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Fortman G.C.,University of St. Andrews | Jacobsen H.,KemKom | Cavallo L.,University of Salerno | Nolan S.P.,University of St. Andrews
Chemical Communications | Year: 2011

The catalytic activity of a series of coordinatively unsaturated NHC-M(iii) (M = Rh, Ir; NHC = N-heterocyclic carbene) complexes was tested in the deuteration of secondary and tertiary silanes. Among these, [IrCl(I tBu′)2] provides the highest conversions to the deuterated species. Mechanistic studies highlight the reversible nature of the ortho-metalation reaction. © The Royal Society of Chemistry 2011.


Jacobsen H.,KemKom | Jacobsen H.,Tulane University
Chemistry - A European Journal | Year: 2010

The role of electrostatic interactions in covalent bonding of heavier main group elements has been evaluated for the exemplary set of molecules X 2H2 (X = C, Si, Ge, Sn, Pb). Density functional calculations at PBE/QZ4P combined with energy decomposition procedures and kinetic energy density analyses have been carried out for a variety of different structures, and two factors are responsible for the fact that the heavier homologues of acetylene exhibit doubly hydrogen-bridged local minimum geometries. For one, the extended electronic core with at least one set of p orbitals of the Group 14 elements beyond the first long period is responsible for favorable electrostatic E-H interactions. This electrostatic interaction is the strongest for the isomer with two bridging hydrogen atoms. Secondly, the H substituent does not posses an electronic core or any bonding-inactive electrons, which would give rise to a significant amount of Pauli repulsion, disfavoring the doubly bridged isomer. When one of two criteria is not met the unusual doubly bridged structure no longer constitutes the energetically preferred geometry. The bonding model is validated in calculations of different structures of Si2(CH3)2. © 2010 Wiley-VCH Verlag GmbH & Co. KGaA. Weinheim.


Jacobsen H.,KemKom
Physical Chemistry Chemical Physics | Year: 2013

Analysis of the kinetic energy density within a molecule identifies patterns in its electronic structure that are intuitively linked to familiar concepts of chemical bonding. The function ν(r), termed localized-orbital locator and based on the positive-definite kinetic energy density τ+, is employed to characterize classes of covalent bonds in terms of its full topology of all critical points of rank three. Not only does ν(r) reveal patterns in chemical bonding, it also discloses features and the influence of extended electronic cores. Gradient paths define the extension of the valence space around an atomic centre; they separate various core level regions from bonding domains, and partition molecules in sensible bonded subunits. Location and ν(r)-values of critical points add a quantitative aspect to the bond characterization; profiles of unconventional chemical linkages such as charge-shift bonds emerge in a natural way. © 2013 The Owner Societies.


An analysis of the kinetic energy density within a molecule identifies patterns within its electronic structure that are intuitively linked to familiar concepts of chemical bonding. Proposed are bond descriptors based on local kinetic energies in an extended mapping onto a finite range of values, so called RoSE-indicators. The usefulness and performance of RoSE-indicators is judged in applications on aromaticity. Results are presented for benzene, cyclobutadiene, borazine and the cyclic hydrogen fluoride trimer as examples for agreed-upon aromaticity and antiaromaticity, as well as for questionable aromaticity. All-metal aromaticity is discussed based on results obtained for tetra aluminum dianion. © 2013 Elsevier B.V. All rights reserved.


An analysis of the kinetic energy density within a molecule identifies patterns within its electronic structure that are intuitively linked to familiar concepts of chemical bonding. © 2010 The Royal Society of Chemistry.


Jacobsen H.,KemKom
Journal of Chemical Theory and Computation | Year: 2011

The claim that DFT does not provide an accurate description of a weak Ru-C interaction (J. Chem. Theory Comput.2007, 3, 665-670) is put into broader perspective. The mismatch between structures obtained from DFT (BP86) as well as DFT-D (BP86-D2) calculations of isolated molecules in the gas phase and geometries resulting from X-ray crystal structure determination is due to a dissatisfactory chemical model system. Intermolecular forces within the molecular surroundings of the crystal obtained from semiempirical lattice energy calculations emerge as likely candidates responsible for the incongruity of experimental results and computation. © 2011 American Chemical Society.


Jacobsen H.,KemKom
Canadian Journal of Chemistry | Year: 2015

Oxygen difluoride most likely does not form stable complexes with transition metal fragments but initiates formation of halides, oxides, and oxyhalides. This conclusion is drawn as the result of density functional calculations (BP86/TZVP). The interaction between OF2 as potential ligand and the transition metal fragment Cr(CO)5 provides the model scenario. A combined charge and energy decomposition scheme (ETS-NOCV) for bond analysis illustrates the difference in bond behavior between typical donor ligands and oxygen difluoride. © 2016 Published by NRC Research Press.


Analysis of the kinetic energy density within a molecule identifies patterns in its electronic structure that are linked to the concept of charge-shift bonding. This is illustrated in a detailed study of twelve molecules, possessing carbon-carbon covalent as well as carbon-carbon charge-shift bonds in various degrees of orders, including propellanes and heteropropellanes. Regions of slow electrons are fundamental for such a correlation, and a RoSE (region of slow electrons) indicator ν±, based on the positive definite kinetic energy density τ, is employed to characterize classes of charge-shift bonds in terms of its full topology of all critical points of rank three. Not either-or anymore: Bond descriptors based on the local kinetic energy not only confirm the essence of charge-shift bonding, but also articulate this concept with nuances. © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Jacobsen H.,KemKom | Cavallo L.,King Abdullah University of Science and Technology
ChemPhysChem | Year: 2012

The performance of a series of density functionals when tested on the prediction of the phosphane substitution energy of transition metal complexes is evaluated. The complexes Fe-BDA and Ru-COD (BDA=benzylideneacetone, COD=cyclooctadiene) serve as reference systems, and calculated values are compared with the experimental values in THF as obtained from calorimetry. Results clearly indicate that functionals specifically developed to include dispersion interactions usually outperform other functionals when BDA or COD substitution is considered. However, when phosphanes of different sizes are compared, functionals including dispersion interactions, at odd with experimental evidence, predict that larger phosphanes bind more strongly than smaller phosphanes, while functionals not including dispersion interaction reproduce the experimental trends with reasonable accuracy. In case of the DFT-D functionals, inclusion of a cut-off distance on the dispersive term resolves this issue, and results in a rather robust behavior whatever ligand substitution reaction is considered. Ne quid nimis: Describing chemical reactions in solution by computational techniques developed for gas-phase scenarios might produce erroneous results (see histogram). Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.


Jacobsen H.,KemKom
Inorganic Chemistry | Year: 2013

The cross-ring sulfur-sulfur bond for seven R′RP(NSN) 2PRR′ molecules 1a (R = R′ = Me), 1b (R = R′ = Ph), 1c (R = R′ = Et), 1d (R = Cl, R′ = CCl3), 1e (R = R′= Cl), 1f (R = R′ = F), and 1g (R = R′ = H) has been scrutinized by a topology analysis for a bond descriptor based on the kinetic energy density, supported by a fragment-based bond energy analysis. Contrary to a regular disulfide bond, the cross-ring connection is only a secondary electron-sharing bond, about half as strong as a common S-S linkage. The regular disulfide bond itself is best described as a charge-shift bond. These analyses are based on results obtained from B3PW91/def2-TZVP density functional calculations. © 2013 American Chemical Society.

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