Structures and thermochemistry of ions formed by methane chemical ionization of Fe(CO)5. Site of protonation and determination of FeH and FeCO bond dissociation energies of HFe(CO)n+ ions

Abstract

AbstractHigh‐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 CH4. Adducts between C2H5+ or C3H5+ and Fe(CO)n are observed. These adducts are probably formed in direct reactions between the respective carbocations and Fe(CO)5.