A zirconocene triazenido hydride complex activates CO.

Starting from the alkyne complex CpZr(py)(η-MeSiCSiMe) (Cp = η-cyclopentadienyl, py = pyridine), the synthesis and complete characterisation of a zirconocene(IV) triazenido hydride complex and its use in the activation of small molecules is reported. The reaction with CO led to the formation of a zirconocene(IV) triazenido-formate complex, which was further investigated for its stability towards different bases with respect to the formation of formic acid. The experimentally observed reaction pathway was investigated computationally using DFT methods, revealing the favourable role of pyridine coordination in the hydrogen transfer from the triazene to the alkyne unit of the zirconocene reagent.

Dehydrocoupling of Ammonia/Amine Boranes and Related Transformations Catalysed by Group 4 Metal Complexes.

Ammonia borane and amine boranes are main group analogues of alkanes, which are characterised by their large gravimetric hydrogen content. This hydrogen can be released in dehydrocoupling and dehydropolymerisation reactions to obtain B-N oligomers and polymers that are of importance as precursors for functional B-N materials. Furthermore, amine boranes are potent reagents for application in transfer hydrogenation reactions, representing a versatile, easy-to-handle alternative to the use of gaseous hydrogen for the reduction of organic compounds.

Improved benchtop P NMR reaction monitoring Multi-Resonance SHARPER.

reaction monitoring of hydrogenation reactions featuring oxygen-sensitive organometallic complexes is done a P benchtop NMR spectrometer using the Multi-Resonance Sensitive Homogeneous And Resolved PEaks in Real time (MR-SHARPER) sequence. Signal enhancement generated by MR-SHARPER enables monitoring of reactivity on the order of minutes that could not be followed with traditional P{H} NMR detection.

A Phosphorus-Centred, Zirconocene-Bridged Tetraradical: Synthesis, Structure and Application as Molecular Double Switch.

Biradicals are important intermediates in the formation and breaking of a chemical bond. Their use as molecular switches is of particular interest. Much less is known about tetraradicals, which can, for example, consist of two biradical(oid) units.

The Mechanism of Rh(I)-Catalyzed Coupling of Benzotriazoles and Allenes Revisited: Substrate Inhibition, Proton Shuttling, and the Role of Cationic vs Neutral Species.

Direct coupling of benzotriazole to unsaturated substrates such as allenes represents an atom-efficient method for the construction of biologically and pharmaceutically interesting functional structures. In this work, the mechanism of the -selective Rh complex-catalyzed coupling of benzotriazoles to allenes was investigated in depth using a combination of experimental and theoretical techniques. Substrate coordination, inhibition, and catalyst deactivation was probed in reactions of the neutral and cationic catalyst precursors [Rh(μ-Cl)(DPEPhos)] and [Rh(DPEPhos)(MeOH)] with benzotriazole and allene, giving coordination, or coupling of the substrates.

A General Concept for the Electronic and Steric Modification of 1-Metallacyclobuta-2,3-dienes: A Case Study of Group 4 Metallocene Complexes.

The synthesis of group 4 metal 1-metallacyclobuta-2,3-dienes as organometallic analogues of elusive 1,2-cyclobutadiene has so far been limited to SiMe substituted examples. We present the synthesis of two Ph substituted dilithiated ligand precursors for the preparation of four new 1-metallacyclobuta-2,3-dienes [rac-(ebthi)M] (M=Ti, Zr; ebthi=1,2-ethylene-1,10-bis(η-tetrahydroindenyl)). The organolithium compounds [Li(RCPh)] (1 b: R=Ph, 1 c: R=SiMe) as well as the metallacycles of the general formula [rac-(ebthi)M(RCR)] (2 b: M=Ti, R=R=Ph, 2 c: M=Ti, R=Ph, R=SiMe; 3 b: M=Zr, R=R=Ph; 3 c: M=Zr, R=Ph, R=SiMe) were fully characterised.

Mechanochemical Oxidative Degradation of Thienopyridine Containing Drugs: Toward a Simple Tool for the Prediction of Drug Stability.

The long-term stability of an active-pharmaceutical ingredient and its drug products plays an important role in the licensing process of new pharmaceuticals and for the application of the drug at the patient. It is, however, difficult to predict degradation profiles at early stages of the development of new drugs, making the entire process very time-consuming and costly. Forced mechanochemical degradation under controlled conditions can be used to realistically model long-term degradation processes naturally occurring in drug products, avoiding the use of solvents, thus excluding irrelevant solution-based degradation pathways.

Solution and solid-state studies of hydrogen and halogen bonding with N-heterocyclic carbene supported nickel(II) fluoride complexes.

Nickel fluoride complexes of the type [Ni(F)(L)(Ar)] (L = phosphine, Ar = fluorinated arene) are well-known to form strong halogen and hydrogen bonds in solution and in the solid state. A comprehensive study of such non-covalent interactions using bis(carbene) complexes as acceptors and suitable halogen and hydrogen bond donors is presented. In solution, the complex [Ni(F)(iPrIm)(CF)] forms halogen and hydrogen bonds with iodopentafluorobenzene and indole, respectively, which have formation constants () an order of magnitude greater than those of structurally related phosphine supported nickel fluorides.

