Abstract
Nickel catalysis has recently emerged as an important addition to the suite of transition metal-catalysed C-H bond functionalization methods. Here we report density functional theory calculations to elucidate the mechanism of Ni(II)-catalysed C–H arylation with a diaryliodonium salt or a phenyliodide. The effect of the choice of oxidant on the order of oxidative addition and C–H bond cleavage is investigated. When the active catalyst is oxidized by the diaryliodonium salt oxidant, C–H bond cleavage occurs to give an alkyl-aryl-Ni(IV) species. Conversely, the relatively weak oxidant phenyliodide leads to an alternative reaction sequence. The active catalyst first undergoes C–H bond cleavage, followed by oxidative addition of the phenyliodide to give a Ni(IV) species. Frontier molecular orbital analysis demonstrates that the reaction sequence of oxidative addition and C–H bond cleavage is determined by the unoccupied Caryl–I bond antibonding orbital level of the oxidant.
Highlights
Nickel catalysis has recently emerged as an important addition to the suite of transition metal-catalysed C-H bond functionalization methods
It is widely held that oxidative addition occurs immediately after C–H bond cleavage in transition-metal catalysed C–H bond functionalization reactions[41], the order of these two steps is still not certain
Our prior work has shown that the use of strong oxidants may change the reaction order of the C–H cleavage and oxidative addition steps in Rh-catalysed C–H bond functionalization reactions
Summary
Nickel catalysis has recently emerged as an important addition to the suite of transition metal-catalysed C-H bond functionalization methods. Chatani’s group reported two series of Ni(II)-catalysed arylation reactions involving C–H bonds in aliphatic amides (Fig. 1)[39,40] In these reactions, a strongly oxidizing diaryliodonium salt (Fig. 1a) or a relatively weakly oxidizing aryl halide (Fig. 1b) is used as an efficient aryl source. In addition to the proposed mechanism, five subsequent processes are involved in the catalytic cycle of the aforementioned reactions: These include coordination of the directing group, C–H bond cleavage, oxidative addition, reductive elimination, and protonation. It is widely held that oxidative addition occurs immediately after C–H bond cleavage in transition-metal catalysed C–H bond functionalization reactions[41], the order of these two steps is still not certain. The sequence of these two steps could potentially affect the mechanism of the following steps due to the change in the oxidation state of the metal
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