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Nucleophilic substitution of [(η5‐cyclopentadienyl)(η6‐chlorobenzene)iron(II)] hexafluorophosphate with sodium imidazolate resulted in the formation of [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]imidazole hexafluorophosphate. The corresponding dicationic imidazolium salt, which was obtained by treating this imidazole precursor with methyl iodide, underwent cyclometallation with bis[dichlorido(η5‐1,2,3,4,5‐pentamethylcyclopentadienyl]iridium(III) in the presence of triethyl amine. The resulting bimetallic iridium(III) complex is the first example of an NHC complex bearing a cationic and cyclometallated [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]+ substituent. As its iron(II) precursors, the bimetallic iridium(III) complex was fully characterized by means of spectroscopy, elemental analysis and single crystal X‐ray diffraction. In addition, it was investigated in a catalytic study, wherein it showed high activity in transfer hydrogenation compared to its neutral analogue having a simple phenyl instead of a cationic [(η5‐cyclopentadienyl)(η6‐phenyl)iron(II)]+ unit at the NHC ligand. [ABSTRACT FROM AUTHOR]

New salts based on imidazolium, pyrrolidinium, phosphonium, guanidinium, and ammonium cations together with the 5-cyanotetrazolide anion [C2N5]− are reported. Depending on the nature of cation-anion interactions, characterized by XRD, the ionic liquids (ILs) have a low viscosity and are liquid at room temperature or have higher melting temperatures. Thermogravimetric analysis, cyclic voltammetry, viscosimetry, and impedance spectroscopy display a thermal stability up to 230 °C, an electrochemical window of 4.5 V, a viscosity of 25 mPa s at 20 °C, and an ionic conductivity of 5.4 mS cm−1 at 20 °C for the IL 1-butyl-1-methylpyrrolidinium 5-cyanotetrazolide [BMPyr][C2N5]. On the basis of these results, the synthesized compounds are promising electrolytes for lithium-ion batteries. [ABSTRACT FROM AUTHOR]

The sulfonated bipyridine derivative disodium 6,6′-bis(sulfonatomethyl)-2,2′-bipyridine [Na2(smbipy)] was synthesized, and its complexation behaviour towards divalent 3d metals in aqueous solution was explored. The complexes of late 3d metals [M(smbipy)(H2O)2] ·H2O (M = Co, Ni, Zn) and [Cu(smbipy)(H2O)] are sparingly soluble in water, and their crystal structures show fourfold equatorial coordination (κ4 N, N′, O, O′) of the smbipy ligand. Ammonia-rich solutions of the NiII and CuII aqua complexes yield the decomplexation products [Ni(NH3)6](smbipy), [Ni(NH3)5(H2O)](smbipy) and [Cu(NH3)4](smbipy) ·2H2O. Buffered solutions with a reduced ammonia content lead to [Ni(smbipy)(NH3)2] and [Cu(smbipy)(NH3)3] ·2H2O, and the latter shows twofold coordination of the smbipy ligand through the nitrogen atoms only (κ2 N, N′). When nearly quantitative amounts of ammonia are applied, two closely related complexes with the core motif [(smbipy)Cu(μ-OH)2Cu] form. Crystal structures of all complexes were obtained, and their features are discussed. [ABSTRACT FROM AUTHOR]

The chemistry of coinage metal bis(triflyl)imides of technological interest, CuNTf2 and AgNTf2, their synthesis and complexes with excess of comparatively weakly coordinating NTf2− as well as with ether, olefins, and the arene mesitylene are described. The existence of the solvent-free pure phase [CuNTf2]∞ has not been evidenced so far. Contrary to the literature, in which the preparation of [CuNTf2]∞ is supposed to be carried out by reacting mesityl copper, [Cu(Mes)]5, and HNTf2, we found that in fact this reaction leads reproducibly to the interesting copper diarene sandwich complex [Cu(η3-MesH)2][Cu(NTf2)2] ( 1) (MesH=1,3,5-trimethylbenzene). The unexpectedly stable molecular etherate [Cu(Et2O)(NTf2)] ( 2) turned out to be the best precursor for CuNTf2 having only an inert and easily exchangeable solvent ligand. The coordination mode of NTf2− in 1 and 2 as well as in the hitherto unknown crystalline phase of [AgNTf2]∞ ( 3) is described. The complex formation, which takes place when dissolving 2 or 3 in the room temperature ionic liquid (RTIL) [emim]NTf2 ([emim]+=1-ethyl-3-methylimidazolium), has been studied. Furthermore, the reaction of 1- 3 towards the diolefins 1,5-cyclooctadiene (COD), 2,5-norbornadiene (NBD) and isoprene (2-methylbuta-1,3-diene) and towards ethylene has been investigated. The products 4- 13 of these conversions have been isolated and fully characterized by NMR- and IR spectroscopies, mass spectrometry, and elemental- and XRD analyses. The potential of [Cu(η3-MesH)2][Cu(NTf2)2] ( 1), [Cu(Et2O)(NTf2)] ( 2) and [AgNTf2]∞ ( 3) as well as of [emim][M(NTf2)2] (M=Cu 4, Ag 5) as chemisorbers for ethylene was studied by NMR spectroscopy. [ABSTRACT FROM AUTHOR]

