A Crystalline Iron Terminal Methylidene

Iron methylidene species are alleged intermediates in the Fischer-Tropsch process and in olefin cyclopropanation, yet iron methylidene complexes with unambiguously established molecular and electronic structures remain elusive. In this study, we characterize an iron terminal methylidene complex by single-crystal X-ray diffractometry (scXRD), CHN combustion elemental analysis, H-1/C-13/P-31/H-1-C-13 NMR, and zero-field Fe-57 Mossbauer spectroscopy and study its reactivity. A series of closely related complexes in different oxidation states were synthesized, isolated and characterized in order to validate the electronic structure of the title methylidene complex. The computational analysis substantiates the proposed Fischer-type electronic description while emphasizing high Fe = CH2 bond covalency, considerable double bond order, and thus, substantial alkylidene character.

Automated summary

Iron methylidene species are important intermediates in the Fischer-Tropsch process and olefin cyclopropanation. In this study, an iron terminal methylidene complex has been characterized and its electronic structure validated. Computational analysis shows high Fe = CH2 bond covalency, considerable double bond order, and substantial alkylidene character in the complex.