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(O2CR)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(O2CR)2(p-cymene)] and [Ru(t-BuCN)5(H2O)](BF4)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.