Predicting Solvation Free Energies Using Electronegativity-Equalization Atomic Charges and a Dense Neural Network: A Generalized-Born Approach.

I propose a dense Neural Network, ESE-GB-DNN, for evaluation of solvation free energies Δ° for molecules and ions in water and nonaqueous solvents. As input features, it employs generalized-Born monatomic and diatomic terms, as well as atomic surface areas and the molecular volume. The electrostatics calculation is based on a specially modified version of electronegativity-equalization atomic charges.

Dense Neural Network for Calculating Solvation Free Energies from Electronegativity-Equalization Atomic Charges.

I propose a dense Neural Network for evaluation of solvation free energies Δ for molecules and ions in water and nonaqueous solvents, Easy Solvation Energy with Electronegativity Equalization charges and Dense Neural Network (ESE-EE-DNN). As input features, it uses the Conductor-like Screening Model (COSMO) electrostatic energy, atomic cavity surface areas, total cavity volume, and induced surface charges. For the COSMO calculation, electronegativity-equalization atomic charges are employed.

Base-Stabilized Phosphinidene Oxide, Imide and Sulfide.

Oxidation of a base-stabilized phosphinidene (κ -NNP)P (12, NNP=phosphinoamidinate) with N O afforded a labile phosphinidene oxide (κ -NNP)P=O (16) which was characterized by NMR spectroscopy. Further oxidation of 16 by N O or reaction of 12 with two equivalents of pyridine oxide afforded the isolable dioxide (κ -NNP)PO which was characterized by NMR and SC XRD. Trapping of 16 with tolyl isocyanate resulted in P=O/N=C metathesis, eventually affording a urea-ligated phosphine (κ -NNP)P(NTol) C=O (17) The mechanism of this reaction was elucidated by DFT calculations.

The Insertion of E and E Chlorides (E=Si, Ge) into the Si-Si Bond of Disilylene.

Reactions of silicon and germanium dichlorides L⋅ECl (E=Si, L=IPr; E=Ge, L=dioxane) with the phosphinoamidinato-supported disilylene ({κ (N,P)-NNP}Si) resulted in formal tetrylene insertions into the Si-Si bond. In the case of the reaction with silylene, two products were isolated. The first product ({κ (N,P)-NNP}Si) SiCl , is the formal product of direct SiCl insertion into the Si-Si bond of ({κ (N,P)-NNP}Si) and thus features two separated silylamido silylene centers.

A quick solvation energy estimator based on electronegativity equalization.

ESE-EE (Easy Solvation Estimation with Electronegativity equalization) is a quick method for estimation of solvation-free energies ΔGº , which uses a thoroughly fitted electronegativity equalization (EE) scheme to obtain atomic charges, which are further employed in a scaled noniterative COSMO-like calculation to evaluate the electrostatic component of ΔGº . Nonelectrostatic corrections including adjustable parameters are also added. For neutral solutes, ESE-EE yields a mean absolute error (MAE) in ΔG ° of 1.

Solvation Free Energies for Aqueous and Nonaqueous Solutions Computed Using PM7 Atomic Charges.

We describe a simple and accurate method, ESE-PM7, for calculating solvation free energies Δ in aqueous and nonaqueous solutions. The method is based on a noniterative COSMO algorithm. Molecular geometries and atomic charges calculated using the semiempirical method PM7 are used to calculate Δ.

Fast non-iterative calculation of solvation energies for water and non-aqueous solvents.

We propose an efficient and accurate non-iterative method, dubbed uESE, for calculating solvation free energies. Apart from a COSMO-like electrostatic term, the model takes into account non-electrostatic contributions, which depend on atomic surfaces, induced surface charge densities, and the molecular volume. uESE is tested on 35 polar and 57 non-polar solvents.

Fast and accurate calculation of hydration energies of molecules and ions.

We present an efficient method with adjustable parameters for calculating the hydration free energy of molecules and ions using the gas-phase geometry and atomic charges. In most cases, the method yields accurate results, with a mean absolute error for neutral molecules below 1 kcal mol-1 and for ions about 3 kcal mol-1. Overall, despite its simplicity, the proposed method shows the best performance among major computational approaches applied to estimate hydration free energies.

Sequential Oxidation and C-H Bond Activation at a Gallium(I) Center.

