Weakly Coordinated Cobaltacycles: Trapping Catalytically Competent Intermediates in Cp*Co^IIICatalysis

Abstract

Herein, we disclose the synthesis of metallacyclic Cp*CoIII complexes containing weakly chelating functional groups. We have employed these compounds not only as an exceptional platform for accessing some of the most widely invoked transient intermediates in C−H functionalization processes but also as competent catalysts in different Cp*Co‐catalyzed transformations, including a benchmark coupling reaction.

Making Base-Assisted C–H Bond Activation by Cp*Co(III) Effective: A Noncovalent Interaction-Inclusive Theoretical Insight and Experimental Validation

“…The condensation of alkyne with metallacycles 122-126 is a well established process that has recently been ported to Cp*Co(III) catalysis by the groups of Zhu, 54 Cheng 11 and Perez-Temprano. 53,55,56,127 In the latter's reports particularly, the outlying feature of this catalytic process is the putative electrophilic activation of the C-H bond of the main heterocyclic substrate by [Cp*Co(MeCN)3] + . Given the accessibility of [Cp*CoI2]2 and its great temperature and air stability, several attempts to achieve the condensation of diphenylacetylene with 2-phpyH were undertaken in this study so as to figure out whether an auxiliary base could be beneficial.…”

“…It was found that one way to reduce this barrier with Ni(II) was to replace the auxiliary base and ligand, i.e the acetato, by a more basic one, i.e an acetamidato, which abates the repulsive C-H-to-metal electrostatic burden. 49 We now decided to test experimentally the conclusions drawn from the theoretical study of the Ni(II)/Pd(II) model dyad to the CMD mechanism-promoted cyclometallation reaction by focussing our interest on the Cp*Co(III) system, having in scope that a good part of the recent applications of Cp*Co(III) catalysts 17,55,56 to C-H bond functionalization apparently proceed by a different mechanism, i.e via the electrophilic activation 57 of the C-H bond. Recent reports tend indeed to priviledge the electrophilic pathway 58,59 even though in some cases the formal formulation of the mechanism makes the distinction with the CMD 16,60,61 one rather difficult.…”

Insertion of BH3 into a Cobalt–Aryl Bond: Synthetic Routes to Arylborohydride and Borane-Amino Hydride Complexes

“…The solid-state structure of the oxidized complex was determined by X-ray diffraction, which established a framework of [Cp*Co­(THF)­(2-Ph 2 PC 6 H 4 )] + containing a THF solvent molecule as a ligand (Figure S32). Addition of H 3 B·THF into the solution of [ 1 -THF] + gave 2 + unambiguously, as indicated by the 31 P and 11 B NMR spectra.…”

Traceless Directing Groups in Sustainable Metal-Catalyzed C–H Activation

“…Under the optimized conditions (Scheme 4), authors investigated the substrate scope, firstly, in regard of alkynes and found that aryl substituted terminal alkynes bearing either electron-withdrawing or -donating groups on various positions of the aromatic ring afforded products in high yields (38)(39)(40)(41)(42). Moreover, terminal alkynes with aromatic substituents like naphthyl, pyrene, and heterocycles led to high yields (43)(44)(45)(46), while terminal aliphatic substituted alkynes resulted in low to high yields (47)(48)(49)(50)(51). There were only a few examples for internal alkynes with yields being low to moderate (52,53).…”

“…Transition metals can temporarily coordinate to these specific sites on the starting materials, thus leading to the formation of key intermediates that would not form otherwise. The formation of thermodynamically favored 5-and 6-membered rings, along with the kinetic lability of 3d n ions, can then provide energetically advantageous reaction pathways towards the desired product [49][50][51][52]. The directing groups can be categorized, either by their structure (e.g., denticity, identity of the coordinating atoms and moieties), or by their utilization strategy.…”