Partial Loss of Deuterium Label in Wilkinson's Catalyst Promoted Decarbonylations of Deuterioaldehydes

Article abstract of DOI:10.1021/jo00391a023

Decarbonylations of trans-2-phenylcyclopropanedeuteriocarboxaldehyde and cycloheptanedeuteriocarboxaldehyde with Wilkinson's catalyst give phenylcyclopropane and cycloheptane with partial loss of deuterium label.Loss of deuterium label is not a consequence of orthometalation of deuteriotris(triphenylphosphine)rhodium(I), a plausible reactive intermediate, for the loss is observed even when RhCl(P(C6D5)3)3 is used to effect the decarbonylation.Decarbonylations of trans-2-phenylcyclopropanecarboxaldehyde with Wilkinson's catalyst in benzene containing O-deuterioethanolafford d0 and d1 phenylcyclopropane and d0 and d1 aldehyde; neither hydrocarbon product nor recovered aldehyde is deuterium labeled when 1,1-dideuterioethanol is present in the decarbonylation reaction mixture.The hydroxyl hydrogen of ethanol associated with RhCl(P(C6H5)3)3 as normally synthesized, however, is not the hydrogen source: ethanol is not detected by 1H NMR in solutions of the catalyst, loss of deuterium label occurs even when RhCl(PPh3)3 is prepared free of possible contamination by ethanol from 2, and it is seen as well with an alternative ethanol-free decarbonylation catalyst, ClRh(dppp)2.The hydrogen source is water retained in commercial Wilkinson's catalyst.Decarbonylations of deuterioaldehyde in the presence of excess D2O give d1 product with high preservation of label.