The catalytic performance of Co-2 was evaluated with 1-octene as a representative, minimally functionalized alkene. With 4 atm of a 1:1 CO/H2 composition with blue Kessil lamp irradiation (34 W) for 48 hours, a 1:2.1 mixture of 1-nonanol (2a) and n-octane (2b) was obtained (Table , entry 2) with the mass balance of C9 product made up by formate ester (2a'). Because bis(phosphine)cobalt hydrides are effective hydrogenation catalysts upon irradiation with visible light, the relative amount of CO in the syngas mixtures was increased from 50% to 75% (3:1 CO/H2, Table , entry 3), to 90% (9:1 CO/H2, Table , entry 1). CO-rich syngas (9:1 CO/H2) gave the highest selectivity for alcohol 2a suppressing undesired olefin hydrogenation, leaving isomerization as the major competing pathway (Table , entry 1, "standard conditions"). Worth noting is that syngas mixtures in thermal Co-and Rh-catalyzed tandem processes typically contain excess hydrogen to prevent formation of carbonylated metal hydrides (e.g., HCo(CO)4) that show poor activity toward aldehyde reduction as a result of a relatively acidic metal hydride. The bis(phosphine)cobalt hydride precatalyst Co-2 was essential for the desired reactivity given that attempts to generate the catalyst in situ from addition of dcype to Co2(CO)8 furnished alkane 3 as the major product with comparatively low conversion of 1a (Table , entry 5). Combinations of 2 equiv dcype and Co2(CO)8 in toluene generated a diethyl ether-insoluble product with a single sharp resonance at  107.8 in the 31 P NMR spectrum. An FT-IR spectrum recorded in pentane revealed a number of features resembling Co-2 with the exception of a sharp band at 1918 cm -1 , tentatively assigned as the Co(CO)4 -anion. Formation of [(dcype)Co(CO)3][Co(CO)4] likely occurs and is involved in activating H2 in order to generate Co-2. Revisiting the other cobalt hydride precatalysts using optimized conditions still gave poor conversion of starting material as a consequence of rapid dimer formation (entries 10-13). Temperature was found to affect product selectivity: at room temperature, olefin isomerization, yielding 2-octene (4), became the predominant competing reaction (Table , entry 4), whereas hydrogenation was entirely suppressed. In all cases, only the linear isomer of the C1-homologate alcohol (2a) was observed. To our knowledge, this is the only example of a reductive hydroformylation process involving a minimally functionalized alkene (i.e., 1-octene) with exclusive product selectivity. Competing pathways including isomerization can be suppressed by the presence of alkyl groups at the vinylic position. Stanley and coworkers recently employed a class of cationic cobalt(II) catalysts for the hydroformylation of 3,3-dimethylbutene, reporting exceptional activity and selectivity for linear aldehyde (l/b = 58). Having identified conditions for regiocontrolled alcohol synthesis, a variety of feedstock alkenes was subjected to the visible-light-mediated reaction with yields ranging from 44-73%. A series of 6-carbon skeletal isomers including 1-hexene (2c) vinyl cyclobutane (2d), and 3,3-dimethylbutene (2e) illustrates a sensitivity of the cobalt catalyst towards substitution at the α-carbon of terminal alkenes (Table ), with increased substitution suppressing alkene isomerization in favor of hydrogenation as the major competing pathway. Styrenes with electron-withdrawing and donating substituents were tolerated under optimized conditions affording products in 63-78% yield (2f-2h, and 2n). The ability of the catalyst to discriminate between terminal and internal alkenes in the same substrate was demonstrated in the selective reductive hydroformylation of 4-vinyl-cyclohex-1-ene (2i), where the endocyclic olefin was retained in the product alcohol. Alkenes bearing esters (2p, 2r) and alcohols (2q, 2y, 2af) were also tolerated, providing the corresponding alcohol and diol in 34-71% yield.