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σ-Complexes of transition metals are key intermediates in metal-mediated bond activation, but have traditionally been isolable only when chelating or when one of the participating atoms is hydrogen. Here, a complex is isolated with an unsupported borirene ligand bound not through the unsaturated C=C bond, but exclusively via a B–C single bond.

Mild, controllable homocatenation of many elements is a considerable challenge, usually due to their low homonuclear σ-bond enthalpy. This is particularly difficult for boron, despite its high homonuclear σ -bond enthalpy. The controllable metal-templated catenation of four boron atoms is now demonstrated — a step towards oligomers of monovalent boron and polyboranes.

The coupling of carbon monoxide molecules is an attractive prospect for organic synthesis, but only a few metal complexes are known to do this. A compound containing a boron–boron triple bond has now been shown to induce the coupling of four CO molecules, through an intermediate with a single CO.

While transition metals commonly coordinate and substitute hydrocarbons, such reactivity is rare for first-row p-block elements. Now it has been shown that a monovalent boron system can coordinate olefins and mediate their liberation and functionalization through borylene–olefin π complexes.

Among the first-row p-block elements that can form neutral triple-bonded species (boron, carbon, nitrogen and oxygen), all combinations have been realized except that of boron and carbon. Here the synthesis of a neutral, uncoordinated boryne is described, closing the remaining gap in neutral first-row p-block compounds with triple bonds.

A combination of catalytic asymmetric diboration of terminal alkenes and Suzuki–Miyaura cross-coupling has been exploited in the synthesis of a variety of important medicinal agents. The process overcomes a number of problems in the application of these important catalytic processes.

Transition metal–ligand fragments are often able to bind and release several carbon monoxide molecules, such as the catalysts used in industrial-scale acetic acid synthesis and the active sites of hydrogenase enzymes, but main-group elements have never shown an ability to bind more than one carbon monoxide molecule; here a boron-based compound stable to moisture and air is synthesized and shown to contain multiple carbon monoxide units bound to the central boron atom.

Replicating the seminal reactions of transition metals with p-block species is often very challenging. Here, the authors present a step-for-step main-group replica of the historical Fischer carbene synthesis, providing bora-Fischer carbene species.

Attempts to bend and twist multiple bonds in order to alter their reactivities have thus far been met with only modest success. Here, Braunschweig and colleagues isolate double-bond-containing boron-based species and their 90°-twisted diradical analogs, thanks to their stabilization with Lewis basic units.

A form of π backbonding is observed in a π-diborene complex of platinum, and confirmed by calculations. This interaction partially fills a bonding π orbital on the diborene ligand, strengthening the B–B bond. That π backbonding can strengthen bonds overturns ingrained notions that π backbonding is exclusively a bond-weakening phenomenon.

Two neutral compounds containing a zero-valent s-block metal, beryllium, have now been isolated and fully characterized. Structural characterization, supported by calculations, show that these brightly coloured complexes adopt a closed-shell singlet configuration with a Be(0) metal centre and an unusually strong three-centre two-electron π-bond across the C–Be–C unit.

The vast majority of species capable of converting dinitrogen to ammonia rely on transition metals. Now, a boron compound has been shown to mediate the one-pot binding, cleavage and reduction of N₂ to ammonium salts under mild conditions through a complex cascade mechanism involving multiple reduction–protonation sequences.

The activation of very inert small molecules generally requires highly reactive activating species, but the high energy of these species makes their regeneration, and thus also catalytic turnover of the reaction, difficult to achieve. Here, the authors highlight the formidable challenge of overcoming the tradeoff between activating power and catalytic turnover in the context of main-group ambiphiles.