The synthesis and characterization of the monocationic cobalt(III) catecholate complex [Co(L-N 4 t Bu 2 )(Cl 2 cat)] + (L-N 4 t Bu 2 =N,N'-Di-tert.-butyl-2,11-diaza[3.3](2,6)pyridinophane, Cl 2 cat 2- =4,5-dichlorocatecholate) are presented. The complex exhibits valence tautomeric properties in solution; but, in contrast to the usually observed conversion from a cobalt(III) catecholate to a high-spin cobalt(II) semiquinonate state, valence tautomerism of [Co(L-N 4 t Bu 2 )(Cl 2 cat)] + leads to the formation of a low-spin cobalt(II) semiquinonate complex upon raising the temperature. This new type of valence tautomerism for a cobalt dioxolene complex has been unambiguously established by a detailed spectroscopic investigation using variable-temperature NMR, IR and UV-Vis-NIR spectroscopy. Determination of the enthalpies and entropies characterizing the valence tautomeric equilibria in various solutions shows that the influence of the solvent is almost exclusively entropic., (© 2023 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Nucleophilic substitution of [(η 5 -cyclopentadienyl)(η 6 -chlorobenzene)iron(II)] hexafluorophosphate with sodium imidazolate resulted in the formation of [(η 5 -cyclopentadienyl)(η 6 -phenyl)iron(II)]imidazole hexafluorophosphate. The corresponding dicationic imidazolium salt, which was obtained by treating this imidazole precursor with methyl iodide, underwent cyclometallation with bis[dichlorido(η 5 -1,2,3,4,5-pentamethylcyclopentadienyl]iridium(III) in the presence of triethyl amine. The resulting bimetallic iridium(III) complex is the first example of an NHC complex bearing a cationic and cyclometallated [(η 5 -cyclopentadienyl)(η 6 -phenyl)iron(II)] + substituent. As its iron(II) precursors, the bimetallic iridium(III) complex was fully characterized by means of spectroscopy, elemental analysis and single crystal X-ray diffraction. In addition, it was investigated in a catalytic study, wherein it showed high activity in transfer hydrogenation compared to its neutral analogue having a simple phenyl instead of a cationic [(η 5 -cyclopentadienyl)(η 6 -phenyl)iron(II)] + unit at the NHC ligand., (© 2021 The Authors. Chemistry - A European Journal published by Wiley-VCH GmbH.)

