protein binding. Therefore, the right combination of a reactive warhead with a well-suited peptidomimetic sequence is of great importance. Herein, the selectivities of well-known warheads combined with peptidomimetic sequences suited for five different proteases were investigated, highlighting the impact of both structure parts (warhead and peptidomimetic sequence) for affinity and selectivity. Molecular docking gave insights into the predicted binding modes of the inhibitors inside the binding pockets of the different enzymes. Moreover, the warheads were investigated by NMR and LC-MS reactivity assays against serine/threonine and cysteine nucleophile models, as well as by quantum mechanics simulations.},
language = {en}
}
@article{PericEngels1992,
author = {Peric, M. and Engels, Bernd},
title = {Ab initio calculations of the vibronically averaged values for the hyperfine coupling constants in NH\(_2\), NHD and ND\(_2\)},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58941},
year = {1992},
abstract = {Vibronically averaged values for K =0 and K = 1 bending levels in the energy range between 0 and 25 000 cm\(^{-1}\) are computed for the \(^{14}\)N, H, and D atoms in NH\(_2\), NHD, and ND\(_2\) The pure ab initio electronic potentials, as well as those derived by fitting of experimentally observed band positions are employed. Effects of vibronic coupling and local perturbations of close-lying levels belanging to different electronic states are discussed.},
subject = {Organische Chemie},
language = {en}
}
@article{PericEngels1992,
author = {Peric, M. and Engels, Bernd},
title = {Ab initio calculation of the vibronically averaged hyperfine coupling constants in the 1\(^2\)Π\(_u\) electronic state of CH\(_2 ^+\)},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58951},
year = {1992},
abstract = {The results of pure ab initio calculations of the hyperfine coupling constants for the 1 \(^2 \pi _u\) electronic state for various isotopomers of CHi in the energy range between 0 and 20 000 cm\(^{-1}\) are presented. Effects of vibronic and spin-orbit coupling are discussed.},
subject = {Organische Chemie},
language = {en}
}
@article{PericEngelsPeyerimhoff1991,
author = {Peric, M. and Engels, Bernd and Peyerimhoff, S.D.},
title = {Ab initio investigation of the vibronic structure of the C\(_2\)H spectrum Calculation of the hyperfine coupling constants for the three lowest lying electronic states},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58901},
year = {1991},
abstract = {The hyperfine coupling constants (isotropic hfcc and four Cartesian components of the ani~ tropic tensor) are calculated for all three atoms of C\(_2\)H in its three lowest-lying electronic states at various molecu)ar geometries by means of the ab initio configuration interaction ( MRO.CI) method. The off-diagonal electronic matrix elements involving the two species ofthe A' symmetry are also computed. A diabatic transforrnation is perforrned Jeading to simple geometrical depen· dences of the hyperline coupling constants.},
subject = {Organische Chemie},
language = {en}
}
@article{PericEngelsPeyerimhoff1991,
author = {Peric, M. and Engels, Bernd and Peyerimhoff, S.D.},
title = {Ab initio investigation of the vibronic structure of the C\(_2\)H spectrum Computation of the vibronically-averaged values for the Hyperfine Coupling Constants},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58915},
year = {1991},
abstract = {The vibronically averaged values for tbe hyperfine coupling constants in the X\(^2 \sum\)-A\(^2 \Pi\) system of the ethynyl radical are computed by means of tbe ab initio metbod calculations. The results point at tbe importance of taking into account the coupling of a1l tbree electronic states in question ( I\(^2\)A', 2\(^2\)A', and 1\(^2\)A") for a reliable explanation of the available experimental findings. The mean values of the hfcc's for K = 0 and 1 levels in \(^{13}\)C\(_2\)H and \(^{13}\)C\(_2\)D in the energy range up to 6000 cm\(^{-1}\) are predicted.},
