ピリジルフェニル配位子をもつ9族金属錯体上でのアルキンの酸素酸化および関連反応

概要

Transition-metal-mediated transformation of alkynes provides a useful synthetic tool in organic chemistry. Especially, the metal-catalyzed oxygenation of alkynes to the corresponding diketones have drawn notable attention. For instance, Lo has reported the catalytic transformation of alkynes to the 1,2-diketone derivatives via a coordinatively unsaturated Ru(II) alkynylvinyl complex.

1 However, the reactivity of such 16-electron alkynylvinyl complexes still remains to be investigated. In the course of our investigation into the vinylidene rearrangement of internal alkynes at a cationic Ir(III) pyridylphenyl complex [Cp*Ir(ppy-F4)]+ (ppy-F4 = 2,3,4,5-tetrafluoro-6-pyridylphenyl), we have observed a competition between vinylidene rearrangement and 1,2-insertion of the alkynes.2 Importantly, it was revealed that the fluorine substituents on the ppy ligand strongly favor the vinylidene formation. On the contrary, when 1,4-diferrocenyl-1,3-butadiyne was used as a substrate, selective 1,2-insertion proceeded to give the alkynylvinyl complex. In this study, the author investigated the reactivity of such alkynylvinyl complexes toward various oxidants. Effects of the metal center (Ir, Rh) and the fluorine substituents on the oxidation were studied.

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