SYNTHESIS, STRUCTURE AND DYNAMICS OF [FE2(CN)(ETA-C5H5)2(CO)3]-

[Na(MeOCH2CH2OMe)2][Fe2(CN)Cp2(CO)3] (1a) is prepared from [FeCp(CO)2]2 and NaCN in hot 1,2-dimethoxyethane; the [N(PPh3)2]+- (1b), N(n)Bu4+- (1d) and PPh4+-salts (1e) are obtained by cation exchange, the NEt4+-salt (1c) by reaction of Fe2Cp2(CO)3NCMe with NEt4CN. The X-ray structure analysis of 1b shows a cis-configurated complex anion with long C-O distances in the bridge and a cyano ligand which is disordered between the two terminal positions. In solution, a temperature and solvent dependent equilibrium exists between the more stable cis and the trans complex which is analyzed by IR and H-1-NMR. It is superimposed by a CN migration between the iron centers via the bridging position which is rapid at -13-degrees-C (trans isomer) and +18-degrees-C (cis isomer), respectively, leading to a coalescence of the Cp signals.