How solvents affect the stability of cationic Rh(I) diphosphine complexes: a case study of MeCN coordination.

Cationic rhodium(I) diphosphine complexes, referred to as Schrock-Osborn catalysts, are privileged homogeneous catalysts with a wide range of catalytic applications. The coordination of solvent molecules can have a significant influence on reaction mechanisms and kinetic scenarios. Although solvent binding is well documented for these rhodium species, comparative quantifications for structurally related systems are not available to date.

Mono- and dinuclear zirconocene(iv) amide complexes for the catalytic dehydropolymerisation of phenylsilane.

The dehydropolymerisation of phenylsilane is investigated using group 4 metallocene amide complexes as catalysts. The dinuclear zirconocene amide complex CpZr(NMe)(μ-MeSiCSiMe)Zr(NMe)Cp (2) (Cp = η-cyclopentadienyl) shows high activity in dehydrocoupling reactions, producing polyphenylsilanes with molecular weights ranging from 200 to 3000 g mol and linear-to-cyclic product ratios of up to 80 : 20. Likewise, different ratios of oligomers and polymers with different tacticities could be described.

Synthesis, Coordination Chemistry, and Mechanistic Studies of P,N-Type Phosphaalkene-Based Rh(I) Complexes.

The synthesis of P,N-phosphaalkene ligands, py-CH═PMes* (, py = 2-pyridyl, Mes* = 2,4,6-Bu-CH) and the novel quin-CH═PMes* (, quin = 2-quinolinyl) is described. The reaction with [Rh(μ-Cl)cod] produces Rh(I) bis(phosphaalkene) chlorido complexes and with distorted trigonal bipyramidal coordination environments. Complexes and show a pronounced metal-to-ligand charge transfer (MLCT) from Rh into the ligand P═C π* orbitals.

Iridium(III) bis(thiophosphinite) pincer complexes: synthesis, ligand activation and applications in catalysis.

Iridium(III) bis(thiophosphinite) complexes of the type [(PSCSP)Ir(H)(Cl)(py)] (PSCSP = κ-(2,6-SPR)CH) (R = Bu, iPr, Ph) can be prepared from the ligand precursors 1,3-(SPR)CH by C-H activation at Ir using [Ir(COE)Cl] or [Ir(COD)Cl]. Optimisation of the protocol for complexation showed that direct cyclometallation in the absence or presence of pyridine, as well as C-H activation in the presence of H are viable options that, depending on the phosphine substituent furnish the five-coordinate Ir(III) hydride chloride complexes 2-R or the base stabilised species 3-R in good yields. In case of the PSCSP ligand, P-S activation results in the formation of a thiophosphine stabilised Ir(III) hydride complex [(PSCSP)Ir(H)(Cl)(PPhSH)] (4).

Model-based signal tracking in the quantitative analysis of time series of NMR spectra.

Hard modeling of NMR spectra by Gauss-Lorentz peak models is an effective way for dimensionality reduction. In this manner high-dimensional measured data are reduced to low-dimensional information as peak centers, amplitudes or peak widths. For time series of spectra these parameters can be assumed to be smooth functions in time.

Molecular Catalysts for the Reductive Homocoupling of CO towards C Compounds.

The conversion of CO into multicarbon (C ) compounds by reductive homocoupling offers the possibility to transform renewable energy into chemical energy carriers and thereby create "carbon-neutral" fuels or other valuable products. Most available studies have employed heterogeneous metallic catalysts, but the use of molecular catalysts is still underexplored. However, several studies have already demonstrated the great potential of the molecular approach, namely, the possibility to gain a deep mechanistic understanding and a more precise control of the product selectivity.

1-Zirconacyclobuta-2,3-dienes: synthesis of organometallic analogs of elusive 1,2-cyclobutadiene, unprecedented intramolecular C-H activation, and reactivity studies.

The structure, bonding, and reactivity of small, highly unsaturated ring systems is of fundamental interest for inorganic and organic chemistry. Four-membered metallacyclobuta-2,3-dienes, also referred to as metallacycloallenes, are among the most exotic examples for ring systems as these represent organometallic analogs of 1,2-cyclobutadiene, the smallest cyclic allene. Herein, the synthesis of the first examples of 1-zirconacyclobuta-2,3-dienes of the type [Cp'Zr(MeSiCSiMe)] (Cp' = -(ebthi), (ebthi = 1,2-ethylene-1,1'-bis(η-tetrahydroindenyl)) (2a); -MeSi(thi), thi = (η-tetrahydroindenyl), (2b)) is presented.

Ball milling - a new concept for predicting degradation profiles in active pharmaceutical ingredients.

A method for forced oxidative mechanochemical degradation of active pharmaceutical ingredients (APIs) using clopidogrel hydrogensulfate as a model compound is presented. Considerable and selective formation of degradants occurs already after very short reaction times of less than 15 minutes and the nature of the products is strongly dependent on the used oxidant.

