Highly active cationic cobalt bisphosphine hydroformylation catalysts: Be positive!

A new class of highly active cationic cobalt(II) bisphosphine hydroformylation catalysts will be discussed. They are at least a hundred times more active than the known industrial cobalt catalysts: HCo(CO)₄ and HCo(CO)₃(PR₃). These catalysts have the general form: [HCo(CO)_x(P₂)](BF₄), where x = 1-3, and P₂ = chelating bisphosphine. Unlike all other hydroformylation catalysts this new class has higher activity with electron-donating alkylated phosphine ligands. Unlike rhodium hydroformylation catalysts, these catalysts are remarkably resistant to metal-induced phosphine ligand degradation reactions and are capable of extremely high turnover numbers (e.g., > one million). The high activity of these catalysts allow them to operate under far lower temperatures and pressures relative to HCo(CO)₄ and HCo(CO)₃(PR₃). These cationic Co(II) catalysts are very active at alkene isomerization, similar to neutral cobalt(I) hydroformylation catalysts and HRh(CO)₄. They are especially effective at hydroformylating internal branched alkenes to produce linear aldehydes. Comparisons with rhodium phosphine/phosphite catalysts and HCo(CO)₄ will be presented.