A Fluorinated Chaperone Gives X-ray Crystal Structures of Acyclic Natural Product Derivatives up to 338 Molecular Weight.

Crystallizing molecules with long flexible chains is a challenge, making it difficult to perform X-ray crystallography. Chaperones can assist in the crystallization of compounds that do not crystallize by themselves by producing solvate crystals that contain the analyte in their three-dimensional lattices. Among the most versatile chaperones for liquid analytes are tetraaryladamantanes (TAAs), but the size of the compounds that can be encapsulated is limited, and attempts to surpass this limit with known TAAs were unsuccessful. Here we report that 1,3,5,7-tetrakis(2-fluoro-4-methoxyphenyl)adamantane (TFM) is a crystallization chaperone for acyclic molecules up to the molecular weight of phytyl acetate (338 g/mol). Encapsulation of such a large acyclic compound was achieved when the analyte was esterified and when a two-step temperature protocol was used for crystallization. Exploratory work indicates that a drop to -20 °C allows for encapsulation of squalene (Mr 411 g/mol), albeit with positional disorder of the analyte. Our X-ray crystal structures of solvates with flexible analytes shed light on how crystalline order can be imposed on large acyclic analytes. The new, fluorinated TAA gives access to crystal structures that were inaccessible thus far.

Electron crystallography and dedicated electron-diffraction instrumentation.

Electron diffraction (known also as ED, 3D ED or microED) is gaining momentum in science and industry. The application of electron diffraction in performing nano-crystallography on crystals smaller than 1 µm is a disruptive technology that is opening up fascinating new perspectives for a wide variety of compounds required in the fields of chemical, pharmaceutical and advanced materials research. Electron diffraction enables the characterization of solid compounds complementary to neutron, powder X-ray and single-crystal X-ray diffraction, as it has the unique capability to measure nanometre-sized crystals. The recent introduction of dedicated instrumentation to perform ED experiments is a key aspect of the continued growth and success of this technology. In addition to the ultra-high-speed hybrid-pixel detectors enabling ED data collection in continuous rotation mode, a high-precision goniometer and horizontal layout have been determined as essential features of an electron diffractometer, both of which are embodied in the Eldico ED-1. Four examples of data collected on an Eldico ED-1 are showcased to demonstrate the potential and advantages of a dedicated electron diffractometer, covering selected applications and challenges of electron diffraction: (i) multiple reciprocal lattices, (ii) absolute structure of a chiral compound, and (iii) R-values achieved by kinematic refinement comparable to X-ray data.

Extending the chemistry of weakly basic ligands: solvates of Ag+ and Cu+ stabilized by [Al{OC(CF3)3}4]- anion as model examples in the screening of useful weakly interacting solvents.

Weakly Coordinating Anions (WCAs) facilitate the formation of exotic "naked" cationic species. However, the feasibility of the respective synthesis approaches may be limited by the basicity of the solvent utilized, as the latter is one of the most important factors determining the solvation ability. In this work, we focus on a series of novel complexes of Ag(i) and Cu(i) with weakly basic ligands such as CH2Cl2, Cl3CCN and SO2 stabilized by perfluorinated alkoxyaluminate, Al[(ORF)4]-, RF = C(CF3)3. The discussion includes their synthesis protocols, crystal structures, vibrational spectra and thermal stability (TGA/DSC/EGA). We show that the Cu-SO2 adducts present exceptional stability in relation to other metal-SO2 complexes. To broaden the scope of weakly basic ligands which could prove helpful in the development of chemistry with WCAs, the screening of potential candidates based on DFT calculations is presented.

Rapid Structure Determination of Microcrystalline Molecular Compounds Using Electron Diffraction.

