Main-group Chemistry on a Metal Framework: Preparation and Characterization of B₂H₆Fe₂(CO)₆ and Its Conjugate Base [B₂H₅Fe₂(CO)₆]⁻

The preparation and spectroscopic characterization of B2H6Fe2(CO)6 and the anion [B2H5Fe2(CO)6]- are described. The proposed structures of both compounds contain diboron-bridged diiron hexacarbonyl cores. The static structure of the former has two terminal, one B-B bridging, and three Fe-B bridging hydrogens while the latter has two terminal, one B-B bridging, and two Fe-B bridging hydrogens. Both compounds exhibit fluxional processes involving terminal and bridging hydrogens via mechanisms involving correlated hydrogen movements of a type that depends on the number of bridging hydrogens. The neutral and anionic compounds react with Fe2(CO)9 to produce HFe4(CO)12BH2 and [HFe4(CO)12BH]- plus [Fe3(CO)10BH2]-, respectively. These reactions are viewed as cluster expansion by the addition of Fe(CO)3 fragments and formal replacement of a BH fragment by a Fe(CO)3 fragment. Fenske-Hall calculations are used to explore some of the consequences of different hydrogen atom arrangements on a two-boron-two-iron framework. © 1987 American Chemical Society.