The local kinetic energy profile of an inverted carbon-carbon bond reveals and refines its charge-shift character.

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.

More on diphosphadithiatetrazocines and the importance of being bonded.

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.

Topology maps of bond descriptors based on the kinetic energy density and the essence of chemical bonding.

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.

Electronic bond tuning with heterocyclic carbenes.

We discuss the impact of the nature of the heterocyclic carbene ring, when used as a complex forming ligand, on the relative stability of key intermediates in three typical Ru, Pd and Au promoted reactions. Results show that P-heterocyclic carbenes have a propensity to increase the bonding of the labile ligand and of the substrate in Ru-promoted olefin metathesis, whereas negligible impact is expected on the stability of the ruthenacycle intermediate. In the case of Pd cross-coupling reactions, dissociation of a P-heterocyclic carbene is easier than dissociation of the N-heterocyclic analogue.

On the accuracy of DFT methods in reproducing ligand substitution energies for transition metal complexes in solution: the role of dispersive interactions.

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.

A Failure of DFT Is Not Necessarily a DFT Failure-Performance Dependencies on Model System Choices.

The claim that DFT does not provide an accurate description of a weak Ru-C interaction (J. Chem. Theory Comput.

Catalytic deuteration of silanes mediated by N-heterocyclic carbene-Ir(III) complexes.

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(t)Bu')(2)] provides the highest conversions to the deuterated species. Mechanistic studies highlight the reversible nature of the ortho-metalation reaction.

A tungsten-mediated closed cycle of reactivity for the reduction of CO(2) to CO.

The recycling of CO(2) by reduction to CO is an important objective in the context of renewable carbon feedstock chemicals. A tungsten-mediated reduction of CO(2) to CO reported by Mayer and coworkers has been re-examined, and it is shown that a series of four well-defined stoichiometric steps can be executed which form a closed cycle and sum as CO(2) + 2H(+) + 2e(-)→ CO + H(2)O. Energetic parameters of this system are probed by cyclic voltammetry, by calculations of gas-phase reaction enthalpies for each of the four steps, and by calculation of the W[triple bond, length as m-dash]O bond dissociation energy for the tungsten species that results from oxidation addition of CO(2).

Kinetic energy density and covalent bonding - a complementary analysis at the border of bond and no bond.

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.

Shifting paradigms: electrostatic interactions and covalent bonding.

The role of electrostatic interactions in covalent bonding of heavier main group elements has been evaluated for the exemplary set of molecules X(2)H(2) (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.

Fluorine substituent effects on dihydrogen bonding of transition metal hydrides.

Hydrogen and dihydrogen bonding of the fluorinated alcohol (CF(3))(2)CHOH with the transition metal complex WH(CO)(2)(NO)(PMe(3))(2) has been explored by a set of four exemplary density functional theory methods that comprises the BP86, PBE, B3LYP and TPSS functionals. The hydride, nitrosyl and carbonyl ligands of the tungsten complex have been considered as sites of protonation. The main effect of fluorination is an increased dihydrogen bond strength by about 15 kJ mol(-1).

Activation of hydrogen by palladium(0): formation of the mononuclear dihydride complex trans-[Pd(H)2(IPr)(PCy3)].

An even split: In sharp contrast with the general behavior of Pd(0) complexes, [Pd(IPr)(PCy(3))] is able to activate the H-H bond. The resulting trans-[Pd(H)(2)(IPr)(PCy(3))] is the first isolated mononuclear dihydride palladium compound. Its formation is supported by multinuclear NMR spectroscopy, density functional calculations, and X-ray diffraction studies.

Hypovalency--a kinetic-energy density description of a 4c-2e bond.

A bond descriptor based on the kinetic energy density, the localized-orbital locator (LOL), is used to characterize the nature of the chemical bond in electron deficient multi-center bonds. The boranes B(2)H(6), B(4)H(4), B(4)H(10), [B(6)H(6)](2-), and [B(6)H(7)](-) serve as prototypical examples of hypovalent 3c-2e and 4c-2e bonding. The kinetic energy density is derived from a set of Kohn-Sham orbitals obtained from pure density functional calculations (PBE/TZVP), and the topology of LOL is analyzed in terms of (3,-3) attractors (Gamma).