subject = {Organische Chemie},
language = {en}
}
@article{PlessSuterEngels1994,
author = {Pleß, V. and Suter, H. U. and Engels, Bernd},
title = {Ab initio study of the energy difference between the benzene and the cumulene form of the C\(_6\) molecule},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59059},
year = {1994},
abstract = {The energy difference between the three lowest-lying isomers of C\(_6\) the linear \(^3 \sum ^-\) state and the two ring forms,the benzene structure (\(^1\)A\(_{18}\)) possessing D\(_{6h}\) symmetry and a distorted cyclic form ( \(^1\)A'\(_1\), D\(_{3h}\) symmetry) have been calculated using various ab initio methods. Variational methods such as multireference configuration interaction (MR-CI) and complete active space second order perturbatiOn treatment (CASPT2) have been applied, as weil as perturbational treatments and coupled cluster calculations (CCD). The correlation of all valence shell electrons is found to be important for a balanced description of the isomers of C\(_6\) . Methods which do not account for higher-order effects appropriately proved to be unsuitable for calculating the energy difference correctly. The results from multireference configuration interaction methods show that the isomers are close in energy with the cyclic forms somewhat lower than the linear form. The ring form possessing D\(_{3h}\) symmetry (\(^1\)A'\(_1\)} is found tobe the lowest-lying structure.},
subject = {Organische Chemie},
language = {en}
}
@article{RamlerFantuzziGeistetal.2021,
author = {Ramler, Jaqueline and Fantuzzi, Felipe and Geist, Felix and Hanft, Anna and Braunschweig, Holger and Engels, Bernd and Lichtenberg, Crispin},
title = {The dimethylbismuth cation: entry into dative Bi-Bi bonding and unconventional methyl exchange},
series = {Angewandte Chemie International Edition},
volume = {60},
journal = {Angewandte Chemie International Edition},
doi = {10.1002/anie.202109545},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256543},
pages = {24388-24394},
year = {2021},
abstract = {The dimethyl bismuth cation, [BiMe\(_2\)(SbF\(_6\))], has been isolated and characterized. Reaction with BiMe\(_3\) allows access to the first compound featuring Bi→Bi donor-acceptor bonding. In solution, dynamic behavior with methyl exchange via an unusual S\(_E\)2 mechanism is observed, underlining the unique properties of bismuth species as soft Lewis acids with the ability to undergo reversible Bi-C bond cleavage.},
language = {en}
}
@article{RangFantuzziArrowsmithetal.2021,
author = {Rang, Maximilian and Fantuzzi, Felipe and Arrowsmith, Merle and Krummenacher, Ivo and Beck, Eva and Witte, Robert and Matler, Alexander and Rempel, Anna and Bischof, Tobias and Radacki, Krzysztof and Engels, Bernd and Braunschweig, Holger},
title = {Reduktion und Umlagerung eines Bor(I)-Carbonylkomplexes},
series = {Angewandte Chemie},
volume = {133},
journal = {Angewandte Chemie},
number = {6},
doi = {10.1002/ange.202014167},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-224409},
pages = {3000 -- 3005},
year = {2021},
abstract = {Bei der Einelektronenreduktion eines durch eine cyclisches (Alkyl)(amino)carben (CAAC) stabilisierten Arylborylen-Carbonylkomplexes erfolgt die Bildung eines dimeren Borylketyl-Radikalanions, bedingt durch eine intramolekulare Arylmigration zum CO Kohlenstoffatom. Computergest{\"u}tzte Analyse liefert Hinweise auf eine radikalanionische [(CAAC)B(CO)Ar]\(^{.-}\) Zwischenstufe. Weiterf{\"u}hrende Reduktion des entstandenen Komplexes liefert ein hoch nukleophiles (Boranyliden)methanolat.},
language = {de}
}
@article{ReuterEngelsPeyerimhoff1992,
author = {Reuter, W. and Engels, Bernd and Peyerimhoff, S.D.},
title = {The Reaction of Singlet and Triplet Methylen with Ethene - A Multi-Reference CI Study},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58923},
