Reactivity of hydride bridges in a high-spin [Fe3(μ-H)3]3+ cluster: reversible H2/CO exchange and Fe-H/B-F bond metathesis.

The triiron trihydride complex Fe3H3L (1) [where L3- is a tris(β-diketiminate)cyclophanate] reacts with CO and with BF3·OEt2 to afford (FeICO)2FeII(μ3-H)L (2) and Fe3F3L (3), 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 2. Preliminary studies support a CO-induced reductive elimination of H2 from 1, rather than CO trapping a species from an equilibrium mixture. This complex reacts with H2 to regenerate 1 under a dihydrogen atmosphere, which represents a rare example of reversible CO/H2 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 3 proceeds through a previously unreported net fluoride-for-hydride substitution, and 3 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.