THERMODYNAMIC ACIDITIES AND HOMOLYTIC METAL-HYDROGEN BOND-ENERGIES OF GROUP-8 PROTONATED DECAMETHYLMETALLOCENES CP-ASTERISK(2)MH(+) (M=RU, OS)

The first thermodynamic acidities and homolytic metal-hydrogen bond dissociation energies (BDE) of metal-protonated metallocenes in solution are reported. The pK(a) of Cp*2OsH+ in acetonitrile has been determined as 9.9 +/- 0.1 from proton-transfer equilibrium measurements. For Cp*2RuH+, the pK(a) has been estimated as 4.3 on the assumption that pK(a) differences in acetonitrile are straight-forwardly related to differences in the reported heats of protonation of Cp*Os-2 and Cp*Ru-2 in 1,2-dichloroethane. The pK(a) data are used in conjunction with reversible oxidation potential data for the metallocenes to obtain metal-hydrogen BDE values of 284 kJ mol(-1) for Cp*2RuH+ and 298 kJ mol(-1) for Cp*2OsH+ respectively. The BDE value for Cp*2RuH+ is essentially equal to that of Cp(2)RuH(+) in the gas phase.