Chemistry of boryllithium: synthesis, structure, and reactivity

A series of lithium salts of boryl anion, boryllithiums, were synthesized and characterized by NMR spectroscopy and crystallographic analysis. In addition to the parent boryllithium compound 35a, structural modification of boryllithium, using saturated C-C and benzannulated C=C backbones in the five-membered ring and mesityl groups on the nitrogen atoms, also allowed generation of the corresponding boryllithium. The solid state structures of boryllithium showed that the boron-lithium bond is polarized where the boron atom is anionic in all (35a x DME)(2), 35a x (THF)(2), 35b x (THF)(2), and 35c x (THF)(2) when compared to the structures of hydroborane 38a-c and optimized free boryl anion opt-46a-c. Dissolution of the isolated single crystals of (35a x DME)(2) and 35a x (THF)(2) in THF-d(8) showed that the boron-lithium bond remained in solution and free DME or THF molecules were observed. Temperature-dependent (11)B NMR chemical shift changes of 35a were observed in THF-d(8) or methylcyclohexane-d(14), suggesting a change of chemical shift anisotropy around the boron center. The HOMO of opt-35a x (THF)(2) had a lone pair character on the boron atom, as observed for phenyllithium, whereas the HOMO of hydroborane 38a corresponds to the pi-orbital of the boron-containing five-membered heterocycle. The polarity of the B-Li bond, estimated by AIM analysis, was similar to that of alkyllithium. Boryllithiums 35a and 35b behave as a base or a boron nucleophile in reaction with organic electrophiles via deprotonation, S(N)2-type substitution, halogen-metal exchange or electron-transfer, 1,2-addition to a carbonyl group, and S(N)Ar reaction. In the case of the reaction with CO(2), intramolecular cyclization followed by CO elimination from borylcarboxylate anion and subsequent protonation gave hydroxyboranes 64a and 64b. The characters of the carbonyl groups in the borylcarbonyl compounds 60a, 60b, 61, 62, and 63a, which were obtained from the reaction of boryllithiums 35a and 35b, were investigated by X-ray crystallography, IR, and (13)C NMR spectroscopy to show that the boryl substituent weakened the C=O bond when compared to carbon substituted analogues.     

Copolymerization of Ethylene and Polar Monomers by Using Ni/IzQO Catalysts

The replacement of precious metals in catalysis by earth‐abundant metals is currently one of the urgent challenges for chemists. Whereas palladium‐catalyzed copolymerization of ethylene and polar monomers is a valuable method for the straightforward synthesis of functionalized polyolefins, the corresponding nickel‐based catalysts have suffered from poor thermal tolerance and low molecular weight of the polymers formed. Herein, we report a series of neutral nickel complexes bearing imidazo[1,5‐a]quinolin‐9‐olate‐1‐ylidene (IzQO) ligands. The Ni/IzQO system can catalyze ethylene polymerization at 50–100 °C with reasonable activity in the absence of any cocatalyst, whereas most known nickel‐based catalysts are deactivated at this temperature range. The Ni/IzQO catalyst was successfully applied to the copolymerization of ethylene with allyl monomers to obtain the corresponding copolymers with the highest molecular weight reported for a Ni‐catalyzed system.     

Crystalline Isotactic Polar Polypropylene from the Palladium‐Catalyzed Copolymerization of Propylene and Polar Monomers

Moderately isospecific homopolymerization of propylene and the copolymerization of propylene and polar monomers have been achieved with palladium complexes bearing a phosphine‐sulfonate ligand. Optimization of substituents on the phosphorus atom of the ligand revealed that the presence of bulky alkyl groups (e.g. menthyl) is crucial for the generation of high‐molecular‐weight polypropylenes (M_w≈10⁴), and the substituent at the ortho‐position relative to the sulfonate group influences the molecular weight and isotactic regularity of the obtained polypropylenes. Statistical analysis suggested that the introduction of substituents at the ortho‐position relative to the sulfonate group favors enantiomorphic site control over chain end control in the chain propagation step. The triad isotacticity could be increased to mm=0.55–0.59, with formation of crystalline polar polypropylenes, as supported by the presence of melting points and sharp peaks in the corresponding X‐ray diffraction patterns.     

