Halide Abstraction Competes with Oxidative Addition in the Reactions of Aryl Halides with [Ni(PMen Ph(3-n) )4 ]

Ignacio Funes-Ardoiz; David J Nelson; Feliu Maseras

doi:10.1002/chem.201702331

Halide Abstraction Competes with Oxidative Addition in the Reactions of Aryl Halides with [Ni(PMe_n Ph_(3-n) )₄ ]

Chemistry. 2017 Nov 27;23(66):16728-16733. doi: 10.1002/chem.201702331. Epub 2017 Nov 20.

Authors

Ignacio Funes-Ardoiz¹, David J Nelson², Feliu Maseras^{1

3}

Affiliations

¹ Institute of Chemical Research of Catalonia, The Barcelona Institute of Science and Technology, Avgda. Països Catalans 16, 43007, Tarragona, Spain.
² WestCHEM Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street, Glasgow, G1 1XL, UK.
³ Departament de Química, Universitat Autònoma de Barcelona, 08193, Bellaterra, Catalonia, Spain).

Abstract

Density functional theory (DFT) calculations have been used to study the oxidative addition of aryl halides to complexes of the type [Ni(PMe_n Ph_(3-n) )₄ ], revealing the crucial role of an open-shell singlet transition state for halide abstraction. The formation of Ni^I versus Ni^II has been rationalised through the study of three different pathways: (i) halide abstraction by [Ni(PMe_n Ph_(3-n) )₃ ], via an open-shell singlet transition state; (ii) S_N 2-type oxidative addition to [Ni(PMe_n Ph_(3-n) )₃ ], followed by phosphine dissociation; and (iii) oxidative addition to [Ni(PMe_n Ph_(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 Ni^I and Ni^II when the PEt₃ complex is used. Importantly, [Ni(PMe_n Ph_(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.

Keywords: density functional calculations; electron transfer; homogeneous catalysis; ligand effects; nickel.