Water-soluble [RuCKNHC)(L)(eta(6)-arene)] complexes (NHC=bmim=1-butyl-3-methyl-imidazole-2-ylidene; L= tertiary phosphine, such as mtppms, mtppts, pta, pta-Me and pta-Bn; eta(6)-arene = eta(6)-p-cymene) were succesfully applied for the first time as catalysts in hydrodehalogenation of organic halides by hydrogen transfer from aqueous Na-formate with turnover frequencies up to TOF = 112 h(-1) at 80 degrees C. Simultaneous to hydrodehalogenation, aqueous formate was also decomposed to H-2 and HCO3-. In case of [RuCl(bmim)(pta)(eta(6)-p-cymene)]Cl (pta=1,3,5-triaza-7-phosphaadamantane) a reaction mechanism is suggested on basis of kinetic and NMR measurements which accounts for both hydrodehalogenation and formate dehydrogenation and involves [RuH(bmim)(pta)(eta(6)-p-cymene)](+) as the key catalytic species for both cycles. (C) 2016 Elsevier B.V. All rights reserved.