Pentafluorophenyl substituted boranes and borates are important as co-catalysts in metallocene-based industrial processes for the homogeneous polymerization of olefins. Although first prepared in the early 1960s, the remarkable properties of tris(pentafluorophenyl)borane have only recently been exploited for applications in catalysis. Spurred by these developments, the related compounds bis(pentafluorophenyl)borane and salts of the tetrakis(pentafluorophenyl)borate anion have also found application in olefin polymerization and other fields. In this article, we trace the rise of pentafluorophenyl boron compounds from curiosities to important commodities.

This tutorial review elucidates the fundamental concepts necessary for an understanding of the unique structures and reactivities of tellurium compounds.

The well-known tendency of sulfur to catenate is exemplified by an extensive series of polysulfide dianions [S_n]²⁻ (n = 2–9) and related radical monoanions [S_n]˙⁻. The dianions can be isolated as crystalline salts with appropriate cations and structurally and spectroscopically characterized. Although the smaller radical monoanions may be stabilized in zeolitic matrices, they are usually formed in solution via disproportionation or partial dissociation of the dianions as well as by electrochemical reduction of elemental sulfur. An understanding of the fundamental chemistry of these homoatomic species is key to unravelling their behaviour in a broad variety of chemical environments. This review will critically evaluate the techniques used to characterize polysulfide dianions and radical anions both in solution and in the solid state, i.e. Raman, UV-visible, EPR, NMR and X-ray absorption spectroscopy, X-ray crystallography, mass spectrometry, chromatography and high-level quantum-chemical calculations. This is followed by a discussion of recent advances in areas in which these anionic sulfur species play a crucial role, viz. alkali-metal–sulfur batteries, organic syntheses, biological chemistry, geochemical processes including metal transport, coordination complexes, atmospheric chemistry and materials science.

The trisulfur radical anion [S₃]˙⁻ is well-known from inorganic chemistry textbooks as the blue chromophore in ultramarine blues in which this highly reactive species is trapped in a zeolitic framework. Recent findings have revealed that [S₃]˙⁻ has a multi-faceted role in a variety of media, including alkali metal–sulfur batteries, aqueous solutions at high temperatures and pressures, and ionic liquids; it has also been used to detect trace amounts of water in organic solvents. This tutorial review illustrates how various physical techniques are used to identify a reactive species in solution and shows how elucidation of electronic structures can be used to explain spectroscopic and structural properties. Examples of the function of [S₃]˙⁻ in materials science, electrochemistry, analytical chemistry and geochemistry are used to illustrate the widespread influence of this fundamentally important triatomic sulfur species.

This critical review covers significant recent advances in the chemistry of pnictogen(III)–nitrogen ring systems, also known as cyclopnict(III)azanes. The synthetic methodologies and reactions of the heavier pnictogen systems are compared with the well-developed chemistry of cyclophosph(III)azanes. Particular attention is focused on ring-oligomerization processes and the use of four-membered E₂N₂ rings as building blocks for the synthesis of macrocyclic molecules. Main-group element and transition-metal complexes are also discussed (95 references).