Chemical bonding in view of electron charge density and kinetic energy density descriptors.

Stalke's dilemma, stating that different chemical interpretations are obtained when one and the same density is interpreted either by means of natural bond orbital (NBO) and subsequent natural resonance theory (NRT) application or by the quantum theory of atoms in molecules (QTAIM), is reinvestigated. It is shown that within the framework of QTAIM, the question as to whether for a given molecule two atoms are bonded or not is only meaningful in the context of a well-defined reference geometry. The localized-orbital-locator (LOL) is applied to map out patterns in covalent bonding interaction, and produces results that are consistent for a variety of reference geometries.

Computational study of iron bis(dithiolene) complexes: redox non-innocent ligands and antiferromagnetic coupling.

The molecular and electronic structure of monomeric ([Fe(S2C2H2)2](z), [Fe(S2C2(C6H4-p-OCH3)2)2](z)) and dimeric ([{Fe(S2C2H2)2}2](z)) iron bis(dithiolene) complexes, and of their phosphine adducts ([(PH3)Fe(S2C2H2)2](z), [(P(C6H5)3)Fe(S2C2H2)2](z), [(PH3)Fe(S2C2(C6H4-p-OCH3)2)2](z)), carrying various charges (z = 0, 1-, 2-), have been investigated by density functional theory (DFT). Net total spin polarization values S of zero, two, and four have been considered for all neutral model compounds and their dianions, whereas all monoanions have been examined with net total spin polarization values S of one, three, and five. The DFT calculations utilized the pure functional BP86, as well as the hybrid functionals B3LYP and B3LYP*.

Reversible, electrochemically controlled binding of phosphine to iron and cobalt bis(dithiolene) complexes.

The homoleptic bis(dithiolene) complexes [M(S(2)C(2)R(2))(2)](2) (M = Fe, Co; R = p-anisyl) undergo two successive reductions to form anions that display [M(S(2)C(2)R(2))(2)](2)(2-) <--> 2[M(S(2)C(2)R(2))(2)](1-) solution equilibria. The neutral dimers react with Ph3P to form square pyramidal [M(Ph(3)P)(S(2)C(2)R(2))(2)](0). Voltammetric measurements upon [M(Ph(3)P)(S(2)C(2)R(2))(2)](0) in CH(2)Cl(2) reveal only irreversible features at negative potentials, consistent with Ph(3)P dissociation upon reduction.

Dicoordinate copper(I) silanechalcogenolates.

The copper silanechalcogenolates tBu3PCuESiPh3 (1, E = O; 2, E = S; 3, E = Se) were prepared from the reaction of [tBu3PCu(CH3CN)3]BF4 with [Ph3SiELi(THF)2]2 in acetonitrile. The compounds were obtained as colorless, crystalline, but thermally labile solids. X-ray crystallography shows that complexes 1-3 are monomeric in the solid state with no Cu.

Dynamic processes in silyl palladium complexes: evidence for intermediate Si-H and Si-Si sigma-complexes.

The silyl palladium complexes (dcpe)PdH(SiHtBu2) and (dcpe)Pd(SiHMe2)2 display NMR spectra that vary with temperature. The dynamic NMR behavior is consistent with long-lived sigma-complexes as intermediates. In the case of (dcpe)PdH(SiHtBu2), the intermediate is believed to be a symmetric complex with doubly bridged hydrogen atoms between the silicon and palladium.

P-Heterocyclic carbenes as potential ligands in the design of new metathesis catalysts. A computational study.

Density functional calculations are reported concerning the olefin metathesis characteristics of a variety of P-heterocyclic carbene (PHC) complexes. The calculations employ model catalysts of the type (PMe3)(PHC)Cl2Ru=CH2, the PHC ligands being 1,3-dihydro-1,3-diphosphol-2-ylidene PH, 1,3-diphenyl-1,3-diphosphol-2-ylidene PPH, and 1,4-dihydro-1,4-diphosphol-2-azol-5-ylidene PNH. Complexes with N-heterocyclic carbenes (NHC) are included for comparison.

