Control of Product Selectivity by a Styrene Additive in Ruthenium-Catalyzed C−H Arylation

A unique effect of styrene additive on product selectivity was observed for RuH(2)(CO)(PPh(3))(3)-catalyzed C-H arylation of acetophenone derivatives bearing two ortho C-H bonds. Without styrene, the C-H arylation with arylboronates gives diarylation products as the major products throughout the reaction, but the use of styrene as an additive switches the product selectivity and leads to selective formation of monoarylation products.