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A diglyme solution of Na[cyclo‐P5] (1) reacts with alkynes and isolobal nitriles and phosphaalkynes to afford the otherwise elusive (aza)phospholide anions 2 a–c, 4 a,b, and 6. The reaction of Na[cyclo‐P5] with alkynes and nitriles was studied by means of DFT methods, which suggested a concerted mechanism for the formation of 2 a and 4 b. The anions 2 a–c, 4 a,b, and 6 coordinate in an η5‐fashion towards FeII to give the sandwich (aza)phosphametallocenes 3 a–c, 5 a,b and 7 in moderate to good yields. The new compounds were characterized by means of multinuclear NMR spectroscopy, single‐crystal X‐ray diffraction and cyclic voltammetry. [ABSTRACT FROM AUTHOR] more...

A series of substituted phosphinines, 1‐phosphabarrelenes and 5‐phosphasemibullvalenes were synthesized and evaluated for their potential application as ligands in homogeneous catalytic reactions. While their buried volume (%Vbur) was calculated to get insight into the steric properties, [LNi(CO)3] complexes were prepared in order to determine the corresponding Tolman electronic parameter. ETS‐NOCV (extended‐transition‐state natural orbital for chemical valence) calculations on [LAuCl] complexes further allowed an estimation of the σ‐ and π‐contributions to the L−M interaction. AuI coordination compounds of selected examples were prepared and characterized by single crystal X‐ray diffraction. Finally, the three classes of PIII compounds were successfully used in the AuI‐catalyzed cycloisomerization of N‐2‐propyn‐1‐ylbenzamide, showing very good activities and selectivities, which are comparable with the reported data of cationic phosphorus‐based gold catalysts. [ABSTRACT FROM AUTHOR] more...

The facile access to 3-bromo-2-pyrone allows the preparation of 6-bromo-2-trimethylsilyl-phosphinine by a [4+2] cycloaddition with Me3Si-C≡P for the first time. The regioselectivity of this reaction could be verified by means of single crystal X-ray diffraction of the corresponding W0 complex. In the presence of ZnBr2 and dppp (1,3-bis(diphenylphosphino)propane) as a bidentate ligand, the bromo-phosphinine quantitatively undergoes a Negishi cross-coupling reaction with PhLi that selectively leads to 6-phenyl-2-trimethylsilyl-phosphinine. This heterocycle could again be characterized by means of X-ray diffraction as a W0 complex. These results describe a new and convenient route to 2,6-disubstituted phosphinines that makes use of readily available starting materials. [ABSTRACT FROM AUTHOR] more...

It is still a challenge to predict a compound's reactivity from its ground-state electronic nature although Bader-type topological analyses of the electron density (ED) and electron localizability indicator (ELI) give detailed and useful information on electron concentration and electron-pair localization, respectively. Both ED and ELI can be obtained from theoretical calculations as well as high-resolution X-ray diffraction experiments. Besides ED and ELI descriptors, the delocalization index is used here; it is likewise derived from theoretical calculations as well as from experimental X-ray results, but in the latter case, demonstrated here for the first time. We investigate αβ-unsaturated carbonyl and hydrazone compounds because resonance exhibited by these compounds in the electronic ground-state determines their reactive behavior. The degree of resonance as well as the reactivity contrast are quantified with the electronic descriptors. Moreover, competitive mesomeric substituent effects are studied using the two biologically important compounds acrolein and acrylamide. The reactivity differences predicted from the analyses are in line with the known reactivity of these compounds in organic synthesis. Hence, the capability of the ED and ELI for rationalizing and predicting different and competing substituent effects with respect to reactivity is demonstrated. [ABSTRACT FROM AUTHOR] more...

Bergenin, which has been isolated from a variety of tropical plants, has several pharmacological applications in traditional Asian medicine. Its electron-density distribution was obtained from a room-temperature low-resolution X-ray data set measured with point detection making use of multipole populations from the invariom library. Two refinement models were considered. In a first step, positional parameters and ADPs were refined with fixed library multipoles (model El). This model was suitable to be input into a second refinement of multipoles (model E2), which converged smoothly although based on Cu Kαroom-temperature data. Quantitative results of a topological analysis of the electron density from both models were compared with Hartree-Fock and density- functional calculations. With respect to the independent atom model (JAM) more information can be extracted from invariom modelling, including the electrostatic potential and hydrogen-bond energies, which are highly useful, especially for biologically active compounds. The reliability of the applied invariom formalism was assessed by a comparison of bond-topological properties of sucrose, for which high- resolution multipole and invariom densities were available. Since a conventional X-ray diffraction experiment using basic equipment was combined with the easy-to-use invariom formalism, the procedure described here for bergenin illustrates how it can be routinely applied in pharmacological research. [ABSTRACT FROM AUTHOR] more...

In the last decade three different data bank approaches have been developed that are intended to make electron-density examinations of large biologically important molecules possible. They rely on Bader's concept of transferability of submolecular fragments with retention of their electronic properties. Therefore, elaborate studies on the quantification of transferability in experiment and theory are still very important. Tripeptides of the type L-alanyl-X-L-alanine (X being any of the 20 naturally encoded amino acids) serve as a model case between amino acids and proteins. The two experimental electron-density determinations (L-alanyl-L-histidinyl-L-alanine and L-alanyl-L-phenylalanyl-L-alanine, highly resolved synchrotron X-ray diffraction data sets) performed in this study and theoretical calculations on all 20 different L-alanyl-X-L-alanine molecules contribute to a better estimation of transferability in the peptide case. As a measure of reproducibility and transferability, standard deviations from averaging over bond-topological and atomic properties of atoms or bonds that are considered equal in their chemical environments were calculated. This way, transferability and reproducibility indices were introduced. It can be shown that experimental transferability indices generally slightly exceed experimental reproducibility indices and that these larger deviations can be attributed to chemical effects such as changes in the geometry (bond lengths and angles), the polarization pattern and the neighboring sphere due to crystal packing. These effects can partly be separated from each other and quantified with the help of gas-phase calculations at optimized and experimental geometries. Thus, the degree of transferability can be quantified in very narrow limits taking into account experimental errors and chemical effects. [ABSTRACT FROM AUTHOR] more...

Highlights from the article: Cover Feature: Phosphinine-Based Ligands in Gold-Catalyzed Reactions (Chem. Eur. J. 37/2019) Keywords: density functional calculations; heterocycles; homogeneous gold catalysis; phosphorus ligands; X-ray diffraction Density functional calculations, heterocycles, homogeneous gold catalysis, phosphorus ligands, X-ray diffraction. more...