Chemists of all fields currently publish about 50 000 crystal structures per year, the vast majority of which are X-ray structures. We determined two molecular structures by employing electron rather than X-ray diffraction. For this purpose, an EIGER hybrid pixel detector was fitted to a transmission electron microscope, yielding an electron diffractometer. The structure of a new methylene blue derivative was determined at 0.9 Šresolution from a crystal smaller than 1×2 µm2 . Several thousand active pharmaceutical ingredients (APIs) are only available as submicrocrystalline powders. To illustrate the potential of electron crystallography for the pharmaceutical industry, we also determined the structure of an API from its pill. We demonstrate that electron crystallography complements X-ray crystallography and is the technique of choice for all unsolved cases in which submicrometer-sized crystals were the limiting factor.

Zero-Valent Amino-Olefin Cobalt Complexes as Catalysts for Oxygen Atom Transfer Reactions from Nitrous Oxide.

The synthesis and characterization of several zero-valent cobalt complexes with a bis(olefin)-amino ligand is presented. Some of these complexes proved to be efficient catalysts for the selective oxidation of secondary and allylic phosphanes, as well as diphosphanes, even with a direct P-P bond. With 5 mol % catalyst loadings the oxidations proceed under mild conditions (25-70 °C, 7-22 h, 2 bar N2 O) and afford good to excellent yields (65-98 %). In this process, the greenhouse gas N2 O is catalytically converted into benign N2 and added-value organophosphorus compounds, some of which are difficult to obtain otherwise.

Nitrous Oxide as a Hydrogen Acceptor for the Dehydrogenative Coupling of Alcohols.

The oxidation of alcohols with N2O as the hydrogen acceptor was achieved with low catalyst loadings of a rhodium complex that features a cooperative bis(olefin)amido ligand under mild conditions. Two different methods enable the formation of either the corresponding carboxylic acid or the ester. N2 and water are the only by-products. Mechanistic studies supported by DFT calculations suggest that the oxygen atom of N2O is transferred to the metal center by insertion into the Rh-H bond of a rhodium amino hydride species, generating a rhodium hydroxy complex as a key intermediate.

Simple one-pot syntheses of water-soluble bis(acyl)phosphane oxide photoinitiators and their application in surfactant-free emulsion polymerization.

The sodium salt of the new bis(mesitoyl)phosphinic acid (BAPO-OH) can be prepared in a very efficient one-pot synthesis. It is well soluble in water and hydrolytically stable for at least several weeks. Remarkably, it acts as an initiating agent for the surfactant-free emulsion polymerization (SFEP) of styrene to yield monodisperse, spherical nanoparticles. Time-resolved electron paramagnetic resonance (TR-EPR) and chemically induced electron polarisation (CIDEP) indicate preliminary mechanistic insights.

Sodium phosphaethynolate as a building block for heterocycles.

Phosphorus-containing heterocycles have evolved from laboratory curiosities to functional components, such as ligands in catalytically active metal complexes or molecular constituents in electronic devices. The straightforward synthesis of functionalized heterocycles on a larger scale remains a challenge. Herein, we report the use of the phosphaethynolate (OCP)(-) anion as a building block for various sterically unprotected and functionalized hydroxy substituted phosphorus heterocycles. Because the resulting heterocycles are themselves anions, they are building blocks in their own right and allow further facile functionalization. This property may be of interest in coordination chemistry and material science.

Ru(II)-hydride-trop complexes: X-ray single-crystal determination and quantum-chemical calculations.

