Gram-scale synthesisCarboxylic acidsAcceptorless dehydrogenative coupling (ADC)N-heterocyclic carbene-Ru (NHC-Ru)Ultralow loadingTRANSITION-METAL-COMPLEXESFREE AEROBIC OXIDATIONRECYCLABLE CATALYSTSELECTIVE OXIDATIONRUTHENIUM CATALYSTWATEREFFICIENTLIGANDSALTSCONVERSION