Decomposition reactions of cationic ruthenium formyl complexes
Abstract
trans-[Ru(CHO)(CO)(dppe)2][SbF6](dppe = Ph2PCH2CH2PPh2) decomposes in CH2Cl2 with first-order kinetics (t½= 9.25 min, k= 11 × 10–4 s–1) to give cis-[RuH(CO)(dppe)2][SbF6] which subsequently isomerises to the trans isomer (t½≃ 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].