Sustainable Knowledge-Driven Approaches in Transition-Metal-Catalyzed Transformations

The sustainable synthesis of relevant scaffolds for their use in the pharmaceutical, agrochemical, and materials sectors constitutes one of the most urgent challenges that the chemical community needs to overcome. In this context, the development of innovative and more efficient catalytic processes based on a fundamental understanding of the underlying reaction mechanisms remains a largely unresolved challenge for academic and industrial chemists. Herein, selected examples of computational and experimental knowledge-driven approaches for the rational design of transition-metal-catalyzed transformations are discussed.

Cobalt(ii)-catalyzed regioselective C-H halogenation of anilides

A cobalt-catalyzed regioselective C-H halogenation methodology is reported herein. The highlight of this work is the highly selective C-H functionalization of anilides, which results in high-yielding, versatile, and practical halogenated products. Thereby, brominations, chlorinations and iodinations of many electron-rich and electron-deficient anilides were achieved in a highly selective fashion. Mechanistic studies with respect to the pathway of the reaction are also described.

Recent advances in cobalt-catalysed C–H functionalizations

Ready availability, low cost and low toxicity of cobalt salts have redirected the attention of researchers away from noble metals, such as Pd, Rh, and Ir, towards Co in the field of C–H functionalisation.

Synthesis of 1-naphthols via Cp*Co(iii)-catalyzed C–H activation and cyclization of sulfoxonium ylides with alkynes

A highly practical synthesis of 1-naphthols was developed via Cp*Co(iii)-catalyzed C–H activation and cyclization between sulfoxonium ylides and alkynes.

Co-catalyzed ortho-C–H functionalization/annulation of arenes and alkenes with alkynylsilanes: access to isoquinolone and pyridone motifs

A method for cobalt-catalyzed ortho-C–H functionalization annulation of arenes and alkenes with alkynylsilanes assisted by 8-aminoquinolyl auxiliary has been described. Alkynylsilanes were employed as the coupling partners to react with a broad range of benzamides and acrylamides, affording the corresponding isoquinolone and pyridone derivatives in moderate to high yields. It is worth noting that the silyl group in the final products can be retained or removed by switching the reaction conditions.

A method for cobalt-catalyzed ortho-C–H functionalization annulation of arenes and alkenes with alkynylsilanes assisted by 8-aminoquinolyl auxiliary.

Cobalt(iii)-catalyzed C–H amidation of weakly coordinating sulfoxonium ylides and α-benzoylketene dithioacetals

Cobalt(iii)-catalyzed mild C–H amidation of weakly coordinating sulfoxonium ylides and α-benzoylketene dithioacetals has been realized.

Cobalt-catalyzed cross-dehydrogenative coupling between N-(2-pyridyl) and free indoles for the synthesis of unsymmetrical 2,2′-biindoles

Cobalt-catalyzed cross-dehydrogenative coupling of N-(2-pyridyl) indoles with free indoles for the construction of unsymmetrical 2,2′-biindoles is developed.

Cp*CoIII-catalyzed formal [4+2] cycloaddition of benzamides to afford quinazolinone derivatives

A Cp*Co^III-catalyzed arene C–H bond amidation/annulation of benzamides was developed to afford quinazolinone derivatives in one-pot with high yields and broad substrate scope.

C–H and N–H bond annulation of aryl amides with unactivated olefins by merging cobalt(iii) and photoredox catalysis

A mild, environment-friendly protocol has been developed to carry out the [4+2] annulation of aryl amides with unactivated olefins.

Recent Advances on Mechanistic Studies on C–H Activation Catalyzed by Base Metals

During the last ten years, base metals have become very attractive to the organometallic and catalytic community on activation of C-H bonds for their catalytic functionalization. In contrast to the statement that base metals differ on their mode of action most of the manuscripts mistakenly rely on well-studied mechanisms for precious metals while proposing plausible mechanisms. Consequently, few literature examples are found where a thorough mechanistic investigation have been conducted with strong support either by theoretical calculations or experimentation. Therefore, we consider of highly scientific interest reviewing the last advances on mechanistic studies on Fe, Co and Mn on C-H functionalization in order to get a deep insight on how these systems could be handle to either enhance their catalytic activity or to study their own systems in a similar systematic fashion. Thus, in this review we try to cover the most insightful articles for mechanistic studies on C-H activation catalyzed by Fe, Co and Mn based on kinetic and competition experiments, stoichiometric reactions, isolation of intermediates and theoretical calculations.