In situ oxidation of the Ga compound NacNacGa by either N O or pyridine oxide results in the generation of a labile monomeric oxide, NacNacGa(O), which can easily cleave the C-H bonds of aliphatic and aromatic substrates featuring good donor sites. The products of this reaction are gallium organyl hydroxides. DFT calculations show that these reactions start with the formation of NacNac-Ga(O)(L) adducts, the oxo ligand of which can easily abstract protons from nearby C-H bonds, even for sp -hybridized carbon centers.

A simple COSMO-based method for calculation of hydration energies of neutral molecules.

A simple, non-iterative method to estimate hydration free energies of neutral molecules, ESE, is developed. It requires only atomic charges computed for isolated species. To obtain the solvation free energy, the COSMO electrostatic term is supplemented by an extra correction that describes the cavitation energy, van der Waals and specific interactions.

Iterative Atomic Charge Partitioning of Valence Electron Density.

We propose an atomic charge partitioning scheme, iterative adjusted charge partitioning (I-ACP), belonging to the stockholder family and based on partitioning of the valence molecular electron density. The method uses a Slater-type weighting factor c r exp(-α r), where α is a fixed parameter and c is determined iteratively. The parameters α were fitted for 17 main-group elements.

A simple model for calculating atomic charges in molecules.

We propose a new atomic-charge analysis, termed adjusted charge partitioning (ACP) scheme. To partition the molecular electronic density into atomic components, weighting factors cAr2n-2exp(-αAr) with atomic parameters cA and αA are used. Extensive numerical tests were performed for 540 molecules containing 17 main-group elements H, Li to F, Na to Cl, Br, and I.

A Simple Local Correlation Energy Functional for Spherically Confined Atoms from ab Initio Correlation Energy Density.

We propose a simple method of calculating the electron correlation energy density e (r) and the correlation potential V (r) from second-order Møller-Plesset amplitudes and its generalization for the case of a configuration interaction wavefunction, based on Nesbet's theorem. The correlation energy density obtained by this method for free and spherically confined Be and He atoms was employed to fit a local analytical density functional based on Wigner's functional. The functional is capable of producing a strong increase in the correlation energy with decreasing confined radius for the Be atom.

Oxidative Cleavage of the C═N Bond on Al(I).

Reaction of the cyclic guanidine TolN═SIMe with the aluminum(I) compound NacNacAl (1) results in the unprecedented cleavage of the C-N multiple bond to give, after rearrangement, the carbene-ligated Al(III) amide, NacNac'Al(NHTol)(SIMe) (6). DFT calculations revealed that these reactions proceed via a bimolecular mechanism in which either the basic Al(I) center or the transient Al═NTol species deprotonates the methyl group of the NacNac ligand.

Unusual Reactions of NacNacAl with Urea and Phosphine Oxides.

The reaction of cyclic urea 1,3-dimethyl-2-imidazolidinone with the aluminum(I) compound NacNacAl (1) gives an unexpected adduct of urea with the isomerized aluminum(III) hydride NacNac'AlH(O═SIMe) (3). A related reaction of 1 with phosphine oxides results in cleavage of the P═O bond and formation of hydroxyl derivatives NacNac'Al(OH)(O═PR) [R = Ph (5) and Et (6)]. Density functional theory calculations revealed that these reactions proceed via a bimolecular mechanism in which either the basic aluminum(I) center or the transient Al═O species deprotonate the methyl group of the NacNac ligand.

Correlation energy, correlated electron density, and exchange-correlation potential in some spherically confined atoms.

We report correlation energies, electron densities, and exchange-correlation potentials obtained from configuration interaction and density functional calculations on spherically confined He, Be, Be , and Ne atoms. The variation of the correlation energy with the confinement radius R is relatively small for the He, Be , and Ne systems. Curiously, the Lee-Yang-Parr (LYP) functional works well for weak confinements but fails completely for small R .

Oxidative Cleavage of C=S and P=S Bonds at an Al Center: Preparation of Terminally Bound Aluminum Sulfides.

The treatment of cyclic thioureas with the aluminum(I) compound NacNacAl (1; NacNac=[ArNC(Me)CHC(Me)NAr] , Ar=2,6-Pr C H ) resulted in oxidative cleavage of the C=S bond and the formation of 3 and 5, the first monomeric aluminum complexes with an Al=S double bond stabilized by N-heterocyclic carbenes. Compound 1 also reacted with triphenylphosphine sulfide in a similar manner, which resulted in cleavage of the P=S bond and production of the adduct [NacNacAl=S(S=PPh )] (8). The Al=S double bond in 3 can react with phenyl isothiocyanate to furnish the cycloaddition product 9 and zwitterion 10 as a result of coupling between the liberated carbene and PhN=C=S.