year = {1992},
abstract = {Large-scale multireference configuration interaction (MRD-CI) calculations in a flexible atomic orbital (AO) basis are employed to study the reaction of C\(_2\)H\(_4\) with CH\(_2\) in its firSt triplet and singlet state. The minimum energy path (MEP) of both reactions is calculated, and different mechanisms are discussed. To examine the possible participation of the singlet state in the overall reaction starting from the triplet channel and terminating in the singlet-state c-C\(_3\)H\(_6\), various cuts through both hypersurfaces are calculated. lt is found that favorable interconversion from the trip1et to the singlet surface can only occur at !arge separations of the two fragments of CH2 and C\(_2\)H\(_4\). Experimental data considering the vibrational motion of CH\(_2\) in connection with the relative position of both surfaces are used to obtain an estimate for the overall barrier of the reaction. The height of the barrier is about 6 kcal/mol, while the barrier of the pure triplet reaction is calculated to be 7-9 kcal/mol.},
subject = {Organische Chemie},
language = {en}
}
@article{RoyTroesterFantuzzietal.2021,
author = {Roy, Dipak Kumar and Tr{\"o}ster, Tobias and Fantuzzi, Felipe and Dewhurst, Rian D. and Lenczyk, Carsten and Radacki, Krzysztof and Pranckevicius, Conor and Engels, Bernd and Braunschweig, Holger},
title = {Isolation and Reactivity of an Antiaromatic s-Block Metal Compound},
series = {Angewandte Chemie International Edition},
volume = {60},
journal = {Angewandte Chemie International Edition},
number = {7},
doi = {10.1002/anie.202014557},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-224447},
pages = {3812 -- 3819},
year = {2021},
abstract = {The concepts of aromaticity and antiaromaticity have a long history, and countless demonstrations of these phenomena have been made with molecules based on elements from the p, d, and f blocks of the periodic table. In contrast, the limited oxidation-state flexibility of the s-block metals has long stood in the way of their participation in sophisticated π-bonding arrangements, and truly antiaromatic systems containing s-block metals are altogether absent or remain poorly defined. Using spectroscopic, structural, and computational techniques, we present herein the synthesis and authentication of a heterocyclic compound containing the alkaline earth metal beryllium that exhibits significant antiaromaticity, and detail its chemical reduction and Lewis-base-coordination chemistry.},
language = {en}
}
@article{SaalfrankFantuzziKupferetal.2020,
author = {Saalfrank, Christian and Fantuzzi, Felipe and Kupfer, Thomas and Ritschel, Benedikt and Hammond, Kai and Krummenacher, Ivo and Bertermann, R{\"u}diger and Wirthensohn, Raphael and Finze, Maik and Schmid, Paul and Engel, Volker and Engels, Bernd and Braunschweig, Holger},
title = {cAAC-Stabilized 9,10-diboraanthracenes—Acenes with Open-Shell Singlet Biradical Ground States},
series = {Angewandte Chemie International Edition},
volume = {59},
journal = {Angewandte Chemie International Edition},
number = {43},
doi = {10.1002/anie.202008206},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-217795},
pages = {19338 -- 19343},
year = {2020},
abstract = {Narrow HOMO-LUMO gaps and high charge-carrier mobilities make larger acenes potentially high-efficient materials for organic electronic applications. The performance of such molecules was shown to significantly increase with increasing number of fused benzene rings. Bulk quantities, however, can only be obtained reliably for acenes up to heptacene. Theoretically, (oligo)acenes and (poly)acenes are predicted to have open-shell singlet biradical and polyradical ground states, respectively, for which experimental evidence is still scarce. We have now been able to dramatically lower the HOMO-LUMO gap of acenes without the necessity of unfavorable elongation of their conjugated π system, by incorporating two boron atoms into the anthracene skeleton. Stabilizing the boron centers with cyclic (alkyl)(amino)carbenes gives neutral 9,10-diboraanthracenes, which are shown to feature disjointed, open-shell singlet biradical ground states.},