Anisotropic growth of conducting polymers along heparin-modified surfaces

We have studied the possibility of making biocompatible, conductive patterns on a substrate by controlling the lateral growth rate of conducting polymers upon electropolymerization. Surface modification with heparin was found to enhance the lateral growth of polypyrrole, especially in the presence of dodecylbenzenesulfonate, and thus the micropatterning of heparin around electrodes leads to the formation of polypyrrole patterns.     

Efficient Generation of Microdroplets Using Tail Breakup Induced with Multi-Branch Channels

In recent years, research on the application of microdroplets in the fields of biotechnology and chemistry has made remarkable progress, but the technology for the stable generation of single-micrometer-scale microdroplets has not yet been established. In this paper, we developed an efficient and stable single-micrometer-scale droplet generation device based on the fragmentation of droplet tails, called “tail thread mode”, that appears under moderate flow conditions. This method can efficiently encapsulate microbeads that mimic cells and chemical products in passively generated single-micrometer-scale microdroplets. The device has a simple 2D structure; a T-junction is used for droplet generation; and in the downstream, multi-branch channels are designed for droplet deformation into the tail. Several 1–2 µm droplets were successfully produced by the tail’s fragmentation; this continuous splitting was induced by the branch channels. We examined a wide range of experimental conditions and found the optimal flow rate condition can be reduced to one-tenth compared to the conventional tip-streaming method. A mold was fabricated by simple soft lithography, and a polydimethylsiloxane (PDMS) device was fabricated using the mold. Based on the 15 patterns of experimental conditions and the results, the key factors for the generation of microdroplets in this device were examined. In the most efficient condition, 61.1% of the total droplets generated were smaller than 2 μm.     

Magnetic phase diagram of layered cobalt dioxide LixCoO2

The magnetism of LixCoO2 (LCO), which has a similar structure to NaxCoO2 (NCO), has been investigated by muon-spin spectroscopy and susceptibility measurements using samples with x=0.1-1 prepared by an electrochemical reaction. In the x range below 0.75, LCO was found to be Pauli paramagnetic down to 1.8 K, suggesting an intermediate- or weak-coupling regime, although disordered local moments, with volume fractions below approximately 20%, appear at low T for LCO with x > or = 0.5. The phase diagram and interactions of LCO are thus strikingly different from NCO, while the differences cannot be explained simply by structural differences between the two systems.     

Syntheses and properties of triborane(5)s possessing bulky diamino substituents on terminal boron atoms

The present communication reports the chemistry of three linear triborane(5) compounds possessing bulky diamino substituents on the terminal boron atoms. Fluorotriborane 2 was synthesized by a reaction of boryllithium and BF(3)·OEt(2). Halogen exchange reaction of 2 took place by a treatment with ClSiMe(3) to give the corresponding chlorotriborane(5) 3. Addition of silver tetraarylborate to 3 in ether afforded a hydroxylated triborane(5) compound 5 probably via an unstable cationic boron intermediate 4.     

Morphology and Growth of Single Crystals of Isotactic Polypropylene from the Melt

Isolated single crystals of isotactic polypropylene (iPP) grown from the melt were studied by optical microscopy and atomic force microscopy (AFM). The single crystals had a well-known rectangular shape when crystallized at high temperatures (T_c) above 155°C. The width increased with decreasing T_c, and the shape became hexagonal below 130°C. The single crystals were sectored with thickness difference between them. The growth rate along the a*-axis, G_a*, agreed well with the growth rate of spherulites, as expected. G_a* had two inflection points on the plots against (TΔT)^?1. The lower temperature inflection corresponds to the regime II-III transition, and the higher temperature one is accompanied by an inflection of the growth rate in the b-axis direction, G_b, which has been measured for the first time. The inflection of G_b at the lower inflection temperature of G_a* was much smaller than that of G_a* and may not exist. The crystals are basically surrounded with flat surfaces and no indications of kinetic roughening in the regime III were recognized in the AFM images. The inflections of G_a* and G_b caused a complicated shape change of the aspect ratio, having a minimum at around 135°C.