Alkyl-eta2-alkene niobocene and tantalocene complexes with the allyldimethylsilyl-eta5-cyclopentadienyl ligand: synthesis, NMR studies and DFT calculations.

Group 5 metal complexes [M(eta5-C5H5)[eta5-C5H4SiMe2(CH2-eta]2-CH=CH2)]X] (M = Nb, X = Me, CH2Ph, CH2SiMe3; M = Ta, X = Me, CH2Ph) and [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2-eta2-CH=CH2)]X] (X = Cl, Me, CH2Ph, CH2SiMe3) containing a chelating alkene ligand tethered to a cyclopentadienyl ring have been synthesized in high yields by reduction with Na/Hg (X = Cl) and alkylation with reductive elimination (X = alkyl) of the corresponding metal(iv) dichlorides [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]Cl2] (Cp = C5H5, M = Nb, Ta, Cp = C5Me5, M = Ta). These chloro- and alkyl-alkene coordinated complexes react with CO and isocyanides [CNtBu, CN(2,6-Me2C6H3)] to give the ligand-substituted metal(III) compounds [M(eta5-Cp)[eta5-C5H4SiMe2(CH2CH=CH2)]XL] (X = Cl, Me, CH2Ph, CH2SiMe3). Reaction of the chloro-alkene tantalum complex with LiNHtBu results in formation of the imido hydride derivative [Ta(eta5-C5Me5)[eta5-C5H4SiMe2(CH2CH=CH2)]H(NtBu)].

Toward a catalytic cycle for the Mn-salen mediated alkene epoxidation: a computational approach.

BP86 density functional calculations for the title reaction are presented, where a model catalyst with hypochlorite as oxygen-containing counter ligand, (ClO)(O)Mn(acacen') (acacen' = -O(CH)3N-C2H4-N(CH)3O-), is employed. The epoxidation reaction on potential energy surfaces corresponding to an overall spin-density of two and four unpaired electrons is investigated. The presence of the hypochlorite ligand is found to cause the reaction to proceed under conservation of spin.

Electronic effects in (salen)Mn-based epoxidation catalysts.

Presented are density functional calculations on various Mn(salen) systems that are active catalysts in the epoxidation of olefins. Correlation of various structural properties such as Mn=O bond strengths, atomic charges, and C-O distances of evolving bonds in transition state geometries with modified Hammett constants reveal a mechanistic picture of the epoxidation reaction, supporting previous experimental results. Enantioselectivity is tied to the position of a transition state along the reaction coordinate for the first C-O bond formation step, when an olefin is approaching the epoxidation catalyst.

An unusual (10,3)-a racemic twofold interpenetrating network assembled from isolable tris(cyclopentadienyl)manganate and cesocene building blocks.

The syntheses and X-ray crystal structures of [([18]crown-6)2Cs](+)-[Cp3Mn]- (1), [([18]crown-6)2Cs](+)-[Cp'3Mn]- (2), [CsCp'] (3), [(CsCp')2-([18]crown-6)] (4), and Cs[MnCp3] (5), and the synthesis of Cs[MnCp'3] (6) are reported (Cp' = C5H4Me). The anions [Cp3Mn]- (1-) and [Cp'3Mn]- (2-) are characterized by eta 2 coordination of all three Cp or Cp' rings. Measurements of the magnetic susceptibilities chi M resulted in values of mu eff = 6.

Formation of cyclodimeric (sp(2)-C(1))-bridged Cp/-oxido ("CpC(1)O"M(IV)X(2)) group 4 metal Ziegler-Natta catalyst systems--how important is the "constrained geometry" effect?

Deprotonation of sodium acetylcyclopentadienide (11) was achieved by treatment with LDA in THF to generate the dianion equivalent [Cp-C(=CH(2))-O](2-)(12). Transmetalation with Cl(2)Ti(NMe(2))(2) gave ([Cp-C(=CH(2))-O]Ti(NMe(2))(2))(2) (17); treatment of 12 with Cl(2)Zr(NEt(2))(2)(THF)(2) furnished (([Cp-C(=CH(2))-O]Zr(NEt(2))(2))(2) (18). Cryoscopy in benzene revealed a dimeric structure of 18 in solution.