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

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.

SUBMITTER: Funes-Ardoiz I 

PROVIDER: S-EPMC5725734 | biostudies-literature | 2017 Nov

REPOSITORIES: biostudies-literature