Reactivity of Cationic Agostic and Carbene Structures Derived from Platinum(II) Metallacycles

This paper describes the formation of new platinacyclic complexes derived from the phosphine ligands PiPr₂Xyl, PMeXyl₂, and PMe₂Ar (Xyl=2,6‐Me₂C₆H₃ and Ar=2,6‐(2,6‐Me₂C₆H₃)₂‐C₆H₃) as well as reactivity studies of the trans‐[Pt(C^P)₂] bis‐metallacyclic complex 1 a derived from PiPr₂Xyl. Protonation of compound 1 a with [H(OEt₂)₂][BAr_F] (BAr_F=B[3,5‐(CF₃)₂C₆H₃]₄) forms a cationic δ‐agostic structure 4 a , whereas α‐hydride abstraction employing [Ph₃C][PF₆] produces a cationic platinum carbene trans‐[Pt{PiPr₂(2,6‐CH(Me)C₆H₃}{PiPr₂(2,6‐CH₂(Me)C₆H₃}][PF₆] ( 8 ). Compounds 4 a and 8 react with H₂ to yield the same 1:3 equilibrium mixture of 4 a and trans‐[PtH(PiPr₂Xyl)₂][BAr_F] ( 6 ), in which one of the phosphine ligands participates in a δ‐agostic interaction. DFT calculations reveal that H₂ activation by 8 occurs at the highly electrophilic alkylidene terminus with no participation of the metal. The two compounds 4 a and 8 experience C–C coupling reactions of a different nature. Thus, 4 a gives rise to complex trans‐[PtH{(E)‐1,2‐bis(2‐(PiPr₂)‐3‐MeC₆H₃)CH?CH}] ( 7 ) that contains a tridentate diphosphine–alkene ligand, through agostic C?H oxidative cleavage and C–C reductive coupling steps, whereas the C–C coupling reaction in 8 involves classical migratory insertion of its [Pt?CH] and [Pt?CH₂] bonds promoted by platinum coordination of CO or CNXyl. The mechanisms of the C?C bond‐forming reactions have also been investigated by computational methods.     

High-pressure DSC study on the hydriding and dehydriding of Mg/C nanocomposites

High-pressure DSC was applied to study the hydriding and dehydriding behavior of Mg 95 mass%–C 5 mass% composites, synthesized by ball milling with two different kinds of carbon additives (activated carbon derived from apricot stones AS and from bean pods BP) and magnesium with different particle sizes. The composites containing finer magnesium experience absorption capacity deterioration with hydriding/dehydriding cycling, but for the Mg–AS, this worsening is in lower degree compared to Mg–BP. The activated carbon derived from the AS, used for the composites preparation, has more pronounced positive effect on the hydrogen sorption characteristics of magnesium (with both finer and coarser particles), compared with the carbon derived from BP, due to its better protection of the Mg surface from oxidation and particles agglomeration during hydriding/dehydriding cycling.     

Reactivity of TpIr(C2H4)(DMAD) with carboxylic acids. A DFT study on geometrical isomers and structural characterization

The thermally unstable adduct Tp^Me2Ir(C₂H₄)(DMAD), which was generated “in situ” by the reaction of DMAD with Tp^Me2Ir(C₂H₄)₂ (1) at low temperature, reacted with different carboxylic acids to produce the following compounds: Tp^Me2Ir(E-C(CO₂Me)CH(CO₂Me))(H₂O)(OC(O)C₆H₄R), (R = H, 2a; o-OH, 2b; o-Cl, 2c; m-Cl, 2d; o-NO₂, 2e; m-NO₂, 2f;o-Me, 2g;p-Me, 2h) and Tp^Me2Ir(E-C(CO₂Me)CH(CO₂Me))(H₂O)(OC(O)Me) 3. In the reaction of derivative 2a with Lewis bases, Tp^Me2Ir(E-C(CO₂Me)CH(CO₂Me))(L)(OC(O)C₆H₅), (L = Py, 4a; m-Br-Py, 4b; m-Cl-Py, 4c; NCMe, 5) were obtained, of which 4b and 4c were isolated as a mixture of two isomers in which the substituted pyridine ring was present at different rotational orientations. All new compounds prepared were characterized by ¹H and ¹³C{¹H} NMR spectroscopy, the structure of compounds 2d, 2h and 4a being determined by X-ray diffraction analysis. DFT was used to analyze the relative stability and the structural orientation of the isomers.     

