SYNTHESIS, CHARACTERIZATION AND STRUCTURE OF A STRAINED RING-TILTED BIS(INDENYL)IRON COMPLEX

The new bridged ligand (C(9)Me(6)H)(2)SiMe(2) 9 has been prepared and used to synthesise the first strained ansa-bridged bis(indenyl)iron co mplex Fe(eta(5)-C(9)Me(6))(2)SiMe(2) 11. The properties of 11 are comp ared with those of other SiMe(2)-bridged [1]-ferrocenophanes and with the unbridged analogue Fe(eta(5)-C(9)Me(6)H)(2) 8. UV-vis and C-13 NMR data are consistent with a ring-tilted structure for 11; the strain i n the molecule is demonstrated by the observation of alcoholysis and h ydrolysis products in its FAB mass spectrum. The crystal structure of rac-Fe(eta(5) - C(9)Me(6))(2)SiMe(2) 11a has been determined; the ring tilt angles of 13.0 and 13.8 degrees (for the two independent molecul es in the cell) are the lowest so far reported for a silicon-bridged [ 1]-ferrocenophane, whilst the distortion of the bridgehead atoms from ideal sp(2) geometry is reflected in the angles beta between the plane s of the five-membered indenyl rings and the C-Si bonds of 43.1 and 41 .2 degrees. Fe-57 Mossbauer spectra of 11a and 8 suggest the presence of Fe-Si interactions in the former compound.