Ferralactone formation from iron acetylides and carbon dioxide

•Formation of ferralactones by reaction of iron hydrido acetylide complexes with carbon dioxide.•Spectroscopic characterization of unstable side-on-bound acetylene and phenylacetylene complexes.•Reaction of side-on-bound phenylacetylene complexes with carbon dioxide affords a different isomer of ferralactone where the phenyl ring is attached the metal-bound carbon of the metalalactone ring.