The decarbonylation of saturated aldehydes by the ruthenium–diethylphenylphosphine complex, tri-µ-chloro-hexakis(diethylphenylphosphine)diruthenium chloride

Abstract

The complex [Ru₂Cl₃(Et₂PhP)₆]⁺Cl^– abstracts a carbonyl group from saturated aldehydes to give RuCl₂(CO)(Et₂PhP)₃. With acetaldehyde the other product is methane. With propanol and butanal the hydrocarbons formed comprise the alkane and the alkane derived from the alkyl chain: the alcohol corresponding to the aldehyde is also observed as a reaction product. This system differs from the decarbonylation of aldehydes by RhCl(Ph₃P)₃ in which, under similar conditions, the hydrocarbon formed is predominantly the alkane. The difference is further illustrated by the reactions of the ruthenium and rhodium complexes with the deuteriated aldehydes C₂H₅CDO and CD₃CH₂CHO. Whereas the rhodium complex leads to C₂H₅D and CD₃CH₃ respectively, supporting published evidence of an intramolecular transfer (with respect to one molecule of aldehyde) of the aldehydic hydrogen to the alkyl group, the ruthenium system gives rise to a variety of deuteriated hydrocarbons showing labilisation of both α-and β-hydrogen atoms. No evidence for free-radical participation has been obtained for the ruthenium system, for which possible reaction mechanisms are discussed: participation of a 3π-ketyl system provides an attractive rationalisation of the exchange observations.