NH3 Synthesis in the N2/H2 Reaction System using Cooperative Molecular Tungsten/Rhodium Catalysis in Ionic Hydrogenation: A DFT Study

The ionic hydrogenation of N₂ with H₂ to give NH₃ is investigated by means of density functional theory (DFT) computations using a cooperatively acting catalyst system. In this system, N₂ binds to a neutral tungsten pincer complex of the type [(PNP)W(N₂)₃] (PNP=pincer ligand) and is reduced to NH₃. The protons and hydride centers necessary for the reduction are delivered by heterolytic cleavage of H₂ between the N₂–tungsten complex and the cationic rhodium complex [Cp*Rh{2‐(2‐pyridyl)phenyl}(CH₃CN)]⁺. Successive transfer of protons and hydrides to the bound N₂, as well as all N_xH_y units that occur during the reaction, enable the computation of closed catalytic cycles in the gas and in the solvent phase. By optimizing the pincer ligands of the tungsten complex, energy spans as low as 39.3 kcal mol^?1 could be obtained, which is unprecedented in molecular catalysis for the N₂/H₂ reaction system.     

Attempts to separate (–)‐α‐thujone, (+)‐β‐thujone epimers from camphor enantiomers by enantioselective HPLC with polarimetric detection

In a first step, 26 chiral stationary phases (CSPs) have been screened for the separation of (–)‐α‐thujone, (+)‐β‐thujone epimers and camphor enantiomers by LC. The separations were monitored by a polarimeter detector. None of these CSPs provided a noticeable resolution for camphor enantiomers. The three components of a test mixture were clearly baseline separated on Chiralpak AS‐H, Chiralpak AZ‐H and TCI‐MBS (poly(N‐alpha‐(S)‐methylbenzylmaleimide) coated on silica gel) in a mobile phase composed of hexane/2‐PrOH (99:1 v/v). Interestingly, for a preparative application, the three CSPs produced different elution orders for the three constituents of the mixture. In a second step, it is shown that the use of online polarimetric detection constitutes an unprecedented method to reveal the occurrence and the relative content of thujone epimers and the chirality of the major camphor enantiomer in crude essential oils. A proof of concept is illustrated on crude essential oils from Rosmarinus tournefortii, Artemisia herba alba and A. arborescens, which grow in Morocco and have several traditional uses there. In a third step, pure (+)‐β‐thujone was quantitatively collected from A. arborescens crude oil by semi‐preparative HPLC on Chiralpak AZ‐H monitored by a polarimeter.     

Four related diethyl [(arylamino)(4‐ethynylphenyl)methyl]phosphonates

Crystal structures are reported for four related diethyl [(arylamino)(4‐ethynylphenyl)lmethyl]phosphonate derivatives, namely diethyl [(4‐bromoanilino)(4‐ethynylphenyl)methyl]phosphonate, C₁₉H₂₁BrNO₃P, (I), diethyl ((4‐chloro‐2‐methylanilino){4‐[2‐(trimethylsilyl)ethynyl]phenyl}methyl)phosphonate, C₂₃H₃₁ClNO₃PSi, (II), diethyl ((4‐fluoroanilino){4‐[2‐(trimethylsilyl)ethynyl]phenyl}methyl)phosphonate, C₂₂H₂₉FNO₃PSi, (III), and diethyl [(4‐ethynylphenyl)(naphthalen‐2‐ylamino)methyl]phosphonate, C₂₃H₂₄NO₃P, (IV). The conformation of the anilinobenzyl group is very similar in all four compounds. The P—C bond has an approximately staggered conformation, with the aniline and ethynylphenyl groups in gauche positions with respect to the P=O double bond. The two six‐membered rings are almost perpendicular. The sums of the valence angles about the N atoms vary from 344 (2) to 351 (2)°. In the crystal structures, molecules of (I), (III) and (IV) are arranged as centrosymmetric or pseudocentrosymmetric dimers connected by two N—H...O=P hydrogen bonds. The molecules of (II) are arranged as centrosymmetric dimers connected by C_methyl—H...O=P hydrogen bonds. The N—H bond of (II) is not involved in hydrogen bonding.     

New one step synthesis of 3,5‐disubstituted pyrazoles under microwave irradiation and classical heating

A convenient one pot procedure for the synthesis of 3,5-disubstituted pyrazoles by condensation of chalcones, hydrazine hydrate and sulfur in ethanol under microwave irradiation and conventional heating method is reported. The hydrogen sulfide is produced during the reaction. The pyrazoles are obtained in good yields and excellent state of purity. The structures of new compounds were confirmed by IR, ¹H, and ¹³C NMR, MS and elemental analysis.