Addition of Ethylene or Hydrogen to a Main‐Group Metal Cluster under Mild Conditions

Reaction of the tin cluster Sn₈(Ar)₄ (Ar=C₆H₂‐2,6‐(C₆H₃‐2,4,6‐Me₃)₂) with excess ethylene or dihydrogen at 25 °C/1 atmosphere yielded two new clusters that incorporated ethylene or hydrogen. The reaction with ethylene yielded Sn₄(Ar)₄(C₂H₂)₅ that contained five ethylene moieties bridging four aryl substituted tin atoms and one tin–tin bond. Reaction with H₂ produced a cyclic tin species of formula (Sn(H)Ar)₄, which could also be synthesized by the reaction of {(Ar)Sn(μ‐Cl)}₂ with DIBAL‐H. These reactions represent the first instances of direct reactions of isolable main‐group clusters with ethylene or hydrogen under mild conditions. The products were characterized in the solid state by X‐ray diffraction and IR spectroscopy and in solution by multinuclear NMR and UV/Vis spectroscopies. Density functional theory calculations were performed to explain the reactivity of the cluster.     

The Instability of Ni{N(SiMe3)2}2: A Fifty Year Old Transition Metal Silylamide Mystery

The characterization of the unstable Ni^II bis(silylamide) Ni{N(SiMe₃)₂}₂ ( 1 ), its THF complex Ni{N(SiMe₃)₂}₂(THF) ( 2 ), and the stable bis(pyridine) derivative trans‐Ni{N(SiMe₃)₂}₂(py)₂ ( 3 ), is described. Both 1 and 2 decompose at ca. 25 °C to a tetrameric Ni^I species, [Ni{N(SiMe₃)₂}]₄ ( 4 ), also obtainable from LiN(SiMe₃)₂ and NiCl₂(DME). Experimental and computational data indicate that the instability of 1 is likely due to ease of reduction of Ni^II to Ni^I and the stabilization of 4 through dispersion forces.     

A germanium isocyanide complex featuring (n → π*) back-bonding and its conversion to a hydride/cyanide product via C-H bond activation under mild conditions

Reaction of the diarylgermylene Ge(Ar(Me(6)))(2) [Ar(Me(6)) = C(6)H(3)-2,6-(C(6)H(2)-2,4,6-(CH(3))(3))(2)] with tert-butyl isocyanide gave the Lewis adduct species (Ar(Me(6)))(2)GeCNBu(t), in which the isocyanide ligand displays a decreased C-N stretching frequency consistent with an n → π* back-bonding interaction. Density functional theory confirmed that the HOMO is a Ge-C bonding combination between the lone pair of electrons on the germanium atom and the C-N π* orbital of the isocyanide ligand. The complex undergoes facile C-H bond activation to produce a new diarylgermanium hydride/cyanide species and isobutene via heterolytic cleavage of the N-Bu(t) bond.     

Trapping and Reactivity of a Molecular Aluminium Oxide Ion

Aluminium oxides constitute an important class of inorganic compound that are widely exploited in the chemical industry as catalysts and catalyst supports. Due to the tendency for such systems to aggregate via Al‐O‐Al bridges, the synthesis of well‐defined, soluble, molecular models for these materials is challenging. Here we show that reactions of the potassium aluminyl complex K₂[( NON )Al]₂ ( NON =4,5‐bis(2,6‐diiso‐propylanilido)‐2,7‐di‐tert‐butyl‐9,9‐dimethylxanthene) with CO₂, PhNCO and N₂O all proceed via a common aluminium oxide intermediate. This highly reactive species can be trapped by coordination of a THF molecule as the anionic oxide complex [( NON )AlO(THF)]^?, which features discrete Al?O bonds and dimerizes in the solid state via weak O???K interactions. This species reacts with a range of small molecules including N₂O (to give a hyponitrite ([N₂O₂]^2?) complex) and H₂, the latter offering an unequivocal example of heterolytic E?H bond cleavage across a main group M?O bond.     

Comparison Between Two Different Synthetic Routes of Pyrrolidinium Functional Polymeric Ionic Liquids

Summary: Two separate synthetic routes of preparation of new pyrrolidinium-based polymeric ionic liquids were compared. The first method utilized the modification of a commercial poly(diallyldimethylammonium) chloride via a direct anion exchange with several anions. The second route involved the anion exchange leading to several diallyldimethylammonium ionic liquid monomers having different anions and a subsequent polymerization. The latter method is particularly interesting for attaining tunable copolymers according to the desired properties of PILs. Both methods successfully resulted in ionic liquid polymers that are finding their way in a wide range of emerging applications.     

Ex Situ Prepared Antimony Film Electrode for Electrochemical Stripping Measurement of Heavy Metal Ions

The antimony film electrode (SbFE) was prepared ex situ for anodic and adsorptive stripping voltammetric measurement of selected heavy metal ions. The electrode revealed good linearity for Cd(II) and Pb(II) in a nondeaerated solution of 0.01 M HCl in the examined concentration range from 25 to 80 μg L^?1 with limits of detection of 1.1 μg L^?1 for Cd(II) and 0.3 μg L^?1 for Pb(II) and an excellent reproducibility. The preplated SbFE was also preliminary tested for measuring low levels of Ni(II) using adsorptive stripping voltammetry exhibiting good linearity and sensitivity in combination with only a 30 s deposition step.     

An empirical study of hybrid genetic algorithms for the set covering problem

The purpose of this paper is to explore the computational performance of several hybrid algorithms that are extensions of a basic genetic algorithm (GA) approach for solving the set covering problem (SCP). We start by making several enhancements to a GA for the SCP that was proposed by Beasley and Chu. Next, several hybrid solution approaches are introduced that combine the GA with various local neighbourhood search approaches, with a form of the greedy randomized adaptive search procedure, and with an estimation of distribution algorithms approach. Using Beasley's library of SCPs extensive computational results are generated for the hybrid solution approaches defined in this paper. Statistical analyses of the results are performed.     

Infrared studies of chain folding in polymers. VII. Amylose

Studies of chain folding in amylose employing spectroscopic techniques have led to an assignment of the 1295-cm^?1 band to a unique fold conformation. Irregular folds, present in single crystals, are regularized to the unique fold conformation during annealing. Annealing of solution-cast films, which initially contain a small amount of regular folding, increases the amount of regular folds. Swelling of these annealed films with water vapor destroys this unique folded conformation.     

Miniaturized universal imaging device using fluidic lens

We report the achievement of a highly versatile imager consisting of a tunable fluidic lens with a wide tuning range and three fixed lenses. The device has a volume of less than 1 cm(3) and a short total track length of 12.5 cm. It can function as a regular camera with an ultrawide autofocusing range and as a microscope with 3 microm resolution.     

Using a Facility Location Algorithm to Determine Optimum Cast Bloom Lengths

The dimensions of a bloom, which is a rectangular piece of steel, are critical for efficiently and effectively rolling the bloom into a finished structural shape (I-beam) for sale to the customer. To achieve maximum productivity and yield, the bloom size (thickness, width and length) to be rolled on a finishing mill into a structural shape must be determined by steel deformation experts. Suppose, for a particular finishing mill, these ‘rolled' blooms are all produced from a ‘cast' bloom of the same cross-section but with many different lengths. It is necessary to consolidate the many ‘cast' bloom length-metallurgical grade combinations to a number that can be managed by the casting operation and bloom stockyard without significantly impacting productivity and yield. An uncapacitated facility location problem formulation and algorithm were used to solve this problem. The way in which this approach was used to solve a real-world application is discussed.