Recent advances in the chemistry of 1,1’-bis(ortho-carborane)

Chemistry of 1,1'-bis(ortho-carborane) is rapidly developing during the last years when convenient method of itssynthesis was elaborated. Here we review the recent progress in this field with main imphasis on synthesis of 1,1'-bis(ortho-carborane) based transition metal complexes and heterocycles

Analysis of Arc Processes in Multi-chamber Arrester for Lightning Protection at High-voltage Overhead Power Lines

Nowadays multi-chamber arresters are widely distributed as devices of lightning protection of overhead power lines. A mathematical modelling of processes in the discharge chamber of multichamber arrester is necessary to carry out in order to improve its breaking capacity. A three-dimensional mathematical transient model of thermal, gas-dynamic and electromagnetic processes taking place in the discharge chamber of multi-chamber arrester is presented in the article. Basic assumptions, model equations, a computational domain and the boundary conditions are described. Plasma turbulence is taken into account. The results of the calculation i.e. distributions of plasma temperature and overpressure in the discharge chamber at different time points are shown. The analysis of the results was carried out. It is shown that the presence of cavities in the electrodes design promotes electric arc extinction in the discharge chamber of multi-chamber arrester

Lightning Protection of Electric Power Overhead Distribution Lines by Long-Flashover Arresters in Russia

A simple and effective method for lightning protection of power overhead distribution lines by long flashover arresters (LFAs) is presented. Even large lightning currents do not pose any threat to these arresters because the discharge develops in the air and not inside the device. LFAs, which are based on the creeping discharge effect, increase the lightning flashover length significantly and thus eliminate Power Arc Follow (PAF). To protect a line against induced overvoltages, a single arrester should be mounted on a pole. To protect a line against direct lightning strokes, LFA-M arresters should be mounted in parallel with each insulator. For covered-conductor overhead lines (CCL) using conductors with three-layer insulation a new lightning protection approach is suggested, involving use of antenna-type long flashover arresters whose essential component is the protected conductor itself. The essence of antennatype long flashover arresters (LFA-A) is that the arrester which is connected to the antenna gets flashed over well before the lightning leader comes in immediate contact with the line. The toroid-shaped antenna made of a metal tube is mounted on the covered conductor’s surface midway between the protector’s edge and the piercing clamp with the help of the toroid fixation unit. As the lightning leader progresses from a thunderstorm cloud to the CCL a high potential gets induced on the LFA antenna. A voltage drop that develops between the electrode and the zero-potential conductor core gives rise to development of a creeping discharge. Even before the lightning leader hits the line the creeping discharge channel flashes over the covered conductor’s surface Thereby the conductor insulation get bypassed by the discharge channel and thus protected against puncture. LFA’s main applications and field experience are presented

Unprecedented flexibility of the 1,1′-bis(o-carborane) ligand:catalytically-active species stabilised by B-agostic B–H⇀Ru interactions

The compound (p-cymene)Ru[(C2B10H10)2], an effective Lewis acid catalyst, is the precursor to a number of products in which the 1,1′-bis(o-carborane) unit displays an unprecedented range of ligating modes.</p

H2 activation using the first 1:1:1 hetero-tri(aryl)borane

The novel 1:1:1 hetero-tri(aryl)borane (pentafluorophenyl){3,5-bis(trifluoromethyl)phenyl}(pentachlorophenyl)borane has been synthesised and structurally characterised. This has been show to act as the Lewis acidic component in FLPs for the heterolytic cleavage of H2 with three Lewis bases

Exploring structural and electronic effects in three isomers of tris{bis(trifluoromethyl)phenyl}borane: Towards the combined electrochemical-frustrated Lewis pair activation of H2

Three structural isomers of tris{bis(trifluoromethyl)phenyl}borane have been studied as the acidic com- ponent of frustrated Lewis pairs. While the 3,5-substituted isomer is already known to heterolytically cleave H2 to generate a bridging-hydride; ortho-substituents in the 2,4- and 2,5-isomers quench such reactivity through electron donation into the vacant boron pz orbital and steric blocking of the boron centre; as shown by electrochemical, structural and computational studies. Electrochemical studies of the corresponding borohydrides identify that the two-electron oxidation of terminal-hydrides occurs at more positive potentials than observed for [HB(C6F5)3]−, while the bridging-hydride oxidizes at a higher poten- tial still, comparable to that of free H2

Novel B(Ar')2(Ar'') hetero-tri(aryl)boranes: a systematic study of Lewis acidity

A series of homo- and hetero-tri(aryl)boranes incorporating pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl, and pentachlorophenyl groups, four of which are novel species, have been studied as the acidic component of frustrated Lewis pairs for the heterolytic cleavage of H2. Under mild conditions eight of these will cleave H2; the rate of cleavage depending on both the electrophilicity of the borane and the steric bulk around the boron atom. Electrochemical studies allow comparisons of the electrophilicity with spectroscopic measurements of Lewis acidity for different series of boranes. Discrepancies in the correlation between these two types of measurements, combined with structural characterisation of each borane, reveal that the twist of the aryl rings with respect to the boron-centred trigonal plane is significant from both a steric and electronic perspective, and is an important consideration in the design of tri(aryl)boranes as Lewis acids

New outcomes of Lewis base addition to diboranes(4): electronic effects override strong steric disincentives

Two surprising new outcomes of the reaction of Lewis bases with dihalodiboranes(4) are presented, including sp2–sp3 diboranes in which the Lewis base unit is bound to a highly sterically congested boron atom, and a rearranged double base adduct. The results provide a fuller understanding of the reactivity of diboranes, a poorly-understood class of molecule of critical importance to synthetic organic chemistry