Structures and reactivity of doubly-bridged dicyclopentadienyl dinuclear iron complexes

• Molecular structures of 1a and 1b exhibit different coordination mode of carbonyl ligands and Fe–Fe bond distance.
• The flexibility of doubly-bridged ligands results in structural difference of 1a and 1b.
• Complexes 1a and 1b show different reactivity in some cases.
• Molecular structures of 1b, 2a, and 3b were determined by X-ray diffraction.

The molecular structure of the doubly-bridged bis(cyclopentadienyl) diiron complex [(η5-C5H3)2(SiMe2)2]Fe2(CO)2(μ-CO)2 (1b) was determined, and compared with that of the other analogue [(η5-C5H3)2(CMe2)(SiMe2)]Fe2(CO)4 (1a). The former involves two bridging and two terminal carbonyls, and a normal Fe–Fe bond distance, while the latter contains all-terminal carbonyls and a longer than normal Fe–Fe bond distance. The possible reason for different coordination modes is discussed. Complexes (1a–b) react with I2 to give the corresponding diiodo products [(η5-C5H3)2(EMe2)(SiMe2)]Fe2(CO)4I2 (E = C, 2a; E = Si, 2b) and with phenylacetylene to give the bridging μ-CCHPh products [(η5-C5H3)2(EMe2)(SiMe2)]Fe2(CO)2(μ-CO)(μ-CCHPh) (3a–b). Reaction of 1a with Na/Hg, then with MeI yields the unexpected desilylated product [(η5-C5H4)2(CMe2)][Fe(CO)2Me]2 (5a). Reaction of 1b with LiBHEt3 affords the bridging methylene product [(η5-C5H3)2(SiMe2)2]Fe2(CO)2(μ-CO)(μ-CH2) (6b). The molecular structures of 2a and 3b were also determined by X-ray diffraction.

Structural difference of two doubly-bridged bis(cyclopentadienyl) diiron complexes (1a–b) was discussed. A plausible regularity was described that the flexibility of doubly-bridged ligands controls the Fe–Fe bond distance and coordination mode of carbonyl ligands. Reactions of 1a–b with I2, phenylacetylene, Na/Hg, and LiBHEt3 were explored, for the purpose of reactivity comparison.Figure optionsDownload as PowerPoint slide