Ruthenium complexes of 1,4-diazabutadiene ligands with a cis-RuCl2 moiety for catalytic acceptorless dehydrogenation of alcohols: DFT evidence of chemically non-innocent ligand participation.

The acceptorless dehydrogenative coupling (ADC) of primary alcohols to esters by diazabutadiene-coordinated ruthenium compounds is reported. Treatment of cis-Ru(dmso)4Cl2 in acetone at 56 °C with different 1,4-diazabutadienes [p-XC6H4N[double bond, length as m-dash]C(H)(H)C[double bond, length as m-dash]NC6H4X-p; X = H, CH3, OCH3, and Cl; abbreviated as DAB-X], gives trans-Ru[κ2-N,N-DAB-X]2Cl2 as the kinetic product of substitution. Heating these products in o-xylene at 144 °C gives the thermodynamically favored cis-Ru[κ2-N,N-DAB-X]2Cl2 isomers. Electronic structure calculations confirm the greater stability of the cis diastereomer. The molecular structures for each pair of geometric isomers have been determined by X-ray diffraction analyses. Cyclic voltammetry experiments on the complexes show an oxidative response and a reductive response within 0.50 to 0.93 V and -0.76 to -1.24 V vs. SCE respectively. The cis-Ru[κ2-N,N-DAB-X]2Cl2 complexes function as catalyst precursors for the acceptorless dehydrogenative coupling of primary alcohols to H2 and homo- and cross-coupled esters. When 1,4-butanediol and 1,5-pentanediol are employed as substrates, lactones and hydroxyaldehydes are produced as the major dehydrogenation products, while secondary alcohols afforded ketones in excellent yields. The mechanism for the dehydrogenation of benzyl alcohol to benzyl benzoate and H2 using cis-Ru[κ2-N,N-DAB-H]2Cl2 (cis-1) as a catalyst precursor was investigated by DFT calculations. The data support a catalytic cycle that involves the four-coordinate species Ru[κ2-N,N-DAB-H][κ1-N-DAB-H](κ1-OCH2Ph) whose protonated κ1-diazabutadiene moiety functions as a chemically non-innocent ligand that facilitates a ß-hydrogen elimination from the κ1-O-benzoxide ligand to give the corresponding hydride HRu[κ2-N,N-DAB-H][κ1-N-DAB-H](κ2-O,C-benzaldehyde). H2 production follows a Noyori-type elimination to give (H2)Ru[κ2-N,N-DAB-H][κ1-N-DAB-H](κ1-O-benzaldehyde) as an intermediate in the catalytic cycle.

A wideband hybrid combiner design for ITER ion cyclotron radio frequency source.

The high-power radio frequency source for ion cyclotron heating and current drive of ITER tokamak consists of two identical 1.5 MW amplifier chains. These two chains will be combined using a wideband hybrid combiner with adequate coupling flatness, phase balance, return loss, and isolation response to generate 2.5 MW radio frequency (RF) power in the frequency range of 36 to 60 MHz. As part of the in-house development program at ITER-India, a wideband hybrid combiner with coupling flatness and return loss/isolation better than 0.4 and -25 dB, respectively, has been simulated. A detailed analysis for matched load performance of the hybrid combiner for the output power level of 3 MW as well as mismatched load performance for load power of 2.5 MW with voltage standing wave ratio 2.0 and 3.0 MW with voltage standing wave ratio 1.5 has been performed. Based on the simulation, a prototype model was in-house fabricated, and the simulated results have been validated experimentally in splitter and combiner mode. To evaluate performance as a combiner, two solid-state power amplifiers were combined through the prototype combiner for input power levels up to 2.5 kW on matched and mismatched load conditions. In the power splitter experiment, the RF power level up to 1.5 MW from a single amplifier chain was split through the prototype combiner to be dumped in the high power loads in the frequency range of 36 to 60 MHz.

Dual utility of a single diphosphine-ruthenium complex: a precursor for new complexes and, a pre-catalyst for transfer-hydrogenation and Oppenauer oxidation.

The diphosphine-ruthenium complex, [Ru(dppbz)(CO)2Cl2] (dppbz = 1,2-bis(diphenylphosphino)benzene), where the two carbonyls are mutually cis and the two chlorides are trans, has been found to serve as an efficient precursor for the synthesis of new complexes. In [Ru(dppbz)(CO)2Cl2] one of the two carbonyls undergoes facile displacement by neutral monodentate ligands (L) to afford complexes of the type [Ru(dppbz)(CO)(L)Cl2] (L = acetonitrile, 4-picoline and dimethyl sulfoxide). Both the carbonyls in [Ru(dppbz)(CO)2Cl2] are displaced on reaction with another equivalent of dppbz to afford [Ru(dppbz)2Cl2]. The two carbonyls and the two chlorides in [Ru(dppbz)(CO)2Cl2] could be displaced together by chelating mono-anionic bidentate ligands, viz. anions derived from 8-hydroxyquinoline (Hq) and 2-picolinic acid (Hpic) via loss of a proton, to afford the mixed-tris complexes [Ru(dppbz)(q)2] and [Ru(dppbz)(pic)2], respectively. The molecular structures of four selected complexes, viz. [Ru(dppbz)(CO)(dmso)Cl2], [Ru(dppbz)2Cl2], [Ru(dppbz)(q)2] and [Ru(dppbz)(pic)2], have been determined by X-ray crystallography. In dichloromethane solution, all the complexes show intense absorptions in the visible and ultraviolet regions. Cyclic voltammetry on the complexes shows redox responses within 0.71 to -1.24 V vs. SCE. [Ru(dppbz)(CO)2Cl2] has been found to serve as an excellent pre-catalyst for catalytic transfer-hydrogenation and Oppenauer oxidation.

Performance optimization of test facility for coaxial transmission line components based on traveling wave resonator.

As part of development program for a high power co-axial transmission line component test facility, an existing traveling wave resonator based test stand is modified to improve power gain and ring return loss. The 10 dB directional coupler in the earlier test stand is replaced with a 14 dB directional coupler to couple radio frequency power with the ring. To achieve an improved isolation and return loss, the 14 dB directional coupler design is equipped with two broadside strip-lines with a tunable gap between them. Detailed design and optimization of the 14 dB directional coupler with and without the traveling wave resonator setup is performed using a high frequency simulator Computer Simulation Technology Microwave Studio. The low power test of the fabricated directional coupler is performed at several tuning positions to achieve an optimum operating frequency for the traveling wave resonator. Furthermore, after optimization, the maximum power gain of around 18 dB and minimum return loss of about -22 dB inside the ring are obtained. Finally, a preliminary study of the future 3 MW test facility is discussed.

A new diphosphine-carbonyl complex of ruthenium: an efficient precursor for C-C and C-N bond coupling catalysis.

Reaction of 1,2-bis(diphenylphosphino)benzene (dppbz) with [{Ru(CO)2Cl2}n] affords [Ru(dppbz)(CO)2Cl2], where the two carbonyls are mutually cis and the two chlorides are trans. The molecular structure of [Ru(dppbz)(CO)2Cl2], has been determined by X-ray crystallography, and the stability of the different available stereoisomers has been computationally evaluated. [Ru(dppbz)(CO)2Cl2] has been found to serve as an excellent pre-catalyst for catalytic Suzuki-type C-C coupling and Buchwald-type C-N coupling reactions.