Molecular addition compounds. 16. New, highly reactive borane adducts with N,N-dialkyl-tert-alkylamines for hydroboration

Several N,N-diethyl-tert-alkylamines, such as N,N-diethyl-2-methyl-2-butylamine (1, t-PentNEt2), N,N-diethyl-2,3-dimethyl-2-butylamine (2, t-HexNEt2), N,N-diethyl-2,3,3-trimethyl-2-butylamine (3, t-HeptNEt2), and N,N-diethyl-1,1,3,3-tetramethylbutylamine (4, t-OctNEt2) with varying steric bulk around nitrogen (by changing the tert-alkyl group) have been prepared and examined as borane carriers. The complexing ability of these N,N-diethyl-tert-alkylamines with borane decreases in the order: t-BuNEt2 > t-PentNEt2 > t-HeptNEt2 > t-HexNEt2 > or = t-OctNEt2. From these preliminary studies, the more promising tert-octyldialkylamines were selected for detailed studies. The optimum steric bulk around the nitrogen atom was established by comparing various tert-octyldialkylamines containing variable steric requirements for both the alkyl groups. The complexing ability of these amines with borane decreases in the order shown: t-OctNMe2 (5) > t-OctNEtMe (6) > t-OctN-(CH2CH2)2O (7) > t-OctNEt2 (4) > t-OctNBuiMe (8) > t-OctNPr(n)2 (9). The reactivity of the corresponding borane adducts toward 1-octene increases in the reverse order. Among the various tert-octyldialkylamine-boranes prepared and examined, only t-OctNEt2 (4) forms a highly reactive liquid borane adduct, which hydroborates 1-octene in tetrahydrofuran rapidly at room temperature. Accordingly, detailed hydroboration studies with this new, highly reactive amine-borane adduct, t-OctEt2N:BH3 (10) and representative mono-, di-, tri-, and tetra-substituted olefins were carried out at room temperature (22 +/- 3 degrees C) in selected solvents, tetrahydrofuran, dioxane, tert-butyl methyl ether, n-pentane and dichloromethane. Simple unhindered olefins were hydroborated to the trialkylborane stage, whereas hindered olefins were partially hydroborated to the mono or dialkylborane stage. The hydroborations can be carried out conveniently in a variety of solvents. The amine-borane adduct showed enhanced reactivity in dioxane but low reactivity in dichloromethane. The alkylboranes obtained after hydroboration were oxidized with hydrogen peroxide/sodium hydroxide and the product alcohols were obtained in quantitative yields, as established by GC analysis. The carrier amine was recovered by simple acid-base manipulations in good yield and can be readily recycled back to the borane adduct.     

Design of compact two-port dual-band dual-polarized MIMO antenna for CBRS and WLAN sub-6-GHz applications

This communication presents a compact field de-correlation lines integrated dual band with dual-polarized (LP & CP) multiple-input multiple-output (MIMO) antenna for the fifth generation (5G) sub-6-GHz wireless communication systems. Dual working bandwidths, smaller interelement gaps, and superior isolation within the MIMO components are the distinguishing characteristics that give the proposed MIMO system an aspect of novelty. The modeled MIMO antenna has compact configurations of 20 × 21 × 0.8 mm³. The unit cell consists of a microstrip feed line with optimized rectangular slots branches etched from the radiated patch. The MIMO module is generated by the antiparallel replication of a single unit cell. To enhance the isolation, two rectangular slots are incorporated on the patch between the unit elements, which act as field de-correlation lines. The MIMO identity is supported by diversity performance calculations in terms of ECC, DG, and TARC. Simulated and measured counterparts are found in the agreement.     

Iron(III) chloride catalysed three-component Grieco condensation: Synthesis of tetrahydropyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidines/quinazolines

Three-component Grieco condensation reaction of 3-aminopyrazolo[3,4-b]pyridine, formaldehyde/benzaldehyde and electron rich alkenes in presence of iron(III) chloride gave tetrahydropyrido[2′,3′:3,4]pyrazolo[1,5-a]pyrimidines/quinazolines in single pot. The sequence of reactions is formation of di-azadiene in situ and the subsequent regioselective addition of alkenes in aza-Diels Alder type reaction. The structure and stereochemistry of the products were confirmed by spectral data and single crystal X-ray crystallography.     

Dichloroborane-dioxane: an exceptional reagent for the preparation of alkenyl- and alkylboronic acids

Terminal alkynes and alkenes were conveniently hydroborated to the corresponding alkenyl- and alkyldichloroboranes using dichloroborane-dioxane in dichloromethane. These dichloroboranes were hydrolyzed by water to the corresponding alkenyl- and alkylboronic acids in moderate to good yields. With terminal alkenes and alkynes boron was predominantly attached to terminal carbon. Alkynes gave exclusively trans-vinylboronic acids.     