Modeling exact exchange potential in spherically confined atoms.

In this work, local exchange potentials corresponding to the Hartree-Fock (HF) electron density have been obtained using the Zhao-Morrison-Parr method for a number of closed-shell confined atoms and ions. The exchange potentials obtained and the resulting density were compared with those given by the Becke-Johnson (BJ) model potential. It is demonstrated that introducing a scaling factor to the BJ potential allows improving the quality of the resulting density.

Si⋅⋅⋅H Interligand Interactions in Cobalt(V) and Iridium(V) Bis(silyl)bis(hydride) Complexes.

A series of bis(silyl)bis(hydride) cobalt complexes [Cp*Co(H) (SiR ) ] (Cp*=pentamethylcyclopentadienyl; SiR =SiPh H, SiMe , SiH , SiF , SiCl , SiBr , Si(CF ) ; Co1-Co7) as well as the analogous iridium complexes [Cp*Ir(H) (SiR ) ] (SiR =SiEt , SiMe , SiH , SiF , SiCl , SiBr , Si(CF ) ; Ir1-Ir7) were studied to detect possible residual Si⋅⋅⋅H interactions. Tests of several density functionals by comparison with coupled-cluster results indicate that the TPSSh functional performs better than B3LYP, BP86, M06, M06L, and PBEPBE. Based on molecular structures, as well as Wiberg bond indices and J(Si,H) spin-spin coupling constants as indicators of a possible Si⋅⋅⋅H interaction, at least two residual Si⋅⋅⋅H interactions in Co2, Co5, and all four possible Si⋅⋅⋅H interactions in Co3 and Co4 have been detected.

Facile activation of H-H and Si-H bonds by boranes.

The borane B(C(6)F(5))(3) is a precatalyst for H/Dexchange between H(2) and deuterium-labeled silanes (D(3)SiPh, D(2)SiMePh, DSiMe(2)Ph, DSiEt(3)). Experimental and DFT studies reveal that B(C(6)F(5))(3) itself cannot activate dihydrogen but converts to HB(C(6)F(5))(2) under the action of hydrosilane. The latter species easily activates H-H and Si-H bonds by a σ-bond metathesis mechanism, which was further confirmed by the reactions of BD(3)·THF with H(2).

A Hirshfeld Partitioning of the MP2 Correlation Energy: Method and Its Application to the Benzene Dimers.

In this work a method is presented for the partitioning of MP2 correlation energies through a grid-space partitioning using the iterative Hirshfeld weight function. The correlation energies are partitioned into mono- and diatomic contributions using two alternative schemes, which allow different levels of parallelization. The method is tested on a set of 24 molecules containing various atoms, leading to the conclusion that, while the numerical results of the two schemes slightly differ, the chemical information contained in them is similar.

Hydrogen motion in proton sponge cations: a theoretical study.

This work presents a study of intramolecular NHN hydrogen bonds in cations of the following proton sponges: 2,7-bis(trimethylsilyl)-1,8-bis(dimethylamino)naphthalene (1), 1,6-diazabicyclo[4.4.4.

Properties of harmonium atoms from FCI calculations: Calibration and benchmarks for the ground state of the two-electron species.

When used in conjunction with appropriate extrapolation schemes, full configuration interaction (FCI) calculations employing systematic sequences of spherical Gaussian primitives with even-tempered exponents shared by functions of different angular momenta are capable of affording ground-state energies of the two-electron harmonium atoms with a few-muHartree accuracy that is sufficient for calibration and benchmarking of approximate electron correlation theories of quantum chemistry. The present approach, which is slated for use in future computations of electronic properties of harmonium atoms with between three and five electrons, calls for a series of 15 FCI runs involving basis sets with between four and eight Gaussian primitives of the sp, spd and spdf type. Its applicability is limited by linear dependencies among basis functions that become significant for small (i.

Cationic silane sigma-complexes of ruthenium with relevance to catalysis.

Hydrosilylation of carbonyls catalyzed by 2 goes via intermediate formation of cationic silane sigma-complexes 4 which undergo nucleophilic abstraction of the silylium cation studied by DFT calculations.

Dynamics of Si-H-Si bridges in agostically stabilized silylium ions.

The silylium ion [C(6)(SiMe(2))(SiHMe(2))(5)](+) offers an amazing example of multiple Si...