Abstract
Density functional theory (DFT) calculations have been used to study the oxidative addition of aryl halides to complexes of the type [Ni(PMenPh(3−n))4], revealing the crucial role of an open‐shell singlet transition state for halide abstraction. The formation of NiI versus NiII has been rationalised through the study of three different pathways: (i) halide abstraction by [Ni(PMenPh(3−n))3], via an open‐shell singlet transition state; (ii) SN2‐type oxidative addition to [Ni(PMenPh(3−n))3], followed by phosphine dissociation; and (iii) oxidative addition to [Ni(PMenPh(3−n))2]. For the overall reaction between [Ni(PMe3)4], PhCl, and PhI, a microkinetic model was used to show that our results are consistent with the experimentally observed ratios of NiI and NiII when the PEt3 complex is used. Importantly, [Ni(PMenPh(3−n))2] complexes often have little, if any, role in oxidative addition reactions because they are relatively high in energy. The behaviour of [Ni(PR3)4] complexes in catalysis is therefore likely to differ considerably from those based on diphosphine ligands in which two coordinate Ni0 complexes are the key species undergoing oxidative addition.
Highlights
The development of catalytic methods that use abundant, sustainable, and less expensive elements is an area of recent and intense focus
Nickel can catalyse a range of reactions, including: cross-coupling reactions of halide and phenol-derived substrates,[2] rearrangement reactions of unsaturated aliphatic substrates,[3] tandem photocatalysis/cross-coupling reactions,[4,5] and reductive cross-coupling reactions.[6]
Further investigation is essential to fully understand when and why NiI arises, and what its role is in catalysis, because this will have an impact upon the development of nickel-catalysed reactions
Summary
The development of catalytic methods that use abundant, sustainable, and less expensive elements is an area of recent and intense focus. Nickel is one such element that has recently received increased attention.[1] Nickel can catalyse a range of reactions, including: cross-coupling reactions of halide and phenol-derived substrates,[2] rearrangement reactions of unsaturated aliphatic substrates,[3] tandem photocatalysis/cross-coupling reactions,[4,5] and reductive cross-coupling reactions.[6] To fully exploit the catalytic potential of nickel, it is essential to understand the mechanistic aspects of these reactions. Further investigation is essential to fully understand when and why NiI arises, and what its role is in catalysis, because this will have an impact upon the development of nickel-catalysed reactions
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