Reactivity of hydride bridges in a high-spin [Fe(μ-H)] cluster: reversible H/CO exchange and Fe-H/B-F bond metathesis.

The triiron trihydride complex FeH () [where is a tris(β-diketiminate)cyclophanate] reacts with CO and with BF·OEt to afford (FeCO)Fe(μ-H) () and FeF (), respectively. Variable-temperature and applied-field Mössbauer spectroscopy support the assignment of two high-spin (HS) iron(i) centers and one HS iron(ii) ion in . Preliminary studies support a CO-induced reductive elimination of H from , rather than CO trapping a species from an equilibrium mixture. This complex reacts with H to regenerate under a dihydrogen atmosphere, which represents a rare example of reversible CO/H exchange and the first to occur at high-spin metal centers, as well as the first example of a reversible multielectron redox reaction at a designed high-spin metal cluster. The formation of proceeds through a previously unreported net fluoride-for-hydride substitution, and is surprisingly chemically inert to Si-H bonds and points to an unexpectedly large difference between the Fe-F and Fe-H bonds in this high-spin system.