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 mu(4)-eta(2):eta(2):eta(1):eta(1)-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)(4)Fe-4(CO)(4)] reacts with LiAlH4 in THF to give [(MeC5H4)(4)Fe-4(HC=CH)(2)].