Reactivity of hydride bridges in a high-spin [Fe(3)(μ-H)(3)](3+) cluster: reversible H(2)/CO exchange and Fe–H/B–F bond metathesis

The triiron trihydride complex Fe(3)H(3) L (1) [where L (3–) is a tris(β-diketiminate)cyclophanate] reacts with CO and with BF(3)·OEt(2) to afford (Fe(I)CO)(2)Fe(II)(μ(3)-H)L (2) and Fe(3)F(3) L (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 H(2) from 1, rather than CO trapping a species from an equilibrium mixture. This complex reacts with H(2) to regenerate 1 under a dihydrogen atmosphere, which represents a rare example of reversible CO/H(2) 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.