Decomposition reactions of cationic ruthenium formyl complexes

Abstract

trans-[Ru(CHO)(CO)(dppe)₂][SbF₆](dppe = Ph₂PCH₂CH₂PPh₂) decomposes in CH₂Cl₂ with first-order kinetics (t_½= 9.25 min, k= 11 × 10^–4 s^–1) to give cis-[RuH(CO)(dppe)₂][SbF₆] which subsequently isomerises to the trans isomer (t_½≃ 72 h). A deuterium isotope effect of 1.8 on the decomposition reaction is interpreted as being primary, the low value being attributable to a three-membered cyclic transition state and movement of the oxygen atom during the rate-determining step. A predissociation of a phosphorus atom of a dppe ligand is followed by rate-determining hydride migration for the decomposition, or fluxionality of the five-membered intermediate for the isomerisation. If the isomerisation of cis-[RuD(CO)(dppe)₂][SbF₆] is carried out at low temperature, significant H/D exchange of the deuteride and both phenyl and methylene hydrogen atoms of the dppe ligand is observed. cis-[Ru(CHO)(CO)(dppm)₂][SbF₆](dppm = Ph₂PCH₂PPh₂) gives [RuH(CO)₂(dppm)₂]-[SbF₆] with a unidentate dppm ligand but chelation occurs on photolysis in CH₂Cl₂ to give trans-[RuCl(CO)(dppm)₂][SbF₆]via trans-[RuH(CO)(dppm)₂][SbF₆].