Evidence for a 1,2-shift mechanism for the rearrangement of σ-cyclopentadienyl compounds of iron, ruthenium, and copper

Abstract

The low-temperature ¹H n.m.r.spectra of the new compounds (π-C₅H₅)Ru(CO)₂(σ-C₅H₄R)(R = H or Me) have been studied and those of (π-C₅H₅)Fe(CO)₂(σ-C₅H₅) and (σ-C₅H₅)CuPEt₃ have been re-examined. Satellite lines due to coupling to ¹³C were observed in the spectra of the compounds (π-C₅H₅)M(CO)₂(σ-C₅H₅)(M = Fe or Ru) by spectrum accumulation at low temperature. The results indicate that in each of the three compounds with an unsubstituted σ-cyclopentadienyl ring the metal migrates round this ring by a sequence of 1,2-shifts. For the compounds (π-C₅H₅)M(CO)₂(σ-C₅H₅)(M = Fe or Ru) the activation energies for this process were found to be 8·5 ± 0·8 and 9·6 ± 1·0 kcal. mole^–1 respectively. Migration of the metal atom round the σ-bonded ring also occurs in (π-C₅H₅)Ru(CO)₂(σ-C₅H₄Me) and this is discussed.