Reactions of the Dirhenium(II) Complexes Re2X4(μ-dppm)2 (X=Cl, Br; dppm=Ph2PCH2PPh2) with Isocyanides. XXII. A Comparison of Mixed Carbonyl–Isocyanide Complexes with Those Formed by Re2Cl4(μ-dcpm)2 (dcpm=Cy2PCH2PCy2)

The reactions of the electron-rich triply bonded dirhenium(II) complex Re₂Cl₄(-dcpm)₂ (dcpm=Cy₂PCH₂PCy₂) with the isocyanide ligands XylNC (Xyl=2,6-dimethylphenyl) and t-BuNC afford the complexes Re₂Cl₄(-dcpm)₂(CNXyl) and Re₂Cl₄(-dcpm)₂(CN-t-Bu)₂ which in turn react with CO to give salts of the [Re₂Cl₃(-dcpm)₂(CO)₂(CNXyl)]⁺ and [Re₂Cl₃(-dcpm)₂(CN-t-Bu)₂(CO)]⁺ cations which exist in different isomeric forms. This chemistry is compared with that developed previously for the analogous complexes derived from Re₂Cl₄(-dppm)₂.     

Reduced order modelling for unsteady fluid flow using proper orthogonal decomposition and radial basis functions

A technique is presented for interpolating unsteady solutions to parameterised fluid flow problems, using a combination of proper orthogonal decomposition and radial basis functions. The technique is validated by considering simulations involving three dimensional unsteady compressible inviscid flow over an oscillating ONERA M6 wing. It is demonstrated that the approach can result in a large reduction in the cpu time required to find solutions at new parameter values, without a significant loss in accuracy.     

Direct Crystallization of Diamine Radical Cations: Carbon-Nitrogen Bond Formation from the Reaction of Triphenylamine with TiCl4, TiBr4, or SnCl4 versus Carbon-Carbon Bond Formation with SbCl5**

Direct synthesis of diamine radical cations in crystalline form proceeding through oxidation of triphenylamine followed by the formation of a new C−N bond is reported. Although the oxidative coupling of triphenylamine is well studied, diamine products are rarely captured in their radical cation state. The neutral diamine most frequently obtained from this reaction pathway is N,N,N’,N’-tetraphenylbenzidine. Herein, the capture of radical cations of diamines in crystalline form in one step starting with neutral triphenylamine was demonstrated, and the formation of two products (the radical cations of N,N,N′,N′-tetraphenyl-1,4-benzenediamine or N,N,N′,N′-tetraphenylbenzidine) depending on the oxidizing agent used was observed. The radical species are characterized by single-crystal X-Ray diffraction, electron paramagnetic resonance spectroscopy, and optical spectroscopy.     

Solvothermal synthesis of cerium oxides

A review of the various hydrothermal and solvothermal methods that have been used for the preparation of cerium oxides is presented. Much work has focussed on the preparation of cerium dioxide (ceria) and its doped analogues because of their extensive applications in catalysis, solid-oxide fuel cells and other technologies. It is shown how the solvothermal method offers a number of distinct advantages in the one-step formation of ceria materials, including control of crystal form and morphology in the nanometre regime from spherical and cubic particles to anisotropic polyhedra and rods. The use of solution additives allows surface capping either preventing aggregation of particles or permitting their assembly into complex hierarchical structures. In terms of doping, the solvothermal synthesis method allows access to phases not possible using high temperatures synthesis, including ceria doped by transition-metal ions. These synthetic advantages all allow fine-tuning of the properties of ceria for practical applications. Finally, some recent work that has focussed on the synthesis of complex mixed-oxide phases containing cerium, both in the +3 and the +4 oxidation state, is presented: this illustrates the potential of solvothermal synthesis in the discovery of new materials.     

