Persistent four-coordinate iron-centered radical stabilized by π-donationElectronic supplementary information (ESI) available: Experimental, crystallographic, computational details, and crystal data for 2, 4, 5 and 8. CCDC 1057111-1057113 and 1425703. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/c5sc02601f

Dinuclear iron carbonyl complex 2 , which contains an elongated unsupported Fe-Fe bond, was synthesized by the reaction between Fe 2 (CO) 9 and phosphinyl radical 1 . Thermal Fe-Fe bond homolysis led to the generation of a four-coordinate carbonyl-based iron-centered radical, 3 , which is stabilized by π-donation. Complex 3 exhibited high reactivity toward organic radicals to form diamagnetic five-coordinate Fe( ii ) complexes. Generation of four-coordinate iron-centered radical 3 was realized by the thermal homolysis of the unsupported Fe-Fe bond of 2 .