Analysis and numerical simulation for a class of time fractional diffusion equation via tension spline

In this work, we prove the weak and strong convergence of a sequence generated by a modified S-iteration process for finding a common fixed point of two G-nonexpansive mappings in a uniformly convex Banach space with a directed graph. We also give some numerical examples for supporting our main theorem and compare convergence rate between the studied iteration and the Ishikawa iteration.     

An X-ray Radiography Study of the Effect of Thermal Cycling on Damage Evolution in Large-Area Sn-3.5Ag Solder Joints

There is a need for next-generation, high-performance power electronic packages and systems utilizing wide-band-gap devices to operate at high temperatures in automotive and electricity transmission applications. Sn-3.5Ag solder is a candidate for use in such packages with potential maximum operating temperatures of about 200°C. However, there is a need to understand the thermal cycling reliability of Sn-3.5Ag solders subject to such high-temperature operating conditions. The results of a study on the damage evolution occurring in large-area Sn-3.5Ag solder joints between silicon dies and direct bonded copper substrates with Au/Ni-P metallization subject to thermal cycling between 200°C and 5°C are presented in this paper. Interface structure evolution and damage accumulation were followed using high-resolution X-ray radiography, cross-sectional optical and scanning electron microscopies, and X-ray microanalysis in these joints for up to 3000 thermal cycles. Optical and scanning electron microscopy results showed that the stresses introduced by the thermal cycling result in cracking and delamination at the copper–intermetallic compound interface. X-ray microanalysis showed that stresses due to thermal cycling resulted in physical cracking and breakdown of the Ni-P barrier layer, facilitating Cu-Sn interdiffusion. This interdiffusion resulted in the formation of Cu-Sn intermetallic compounds underneath the Ni-P layer, subsequently leading to delamination between the Ni-rich layer and Cu-Sn intermetallic compounds.     

Formation of Coanda jet from sharp-edged swirl nozzle with base plate

Experiments were conducted using tufts and PIV to determine the conditions for which a swirled gas jet issuing from a sharp-edge nozzle, in flush with a base plate, would form a Coanda jet. The flow field was also simulated. The inception of the Coanda jet was observed to be associated with the formation of a recirculation bubble at the nozzle exit. A threshold value of swirl number, which increased monotonically with Reynolds number, was required for the formation of the Coanda jet. The Coanda jet was associated with hysteresis. The flow features and transition from a diverging jet to a Coanda jet are discussed.     

Spectroscopic properties of Er3+ ions in cadmium and alkali cadmium borosulphate glasses

Spectroscopic properties of Er³⁺:CBS (CdSO₄+B₂O₃ and R₂SO₄+CdSO₄+B₂O₃, R₂SO₄=Li₂SO₄.H₂O, Na₂SO₄, K₂SO₄ and Gd₂(SO₄)₃.8H₂O) glasses are reported. The assigned energy level data of Er³⁺(4f ¹¹) in these glasses are analysed in terms of a parametrized model Hamiltonian. The standard deviations of the data fits are between 39 and 47 cm⁻¹ so that the energy level schemes of the Er³⁺(4f ¹¹) ions in borosulphate (CBS) glasses are reasonably well reproduced. Radiative properties for the fluorescent levels of Er³⁺:CBS glasses are determined by using the Judd-Ofelt theory. The potential laser transitions are identified with the help of predicted radiative properties which are compared and discussed with similar results.     

New amine-stabilized deuterated borane-tetrahydrofuran complex (BD3-THF): convenient reagent for deuterium incorporations

Convenient methods for the preparation of BD₃-THF complex were developed. Certain amines stabilize the BD₃-THF for long-term storage. Regioselectivity studies were carried out with the new amine-stabilized BD₃-THF with representative olefins. Hydroboration of olefins provides a convenient tool for making corresponding deuterated alcohols after oxidation.     

Spectroscopic investigations on ZnF2-MO-TeO2 (MO=ZnO, CdO and PbO) glasses doped with chromium ions

Differential scanning calorimetric studies, spectroscopic studies (viz., optical absorption, ESR, infrared spectra) and thermoluminescence studies of ZnF₂-MO-TeO₂ (MO=ZnO, CdO and PbO) glasses doped with different concentrations of chromium ions have been investigated. Results have been analyzed in the light of different oxidation states of chromium ion. The analysis indicates chromium ions mostly exist in Cr³⁺ state in ZT, CT and PT glasses when Cr₂O₃ is present upto 0.1%, 0.2% and 0.3%, respectively; these ions seems to be present in Cr⁶⁺ state that take part network forming positions with CrO₄²⁻ structural groups in all the three glasses when the concentration of Cr₂O₃ is greater than the above quantities. Quenching of thermoluminescence light output of the glasses has been observed with increase in Cr₂O₃ concentration upto 0.1%, 0.2% and 0.3%, respectively in ZT, CT and PT glasses. This has been identified due to the killing effect of Cr³⁺ ions. Further it has also been concluded that ZnF₂-PbO-TeO₂ is more favourable glass network for the presence of large concentration of laser-emitting Cr³⁺ ions, among the three glass series studied.