Rhenium-catalysed reactions in chemical synthesis: selected case studies

This Perspective presents and discusses a selection of examples that reinforce the enabling and distinctive reactivity provided by homogeneous rhenium catalysis in chemical synthesis. Specifically, the ability for lower oxidation...

Decarboxylation-triggered homo-Nazarov cyclization of cyclic enol carbonates catalyzed by rhenium complex

Decarboxylative homo-Nazarov cyclization catalyzed by a Lewis acid was achieved using a cyclic enol carbonate bearing a cyclopropane moiety as a substrate. Various substrates were converted into the corresponding multi-substituted cyclohexenones in good yields via decarboxylation, followed by 6-membered ring formation involving cyclopropane-ring-opening.

Manganese/bipyridine-catalyzed non-directed C(sp3)-H bromination using NBS and TMSN3

A Mn(II)/bipyridine-catalyzed bromination reaction of unactivated aliphatic C(sp³)−H bonds has been developed using N-bromosuccinimide (NBS) as the brominating reagent. The reaction proceeded in moderate-to-good yield, even on a gram scale. The introduced bromine atom can be converted into fluorine and allyl groups.

Mechanistic Insights into Rhenium-Catalyzed Regioselective C-Alkenylation of Phenols with Internal Alkynes

A (μ-aryloxo)rhenium complex was isolated and confirmed as a key precatalyst for rhenium-catalyzed ortho-alkenylation (C-alkenylation) of unprotected phenols with alkynes. The reaction exclusively provided ortho-alkenylphenols; the formation of para or multiply alkenylated phenols and hydrophenoxylation (O-alkenylation) products was not observed. Several mechanistic experiments excluded a classical Friedel-Crafts-type mechanism, leading to the proposed phenolic hydroxyl group assisted electrophilic alkenylation as the most plausible reaction mechanism. For this purpose, the use of rhenium, a metal between the early and late transition metals in the periodic table, was key for the activation of both the soft carbon-carbon triple bond of the alkyne and the hard oxygen atom of the phenol, at the same time. ortho-Selective alkenylation with allenes also provided the corresponding adducts with a substitution pattern different from that obtained by the addition reaction with alkynes.

Tricarbonyl rhenium(i) tetrazolato and N-heterocyclic carbene complexes: versatile visible-light-mediated photoredox catalysts

This study demonstrates that structurally-diverse, photoactive rhenium(i) tricarbonyl complexes can mediate representative atom-transfer radical addition, hydrodehalogenation, and α-amino C–H functionalisation reactions.

Rhenium-catalysed dehydrogenative borylation of primary and secondary C(sp3)–H bonds adjacent to a nitrogen atom

A novel rhenium-catalyzed borylation of C(sp³)–H bonds proceeded in the absence of oxidants, hydrogen acceptors, and external ligands with the generation of H₂ as the sole byproduct.

Tuning coordination modes of pyridine/thioether Schiff base (NNS) ligands to mononuclear manganese carbonyls

Manganese carbonyls are ligated by pyridine/thioether Schiff base (NNS) ligands. Coordination of the thioether-S donor to the Mn(i) center is determined by subtle steric changes at the ligand periphery.