Structure and chemistry of a metal cluster with a four-coordinate carbide carbon atom.

Molecular metal clusters with carbide carbon atoms of low coordination number have been prepared; they are the anionic [HFe(4)C(CO)(12) (-)] and [Fe(4)C(CO)(12) (2-)] clusters. An x-ray crystallographic analysis of a tetraaminozinc salt of the latter has established a butterfly array of iron atoms with the carbide carbon atom centered above the wings of the Fe(4) core. Each iron atom was bonded to three peripheral carbonyl ligands. The distances from the carbide carbon to iron were relatively short, particularly those to the apical iron atoms (1.80 A average). Protonation of the anionic carbide clusters reversibly yielded HFe(4)(CH)(CO)(12), and methylation of the dianion gave {Fe(4)[CC(O)CH(3)](CO)(12) (-)}. Oxidation of [Fe(4)C(CO)(12) (2-)] yielded the coordinately unsaturated Fe(4)C(CO)(12) cluster, which was extremely reactive. Hydrogen addition to this iron cluster was rapid below 0 degrees C, and a C-H bond was formed in this transformation.