Ferrocenediyl-Bridged Triiron Complexes^†

The reaction of 2 equiv of CpFe(CO)(2)I and 1,1 ' -dilithioferrocene in the presence of 2 equiv of PPh(3) is an intermolecular version of the reaction of CpFe(CO)(2)I and (eta (5)-C(5)H(4)Li)Fe(C(5)H(4)PPh(2)). In the three-component procedure, the PPh(3) substitution for iodide on CpFe(CO)(2)I is much faster than the nucleophilic Fc-addition at the Fe-center or at a CO ligand of CpFe(CO)(2)I. This one-pot reaction proceeds through [CpFe(CO)(2)PPh(3)(+)] and yields CpFe(CO)(PPh(3))[mu ,C:eta (5)-C(O)C(5)H(4)]Fe [mu,eta (5):eta (4)-5-exo-(1 ' -C(5)H(4))C(5)H(5)]Fe(CO)(2)(PPh(3)) (4) in 50% yield, with the 1,1 ' -dilithioferrocene participating twice in the nucleophilic Fc-additions: at the Cp-ring and at a CO ligand of [CpFe(CO)(2)PPh(3)(+)]. Complex 4 is a ferracenediyl-bridged tri-Fe complex with three different Fe-centers: a metallocene Fe(II), a square-pyramidal pentacoordinate Fe(0), and a half-sandwich acyl-Fe(II). It has been found that, in the second Fc-additions, the pathway from (eta (5)-C(5)H(4)Li)Fe[mu,eta (5):C-C(5)H(4)C(O)]FeCp(CO)(PPh(3)) (9) to 4 proceeds normally, but the pathway from 9 to Fe[(mu,eta (5):C-C(5)H(4))C(O)FeCp(CO)(PPh(3))](2) (5r) has been turned off. The preference of Fc-addition for 9 onto the Cp-ring of [CpFe(CO)(2)PPh(3)(+)] could be reasoned by a localization of the Li(+) cation in 9.