Effect of Chelate Ring Size on the Rate of Hydride Transfer from CpRu(P−P)H (P−P = Chelating Diphosphine) to an Iminium Cation

The rate constants for hydride transfer from CpRu(P−P)H (P−P = bis(diphenylphosphino)methane (dppm), bis(diphenylphosphino)ethane (dppe), bis(diphenylphosphino)benzene
(dpbz), or bis(diphenylphosphino)propane (dppp)) to 1-(1-phenylethylidene)pyrrolidinium
tetrafluoroborate have been measured. The bite angles of the hydride complexes CpRu(dppm)H, CpRu(dppe)H, CpRu(dpbz)H, and CpRu(dppb)H (dppb = bis(diphenylphosphino)butane) have been determined by X-ray diffraction. Hydride transfer is faster when the
chelate ring of the diphosphine is smaller (i.e., CpRu(dppm)H > CpRu(dppe)H ≈ CpRu(dpbz)H > CpRu(dppp)H ≫ CpRu(dppb)H). Boiling CpRu(PPh3)2Cl with dpbz in benzene or
toluene results in the formation of [CpRu(PPh3)(η2-dpbz)]Cl as well as CpRu(dpbz)Cl.