Supported Lanthanum Borohydride Catalyzes CH Borylation Inside Zeolite Micropores

The zeolite‐supported lanthanide La(BH4)x‐HY30 catalyzes C−H borylation of benzene with pinacolborane (HBpin), providing a complementary approach to precious, late transition metal‐catalyzed borylations. The reactive catalytic species are generated from La grafted at the Brønsted acid sites (BAS) in micropores of the zeolite, whereas silanoate‐ and aluminoate‐grafted sites are inactive under the reaction conditions. During typical catalytic borylations, conversion to phenyl pinacolborane (PhBpin) is zero‐order in HBpin concentration. A turnover number (TON) of 167 is accessed by capping external silanols, selectively grafting at BAS sites, and adding HBpin slowly to the reaction. Borylation of unactivated C−H bonds in benzene with pinacolborane (HBpin), catalyzed by a zeolite‐supported lanthanum borohydride, provides the first demonstration of a promising alternative to late‐metal catalysts. High turnovers and yields are achieved by selective grafting of lanthanum at Brønsted acid sites and limiting HBpin degradation. C−H bond activation, likely via the σ‐bond metathesis mechanism, is probably the turnover limiting step.