C–H Activation/Functionalization Catalyzed by Simple, Well-Defined Low-Valent Cobalt Complexes

Abstract

A facile C-H activation and functionalization of aromatic imines is presented using low-valent cobalt catalysts. Using Co(PMe3)4 as catalyst we have developed an efficient and simple protocol for the C-H/hydroarylation of alkynes with an anti selectivity. Deuterium-labeling experiments, DFT calculations coupled with the use of a well-defined catalyst have for the first time shed light on the elusive black box of cobalt catalyzed C-H functionalization.

Alkene Metalates as Hydrogenation Catalysts

“…Possibly, this diene originated from the dehydrogenation of one cobalt‐bound styrene molecule and the addition of a second cobalt‐bound styrene to the resulting C≡C triple bond. Low‐valent cobalt complexes are known to catalyze related C−H activation reactions …”

“…Low-valent cobaltc omplexes are knowntoc atalyzer elatedC ÀHa ctivation reactions. [36] Finally,w ep robed the unimolecular gas-phaser eactivity of the mass-selected cobaltate complexes. These experiments have the advantage of excluding any interference from dynamic equilibria, counterion, or solvente ffects, which may operate in solution.…”

Synthesis of a Dimeric Base‐Stabilized Cobaltosilylene Complex for Catalytic C−H Bond Functionalization and C−C Bond Formation

“…Subsequent oxidative addition of the ortho ‐C−H bond of arylpyridine to the cobalt center, insertion of alkyne into the Co−H bond and reductive elimination affords a {( E )‐alkenylaryl}‐cobalt complex intermediate ( 2D ). Then, the C=C bond undergoes isomerization from a cis‐ to trans ‐skeleton, resulting in the formation of a ( Z )‐product . In contrast, the rigid skeleton in benzo[ h ]quinoline 3 d may impede effective coordination of the PhC=CPh moiety to the Co center and hence inhibit the cis ‐to‐ trans isomerization, which results in the formation of the ( E )‐product 5 da .…”

“…Then, the C=Cbond undergoes isomerization from a cis-to trans-skeleton, resulting in the formation of a( Z)-product. [12] In contrast, the rigid skeleton in benzo[h]quinoline 3d may impede effective coordination of the PhC= CPh moiety to the Co centera nd hence inhibit the cis-to-trans isomerization,w hichr esults in the formation of the (E)-product 5da.Asimilar situation was found for 4-octyne 4b,i nw hich the sterically hindered propyl substituents may exclude the coordination of the PrC=CPr moiety in a( E)-product (5ab-5db) to the cobalt center, inhibitingt he cis-to-trans isomerization to form a trans-skeleton. Following the above interesting discovery,t he versatile catalytic ability of 2 was furthere valuated towardt ypical Kumadatype coupling reactions between aryl chlorides 6 and the Grignardr eagent 2-mesitylmagnesium bromide 7 ( Table 2).…”

Hydroarylations by cobalt-catalyzed C–H activation

“…In 2015, Petit’s group developed a hydroarylation reaction of internal alkynes with imines using a low-valent cobalt catalyst without reductant or additives (Scheme 10) [52]. The reaction afforded alkenes 13 in excellent yields with anti -selectivity.…”