language = {en}
}
@article{SaalfrankFantuzziKupferetal.2020,
author = {Saalfrank, Christian and Fantuzzi, Felipe and Kupfer, Thomas and Ritschel, Benedikt and Hammond, Kai and Krummenacher, Ivo and Bertermann, R{\"u}diger and Wirthensohn, Raphael and Finze, Maik and Schmid, Paul and Engel, Volker and Engels, Bernd and Braunschweig, Holger},
title = {cAAC-stabilisierte 9,10-Diboraanthracene - offenschalige Singulettbiradikale},
series = {Angewandte Chemie},
volume = {132},
journal = {Angewandte Chemie},
number = {43},
doi = {10.1002/ange.202008206},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-218582},
pages = {19502 -- 19507},
year = {2020},
abstract = {Geringe HOMO-LUMO-Abst{\"a}nde und eine hohe Ladungstr{\"a}germobilit{\"a}t pr{\"a}destinieren die h{\"o}heren Acene f{\"u}r Anwendungen im Bereich der Organoelektronik. Die Leistungsf{\"a}higkeit derartiger Verbindungen steigt hierbei dramatisch mit der Anzahl anellierter Benzolringe. Gr{\"o}ßere Acenmengen sind synthetisch bisher jedoch nur f{\"u}r Acene bis Heptacen verl{\"a}sslich zug{\"a}nglich. Theoretischen Studien zufolge besitzen (Oligo)acene offenschalige Singulettbiradikal- und (Poly)acene polyradikalische Grundzust{\"a}nde. Eindeutige experimentelle Belege f{\"u}r diese Vorhersagen sind hingegen {\"a}ußerst selten. Durch den Einbau von zwei Boratomen in das Anthracengrundger{\"u}st konnten wir den HOMO-LUMO-Abstand von Acenen dramatisch verringern und zwar ohne die Notwendigkeit einer Ausweitung des konjugierten π-Systems. Stabilisierung der Borzentren durch cyclische (Alkyl)(amino)carbene lieferte hierbei neutrale 9,10-Diboraanthracene mit disjunkten, offenschaligen Singulettbiradikal-Grundzust{\"a}nden.},
language = {en}
}
@article{SawatzkyDrakopoulosRoelzetal.2016,
author = {Sawatzky, Edgar and Drakopoulos, Antonios and R{\"o}lz, Martin and Sotriffer, Christoph and Engels, Bernd and Decker, Michael},
title = {Experimental and theoretical investigations into the stability of cyclic aminals},
series = {Beilstein Journal of Organic Chemistry},
volume = {12},
journal = {Beilstein Journal of Organic Chemistry},
doi = {10.3762/bjoc.12.221},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-160976},
pages = {2280-2292},
year = {2016},
abstract = {Background: Cyclic aminals are core features of natural products, drug molecules and important synthetic intermediates. Despite their relevance, systematic investigations into their stability towards hydrolysis depending on the pH value are lacking. Results: A set of cyclic aminals was synthesized and their stability quantified by kinetic measurements. Steric and electronic effects were investigated by choosing appropriate groups. Both molecular mechanics (MM) and density functional theory (DFT) based studies were applied to support and explain the results obtained. Rapid decomposition is observed in acidic aqueous media for all cyclic aminals which occurs as a reversible reaction. Electronic effects do not seem relevant with regard to stability, but the magnitude of the conformational energy of the ring system and pK a values of the N-3 nitrogen atom. Conclusion: Cyclic aminals are stable compounds when not exposed to acidic media and their stability is mainly dependent on the conformational energy of the ring system. Therefore, for the preparation and work-up of these valuable synthetic intermediates and natural products, appropriate conditions have to be chosen and for application as drug molecules their sensitivity towards hydrolysis has to be taken into account.},
language = {en}
}
@article{SchmidtFantuzziKlopfetal.2021,
