One-hydrogen polarization in hydroformylation promoted by platinum-tin and iridium carbonyl complexes: a new type of parahydrogen-induced effect

The first use of parahydrogen-induced polarization (PHIP) in hydroformylation is described including a novel one-hydrogen polarization (oneH-PHIP) in the product RCHO proton. Observed in propanal formed in the reaction of trans-PtCl(COEt)(PPh3)2 + SnCl2 under parahydrogen, oneH-PHIP was examined using the model hydroformylation catalyst Ir(COEt)(CO)2(dppe) (dppe = bis(diphenylphosphino)ethane) that yields the characterized acyl dihydride IrH2(COEt)(CO)(dppe). It is found that oneH-PHIP occurs as a consequence of second-order effects in the acyl dihydride species coupled with stereospecific reductive elimination of aldehyde. Thus, even though hydrogen transfer to substrate in hydroformylation is nonpairwise, parahydrogen effects prove useful mechanistically.