Asymmetric conjugate addition of thioglycolate to a range of chalcones using tetrahydroisoquinoline (TIQ) N,N′-dioxide ligands

A series of novel TIQ based N,N′-oxide ligands were synthesised and screened for their catalytic activity in the enantioselective conjugate addition of thioglycolate to chalcones. Bulky groups on the side chain of the TIQ backbone provided the highest enantioselectivity of up to 88% with 10 mol % catalyst loading. It was also observed that these reactions proceeded optimally in the presence of dichloromethane as a solvent. Screening of various metals emphasized La(OTf)₃ as the ideal pre-catalyst for this particular reaction.     

A family of charged compact objects with anisotropic pressure

Utilizing an ansatz developed by Maurya et al. we present a class of exact solutions of the Einstein–Maxwell field equations describing a spherically symmetric compact object. A detailed physical analysis of these solutions in terms of stability, compactness and regularity indicates that these solutions may be used to model strange star candidates. In particular, we model the strange star candidate Her X-1 and show that our solution conforms to observational data to an excellent degree of accuracy. An interesting and novel phenomenon which arises in this model is the fact that the relative difference between the electromagnetic force and the force due to the pressure anisotropy changing sign within the stellar interior. This may be an additional mechanism required for stability against cracking of the stellar object.     

The Os/Cu-Al-hydrotalcite catalysed hydroxylation of alkenes

A new Os/Cu-Al-hydrotalcite-like catalyst is described which, with N-methylmorpholine oxide as co-oxidant, heterogeneously catalyses the hydroxylation of olefins to give diols selectively and in high yield.     

Pre-equilibrium effects in (n, 2n) reactions at 14.2 MeV+

With a view to study the pre-equilibrium effects in neutron-induced reactions, the activation cross-sections for (n, 2n) reactions at 14.2±0.2 MeV in the heavy mass region have been measured using the versatile mixed powder technique and high resolution Ge(Li) detection. The experimental cross-sections are found to be consistently smaller than the predictions based on the statistical theory and this is attributed to the effect of pre-equilibrium decay in these reactions. The cross-sections due to pre-equilibrium decay were estimated using exciton, hybrid and unified models. When this cross-section was included in comparing the experimental cross-sections with theory, we obtained better agreement, within the limitations of the present-day preequilibrium theories. Preliminary results of this work were reported at the Nuclear Physics and Solid State Physics Symposium, Pune (1978).     

Improved experimental tracking techniques for validating discrete element method simulations of tumbling mills

We report on further developments in the three-dimensional tracking of a particle deep within the tumbling ball charge of an experimental mill. The experimental X-ray program employing the use of bi-planar X-ray angiography now includes the tracking of a typical 6 mm bulk charge particle in three dimensions with a spatial resolution that is accurate to within 0.15 mm. The improved experimental tracking techniques presented were developed for the purpose of generating accurate three-dimensional particle trajectory data against which to validate a numerical method for the simulation of discrete media, namely the discrete element method (DEM). These improvements are complimented with techniques for comparing charge profiles between numerical DEM simulations and three-dimensional experimental trajectory data.     

Collapse of a charged radiating star with shear

The junction conditions for a magnetohydrodynamic fluid sphere undergoing dissipative gravitational collapse in the form of a radial heat flux with shear are obtained. These conditions extend particular results of earlier treatments. We demonstrate that the pressure is proportional to the magnitude of the heat flux as is the case in shear-free models. However in our case the gravitational potentials must be solutions of the Einstein-Maxwell system of equations. The mass function m(v) is increased by a factor related to the charge Q of the radiating star. Physical quantities relating to the local conservation of momentum and surface redshift are obtained.     