Coronaviruses are viral infections that have a significant ability to impact human health. Coronaviruses have produced two pandemics and one epidemic in the last two decades. The current pandemic has created a worldwide catastrophe threatening the lives of over 15 million as of July 2020. Current research efforts have been focused on producing a vaccine or repurposing current drug compounds to develop a therapeutic. There is, however, a need to study the active site preferences of relevant targets, such as the SARS-CoV-2 main protease (SARS-CoV-2 M pro ), to determine ways to optimize these drug compounds. The ensemble docking and characterization work described in this article demonstrates the multifaceted features of the SARS-CoV-2 M pro active site, molecular guidelines to improving binding affinity, and ultimately the optimization of drug candidates. A total of 220 compounds were docked into both the 5R7Z and 6LU7 SARS-CoV-2 M pro crystal structures. Several key preferences for strong binding to the four subsites (S1, S1', S2, and S4) were identified, such as accessing hydrogen binding hotspots, hydrophobic patches, and utilization of primarily aliphatic instead of aromatic substituents. After optimization efforts using the design guidelines developed from the molecular docking studies, the average docking score of the parent compounds was improved by 6.59 -log 10 (Kd) in binding affinity which represents an increase of greater than six orders of magnitude. Using the optimization guidelines, the SARS-CoV-2 M pro inhibitor cinanserin was optimized resulting in an increase in binding affinity of 4.59 -log 10 (Kd) and increased protease inhibitor bioactivity. The results of molecular dynamic (MD) simulation of cinanserin-optimized compounds CM02, CM06, and CM07 revealed that CM02 and CM06 fit well into the active site of SARS-CoV-2 M pro [Protein Data Bank (PDB) accession number 6LU7] and formed strong and stable interactions with the key residues, Ser-144, His-163, and Glu-166. The enhanced binding affinity produced demonstrates the utility of the design guidelines described. The work described herein will assist scientists in developing potent COVID-19 antivirals.