author = {Schmidt, Paul and Fantuzzi, Felipe and Klopf, Jonas and Schr{\"o}der, Niklas B. and Dewhurst, Rian D. and Braunschweig, Holger and Engel, Volker and Engels, Bernd},
title = {Twisting versus delocalization in CAAC- and NHC-stabilized boron-based biradicals: the roles of sterics and electronics},
series = {Chemistry - A European Journal},
volume = {27},
journal = {Chemistry - A European Journal},
number = {16},
doi = {10.1002/chem.202004619},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-256636},
pages = {5160-5170},
year = {2021},
abstract = {Twisted boron-based biradicals featuring unsaturated C\(_2\)R\(_2\) (R=Et, Me) bridges and stabilization by cyclic (alkyl)(amino)carbenes (CAACs) were recently prepared. These species show remarkable geometrical and electronic differences with respect to their unbridged counterparts. Herein, a thorough computational investigation on the origin of their distinct electrostructural properties is performed. It is shown that steric effects are mostly responsible for the preference for twisted over planar structures. The ground-state multiplicity of the twisted structure is modulated by the σ framework of the bridge, and different R groups lead to distinct multiplicities. In line with the experimental data, a planar structure driven by delocalization effects is observed as global minimum for R=H. The synthetic elusiveness of C\(_2\)R\(_2\)-bridged systems featuring N-heterocyclic carbenes (NHCs) was also investigated. These results could contribute to the engineering of novel main group biradicals.},
language = {en}
}
@unpublished{SchmidtFantuzziArrowsmithetal.2020,
author = {Schmidt, Uwe and Fantuzzi, Felipe and Arrowsmith, Merle and Hermann, Alexander and Prieschl, Dominic and Rempel, Anna and Engels, Bernd and Braunschweig, Holger},
title = {Tuneable reduction of cymantrenylboranes to diborenes or borylene-derived boratafulvenes},
series = {Chemical Communications},
journal = {Chemical Communications},
doi = {10.1039/D0CC06398C},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-222149},
year = {2020},
abstract = {Whereas the reduction of N-heterocyclic carbene (NHC)-stabilised cymantrenyldibromoboranes, (NHC)BBr\(_2\)Cym, in benzene results in formation of the corresponding diborenes (NHC)\(_2\)B\(_2\)Cym\(_2\), a change of solvent to THF yields a borylene of the form (NHC)\(_2\)BCym, stabilised through its boratafulvene resonance form.},
language = {en}
}
@article{StaikovaEngelsPeric1994,
author = {Staikova, M. and Engels, Bernd and Peric, M.},
title = {Ab initio investigation of the hyperfine structure in the 1\(^2\)Π\(_u\)(X\(^2\)A\(_1\), A\(^2\)B\(_1\) system of BH\(_2\))},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59000},
year = {1994},
abstract = {No abstract available},
subject = {Organische Chemie},
language = {en}
}
@article{StaikovaEngelsPericetal.1993,
author = {Staikova, M. and Engels, Bernd and Peric, M. and Peyerimhoff, S. D.},
title = {Ab initio calculation of the vibronically averaged hyperfine coupling constants in the two lowest electronic states of H\(_2\)O\(^+\)},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-58998},
year = {1993},
abstract = {No abstract available},
subject = {Organische Chemie},
language = {en}
}
@article{StaikovaPericEngelsetal.1994,
author = {Staikova, M. and Peric, M. and Engels, Bernd and Peyerimhoff, S. D.},
title = {Ab initio Investigation of the Structure of the X\(^2\)A', A\(^2\)A'' (1\(^2\)Π) Spectral System of HCO: Investigation of the Magnetic Hyperfine Effects},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59089},
year = {1994},
abstract = {Results ofan ab initio study ofthe hyperfine structure of the X\(^2\)A', A\(^2\) A" ( 1\(^2 \Pi\)) system ofthe formyl radical are presented. Special attention is paid to the analysis of the interplay between the vibronic and magnetic hyperfine etfects. The results of computations are in very good agreement with the available experimental findings. The values for the hyperfine coupling constants in lower bending Ievels of both electronic species are predicted.},
