Kinetic isotope effects on metal to nitrogen proton transfers

The kinetic isotope effects kH/kD are about 2.5 at 20 degree centigrade for Ru-N proton transfers and 4.2 at 25 degree centigrade for a W-N proton transfers. The study determines the rate constants for proton transfer from the radical cation CpRu(PPh3)2H+ to pyrrolidine and piperidine by cyclic voltammetry. The proposed three models explain different reaction rates of isotopic molecules, but the existing theory does not rationalize any of these models.