Mixed alkyl isocyanide-1,4-diaza-1,3-butadiene complexes of molybdenum(II) and tungsten(II)

The reactions of M(CO)₄(R′-DAB) (M = Mo) or W; R′-DAB = R′-N=CHCH=NR′ (R′ = i-propyl, t-butyl, or cyclohexyl) with SnCl₄ in dichloromethane solution result in the formation, in high yield, of the orange, diamagnetic, seven-coordinate oxidative-addition products M(CO)₃(R′-DAB)(SnCl₃)Cl. The reactions of Mo(CO)₃(R′-DAB)(SnCl₃)Cl (R′ = i-Pr or Cy) with an excess of alkyl isocyanide RNC (R = CHMe₂, CMe₃, or C₆H₁₁) in the presence of KPF₆ lead to the formation of [Mo(CNR)₄(R′-DAB)Cl]PF₆ or [Mo(CNR)₅(R′-DAB)](PF₆)₂ depending upon the reaction stoichiometry and reaction conditions. The monocationic chloro species are converted to [Mo(CNR)₅(R′-DAB)](PF₆)₂ upon reflux with the stoichiometric amount of RNC. Under similar reactions conditions M(CO)₃(t-Bu-DAB)(SnCl₃)Cl (M = Mo or W) derivatives react with alkyl isocyanides with the reductive-elimination of the elements of SnCl₄ and the formation of octahedral M(CO)₃(CNR)(t-Bu-DAB). The dark red compounds [Mo(CNCMe₃)₅(R′-DAB)](PF₆)₂ (R′ = i-Pr or Cy) react readily with cyanide ions at ambient temperatures in methanol to yield [Mo(CNCMe₃)₄(R′-DAB)(CN)]PF₆. Attempts to thermally dealkylate the parent complexes [Mo(CNCMe₃)₅(R′-DAB)](PF₆)₂ (R′ = i-Pr or Cy) to these same cyano species were unsuccessful.     

Imaging Sequences for Hyperpolarized Solids

Hyperpolarization is one of the approaches to enhance Nuclear Magnetic Resonance (NMR) and Magnetic Resonance Imaging (MRI) signal by increasing the population difference between the nuclear spin states. Imaging hyperpolarized solids opens up extensive possibilities, yet is challenging to perform. The highly populated state is normally not replenishable to the initial polarization level by spin-lattice relaxation, which regular MRI sequences rely on. This makes it necessary to carefully “budget” the polarization to optimize the image quality. In this paper, we present a theoretical framework to address such challenge under the assumption of either variable flip angles or a constant flip angle. In addition, we analyze the gradient arrangement to perform fast imaging to overcome intrinsic short decoherence in solids. Hyperpolarized diamonds imaging is demonstrated as a prototypical platform to test the theory.     

A triptycene-based polymer of intrinsic microposity that displays enhanced surface area and hydrogen adsorption

A novel triptycene-based polymer of intrinsic microporosity (Trip-PIM) displays enhanced surface area (1065 m2 g(-1)) and reversibly adsorbs 1.65% hydrogen by mass at 1 bar/77 K and 2.71% at 10 bar/77 K.     

Electron paramagnetic resonance and computational studies of radicals derived from boron-substituted N-heterocyclic carbene boranes

Fifteen second-generation NHC-ligated boranes with aryl and alkyl substituents on boron were prepared, and their radical chemistry was explored by electron paramagnetic resonance (EPR) spectroscopy and calculations. Hydrogen atom abstraction from NHC-BH(2)Ar groups produced boryl radicals akin to diphenylmethyl with spin extensively delocalized across the NHC, BH, and aryl units. All of the NHC-B·HAr radicals studied abstracted Br-atoms from alkyl bromides. Radicals with bulky N,N'-dipp substituents underwent dimerization about 2 orders of magnitude more slowly than first-generation NHC-ligated trihydroborates. The evidence favored head-to-head coupling yielding ligated diboranes. The first ligated diboranyl radical, with a structure intermediate between that of ligated diboranes and diborenes, was spectroscopically characterized during photolysis of di-t-butyl peroxide with N,N'-di-t-butyl-imidazol-2-ylidene phenylborane. The reactive site of B-alkyl-substituted NHC-boranes switched from the boron center to the alkyl substituent for both linear and branched alkyl groups. The β-borylalkyl radicals obtained from N,N'-dipp-substituted boranes underwent exothermic β-scissions with production of dipp-Imd-BH(2)· radicals and alkenes. The reverse additions of NHC-boryl radicals to alkenes are probably endothermic for alkyl-substituted alkenes, but exothermic for conjugated alkenes (addition of an NHC-boryl radical to 1,1-diphenylethene was observed). A cyclopropylboryl radical was observed, but, unlike other α-cyclopropyl-substituted radicals, this showed no propensity for ring-opening.