Quantum Chemical Investigations and Bonding Analysis of Iron Complexes with Mixed Cyano and Carbonyl Ligands^†

The equilibrium structures and vibrational frequencies of the iron complexes [Fe(CN)x(CO)y]q (x = 0−6 and y = 0−5) have been calculated at the BP86 level of theory. The nature of the Fe−CN and Fe−CO has been analyzed with an energy partitioning method. The calculated Fe−CO bond lengths are in good agreement with the results of X-ray structure analysis whereas the Fe−CN bonds are calculated somewhat longer than the experimental values. The theoretically predicted vibrational frequencies of the C−O stretching mode are always lower and the calculated CN- frequencies are higher than the observed fundamental modes. The results of the bonding analysis suggest that the Fe−CO binding interactions have ∼55% electrostatic character and ∼45% covalent character. There is a significant contribution of the π orbital interaction to the Fe−CO covalent bonding which increases when the complexes become negatively charged. The strength of ΔEπ may even be larger than ΔEσ. The Fe−CN- bonds have much less π character. The calculated binding energy of the Fe−CO π-interactions correlates very well with the C−O stretching frequencies

COSMO<i>quick</i>: A Novel Interface for Fast σ‑Profile Composition and Its Application to COSMO-RS Solvent Screening Using Multiple Reference Solvents

We present a novel, simpler to use modification of the standard COSMO-RS solubility prediction scheme which in addition can achieve higher accuracy by the usage of multiple experimental reference solubilities. When only one reference solvent is used, the approach reduces to the original COSMO-RS-based solubility prediction. Considerable speedup and simplification compared to the original COSMO-RS arises from the usage of approximate σ-profiles generated from a database of COSMO-files from 65000 diverse molecules. This method enables fast and accurate solvent screening. Solubility predictions using the novel approach on pure solvents perform favorably when compared to NRTL-SAC calculations. The new method is accessible via a graphical user-interface (COSMO<i>quick</i>) and combines the reliability and broad applicability of COSMO-RS theory with some practical advantages of more empirical solubility models

Prediction of Solubilities and Partition Coefficients in Polymers Using COSMO-RS

Recent results concerning the prediction of thermodynamic properties of solutes in polymers are presented. In particular, the computation of vapor–liquid and gas–liquid equilibria (i.e., liquid and gas solubilities) in different polymers and partition coefficients between the polymer and a solvent phase are addressed. Calculations have been carried out using COSMO-RS theory which combines quantum-chemical calculations with efficient statistical thermodynamics for intermolecular interactions. Predictions for vapor–liquid equilibria and for partition coefficients have been improved by incorporation of polymer-specific entropic contributions due to free volume effects. It is demonstrated that a high predictive accuracy is obtained if the polymer is sufficiently characterized by its composition, density, and crystallinity. The approach is currently limited to gaseous and liquid solutes and to linear, i.e. non-cross-linked polymers without any significant swelling

Ab Initio Kinetic Modeling of Living Anionic and Zwitterionic Chain Polymerization Mechanisms

A scale-bridging study of first-principles calculations and kinetic modeling has been carried out to investigate anionic and zwitterionic chain polymerizations. On the example of the industrially relevant ethyl α-cyanoacrylate, the initiation with anionic and neutral species focusing on the first stages of chain formation is studied. In the first part of our study, we use quantum chemical methods at the DFT level to study the initiation of polymerization with an anionic species (hydroxide anion), leading to anionic chain polymerization, and a neutral species (pyridine), leading to zwitterionic chain polymerization, respectively. The calculation of reaction barriers for the initiation step reveals that the addition of a hydroxide anion to a cyanoacrylate monomer is a barrier-less and strongly exothermic process whereas pyridine addition shows a significant barrier and is slightly endothermic. Subsequent calculations of the reaction energies and barriers of cyanoacrylate polymerization up to a degree of oligomerization of 5 (Xn = 5) show that both initiation reaction and subsequent addition of the next few monomers determine the reactivity and properties of cyanoacrylates. To quantify these findings we use in the second part of our study the results of the quantum chemical calculations to parametrize a kinetic study of the polymerization process of cyanoacrylates. Starting from monomers and initiators the polymerization of the cyanoacrylate and resulting molecular weight built up is simulated. The consequences of the differences in kinetic parameters of anionic and zwitterionic mechanisms on molecular weights and polymer properties are discussed

Atomic and Electronic Structure of Cerium Oxide Stepped Model Surfaces

The atomic and electronic structure of ceria surfaces exhibiting step edges have been studied by means of periodic density functional (LDA+U and GGA+U) calculations. A variety of stoichiometric and nonstoichiometric models of increasing complexity have been designed. The electronic structure has been explored using the topological Bader analysis, the calculated magnetic moments and the ELF (electron localization function) maps. It is concluded that Ce3+ atoms may exist even in stoichiometric extended ceria samples and that the presence of oxygen vacancies in stepped surfaces also induces the presence of Ce3+ atoms although in both cases, the reduced atoms tend to occupy the sites with smallest possible coordination number

