The reaction mechanism of ester hydrogenation catalyzed by a bidentate aminophosphine ligated manganese catalyst was studied by DFT calculations. Particular emphasize was placed on the role of the alkoxide base additives. The presence of such basic promoters as KO`Bu can improve the catalyst activity by lowering the activation barriers of H-2 dissociation as well as the hydrogenation step. The promoting effect of (KOBu)-Bu-t on H-2 activation is much stronger than that of tert-butoxides with other alkali metals, which is crucial for the catalyst regeneration from the deactivated Mn-alkoxide species in the resting state. (C) 2018 The Authors. Published by Elsevier Inc.