Developments in Cp*Co^III‐Catalyzed C−H Bond Functionalizations

Abstract

Transition-metal-catalyzed CÀ H bond functionalization has emerged as a powerful tool in contemporary organic synthesis. In this aspect, precious metal-based high-valent catalysts have been extensively studied. In the past decade, earth-abundant high-valent Cp*Co(III)-catalysts have emerged as a promising alternative to the expensive transition metals, providing unique selectivity and reactivity. In this Minireview, we summarized important progresses in the area of Cp*Co (III)-catalyzed CÀ H bond functionalization until 2017.[a] Mr. . Alkylation of CÀ H bonds with activated alkene. Scheme 3. Alkylation of CÀ H bonds with activated alkene. Scheme 4. Alkylation of CÀ H bonds with maleimides.Scheme 5. Alkylation of CÀ H bonds of (hetero)arene with maleimide. Scheme 6. Alkylation of CÀ H bonds with unactivated alkenes. Scheme 7. Allylation of CÀ H bonds with allyl carbonates. . Allylation of CÀ H bonds with allyl acetate. Scheme 9. Allylation of CÀ H bonds of arenes with allyl carbonates. Scheme 10. Allylation of CÀ H bonds with allyl alcohol. Scheme 11. Cobalt catalyzed allylation using allyl alcohol. Scheme 12. Cobalt catalyzed allylation with activated allylating reagent. . Cobalt catalyzed selective addition of C2À H bond to C=N bond. Scheme 18. Cobalt catalyzed selective addition of CÀ H bond to isocyanate. Scheme 19. Cobalt(III)-catalyzed aryl and alkenyl CÀ H aminocarbonylation. Scheme 20. Cobalt catalyzed hydroarylation to ketenimines. Scheme 21. Cobalt catalyzed synthesis of pyrroloindolones. Scheme 22. Cobalt catalyzed alkenylation through hydroarylation to alkyne. Co(III)-catalyzed alkenylation. Scheme 24. Cobalt catalyzed alkenylation of heterocyclic moiety. Scheme 25. Cp*Co III -Catalyzed branch-selective hydroarylation of alkynes. Scheme 26. Cobalt catalyzed C(sp 3 )À H alkenylation. . Cobalt(III)-catalyzed amidation with dioxazolone. Scheme 40. Mechanism of cobalt catalyzed amidation with dioxazolone. Scheme 41. Cobalt(III)-catalyzed CÀ H bond amidation using dioxazolone.

Fate of Cobaltacycles in Cp*Co-Mediated C–H Bond Functionalization Catalysis: Cobaltacycles May Collapse upon Oxidation via Co(IV) Species

“…If in specific cases the endo migration of a hydrido ligand to Cp* has been reported in the case of a bis-pyridine chelate of Rh­(III), the literature is rather silent on occurrences of explicit reactions of the Cp* ligand with {κ N ,κ C } − heterochelating ligands in metallacycles . This issue has been overlooked in most reports dealing with the use of Cp*Co-based catalysts in aromatic C–H bond functionalizations employing redox cocatalysts where cobaltacycles are central intermediates. , One can find a rare report on the metal-templated collapse of a metallacycle of a CpNi II complex reported by Ustinyuk et al, where an azo-benzene-based nickelacycle undergoes interligand condensation and metal decoordination under oxidative conditions, affording a new organic extended aromatic product (eq ). It is probably because of the scarcity of similar reports that Cp*-bound metallacycles of group 9 metals in the +I and +III formal oxidation states are frequently considered as structurally viable candidate catalysts. , A report by Mayer et al outlined that the two-electron oxidation of Cp*Ir metallacycles by PhI­(OAc) 2 only affects the Cp* ligand in the case of a methyl-Ir­(III) complex, while other chloro- and iodo-Ir­(III) complexes are left untouched.…”

Synthesis of 7-Amido Indolines by Cp*Co(III)-Catalyzed C–H Bond Amidation

“…As part of our research program on the development of transition-metal-catalyzed C–H activation, we recently reported Co­(II)-catalyzed C–H amination. − In fact, cobalt catalyst has received extensive attention because of its abundant reserves on the earth and its unique reactivities . Among them, the high-valent Cp*Co­(III) catalysts, initially proposed by Matsunaga and Kanai, have received widespread concern . On the basis of previous progress, − , we hypothesize that cobalt metal is extremely beneficial for the construction of C–N bonds, and a similar strategy could be followed to devise a Cp*Co­(III)-catalyzed amination of indolines.…”

Oxidative coupling of primary amines to imines catalyzed by CoCl2·6H2O

“…As an earth-abundant, non-toxic and low-cost metal, cobalt has been extensively used as a catalyst in organic syntheses for different reaction systems, such as the industry-scale Fischer-Tropsch process, [27,28] hydroformylation of olefins, [29] hydrogenation, hydroboration, hydrosilylation, [30] and C-H bond functionalization. [31][32][33] Except for a few cobalt complexes, [34][35][36] the cobalt salts are rarely used for the catalytic oxidative coupling of amines.…”