Synthesis and Reactivity of Organometallic Intermediates Relevant to Cobalt-Catalyzed Hydroformylation

Intermediates relevant to cobalt-catalyzed alkene hydroformylation have been isolated and evaluated in fundamental organometallic transformations relevant to aldehyde formation. The 18-electron (R,R)-((iPr)DuPhos)Co(CO)(2)H has been structurally characterized, and it promotes exclusive hydrogenation of styrene in the presence of 50 bar of H-2/CO gas (1:1) at 100 degrees C. Deuterium-labeling studies established reversible 2,1-insertion of styrene into the Co-D bond of (R,R)-((iPr)DuPhos)Co(CO)(2)D. Whereas rapid beta-hydrogen elimination from cobalt alkyls occurred under an N-2 atmosphere, alkylation of (R,R)-((iPr)DuPhos)Co(CO)(2)Cl in the presence of CO enabled the interception of (R,R)-((iPr)DuPhos)Co(CO)(2)C(O)CH2CH2Ph, which upon hydrogenolysis under 4 atm H-2 produced the corresponding aldehyde and cobalt hydride, demonstrating the feasibility of elementary steps in hydroformylation. Both the hydride and chloride derivatives, (X=H-, Cl-), underwent exchange with free (CO)-C-13. Under reduced pressure, (R,R)-((iPr)DuPhos)Co(CO)(2)Cl underwent CO dissociation to form (R,R)-((iPr)DuPhos)Co(CO)Cl.