Asymmetric transfer hydrogenation of imines catalyzed by a Noyori-type Ru(II) complex—a parametric study

We present, to the best of our knowledge, the first parametric study of the asymmetric transfer hydrogenation of imines catalyzed by a Noyori-type catalytic complex based on ruthenium. A model imine for this study was 1-methyl-3,4-dihydroisoquinoline, and a well-known complex RuCl(η⁶-p-cymene)((1S,2S)-N-p-toluenesulfonyl-1,2-diphenylethylenediamine) was chosen as the model catalyst. The reactions were performed in the presence of a formic acid–triethylamine mixture as the source of hydrogen.The parameters examined include general parameters, for example, concentration, temperature, and substrate-to-catalyst molar ratio, as well as parameters specific to this particular reaction, such as the amount of the hydrogenation mixture used, the ratio of its components, or the inhibitive effect of carbon dioxide. During this study, several unexpected parameters worth further investigation have emerged.     

Reactions of β-Pinene with Aromatic Aldehydes

Aromatic aldehydes add to β-pinene under Lewis acid catalyzed Prins reaction conditions and yield the corresponding homoallylic alcohols. The reactions proceed in poor yield when electron donating substituents are present on the aromatic ring.     

Spatiotemporal Studies of the One-Dimensional Coordination Polymer [Fe(ebtz)2(C2H5CN)2](BF4)2: Tug of War between the Nitrile Reorientation Versus Crystal Lattice as a Tool for Tuning the Spin Crossover Properties**

Reaction of 1,2-di(tetrazol-2-yl)ethane (ebtz) with Fe(BF₄)₂⋅6 H₂O in different nitriles yields one-dimensional coordination polymers [Fe(ebtz)₂(RCN)₂](BF₄)₂⋅nRCN (n=2 for R=CH₃ ( 1 ) and n=0 for R=C₂H₅ ( 2 ) C₃H₇ ( 3 ), C₃H₅ ( 4 ), CH₂Cl ( 5 )) exhibiting spin crossover (SCO). SCO in 1 and 3 – 5 is complete and occurs above 160 K. In 2 , it is shifted to lower temperatures and is accompanied by wide hysteresis (T_1/2^↓=78 K, T_1/2^↑=123 K) and proceeds extremely slowly. Isothermal (80 K) time-resolved single-crystal X-ray diffraction studies revealed a complex nature for the HS→LS transition in 2 . An initial, slow stage is associated with shrinkage of polymeric chains and with reduction of volume at 77 % (in relation to the difference between cell volumes V_HS−V_LS) whereas only 16 % of iron(II) ions change spin state. In the second stage, an abrupt SCO occurs, associated with breathing of the crystal lattice along the direction of the Fe–nitrile bonds, while the nitriles reorient. HS→LS switching triggered by light (808 nm) reveals the coupling of spin state and nitrile orientation. The importance of this coupling was confirmed by studies of [Fe(ebtz)₂(C₂H₅CN/C₃H₇CN)₂](BF₄)₂ mixed crystals ( 2 a , 2 b ), showing a shift of T_1/2 to higher values and narrowing of the hysteresis loop concomitant with an increase of the fraction of butyronitrile. This increase reduces the capability of nitrile molecules to reorient. Density functional theory (DFT) studies of models of 1 – 5 suggest a particular possibility of 2 to adopt a low (140–145°) value of its Fe-N-C(propionitrile) angle.     

Calorimetry in testing waste materials from the brown coal combustion

The calorimetric measurements were applied in testing the wastes collected from different furnaces in electric power plants as materials to be used in civil engineering. The fly ash materials were collected from two power stations based on different brown coal deposits and working with conventional and fluidized bed installation. The reactivity of high calcium fly ash from sub-bituminous coal combustion has been proved in calorimetric, conductometric, chemical shrinkage, and rheological measurements before their practical implementation on larger scale. Highly soluble components of fly ash contribute to the hydration products and structure formation, followed by setting and hardening of fly ash–cement mixture. These results have been the base of research project aimed in the innovative solutions dealing with the management of deposits of wastes generated as a result of coal combustion. The standardization and potential use on larger scale of these materials, necessary from the environmental point of view, seems to be the question of nearest future.     

Remote Fluorination and Fluoroalkyl(thiol)ation Reactions

Remote functionalization reactions have the power to transform a C−H (or C−C) bond at a distant position from a functional group. This Review summarizes recent advances and key breakthroughs in remote fluorination, trifluoromethylation, difluoromethylation, trifluoromethylthiolation, and fluoroalkenylation reactions. Several powerful strategies have emerged to control the reactivity and distal selectivity such as the undirected radical approach, the 1,5-hydrogen atom transfer, the metal migration, the use of distant directing groups, and the ring-opening reactions. These unconventional and predictable C−H (and C−C) functionalization transformations should allow for the preparation of a wide range of otherwise-difficult-to-access alkyl, aromatic, heteroaromatic, and structurally complex fluorides.     

Development of chiral heteroleptic magnesium amides; asymmetric deprotonations mediated by six-membered metallocyclic amidomagnesium naphtholates

A series of enantioenriched six-membered metallocyclic amidomagnesium naphtholates were prepared and used to probe the structure–reactivity/selectivity relationships of heteroleptic magnesium base complexes within asymmetric deprotonation reactions. An effective complex was identified and applied within enantioselective enolisation processes, delivering good levels of enantioselectivity and also revealing key structural requirements for achieving such selectivity.     

Thermal and Sc(OTf)3 catalyzed 1,3-dipolar cycloaddition of open-chain nitrones to α,β-unsaturated lactones: combined experimental and computational studies

The stereoselectivity of 1,3-dipolar cycloaddition reactions of C-phenyl open-chain nitrones and α,β-unsaturated γ- and δ-lactones was investigated under thermal and catalytic conditions. It was found that under thermal conditions, the endo approach of the reactants was preferred leading to the thermodynamic product. In the presence of Sc(OTf)₃ the exo adduct was obtained in high yield and selectivity. The energies of the cycloaddition reactions were investigated by means of molecular orbital calculations at the B3LYP/6-31+G(d,p) and MP3/6-31+G(d,p) theory level. Different reaction channels and reactant approaches, fitting the individual regio- and stereochemical preferences, are discussed. The computational results were compared with the corresponding experimental data and found to be in good agreement.     

On the hyperreflexivity of power partial isometries

Necessary and sufficient conditions for hyperreflexivity of completely non-unitary power partial isometries are given.