STRUCTURES AND THERMOCHEMISTRY OF IONS FORMED BY METHANE CHEMICAL-IONIZATION OF FE(CO)5 - SITE OF PROTONATION AND DETERMINATION OF FE-H ANDFE-CO BOND-DISSOCIATION ENERGIES OF HFE(CO)(N)+ IONS

High-energy collisional activation mass spectrometry of HFe(CO)5+ ions shows that Fe(CO)5 is protonated on the iron atom rather than on one of the ligands. This finding is supported by ab initio quantum chemica l calculations. The value of the proton affinity of Fe(CO)5 was measur ed by high-pressure mass spectrometry to be 857 kJ mol-1. The Fe-CO bo nd dissociation energies for HFe(CO)n+ (n = 1-5) were measured by ener gy-variable low-energy collisional activation mass spectrometry. The F e-H bond dissociation energies in HFe(CO)n+ ions were also determined. A synergistic effect on the strengths of the Fe-H and Fe-CO bonds in HFe(CO)+ is noticed. It is demonstrated that the electronically unsatu rated species HFe(CO)n+ (n = 3, 4) formed in exothermic proton-transfe r reactions with Fe(CO)5 form adducts with CH4. Adducts between C2H5or C3H5+ and Fe(CO)n are observed. These adducts are probably formed i n direct reactions between the respective carbocations and Fe(CO)5.