Reductive Coupling of Carbonyl Ligands on a Cubane-Type Tetrairon Cluster [Cp₄Fe₄(CO)₄] or [(MeC₅H₄)₄Fe₄(CO)₄] To Give an Acetylene-Coordinated Cluster [Cp₄Fe₄(HC⋮CH)₂] or [(MeC₅H₄)₄Fe₄(HC⋮CH)₂]

Treatment of [Cp4Fe4(CO)4] with LiAlH4 in tetrahydrofuran (THF) resulted in the reductive coupling of carbonyl ligands to produce a nonsubstituted acetylene-coordinated cluster [Cp4Fe4(HC⋮CH)2]. X-ray structure analysis revealed that the cluster consists of a puckered rhombus of four iron atoms. The coordination mode of the acetylene ligands was determined to be μ4-η2:η2:η1:η1-HC⋮CH. The cyclic voltammogram of the acetylene-coordinated cluster exhibits three reversible or quasireversible one-electron oxidation waves and one irreversible one-electron reduction wave, corresponding to +3/+2, +2/+1, +1/0, and 0/−1 charged couples, respectively. Similarly, [(MeC5H4)4Fe4(CO)4] reacts with LiAlH4 in THF to give [(MeC5H4)4Fe4(HC⋮CH)2].