Hydroformylation of Fluoro Olefins, R_fch=Ch₂, Catalyzed By Group Viii Transition-metal Catalysts: Crucial Factors for Extremely High Regioselectivity

Hydroformylations of fluoro olefins, trifluoroprop-l-ene (TFP), pentafluorobut-l-ene (PFB), heptafluoropent-l-ene (HPFP), heptadecafluorodec-l-ene (HPDFD), vinyl fluoride (VF), pentafluorostyrene (PFS), and allylpentafluorobenzene (4a), promoted by transition-metal catalysts were studied. Remarkable dependency of the regioselectivity of the reaction on the catalyst metal species (Co, Pt, Ru, and Rh) was found in the reactions of TFP and PFS; e.g., n-aldehyde was obtained with >93% selectivity by a cobalt catalyst whereas iso-aldehyde was obtained with >96% selectivity by a rhodium catalyst for the reaction of TFP. On the contrary, the reaction of VF gave 2-fluoropropanal (2-FPA) exclusively, regardless of the metal catalyst species. The effects of temperature and carbon monoxide pressure on the regioselectivity were investigated. Possible mechanisms for the uniquely regioselective hydroformylations are discussed on the basis of the results obtained, and a mechanism that involves an initial formation of isoalkyl-metal species followed by isomerization to n-alkyl-metal species and/or followed by carbon monoxide insertion to form isoacyl-metal intermediate was proposed to be the one operating in these reactions.