Structures and thermochemistry of ions formed by methane chemical ionization of Fe(CO)₅. Site of protonation and determination of FeH and FeCO 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 chemical calculations. The value of the proton affinity of Fe(CO) 5 was measured by high‐pressure mass spectrometry to be 857 kJ mol −1 . The FeCO bond dissociation energies for HFe(CO) n + ( n = 1–5) were measured by energy‐variable low‐energy collisional activation mass spectrometry. The Fe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 unsaturated species HFe(CO) n + ( n = 3, 4) formed in exothermic proton‐transfer reactions with Fe(CO) 5 form adducts with CH 4 . Adducts between C 2 H 5 + or C 3 H 5 + and Fe(CO) n are observed. These adducts are probably formed in direct reactions between the respective carbocations and Fe(CO) 5 .