コバルトやニッケル触媒を用いた有機（擬）ハロゲン化物の還元的化学変換

抄録

Oxidative addition of carbon-halogen bonds to transition metal catalysts is one of the most important elementary reactions in synthetic organic chemistry that catalyzes the conversion of organohalides to organotransition metal intermediates. In particular, palladium catalysts have enabled a variety of carbon-carbon bond formation reactions on numerous carbon skeletons triggered by oxidative addition of organohalides. On the other hand, in recent years, much attention has been paid to investigating new catalytic behaviors of ubiquitous metal catalysts and the development of new catalytic transformations using ubiquitous metal catalysts as an alternative to rare transition metal catalysts. The ubiquitous metal catalysts belonging to the first row of transition metals exhibit a unique redox behavior in which organohalides are oxidatively added to produce high-valent adducts that are converted to low-valent organo-cobalt and -nickel species under reducing conditions. Utilizing the unique redox behavior of the cobalt and nickel catalysts, we have successfully developed stereoselective reductive bifunctionalizations of alkynes consisting of oxidative addition of organohalides, carbometallation, re-oxidative addition, and reductive elimination. Furthermore, we have discovered the excellent nucleophilicity and transmetalation ability of the low-valent organo-cobalt and -nickel species, and have developed reductive functionalization of organohalides, such as stannylation and borylation. On the other hand, monovalent planar cobalt complexes, whose structures are immobilized by planar tetradentate ligands, serve as excellent metallonucleophiles. We have exploited the nucleophilic properties of them to achieve a variety of reductive cross-coupling reactions with alkyl tosylates as ubiquitous carbon sources.