As part of our search for catalytically active Ru(II)-hydride complexes, we have synthesized and crystallographically characterized three different ruthenium species, namely dihydrido[(SR)-(10,11-η)-N-(pyridin-2-ylmethyl-κN)-5H-dibenzo[a,d]cyclohepten-5-amine](triphenylphosphane-κP)ruthenium(II) tetrahydrofuran monosolvate, [RuH2(C21H18N2)(C18H15P)]·C4H8O or (SR)-[Ru(II)(H)2{N-(pyridin-2-ylmethyl)tropNH}(PPh3)]·THF, (1), chlorido{(1SR,2RS)-N,N'-bis[(10,11-η)-5H-dibenzo[a,d]cyclohepten-5-amine]ethane-1,2-diamine-κ(2)N,N'}hydridoruthenium(II) dimethoxyethane hemisolvate, [RuClH(C32H28N2)]·0.5C4H10O2 or (1SR,2RS)-[Ru(II)(H)(Cl){tropNH(CH2)2HNtrop}]·DME, (2), and chlorido{(1SR,2RS)-N,N'-bis[(10,11-η)-5H-dibenzo[a,d]cyclohepten-5-amine]propane-1,3-diamine-κ(2)N,N'}hydridoruthenium(II), [RuClH(C33H30N2)] or (1SR,2RS)-[Ru(II)(H)(Cl){tropNH(CH2)3HNtrop}], (3), where trop is 5H-dibenzo[a,d]cycloheptene. In all three complexes, the Ru(II) center resides in an octahedral coordination environment. For (1)-(3), the hydride atoms were located in a difference Fourier map and were refined freely. In solution, the (1)H NMR spectra of all species show the presence of the hydride resonance. Comparison with quantum-chemical calculations reveals that the crystallographic data sets are plausible. In every case, the prediction is in very good agreement with the observed X-ray data. Not only the observed geometry is predicted well but also the Ru-H(hydride) bond lengths are reproduced remarkably well. Complexes (1) and (2) crystallized in the triclinic P1 space group, while (3) crystallized in the tetragonal space group I4(1)/a. For (3), there is disorder of the axial ligands producing two isomers (in a 98.7:1.3 ratio). Details of the synthesis, characterization, X-ray analysis, and theoretical calculations for complexes (1)-(3) are presented.

A mixed chloride/trifluoromethanesulfonate ligand species in a ruthenium(II) complex.

The compound [2-(aminomethyl)pyridine-κ²N,N'][chlorido/trifluoromethanesulfonato(0.91/0.09)][(10,11-η)-5H-dibenzo[a,d]cyclohepten-5-amine-κN](triphenylphosphane-κP)ruthenium(II) trifluoromethanesulfonate dichloromethane 0.91-solvate, [Ru(CF3SO3)0.09Cl0.91(C6H8N2)(C15H13N)(C18H15P)]CF3SO3·0.91CH2Cl2, belongs to a series of RuII complexes that had been tested for transfer hydrogenation, hydrogenation of polar bonds and catalytic transfer hydrogenation. The crystal structure determination of this complex revealed disorder in the form of two different anionic ligands sharing the same coordination site, which other spectroscopic methods failed to characterize. The reduced catalytic activity of the title compound was not fully understood until the crystallographic data provided evidence for the mixed ligand species. The crystal structure clearly shows that the majority of the synthesized material has a chloride ligand present. Only a small portion of the material is the expected complex [RuII(OTf)(ampy)(η²-tropNH2)(PPh3)]OTf, where OTf is triflate or trifluoromethanesulfonate, ampy is 2-(aminomethyl)pyridine and tropNH2 is 5H-dibenzo[a,d]cyclohepten-5-amine.

A systematic investigation of coinage metal carbonyl complexes stabilized by fluorinated alkoxy aluminates.

The reaction of Cu(I), Ag(I), and Au(I) salts with carbon monoxide in the presence of weakly coordinating anions led to known and structurally unknown non-classical coinage metal carbonyl complexes [M(CO)n][A] (A = fluorinated alkoxy aluminates). The coinage metal carbonyl complexes [Cu(CO)n(CH2Cl2)m](+)[A](-) (n = 1, 3; m = 4-n), [Au2(CO)2Cl](+)[A](-), [(OC)nM(A)] (M = Cu: n = 2; Ag: n = 1, 2) as well as [(OC)3Cu⋅⋅⋅ClAl(OR(F))3] and [(OC)Au⋅⋅⋅ClAl(OR(F))3] were analyzed with X-ray diffraction and partially IR and Raman spectroscopy. In addition to these structures, crystallographic and spectroscopic evidence for the existence of the tetracarbonyl complex [Cu(CO)4](+)[Al(OR(F))4](-) (R(F) = C(CF3)3) is presented; its formation was analyzed with the help of theoretical investigations and Born-Fajans-Haber cycles. We discuss the limits of structure determinations by routine X-ray diffraction methods with respect to the C-O bond lengths and apply the experimental CO stretching frequencies for the prediction of bond lengths within the carbonyl ligand based on a correlation with calculated data. Moreover, we provide a simple explanation for the reported, partly confusing and scattered CO stretching frequencies of [Cu(I)(CO)n] units.

