Unusual kinetics of gas-phase proton transfer to Mn(CO)5−and Re(CO)5−

Abstract

Abstract Rate constants for gas-phase proton transfer to Mn(CO)5 −, Re(CO)6 − and Cl− from reference acids and metal hydrides are determined. Proton-transfer efficiencies to Mn(CO)5 − are small, and less than the efficiencies for proton transfer to Cl−; proton-transfer efficiencies to Re(CO)6 − are larger than those for Mn(CO)5 −, but still generally less than for transfer to Cl−. Proton-transfer efficiencies to Mn(CO)5 − and Re(CO)5 − are substantially more dependent on the nature of the proton donor (e.g. metal hydride versus oxy-acid). The thermoneutral proton transfer between Mn(CO)5 − and 13CO-labelled HMn(CO)6 is particularly inefficient, occurring only in about 1 in 100 collisions. The results are discussed in view of evidence for a short lifetime of the collision complex, and the effects of electronic and structural reorganization of Mn(CO)5 − and Re(CO)5 −, including loss of fluxionality of the metal species, which occur on protonation.