subject = {Organische Chemie},
language = {en}
}
@article{SuterEngels1994,
author = {Suter, H. U. and Engels, Bernd},
title = {Theoretical investigation of ESR parameters: H\(_2\)CN and H\(_2\)CO\(^+\)},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59029},
year = {1994},
abstract = {The hyperfine structure of the two isoelectronic molecules H\(_2\)CN and H\(_2\)CO\(^+\) in their electronic ground state (X\(^2\)B\(_2\)) is studied. The influence of the atomic orbital (AO), basis sets, of the correlation treatment, and of the. equilibrium geometry on the obtained hyperfine propertles 1s - investigated. It is found that the multireference double excitation-configuration interaction (MRD-CI)/ BK treatment in which an MRD-CI wave function is corrected by a modified B\(_K\) method yields equivalent results to quadratic CI [QCISD(T)], coupled cluster single doubles [CCSD(T)), or Brueckner doubled [BD(T)]. Uncertainties in the equilibrium geometries are found to be the major source for discrepancies between theoretically and experimentally determined isotropic hyperfine coupling constants (hfccs). For the heavier centers, the calculated values of the isotropic hfccs agrees nearly perfectly with experimental values (\(\approx\) 1\%-2\%). The calculated values for the hydrogens are too low, but using the equilibrium structure suggested by Yamamoto and Sato [J. Chem. Phys. 96, 4157 ( 1992)], the best estimate deviates by less than 3\%.},
subject = {Organische Chemie},
language = {en}
}
@article{SuterHuangEngels1994,
author = {Suter, H. U. and Huang, M.-B. and Engels, Bernd},
title = {A Multireference Configuration Interaction Study of the Hyperfine Structure of the Molecules CCO, CNN and NCN in their triplet ground states},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59108},
year = {1994},
abstract = {The hyperfine structures of the isoelectronic molecules CCO. CNN, and NCN in their triplet ground states (X\(^3 \sum ^-\)) are investigated by means of ab initio methods. The infrared frequencies and geometries are detennined and compared with experiment. Configuration selected multireference configuration interaction calculations in combination with perturbation theory to correct the wave function (MRD-CI/B\(_K\)) employing extended atomic orbital (AO) basis sets yielded very accurate hyperfine properties. The theoretical values for CCO are in excellent agreement with the experimental values determined by Smith and Weltner [J. Chem. Phys. 62,4592 (1975)]. For CNN, the first assignment of Smith and Weltner for the two nitrogen atoms has to be changed. A qualitative discussion of the electronic structure discloses no simple relation between the structure of the singly occupied orbitals and the measured hyperfine coupling constants. Vibrational effects were found to be of little importance.},
subject = {Organische Chemie},
language = {en}
}
@article{SuterPlessErnzerhofetal.1994,
author = {Suter, H. U. and Pleß, V. and Ernzerhof, M. and Engels, Bernd},
title = {Difficulties in the Calculation of Electron Spin Resonance Parameters using Density Functional Methods},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59113},
year = {1994},
abstract = {Density functional theory is applied to the calculation ofthe isotropic byperfine coupJing constants in some small molecules. Various functionals are tested. The agreement of the calculated values to experimental data and values obtained from sophisticated ab initio methods depends on the functionals used and the system under consideration. With respect to spin density calculations the functional of Lee, Yang and Parr with Becke's excbange functional (BLYP) is found to give good results for tbe heavier center of the CH and the NH molecule, while the spin densities of other molecules such as OH, H\(_2\)CN, H\(_2\)CO\(^+\), NO and O\(_2\) deviate considerably from experimental and/or other theoretical results (30\%-60\%). In cases where the singly occupied orbital can contribute to the isotropic hyperfine coupling constants, accurate results are obtained. The reason fortbis is analyzed.},
