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

Abstract

The triiron trihydride complex Fe₃H₃L (1) [where L³⁻ is a tris(β-diketiminate)cyclophanate] reacts with CO and with BF₃·OEt₂ to afford (Fe^ICO)₂Fe^II(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.