Bacteriostatic activities of N-substituted tris-thioureas bearing amino acid and aniline substituents

A series of tri-substituted thiourea derivatives were synthesized by the reaction of 1,3,5-triacetylbenzoyl isothiocyanate with aminoacids and aniline derivatives. All thiourea derivatives were characterized by FT-IR, ¹H and ¹³C NMR spectroscopy. Antibacterial activities against wild-type Escherichia coli American Type Culture Collection 8739 were determined by use of the turbidimetric methodto evaluate the effect of varying amino groups on the synthesized thioureas. Tris-thiourea derivatives bearing ortho-chloroaryl substituents showed excellent antibacterial activity against E. coli with minimal inhibitory concentration (MIC) of 96 ppm. The optimum inhibition was dependent on the type of amines and the position of the halogen in aniline.     

Recent trends on the implementation of reticular materials in column-centered separations

Advances in the development of column-based analytical separations are strongly linked to the development of novel materials. Stationary phases for chromatographic separation are usually based on silica and polymer materials. Nevertheless, recent advances have been made using porous crystalline reticular materials, such as metal-organic frameworks and covalent organic frameworks. However, the direct packing of these materials is often limited due to their small crystal size and nonspherical shape. In this review, recent strategies to incorporate porous crystalline materials as stationary phases for liquid-phase separations are covered. Moreover, we discuss the potential future directions in their development and integration into suitable supports for analytical applications. Finally, we discuss the main challenges to be solved to take full advantage of these materials as stationary phases for analytical separations.     

Passivation techniques for InAs/GaSb strained layer superlattice detectors

InAs/(In,Ga)Sb Strained Layer Superlattices (SLSs) have made significant progress since they were first proposed as an infrared (IR) sensing material more than three decades ago. The basic material properties of SLS provide a prospective benefit in the realization of IR imagers with suppressed interband tunneling and Auger recombination processes, as well as high quantum efficiency and responsivity. With scaling of single pixel dimensions, the performance of focal plane arrays is strongly dependent on surface effects due to the large pixels’ surface/volume ratio. This article discusses the cause of surface leakage currents and various approaches of their reduction including dielectric passivation, passivation with organic materials (polyimide or various photoresists), passivation by overgrowth of wider bandgap material, and chalcogenide passivation. Performance of SLS detectors passivated by different techniques and operating in various regions of infrared spectrum has been compared.     

Controlling C−OAryl Hydrogenolysis vs Aryl Hydrogenation in Lignin Model Depolymerization Using Ni-, Rh- or Ni/Rh-based Silica Catalysts

This paper focuses on the hydrogenolysis of 2-phenoxy-1-phenylethanone, modelling a pre-oxidized form of lignin using five catalysts of similar metal content, prepared by impregnation of Ni(II), Rh(III) and both metals onto Aerosil-380 in the presence of NH₃, followed by a reduction step. The materials were characterized in the dried as-synthesized state and after consecutive reductive and oxidative treatments, showing the great dispersion of the metal (oxide nanoparticles with sizes<2 nm). Working with 1 mol % of the reduced metal (500 °C) per substrate at 180 °C with isopropanol as H-donor, the most active catalyst, but also the least selective towards phenol, was initially found to be the Ni-based one. Under similar conditions, the lower capacity of the Rh-based catalyst to induce H transfer from isopropanol favoured phenol formation but resulted in much slower C−OAr cleavage. Despite a very high dispersion of the two metals in the bimetallic catalysts, no synergy was found, suggesting that Ni would be segregated at the surface. Finally, the best phenol productivity could be reached by reducing the Ni-based catalyst at 650 °C, which led to a more efficient cleavage of C−OAr bonds. In this way, it was possible to produce 8 times more phenol per hour.