subject = {Organische Chemie},
language = {en}
}
@article{WeiserCuiDewhurstetal.2023,
author = {Weiser, Jonas and Cui, Jingjing and Dewhurst, Rian D. and Braunschweig, Holger and Engels, Bernd and Fantuzzi, Felipe},
title = {Structure and bonding of proximity-enforced main-group dimers stabilized by a rigid naphthyridine diimine ligand},
series = {Journal of Computational Chemistry},
volume = {44},
journal = {Journal of Computational Chemistry},
number = {3},
doi = {10.1002/jcc.26994},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-312586},
pages = {456 -- 467},
year = {2023},
abstract = {The development of ligands capable of effectively stabilizing highly reactive main-group species has led to the experimental realization of a variety of systems with fascinating properties. In this work, we computationally investigate the electronic, structural, energetic, and bonding features of proximity-enforced group 13-15 homodimers stabilized by a rigid expanded pincer ligand based on the 1,8-naphthyridine (napy) core. We show that the redox-active naphthyridine diimine (NDI) ligand enables a wide variety of structural motifs and element-element interaction modes, the latter ranging from isolated, element-centered lone pairs (e.g., E = Si, Ge) to cases where through-space π bonds (E = Pb), element-element multiple bonds (E = P, As) and biradical ground states (E = N) are observed. Our results hint at the feasibility of NDI-E2 species as viable synthetic targets, highlighting the versatility and potential applications of napy-based ligands in main-group chemistry.},
language = {en}
}
@article{WortmannSalehEngelsPeyerimhoff1994,
author = {Wortmann-Saleh, D. and Engels, Bernd and Peyerimhoff, S. D.},
title = {Theoretical Study of the Reaction O(\(^3\)P) + C\(_2\)H\(_4\) and comparison with the \(^3\)CH\(_3\) + C\(_2\)H\(_4\) Reaction},
url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-59076},
year = {1994},
abstract = {The minimum energy path for the reaction O(\(^3\)P\(_g\)) + C\(_2\)H\(_4\)(\(^1\)A\(_g\)) has been calculated by optimizing all relevant geometrical parameters along the approach of oxygen to ethene. A barrier of 4.7 kcal/mol in the \(^3\)A"( ... 9a'\(^2\)- 10a'3a") potential energy surface and an energy difference of 14.4 kcal/mol between the product and the fragments is found at the multireference-configuration interaction level. The corresponding values at the lower-level treatment CASSCF are 9 kcal/mol for the barrier and 9 kcal/mol for the depth of the potential; this shows the importance of inclusion of electron correlation. The barrier for CH\(_2\) rotation for the lowestenergy structure (asymmetric OC\(_2\)H\(_4\)) is around 5 kcal/mol. The energy gap to the first excited state \(^3\)A'( ... 9a'l0a'3a'12) is found tobe 3.6 kcal/mol in MRD-CI calculations at the ground-state minimum. Comparison with \(^3\)CH\(_2\) + C\(_2\)H\(_4\) shows that in this system the lowest-energy surface is \(^3\)A', i.e., the state which is the excited state in 0 + C\(_2\)H\(_4\). This difference in energy ordering of \(^3\)A' and \(^3\)A" states results from the fact that the p\(_x\), p\(_y\), p\(_z\) degeneracy of oxygen orbitals is lifted in \(^3\)CH\(_2\)leading to b\(_1\), b\(_2\). and a\(_1\) MOs whereby the lowest b\(_2\) (a") remains doubly occupied; as a consequence, the reaction pattem between the oxygen and \(^3\)CH\(_2\) approach is different, which is also quite apparent in the calculated charge transfer.},
subject = {Organische Chemie},
language = {en}
}