A challenging redox neutral Cp*Co(III)-catalysed alkylation of acetanilides with 3-buten-2-one: synthesis and key insights into the mechanism through DFT calculations

Traditional, established palladium cross-coupling procedures are widely applied in complex molecule synthesis; however, there is a significant disadvantage in the requirement for pre-functionalised substrates (commonly halides/triflates). Direct C–H activation protocols provide the opportunity for a novel approach to synthesis, although this field is still in its relative infancy and often transferability between substrate classes remains unresolved and limitations not fully understood. This study focuses on the translation of an established Cp*Co(III)-catalysed alkylation of benzamides to related acetanilides using 3-buten-2-one as coupling partner. The developed procedure provides a wide substrate scope in terms of substituted acetanilides, although the optimised conditions were found to be more forcing than those for the corresponding benzamide substrates. Interestingly, density functional theory (DFT) studies reveal that the major impediment in the mechanism is not the C–H activation step, but instead and unexpectedly, effective competition with more stable compounds (resting states) not involved in the catalytic cycle.

Weinreb Amide Directed Versatile C-H Bond Functionalization under (η5 -Pentamethylcyclopentadienyl)cobalt(III) Catalysis

The (η⁵ -pentamethylcyclopentadienyl)cobalt(III) (Cp*Co^III )-catalyzed C-H bond functionalization of aromatic, heteroaromatic, and α,β-unsaturated Weinreb amides was explored. C-H allylation reactions with the use of allyl carbonate and a perfluoroalkene, oxidative alkenylation reactions with the use of ethyl acrylate, iodination reactions with the use of N-iodosuccinimide, and amidation reactions with the use of dioxazolones were catalyzed by Cp*Co(CO)I₂ in the presence of a cationic Ag salt and AgOAc to afford various synthetically useful building blocks. Mechanistic studies of the C-H allylation disclosed that the C-H activation step was rate determining and virtually irreversible.

Mechanistic insights into the SN2-type reactivity of aryl-Co(iii) masked-carbenes for C-C bond forming transformations

Herein we describe the synthesis and characterization of a family of C-metalated aryl-Co(iii) enolates, which can be considered as masked-carbenes, using diazoacetates as coupling partners. These species have been proved to be necessary intermediates in the C(sp2)-C(sp3) bond forming event to obtain cyclic amides, taming the elusive Co(iii)-carbene species. The scope of diazoacetates has been exhaustively examined, varying the nature of the ester and the α-substitution, and a clear preference for electron-poor carbene precursors is observed. Exhaustive experimental and theoretical studies indicate that an unprecedented intramolecular SN2-type process governs the formation of the newly formed C-C bond. Furthermore, the key role of several Lewis acids as carboxylate-activating reagents is further explored by DFT calculations.

Cobalt(iii)-catalysed C–H allylation with vinylaziridines

A cobalt-catalysed C–H allylation of aromatic and heteroaromatic compounds with vinylaziridines is described.

Site-selective C–H bond carbonylation with CO2 and cobalt-catalysis

Utilization of anthropogenic greenhouse gas CO₂ for catalytic C–C bond formation via conversion to essentially valuable C1 synthons like CO is very challenging.

Cp*Co(iii)-catalysed selective alkylation of C–H bonds of arenes and heteroarenes with α-diazocarbonyl compounds

Cp*Co(iii)-catalysed selective alkylation of directed C–H bonds of arenes and heteroarenes has been accomplished employing donor–acceptor carbenes, derived from α-diazocarbonyl compounds.

Isolation of Cp*CoIII -Alkenyl Intermediate in Efficient Cobalt-Catalyzed C-H Alkenylation with Alkynes

A general and efficient procedure for C-H alkenylation of arenes with a broad substrate scope catalyzed by Cp*Co^III was demonstrated with alkynes. A highly selective mono-alkenylation and sequential bis-C-H bond functionalization was displayed to exemplify the versatility of the cobalt catalyst. Isolation of cationic Cp*Co^III -alkenyl intermediate was achieved under identical catalytic conditions to further establish the proposed pathway.