Abstract
The Ni-catalysed hydrogenolysis and cross-coupling of aryl ethers has emerged as a
powerful synthetic tool to transform inert phenol-derived electrophiles into functionalised
aromatic molecules. This has attracted significant interest due to its potential to
convert the lignin fraction of biomass into chemical feedstocks, or to enable orthogonal
reactivity and late-stage synthetic modification. Although the scope of nucleophiles
employed, and hence the C–C and C–heteroatom bonds that can be forged, has expanded
significantly since Wenkert’s seminal work in 1979, mechanistic understanding on how
these reactions operate is still uncertain since the comparatively inert Caryl–O bond of aryl ethers challenge the involvement of classical mechanisms involving
direct oxidative addition to Ni(0). In this review, we document the different mechanisms
that have been proposed in the Ni-catalysed hydrogenolysis and cross-coupling of aryl
ethers. These include: (i) direct oxidative addition; (ii) Lewis acid assisted C–O
bond cleavage; (iii) anionic nickelates, and; (iv) Ni(I) intermediates. Experimental
and theoretical investigations by numerous research groups have generated a pool of
knowledge that will undoubtedly facilitate future discoveries in the development of
novel Ni-catalysed transformations of aryl ethers.
1 Introduction
2 Direct Oxidative Addition
3 Hydrogenolysis of Aryl Ethers
4 Lewis Acid Assisted C–O Bond Cleavage
5 Anionic Nickelates
6 Ni(I) Intermediates
7 The ‘Naphthalene Problem’
8 Conclusions and Outlook
Key words
nickel - catalysis - cross-coupling - mechanism - phenol electrophiles
