Exploiting the Synthetic Potential of Sesquiterpene Cyclases for Generating Unnatural Terpenoids

The substrate flexibility of eight purified sesquiterpene cyclases was evaluated using six new heteroatom‐modified farnesyl pyrophosphates, and the formation of six new heteroatom‐modified macrocyclic and tricyclic sesquiterpenoids is described. GC‐O analysis revealed that tricyclic tetrahydrofuran exhibits an ethereal, peppery, and camphor‐like olfactoric scent.     

Synthesis and Structures of ansa‐Titanocene Complexes with Diatomic Bridging Units for Overall Water Splitting

The synthesis of a series of ansa‐titanocene dichlorides [Cp′₂TiCl₂] (Cp′=bridged η⁵‐tetramethylcyclopentadienyl) and the corresponding titanocene bis(trimethylsilyl)acetylene complexes [Cp′₂Ti(η²‐Me₃SiC₂SiMe₃)] is described. The ethanediyl‐bridged complexes [C₂H₄(C₅Me₄)₂TiCl₂] ( 2 ‐Cl₂) and [C₂H₄(C₅Me₄)₂Ti(η²‐Me₃SiC₂SiMe₃)] ( 2‐ btmsa; btmsa=η²‐Me₃SiC₂SiMe₃) can be obtained from the hitherto unknown calcocenophane complex [C₂H₄(C₅Me₄)₂Ca(THF)₂] ( 1 ). Furthermore, a heterodiatomic bridging unit containing both, a dimethylsilyl and a methylene group was introduced to yield the ansa‐titanocene dichloride [Me₂SiCH₂(C₅Me₄)₂TiCl₂] ( 3 ‐Cl₂) and the bis(trimethylsilyl)acetylene complex [Me₂SiCH₂(C₅Me₄)₂Ti(η²‐Me₃SiC₂SiMe₃)] ( 3 ‐btmsa). Besides, tetramethyldisilyl‐ and dimethylsilyl‐bridged metallocene complexes (structural motif 4 and 5 , respectively) were prepared. All ansa‐titanocene alkyne complexes were reacted with stoichiometric amounts of water; the hydrolysis products were isolated as model complexes for the investigation of the elemental steps of overall water splitting. Compounds 1 , 2 ‐btmsa, 2 ‐(OH)₂, 3 ‐Cl₂, 3 ‐btmsa, 4 ‐(OH)₂, 3 ‐alkenyl and 5 ‐alkenyl were characterised by X‐ray diffraction analysis.     

Isogeometric Reissner-Mindlin shell analysis - employing different control meshes for displacements and rotations

The main purpose of this paper is the development and implementation of a method for the reduction of the so-called locking effect in the isogeometric Reissner-Mindlin shell formulation. In [1] an isogeometric Reissner-Mindlin shell formulation with an exact interpolation of the director vector based on continuum mechanics was introduced. The numerical examples showed that the accuracy and efficiency increased. However, there are only few effective concepts for the prevention of locking effects for low polynomial degrees. In the work of Beirão da Veiga [2], shear locking is prevented for a Reissner-Mindlin plate formulation by using suitable solution spaces. Here, the method is extended to the Reissner-Mindlin shell formulation. Different control meshes are used for displacements and rotations. Furthermore, the basis functions in the direction of the relevant rotation are one degree less than the ones which are chosen for the displacements. That leads to control meshes with different number and location of the control points. The aim is to avoid shear locking due to the coupling of shear strains and curvature since the compatibility requirement for pure bending is then fulfilled. The accuracy and efficiency of this method are investigated for different examples. In addition, the results are compared to the analytical solutions. (© 2016 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)     

3‐tert‐Butyl‐1‐(2‐pyridyl­methyl)‐3H‐imidazolium bromide hydrate

The structure of the title compound, C₁₃H₁₈N₃⁺·Br^?·H₂O, shows that the cation and the bromide anion are linked via the water mol­ecule through weak intermolecular hydrogen bonds. The water was not detected by NMR spectroscopy, but the cell content is in agreement with the elemental analysis. The presence of water plays an important role in further reactions.     

Catalytic asymmetric synthesis of ferrocenes and P-stereogenic bisphosphines

The catalytic asymmetric synthesis of planar chiral ferrocenes and P-stereogenic phosphines and bisphosphines (important classes of chiral ligands for metal-catalyzed asymmetric processes) is successfully demonstrated using n-BuLi or s-BuLi in combination with substoichiometric quantities (0.1-0.5 equiv) of (-)-sparteine or the (+)-sparteine surrogate.     

F K-edge X-ray absorption near-edge structure (XANES) of AlF3 polymorphs: combining ab initio calculations with Walsh correlation diagrams

The X-ray absorption near-edge structures (XANES) at the F K-edge of alpha-AlF(3), beta-AlF(3) and a tetragonal AlF(3) phase are analysed by a combination of ab initio calculations with the FEFF8 code and a phenomenological discussion of local molecular orbital (MO) symmetries at the absorbing fluorine atoms. By means of a Walsh correlation diagram it is shown that the two intense absorption bands observed at the F K-edges of the AlF(3) polymorphs can be interpreted as transitions to anti-bonding MOs in [Al-F-Al]-units that have C(2v) and D(infinity h) point group symmetries. The energies of both anti-bonding orbitals are very insensitive to the angle between the Al-F bonds, which explains the close similarity of the XANES signatures from the three polymorphs. The FEFF8 analysis shows that the increased broadening of the XANES structure for beta-AlF(3) and the tetragonal AlF(3) phase is due to the superposition of the individual absorption spectra from the crystallographically distinct F species. The interpretation in terms of local MOs provides for the first time a "chemically intuitive" approach to investigations of solid fluorides by XANES spectroscopy and provides a simple conceptual framework for the discussion of the electronic structure in AlF(3) materials.