Reactivity of phospha-Wittig reagents towards NHCs and NHOs.

Phospha-Wittig reagents, RPPMe3 (R = Mes* 2,4,6-tBu3-C6H2; MesTer 2,6-(2,4,6-Me3C6H2)-C6H3; DipTer 2,6-(2,6-iPr2C6H3)-C6H3), can be considered as phosphine-stabilized phosphinidenes. In this study we show that PMe3 can be displaced by NHCs or NHOs. Interestingly, phosphinidene-like reactivity results in a subsequent C(sp2)-H activation of the exocyclic CH2 group in NHOs.

Dehydropolymerisation of Methylamine Borane and an N-Substituted Primary Amine Borane Using a PNP Fe Catalyst.

Dehydropolymerisation of methylamine borane (H B⋅NMeH ) using the well-known iron amido complex [(PNP)Fe(H)(CO)] (PNP=N(CH CH PiPr ) ) (1) gives poly(aminoborane)s by a chain-growth mechanism. In toluene, rapid dehydrogenation of H B⋅NMeH following first-order behaviour as a limiting case of a more general underlying Michaelis-Menten kinetics is observed, forming aminoborane H B=NMeH, which selectively couples to give high-molecular-weight poly(aminoborane)s (H BNMeH) and only traces of borazine (HBNMe) by depolymerisation after full conversion. Based on a series of comparative experiments using structurally related Fe catalysts and dimethylamine borane (H B⋅NMe H) polymer formation is proposed to occur by nucleophilic chain growth as reported earlier computationally and experimentally.

A Comparative Study on the Thermodynamics of Halogen Bonding of Group 10 Pincer Fluoride Complexes.

The thermodynamics of halogen bonding of a series of isostructural Group 10 metal pincer fluoride complexes of the type [(3,5-R - POCOP )MF] (3,5-R - POCOP =κ -C HR -2,6-(OPtBu ) with R=H, tBu, COOMe; M=Ni, Pd, Pt) and iodopentafluorobenzene was investigated. Based on NMR experiments at different temperatures, all complexes 1-tBu (R=tBu, M=Ni), 2-H (R=H, M=Pd), 2-tBu (R=tBu, M=Pd), 2-COOMe (R=COOMe, M=Pd) and 3-tBu (R=tBu, M=Pt) form strong halogen bonds with Pd complexes showing significantly stronger binding to iodopentafluorobenzene. Structural and computational analysis of a model adduct of complex 2-tBu with 1,4-diiodotetrafluorobenzene as well as of structures of iodopentafluorobenzene in toluene solution shows that formation of a type I contact occurs.

Nickel(ii) PECEP pincer complexes (E = O, S) for electrocatalytic proton reduction.

Nickel(ii) chloride and thiolate complexes with PECEP (E = O, S) pincer ligands were investigated as electrocatalysts for the hydrogen evolution reaction in CHCN in the presence of acetic acid and trifluoroacetic acid. The bis(thiophosphinite) (S,S) chloride complex reduced protons at the lowest overpotential in comparison with the bis(phosphinite) (O,O) and mixed phosphinite-thiophosphinite (O,S) complexes. A combination of electrochemical, NMR and UV-vis spectroscopic and mass spectrometric experiments provides mechanistic insights into the catalytic cycle for proton reduction to dihydrogen.

A general benzylic C-H activation and C-C coupling reaction of zirconocenes mediated by C-N bond cleavage in tert-butylisocyanide - unusual formation of iminoacyl complexes.

Reactions of the zirconocene alkyne complex [rac-(ebthi)Zr(η2-Me3SiC2SiMe3)] (rac-(ebthi) = rac-1,2-ethylene-1,1'-bis(η5-tetrahydroindenyl)) with tert-butylisocyanide and methylbenzenes were investigated. Depending on the stoichiometry, the solvent and the reaction temperature different products were obtained. Starting with the end-on coordination of the isocyanide to the zirconium centre (2), elevated reaction temperatures and an excess of tert-butylisocyanide resulted after the elimination of the alkyne in the formation of zirconocene η2-iminoacyl cyanide complexes 3a-d.

Inter-molecular hydrogen bonding in isostructural pincer complexes [OH-( POCOP )Cl] ( = Pd and Pt).

In the crystal structure of the isostructural title compounds, namely {2,6-bis-[(di--butyl-phosphan-yl)-oxy]-4-hy-droxy-phen-yl}chlorido-palladium(II), [Pd(CHOP)Cl], , and {2,6-bis-[(di--butyl-phosphan-yl)-oxy]-4-hy-droxy-phen-yl}chlorido-platinum(II), [Pt(CHOP)Cl], , the metal centres are coordinated in a distorted square-planar fashion by the POCOP pincer fragment and the chloride ligand. Both complexes form strong hydrogen-bonded chain structures through an inter-action of the OH group in the 4-position of the aromatic POCOP backbone with the halide ligand.