Syntheses and characterization of mono and dinuclear complexes of platinum group metals bearing benzene-linked bis(pyrazolyl)methane ligands

Reaction of the benzene-linked bis(pyrazolyl)methane ligands, 1,4-bis{bis(pyrazolyl)-methyl}benzene (L1) and 1,4-bis{bis(3-methylpyrazolyl)methyl}benzene (L2), with pentamethylcyclopentadienyl rhodium and iridium complexes [(η⁵-C₅Me₅)M(μ-Cl)Cl]₂ (M = Rh and Ir) in the presence of NH₄PF₆ results under stoichiometric control in both, mono and dinuclear complexes, [(η⁵-C₅Me₅)RhCl(L)]⁺ {L = L1 (1); L2 (2)}, [(η⁵-C₅Me₅)IrCl(L)]⁺ {L = L1 (3); L2 (4)} and [{(η⁵-C₅Me₅)RhCl}₂(μ-L)]²⁺ {L = L1 (5); L2 (6)}, [{(η⁵-C₅Me₅)IrCl}₂(μ-L)]²⁺ {L = L1 (7); L2 (8)}. In contrast, reaction of arene ruthenium complexes [(η⁶­arene)Ru(μ-Cl)Cl]₂ (arene = C₆H₆, p-ⁱPrC₆H₄Me and C₆Me₆) with the same ligands (L1 or L2) gives only the dinuclear complexes [{(η⁶-C₆H₆)RuCl}₂(μ-L)]²⁺ {L = L1 (9); L2 (10)}, [{(η⁶-p-ⁱPrC₆H₄Me)RuCl}₂(μ-L)]²⁺ {L = L1 (11); L2 (12)} and [{(η⁶-C₆Me₆)RuCl}₂(μ-L)]²⁺ {L = L1 (13); L2 (14)}. All complexes were isolated as their hexafluorophosphate salts. The single-crystal X-ray crystal structure analyses of [7](PF₆)₂, [9](PF₆)₂ and [11](PF₆)₂ reveal a typical piano-stool geometry around the metal centers with six-membered metallo-cycle in which the 1,4-bis{bis(pyrazolyl)-methyl}benzene acts as a bis-bidentate chelating ligand.     

Synthesis of tetrahydroisoquinoline (TIQ)–oxazoline ligands and their application in enantioselective Henry reactions

A novel family of eleven new tetrahydroisoquinoline (TIQ)–oxazoline intermediates and five corresponding copper(II) catalysts has been developed and applied to the catalytic asymmetric Henry reaction of various aldehydes with nitromethane to provide β-hydroxy nitroalkanes in high conversion (>99%). This paper describes the synthesis of the TIQ compounds from l-dihydroxyphenylalanine (l-DOPA) as the starting material. The chiral ligands were complexed in situ with various transition metals such as Cu, Sc, Co, Zn, Ni and Mn and tested as a chiral catalyst for the Henry reaction. The reaction was optimized in terms of the metal, counter ion, solvent, temperature and over a range of substrates. The corresponding catalyst with copper(II) acetate and 2-propanol as the solvent provides the best enantioselectivities (up to 77% ee) of the corresponding nitroalcohol for 4-chlorobenzaldehyde.     

Synthesis of tetrahydroisoquinoline-diamine ligands and their application in asymmetric transfer hydrogenation

The use of the tetrahydroisoquinoline scaffold is well documented in biologically active compounds. However, reports of the utilisation of tetrahydroisoquinoline compounds in asymmetric catalysis are limited. The synthesis of novel diamine ligands possessing the tetrahydroisoquinoline (tetrahydroisoquinoline) backbone and evaluation of their activity in the asymmetric transfer hydrogenation of acetophenone are presented. The diamine ligands in conjunction with i-PrOH as the hydrogen source and [RhCl₂(Cp1)]₂ as the metal precursor proved to be the most effective of the tetrahydroisoquinoline derivatives for this catalytic system. Water was found to have a profound influence on the enantioselectivity of the reaction. Optimisation of the amount water, i-PrOH and catalytic loading content rendered the best result of 70% enantioselectivity for the (S)-1-phenylethanol isomer product.