Reaction of Tungsten η¹-Acetylide Complexes [(η⁵-C₅H₅)(NO)(CO)W−C⋮C−R]Li with Iminium Ions

The reaction of alkynyltungsten complexes [(CO)(NO)(Cp)W−C⋮C−R]Li (R = H, C6H5, C(CH3)3) with differently substituted iminium ions is investigated. Due to the relative high acidity of the hydrogen atoms on the β-carbon atom of the η1-vinylidene complex [(CO)(NO)(Cp)WCCH2)] (1), the parent η1-acetylide complex [(CO)(NO)(Cp)W−C⋮C−H)]- is generated in situ simultaneously with the iminium ion by the reaction of η1-vinylidene complex 1 with an enamine. The reaction of 1 with enamines 2a−e leads to vinylcarbene complexes 3a−e in good yield. The first step of this transformation is a Mannich reaction on the β-carbon atom of alkynyltungsten complexes, generating the expected β-amino-alkylated η1-vinylidene complexes 6. This intermediate reacts further to 3a−e by migration of the hydrogen atom adjacent to the nitrogen atom to the α-carbon atom of the η1-vinylidene moiety. The appearance of a η1-vinylidene complex as an intermediate is supported by NMR experiments, and the postulated retro-imino-ene reaction is confirmed by the reaction of deuterated η1-vinylidene complex 1-D with enamine 2b to the vinylcarbene complex 8. The scope of the reaction is demonstrated by the reaction of alkynyltungsten complexes 9, 16, and 17 with a series of differently substituted iminium ions to the corresponding vinylcarbene complexes. Activation parameters for the retro-imino-ene reaction of η1-vinylidene complex 6a to vinylcarbene 3a in THF-d8 were determined using 1H NMR spectroscopy. On the basis of this experiment ΔH⧧, ΔS⧧, and ΔG⧧ (at −1 °C) were found to be 20.5 ± 1.4 kcal/mol, −1.4 ± 0.6 cal/mol, and 20.9 ± 1.4 kcal/mol, respectively. The profile of the postulated retro-imino-ene reaction is calculated on the model compound [(CO)(NO)(Cp)WCCH−CH2−NH−CH3] (6M), yielding [(CO)(NO)(Cp)WCH−CHCH2] using density functional theory at the B3LYP level. The calculation shows the process is more likely a single-step reaction where the hydrogen migration and carbon−nitrogen bond breaking are two consecutive reactions without formation of a true intermediate. Single-crystal X-ray diffraction data of 3a and 4 are reported

Reaction of Tungsten η¹-Acetylide Complexes [(η⁵-C₅H₅)(NO)(CO)W−C⋮C−R]Li with Iminium Ions

The reaction of alkynyltungsten complexes [(CO)(NO)(Cp)W−C⋮C−R]Li (R = H, C6H5, C(CH3)3) with differently substituted iminium ions is investigated. Due to the relative high acidity of the hydrogen atoms on the β-carbon atom of the η1-vinylidene complex [(CO)(NO)(Cp)WCCH2)] (1), the parent η1-acetylide complex [(CO)(NO)(Cp)W−C⋮C−H)]- is generated in situ simultaneously with the iminium ion by the reaction of η1-vinylidene complex 1 with an enamine. The reaction of 1 with enamines 2a−e leads to vinylcarbene complexes 3a−e in good yield. The first step of this transformation is a Mannich reaction on the β-carbon atom of alkynyltungsten complexes, generating the expected β-amino-alkylated η1-vinylidene complexes 6. This intermediate reacts further to 3a−e by migration of the hydrogen atom adjacent to the nitrogen atom to the α-carbon atom of the η1-vinylidene moiety. The appearance of a η1-vinylidene complex as an intermediate is supported by NMR experiments, and the postulated retro-imino-ene reaction is confirmed by the reaction of deuterated η1-vinylidene complex 1-D with enamine 2b to the vinylcarbene complex 8. The scope of the reaction is demonstrated by the reaction of alkynyltungsten complexes 9, 16, and 17 with a series of differently substituted iminium ions to the corresponding vinylcarbene complexes. Activation parameters for the retro-imino-ene reaction of η1-vinylidene complex 6a to vinylcarbene 3a in THF-d8 were determined using 1H NMR spectroscopy. On the basis of this experiment ΔH⧧, ΔS⧧, and ΔG⧧ (at −1 °C) were found to be 20.5 ± 1.4 kcal/mol, −1.4 ± 0.6 cal/mol, and 20.9 ± 1.4 kcal/mol, respectively. The profile of the postulated retro-imino-ene reaction is calculated on the model compound [(CO)(NO)(Cp)WCCH−CH2−NH−CH3] (6M), yielding [(CO)(NO)(Cp)WCH−CHCH2] using density functional theory at the B3LYP level. The calculation shows the process is more likely a single-step reaction where the hydrogen migration and carbon−nitrogen bond breaking are two consecutive reactions without formation of a true intermediate. Single-crystal X-ray diffraction data of 3a and 4 are reported

