Cobalt-Catalyzed Coupling of Aryl Chlorides with Aryl Boron Esters Activated by Alkoxides

Abstract

The cobalt-catalyzed Suzuki biaryl cross-coupling of aryl chloride substrates with aryl boron reagents, activated with more commonly used bases, remained a significant unmet challenge in the race to replace platinum group metal catalysts with Earth-abundant metal alternatives. We now show that this highly desirable process can be realized using alkoxide bases, provided the right counterion is employed, strict stoichiometric control of the base is maintained with respect to the aryl boron reagent, and the correct boron ester is selected. Potassium tert-butoxide works well, but any excess of the base first inhibits and then poisons the catalyst. Lithium tert-butoxide performs very poorly, while even catalytic amounts of lithium additives also poison the catalyst. Meanwhile, a neopentane diol-based boron ester is required for best performance. As well as delivering this sought-after transformation, we have undertaken detailed mechanistic and computational investigations to probe the possible mechanism of the reaction and help explain the unexpected experimental observations.

Remote Editing of Stacked Aromatic Assemblies for Heteroannular C−H Functionalization by a Palladium Switch between Aromatic Rings

“…The observed first order in metal catalyst suggests that only one palladium center is involved in the rate‐determining transition state in the model reaction [43] . The 0.7 order in aldehyde ( 1 ) and 0.9 order in olefin (acrylic acid cyclohexyl ester) indicate their pivotal roles either in the rate‐determining step or an equilibrium before this step [44] . The noninteger orders indicate a complex rate law for this reaction [45] .…”

Cobalt–N-Heterocyclic Carbene Complexes in Catalysis

“…In 2021, Bedford and co-workers reported another approach to cobalt−NHC-catalyzed Suzuki cross-coupling of aryl chlorides with aryl boronic esters to access biaryl motifs, where the organoboron nucleophile is activated by alkoxides (Scheme 14). 87 This reaction employs a catalytic amount of CoCl 2 (5 mol %), IPr•HCl (5 mol %), and 1.5 equiv of KO t Bu in THF as a solvent at 60 °C. The comparison between different alkoxide bases in this reaction showed that KO t Bu was superior to its counterparts (K > Na > Li).…”

Cobalt-Catalyzed C(sp2)–C(sp3) Suzuki–Miyaura Cross-Coupling Enabled by Well-Defined Precatalysts with L,X-Type Ligands

“…Examples of cobalt-catalyzed C­(sp 2 )–C­(sp 2 ) cross-coupling with organoboron nucleophiles have been reported using select neutral ligands, including bis­(phosphino)­pyridine pincers, terpyridine chelates, and aryl-substituted N-heterocyclic carbenes (Scheme A). , The understanding of ligand-to-metal complexation has significant implications on the reproducibility of a cross-coupling reaction and demonstrates the inherent difficulty in cross-coupling reaction development. More broadly, understanding catalytically relevant oxidation states, the nature of the active species, and redox cycles in cobalt-catalyzed cross-coupling lags behind iron- and nickel-catalyzed variants. , …”