Arene Ruthenium(II) Carboxylates for C─H Alkylations and Arylations at Near Room Temperature

Abstract The long‐term pursuit for more efficient catalysts has stimulated the development of C─H activations under mild reaction conditions, with the overarching goal to improve their user‐friendly nature, selectivity, and synthetic utility. Herein, we report mild C─H alkylations enabled by inexpensive and most user‐friendly ruthenium carboxylate complexes. While these bench‐stable arene ruthenium carboxylate complexes catalyzed direct alkylations under ambient conditions, detailed kinetic studies demonstrated a high catalytic performance for the [Ru(O 2 CR) 2 ( p ‐cymene)] during the steady‐state catalytic process. Thus, temperature‐dependent kinetic Arrenhius‐plot analyses of the ruthenium‐catalyzed C─H alkylation revealed a comparable activation enthalpy for [Ru(O 2 CR) 2 ( p ‐cymene)] and [Ru( t‐ BuCN) 5 (H 2 O)](BF 4 ) 2 , hence, implying entropic factors to be of relevance. The robust arene ruthenium(II) carboxylate‐catalyzed C─H alkylation showed broad versatility under mild reaction conditions with respect to primary, secondary as well as tertiary alkyl bromides in a position‐divergent manner, reflecting a wide tolerance of valuable electrophilic functional groups for late‐stage functionalizations.