A homogeneous transition metal complex for clean hydrogen production from methanol-water mixtures.

The development of an efficient catalytic process that mimics the enzymatic function of alcohol dehydrogenase is critical for using biomass alcohols for both the production of H2 as a chemical energy carrier and fine chemicals under waste-free conditions. Dehydrogenation of alcohol-water mixtures into their corresponding acids with molecular hydrogen as the sole by-product from the reaction can be catalysed by a ruthenium complex with a chelating bis(olefin) diazadiene ligand. This complex, [K(dme)2][Ru(H)(trop2dad)], stores up to two equivalents of hydrogen intramolecularly, and catalyses the production of H2 from alcohols in the presence of water and a base under homogeneous conditions. The conversion of a MeOH-H2O mixture proceeds selectively to CO2/H2 gas formation under neutral conditions, thereby allowing the use of the entire hydrogen content (12% by weight). Isolation and characterization of the ruthenium complexes from these reactions suggested a mechanistic scenario in which the trop2dad ligand behaves as a chemically 'non-innocent' co-operative ligand.

Synthesis and characterization of terminal [Re(XCO)(CO)2(triphos)] (X=N, P): isocyanate versus phosphaethynolate complexes.

The terminal rhenium(I) phosphaethynolate complex [Re(PCO)(CO)(2)(triphos)] has been prepared in a salt metathesis reaction from Na(OCP) and [Re(OTf)(CO)(2)(triphos)]. The analogous isocyanato complex [Re(NCO)(CO)(2)(triphos)] has been likewise prepared for comparison. The structure of both complexes was elucidated by X-ray diffraction studies. While the isocyanato complex is linear, the phosphaethynolate complex is strongly bent around the pnictogen center. Computations including natural bond orbital (NBO) theory, natural resonance theory (NRT), and natural population analysis (NPA) indicate that the isocyanato complex can be viewed as a classic Werner-type complex, that is, with an electrostatic interaction between the Re(I) and the NCO group. The phosphaethynolate complex [Re(P=C=O)(CO)(2)(triphos)] is best described as a metallaphosphaketene with a Re(I)-phosphorus bond of highly covalent character.

Cu[Al(OR(F))4] starting materials and their application in the preparation of [Cu(S(n))]+ (n=12, 8) complexes.

An effective route to stable, almost-"naked" Cu(I) salts of weakly coordinating anions (WCAs) of the type [Al(OR(F))4]- has been developed. Born-Fajans-Haber cycles and theoretical calculations suggest that this methodology is useful for the generation of Cu(I) salts regardless of the larger WCA used. The first homoleptic Cu(I)-arene complex [Cu(1,2-F2C6H4)2](+)[Al{OC(CF3)3}4]- (1), the first Cu(I)-methylenechloride complex [Cu(CH2Cl2)Al{OC(CH3)(CF3)2}4] (2), and the donor-free dimer [CuAl{OCH(CF3)2}4]2 (3) were synthesized in quantitative yields by sonicating Li[Al(OR(F))4] (R(F)=C(CF3)3, C(CH3)(CF3)2, or CH(CF3)2), AgF, and a three-fold excess of CuI in 1,2-F2C6H4 (1) or CH2Cl2 (2, 3). Substances 1-3 are good starting materials for further Cu(I) chemistry, and the reaction of 1-3 with the weak Lewis base cyclooctasulfur gave the first Cu(I)-sulfur complexes of type [Cu(S12)(S8)](+)[Al{OC(CF3)3}4]- (4), [Cu(CH2Cl2)(S12)](+)[Al{OC(CF3)3}4]- (5), [A1Cu(1,5-eta1,eta1-S8)CuA1] (6; A1=[Al{OC(CH3)(CF3)2}4]-), and a Cu(I)-S8 1D coordination polymer with [Cu2(S8)2A(2)(2)] (7; A2=[Al{OCH(CF3)2}4]-), as a monomeric repeat unit. Complexes 4 and 5 are the first example of any metal coordinated to cyclo-S12 and 4 is the first example of a complex having an element in two allotropic modifications as a ligand.