Herein we describe an easily accessible class of superbasic proton sponges based on the 1,8-bisphosphazenylnaphthalene (PN) proton pincer motif and P-alkyl substituents ranging from methyl (TMPN) to n-butyl (TBPN), isopropyl (TiPrPN) and cyclopentyl (TcyPPN). These neutral bases with a pK(BH)(+) value (MeCN) of ~30 were accessible via a Kirsanov condensation using commercially available 1,8-diaminonaphthalene, and in case of TMPN and TBPN, simple one-pot procedures starting from trisalkylphosphanes can be performed. Furthermore, the known pyrrolidinyl-substituted superbase TPPN previously synthesized via a Staudinger reaction could also be prepared by the Kirsanov strategy allowing its preparation in a larger scale. The four alkyl-substituted proton sponges were structurally characterized in their protonated form; molecular XRD structures were also obtained for unprotonated TiPrPN and TcyPPN. Moreover, we present a detailed description of spectroscopic features of chelating bisphosphazenes including TPPN and its hyperbasic homologue P2-TPPN on which we reported recently. The four alkyl-substituted superbases were investigated with respect to their basic features by computational means and by NMR titration experiments revealing unexpectedly high experimental pK(BH)(+) values in acetonitrile between 29.3 for TMPN and 30.9 for TBPN. Besides their thermodynamic basicity, we exemplarily studied the kinetic basicity of TMPN and TPPN by means of NMR-spectroscopic methods. Furthermore, the competing nucleophilic versus basic properties were examined by reacting the proton sponges with ethyl iodide. Insight into the coordination chemistry of chelating superbases was provided by reacting TMPN with trimethylaluminum and trimethylgallium to give cationic complexes of Group XIII metal alkyls that were structurally characterized., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Investigations on the Staudinger reaction between 1,8-diazidonaphthalene and phosphorous(III) building blocks, a key step in the synthesis of superbasic bisphosphazene proton sponges, yielded a set of bisphosphazides with a constrained geometry 1,8-disubstituted naphthalene backbone. This compound class has attracted our interest not only due to their surprisingly high stability, but in particular because of their theoretically predicted basicity in the range of their bisphosphazene analogues that can be referred to the constrained geometry interaction of two highly basic nitrogen atoms. Eleven new bisphosphazides bearing simple P-amino groups as well as P-guanidino substituents, azaphosphatrane moieties, P2 building blocks, or chiral P-amino substituents derived from L-proline are presented. They were studied concerning their spectroscopic properties and partly also their chromophoric and structural features. In the case of the pyrrolidino-substituted TPPN(2N2) (TPPN = 1,8-bis(trispyrrolidinophosphazenyl)naphthalene), the stepwise nitrogen elimination is investigated theoretically and experimentally, which led to the isolation and structural characterization of TPPN(1N2) bearing a phosphazide and a phosphazene functionality in one molecule. Attempts to protonate the obtained bisphosphazides and to prove the computationally predicted pKBH(+) values through NMR titration reactions resulted in their decay, which again was rationalized by theoretical calculations. Altogether we present the so far most extensive spectroscopic, structural and theoretical investigation of constrained geometry bisphosphazides and their Brønsted and Lewis basic properties., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Bismetallocenes [Cp2 LuReCp2 ] and [Cp*2 LaReCp2 ] (Cp=cyclopentadienyl; Cp*=pentamethylcyclopentadienyl) were prepared using different synthetic strategies. Salt metathesis-performed in aromatic hydrocarbons to avoid degradation pathways caused by THF-were identified as an attractive alternative to alkane elimination. Although alkane elimination is more attractive in the sense of its less elaborate workup, the rate of the reaction shows a strong dependence on the ionic radius of Ln(3+) (Ln=lanthanide) within a given ligand set. Steric hindrance can cause a dramatic decrease in the reaction rate of alkane elimination. In this case, salt metathesis should be considered the better alternative. Covalent bonding interactions between the Ln and transition-metal (TM) cations has been quantified on the basis of the delocalization index. Its magnitude lies within the range characteristic for bonds between transition metals. Secondary interactions were identified between carbon atoms of the Cp ligand of the transition metal and the Ln cation. Model calculations clearly indicated that the size of these interactions depends on the capability of the TM atom to act as an electron donor (i.e., a Lewis base). The consequences can even be derived from structural details. The observed clear dependency of the LuRu and interfragment LuC bonding on the THF coordination of the Lu atom points to a tunable Lewis acidity at the Ln site, which provides a method of significantly influencing the structure and the interfragment bonding., (© 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The chemistry of coinage metal bis(triflyl)imides of technological interest, CuNTf(2) and AgNTf(2), their synthesis and complexes with excess of comparatively weakly coordinating NTf(2)(-) as well as with ether, olefins, and the arene mesitylene are described. The existence of the solvent-free pure phase [CuNTf(2)](∞) has not been evidenced so far. Contrary to the literature, in which the preparation of [CuNTf(2)](∞) is supposed to be carried out by reacting mesityl copper, [Cu(Mes)](5), and HNTf(2), we found that in fact this reaction leads reproducibly to the interesting copper diarene sandwich complex [Cu(η(3)-MesH)(2)][Cu(NTf(2))(2)] (1) (MesH = 1,3,5-trimethylbenzene). The unexpectedly stable molecular etherate [Cu(Et(2)O)(NTf(2))] (2) turned out to be the best precursor for CuNTf(2) having only an inert and easily exchangeable solvent ligand. The coordination mode of NTf(2)(-) in 1 and 2 as well as in the hitherto unknown crystalline phase of [AgNTf(2)](∞) (3) is described. The complex formation, which takes place when dissolving 2 or 3 in the room temperature ionic liquid (RTIL) [emim]NTf(2) ([emim](+) = 1-ethyl-3-methylimidazolium), has been studied. Furthermore, the reaction of 1-3 towards the diolefins 1,5-cyclooctadiene (COD), 2,5-norbornadiene (NBD) and isoprene (2-methylbuta-1,3-diene) and towards ethylene has been investigated. The products 4-13 of these conversions have been isolated and fully characterized by NMR- and IR spectroscopies, mass spectrometry, and elemental- and XRD analyses. The potential of [Cu(η(3)-MesH)(2)][Cu(NTf(2))(2)] (1), [Cu(Et(2)O)(NTf(2))] (2) and [AgNTf(2)](∞) (3) as well as of [emim][M(NTf(2))(2)] (M = Cu 4, Ag 5) as chemisorbers for ethylene was studied by NMR spectroscopy., (Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

Metal-metal bonding in heterobimetallic complexes is of fundamental interest due to its implications to both bonding theory and new reactivities. In this Concept, structurally authenticated molecular compounds with direct bonds between rare-earth metals or actinoids and transition or main group metals are summarized. Special attention is given to the use of bond polarity as a tool for designing molecular intermetalloids incorporating rare-earth atoms and transition metals., (Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.)

The crystal structure of the title compound, [Cu(C(2)N(3))(C(2)H(3)N)(2)](n), features zigzag chains along the a axis that consist of alternating [Cu(MeCN)(2)] and dicyanamide units, the latter acting as bidentate ligands via both terminal N atoms. The Cu atom shows a slightly distorted tetra-hedral coordination sphere. The anionic and neutral ligands lie on different mirror planes (perpendicular to the b and a axis, respectively), while the Cu atom is situated on their inter-section. The asymmetric unit comprises one fourth of the formula unit.