Regioselective Hydroboration of N-Heteroarenes Catalyzed by a PCNHCP Mn(I) Pincer Complex

Abstract Regioselective dearomative hydroboration of N-heteroarenes provides direct access to partially saturated azacycles of high synthetic value. Herein, we report the highly 1,2-selective hydroboration of pyridines and quinolines catalyzed by a well-defined PCNHCP-supported Mn(I)-hydride. In contrast to previously reported metal–ligand cooperative manganese systems, this strong-field Mn catalyst operates via a noncooperative pathway and exhibits distinct regio- and chemoselectivity profiles. A range of substituted pyridines and fused heteroarenes undergo selective 1,2-dearomatization under mild conditions. Competitive kinetic isotope effect (KIE) experiments (k H/k D ≈ 1.4) suggest involvement of B–H cleavage in the turnover-limiting step, which is further discussed in this report.