FE-B BONDING IN (DIBROMOBORYL)FERROCENE - A STRUCTURAL AND THEORETICAL INVESTIGATION

The geometry and electronic structure of borylferrocenes, FCBR(2), hav e been investigated by X-ray structure analysis (R = Br) and density f unctional theory (DFT) calculations (R = H). An interaction between fi lled d-type orbitals at iron and the empty p orbital of boron causes b ending of the BR(2) substituent toward the central iron atom. The dip angle alpha is 17.7 degrees (18.9 degrees) for FcBBr(2) (X-ray struct ure). Slightly larger values were calculated for the sterically unhind ered model system FcBH(2) (alpha = 21.6 degrees [LDA/NL]). According to the DFT calculations, the Fe-B interaction in FcBH(2) is considerab ly weaker than the Fe-C-exo bond of the isoelectronic cation FcCH(2)() (alpha = 41.0 degrees [LDA/NL]). In 1,1'-diborylated ferrocene no e nergetically preferred rotamer was detected by our DFT calculations.