Tetraalkylammonium salts of weakly coordinating aluminates: ionic liquids, materials for electrochemical applications and useful compounds for anion investigation.

In this study, we investigated the tetraalkylammonium salts of the weakly coordinating fluorinated alkoxyaluminates [pftb](-) ([Al(O(C(CF(3))(3))(4)](-)), [hfip](-) ([Al(OC(H)(CF(3))(2))(4)](-)) and [hftb](-) ([Al(OC(CH(3))(CF(3))(2))(4)](-)) in order to obtain information on their undisturbed spectral and structural properties, as well as to study their electrochemical behavior (i.e., conductivities in non-polar solvents and electrochemical windows). Several of the compounds qualify as ionic liquids with melting points as low as 42 degrees C for [NBu(4)](+)[hfip](-). Simple and almost quantitative metathesis reactions yielding these materials in high purity were developed. These [NR(4)](+) salts serve as model compounds for undisturbed anions and their vibrational spectra--together with simulated spectra based on quantum chemical DFT calculations--were used for the clear assignment of the anion bands. Besides, the ion volumes of the anions (V(ion)([pftb](-)) = 0.736 nm(3), V(ion)([hftb](-)) = 0.658 nm(3), V(ion)([hfip](-)) = 0.577 nm(3)) and their decomposition pathways in the mass spectrometric measurements have been established. The salts are highly soluble in non-polar solvents (up to 1.09 mol L(-1) are possible for [NBu(4)](+)[hftb](-) in CH(2)Cl(2) and 0.41 mol L(-1) for [NBu(4)](+)[hfip](-) in CHCl(3)) and show higher molar conductivities if compared to [NBu(4)](+)[PF(6)](-). The electrochemical windows of CH(2)Cl(2), CH(3)CN and 1,2-F(2)C(6)H(4) using the [NBu(4)](+) aluminate electrolytes are up to +0.5 V/-0.7 V larger than those using the standard [NBu(4)](+)[PF(6)](-).

[Si(SiMe(3))(3)](6)Ge(18)M (M = Cu, Ag, Au): metalloid cluster compounds as unusual building blocks for a supramolecular chemistry.

Very recently it was shown that the metalloid cluster compound {Ge(9)[Si(SiMe(3))(3)](3)}(-) can be used for subsequent reactions as the shielding of the cluster core is rather incomplete. Here further reactions of with M(+) sources of group 11 metals are described, leading to metalloid cluster compounds of the formula {MGe(18)[Si(SiMe(3))(3)](6)}(-) (M = Ag, Cu). These reactions can be seen as first steps into a supramolecular chemistry with metalloid cluster compounds. Beside this feature, the structural properties as well as the bonding situations in these cluster compounds are discussed.

Homoleptic Cu-phosphorus and Cu-ethene complexes.

Stable salts of the first homoleptic Cu-phosphorus and Cu-ethene complexes, [Cu(eta2-P4)2]+ and [Cu(eta2-C2H4)3]+, isolated by the aid of the weakly coordinating anion (WCA) [Al(OC(CF3)3)4]-, were obtained.