A Rationally Designed Iron(II) Catalyst for C(sp³)−C(sp²) and C(sp³)−C(sp³) Suzuki–Miyaura Cross‐Coupling

Abstract

Despite the paramount importance of the Suzuki‐Miyaura coupling (SMC) in academia and industry, and the great promise of iron to offer sustainable catalysis, iron‐catalyzed SMC involving sp3‐hybridized partners is still in its infancy. We herein report the development of a versatile, well‐defined electron‐deficient anilido‐aldimine iron(II) catalyst. This catalyst effectively performed C(sp3)‐C(sp2) and C(sp3)‐C(sp3) SMC of alkyl halide electrophiles and (hetero)aryl boronic ester and alkyl borane nucleophiles respectively, in the presence of a lithium amide base. These couplings operated under mild reaction conditions and displayed wide functional group compatibility including various medicinally relevant N‐, O‐ and S‐based heterocycles. They also tolerated primary, secondary and tertiary alkyl halides (Br, Cl, I), electron‐neutral, ‐rich and ‐poor boronic esters and primary and secondary alkyl boranes. Our methodology could be directly and efficiently applied to synthesize key intermediates relevant to pharmaceuticals and a potential drug candidate. For C(sp3)‐C(sp2) couplings, radical probe experiments militated in favor of a carbon‐centered radical derived from the electrophile. At the same time, reactions run with a pre‐formed activated boron nucleophile coupled to competition experiments supported the involvement of neutral, rather than an anionic, (hetero)aryl boronic ester in the key transmetalation step.