Reaction of Tungsten η¹-Acetylide Complexes [(η⁵-C₅H₅)(NO)(CO)W−C⋮C−R]Li with Iminium Ions

The reaction of alkynyltungsten complexes [(CO)(NO)(Cp)W−C⋮C−R]Li (R = H, C6H5, C(CH3)3) with differently substituted iminium ions is investigated. Due to the relative high acidity of the hydrogen atoms on the β-carbon atom of the η1-vinylidene complex [(CO)(NO)(Cp)WCCH2)] (1), the parent η1-acetylide complex [(CO)(NO)(Cp)W−C⋮C−H)]- is generated in situ simultaneously with the iminium ion by the reaction of η1-vinylidene complex 1 with an enamine. The reaction of 1 with enamines 2a−e leads to vinylcarbene complexes 3a−e in good yield. The first step of this transformation is a Mannich reaction on the β-carbon atom of alkynyltungsten complexes, generating the expected β-amino-alkylated η1-vinylidene complexes 6. This intermediate reacts further to 3a−e by migration of the hydrogen atom adjacent to the nitrogen atom to the α-carbon atom of the η1-vinylidene moiety. The appearance of a η1-vinylidene complex as an intermediate is supported by NMR experiments, and the postulated retro-imino-ene reaction is confirmed by the reaction of deuterated η1-vinylidene complex 1-D with enamine 2b to the vinylcarbene complex 8. The scope of the reaction is demonstrated by the reaction of alkynyltungsten complexes 9, 16, and 17 with a series of differently substituted iminium ions to the corresponding vinylcarbene complexes. Activation parameters for the retro-imino-ene reaction of η1-vinylidene complex 6a to vinylcarbene 3a in THF-d8 were determined using 1H NMR spectroscopy. On the basis of this experiment ΔH⧧, ΔS⧧, and ΔG⧧ (at −1 °C) were found to be 20.5 ± 1.4 kcal/mol, −1.4 ± 0.6 cal/mol, and 20.9 ± 1.4 kcal/mol, respectively. The profile of the postulated retro-imino-ene reaction is calculated on the model compound [(CO)(NO)(Cp)WCCH−CH2−NH−CH3] (6M), yielding [(CO)(NO)(Cp)WCH−CHCH2] using density functional theory at the B3LYP level. The calculation shows the process is more likely a single-step reaction where the hydrogen migration and carbon−nitrogen bond breaking are two consecutive reactions without formation of a true intermediate. Single-crystal X-ray diffraction data of 3a and 4 are reported

The SAMPL6 LogP Virtual Workshop

This provides talks from the SAMPL6 logP virtual workshop, going over early challenge results and analysis. Overview:  The purpose of this workshop was to go over a preliminary evaluation of results, begin considering analysis and lessons learned, and nucleate opportunities for follow up and additional discussion. Part of the goal is to facilitate discussion so that participants can work together to maximize lessons learned in the lead up to the August in-person D3R/SAMPL workshop and the JCAMD special issue. We hope this early workshop will result in additional follow-up afterwards. Agenda: The workshop agenda was (all times US Pacific (PDT; UTC-7)): 7-7:10 am: Welcome, introductions, and purpose; David Mobley (UCI) 7:10-7:50 am: Experiments and overview of results, Mehtap Isik (MSKCC); 30 minute talk + 10 minutes of questions/discussion. 7:50-8:05 am: log P Predictions Using SMx or LSER With Training Data from DrugBank.ca, Andrew Paluch (Miami University, Ohio) 8:05-8:35 am: Christoph Loschen (Cosmologic), COSMO-RS based predictions for the SAMPL6 logP challenge; 20 minute talk + 10 minutes of questions/discussion 8:35-8:55 am: Prediction of partition coefficients for drug-like componds, Nicolas Tielker (TU Dortmund); 12 minute talk + 8 minutes of questions/discussion 8:55-9:15 am: logP results with atom in molecules atomic charges, Esteban Vohringer-Martinez (Univ. Concepción); 15 minute talk + 5 minutes of questions/discussion. 9:15 am-9:25 am: Alexey Nikitin; 5 minute talk + 5 minutes of discussion. 9:25-10 am: Discussion and follow up opportunities. </ul