Reactions of (SiMe2)(SiRR′) doubly-bridged biscyclopentadienes (RR′ = MePh, Ph2) with iron and molybdenum carbonyls

In the reaction of the doubly-bridged biscyclopentadiene (C5H4(SiMe2))(C5H4(SiMePh)) (1b) with Fe(CO)5, migration of the bridging SiMe2 or SiMePh group from the ligand to an iron atom gives the corresponding compound (SiMePh)(η5-C5H3)(η5:η1-C5H3)[(SiMe2)Fe(CO)2][Fe(CO)2] (4) or (SiMe2)(η5-C5H3)(η5:η1-C5H3)[(SiMePh)Fe(CO)2][Fe(CO)2] (5), containing one Fe–Si bond. The reaction also affords the product [(η5-C5H4)2(SiMePh)]Fe2(CO)2(μ-CO)2 (6), in which the SiMe2 group is totally cleaved, and the corresponding doubly-bridged Fe–Fe bonded products [(η5-C5H3(SiMe2))(η5-C5H3(SiMePh))]Fe2(CO)4 (2 and 3) as a pair of isomers. A similar reaction of 1b with Mo(CO)6 only results in the SiMe2 cleaved product [(η5-C5H4)2(SiMePh)]Mo2(CO)6 (9), as well as the normal doubly-bridged Mo–Mo bonded complexes [(η5-C5H3(SiMe2))(η5-C5H3(SiMePh))]Mo2(CO)6 (7 and 8) as a pair of isomers. Reaction of the doubly-bridged biscyclopentadiene (C5H4(SiMe2))(C5H4(SiPh2)) (1c) with Fe(CO)5 or Mo(CO)6, similarly, yields the corresponding SiMe2 removed product (11 or 13) and the doubly-bridged dinuclear complex (10 or 12). The molecular structures of complexes 2, 4, 5 and 7 were determined by X-ray diffraction.

Although the two bridging groups (SiMe2 and SiMePh) show steric and electronic differences, both groups could make a ring-to-metal migration in the reaction of (C5H4(SiMe2))(C5H4(SiMePh)) (1b) with Fe(CO)5 to give products containing one Fe–Si bond. Desilylation occurs in all reactions and the bridging SiMe2 group usually shows a higher activity of desilylation compared to the SiMePh and SiPh2 groups.Figure optionsDownload as PowerPoint slide