Cationic Cobalt(II) Bisphosphine Hydroformylation Catalysis: In Situ Spectroscopic and Reaction Studies

HCo(CO)(x)(bisphosphine)](BF4), x = 1-3, is a highly active hydroformylation catalyst system, especially for internal branched alkenes. In situ infrared spectroscopy (IR), electron paramagnetic resonance (EPR), and nuclear magnetic resonance studies support the proposed catalyst formulation. IR studies reveal the formation of a dicationic Co(I) paramagnetic CO-bridged dimer, [Co-2(mu-CO)(2)(CO)(bisphosphine)2](2+), at lower temperatures formed from the reaction of two catalyst complexes via the elimination of H-2. DFT studies indicate a dimer structure with square-pyramidal and tetrahedral cobalt centers. This monomer-dimer equilibrium is analogous to that seen for HCo(CO)(4), reacting to eliminate H-2 and form Co-2(CO)(8). EPR studies on the catalyst show a high-spin (S = 3/2) Co(II) complex. Reaction studies are presented that support the cationic Co(II) bisphosphine catalyst as the catalyst species present in this system and minimize the possible role of neutral Co(I) species, HCo(CO)4 or HCo(CO)(3)(phosphine), as catalysts.

Automated summary

HCo(CO)(x)(bisphosphine)](BF4), x = 1-3, is a highly active hydroformylation catalyst system, especially for internal branched alkenes. In situ spectroscopy studies provide evidence for the formation of a dicationic Co(I) paramagnetic CO-bridged dimer, which is derived from the reaction of two catalyst complexes. DFT studies reveal the structure of the dimer and EPR studies confirm the presence of a high-spin Co(II) complex in the catalyst.