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, 1H/13C/31P/1H-13C NMR, and zero-field 57Fe Mössbauer 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.