The one-pot tandem hydroformylation-reduction to synthesize alcohols from olefins is in great demand but suffering from low yields, poor selectivity and harsh condition. Herein, 1,10-phenanthroline (L1) modified Ir-catalyst proved to exhibit multiple catalysis in terms of FA dehydrogenation, hydroformylation of olefins, and transfer hydrogenation of aldehydes to accomplish the tandem hydroformylation-transfer hydrogenation of olefins with formic acid (FA) as hydrogen source, as the result of 52-70% yields for the target alcohols and the corresponding formate esters (obtained upon esterification of the alcohol with FA). In this sequence, only the use of FA with trans- and cis-conformers could fulfill the reduction of aldehydes to the alcohols through transfer hydrogenation as well as greatly depress hydrogenation of the olefin, which universally occurred in the high pressured gaseous H-2. Both the in situ FT-IR spectroscopic analysis and the DFT-calculations verified that, over L1-[Ir(COD)Cl](2) catalyst, cis-FA serving as the hydride-ligand was responsible for the efficient dehydrogenation of FA to release H-2 along with CO2, and trans-FA serving as the carbonyl O-containing ligand corresponded to the transfer hydrogenation of the aldehydes to the alcohols under the same catalytic conditions. (C) 2020 Elsevier Inc. All rights reserved.