Scope and mechanism of an iron to cyclopentadienyl ligand silyl group migration in complexes of the type CpFe(CO)2SiMe2R

Article abstract of DOI:10.1021/om00128a004

Reaction of compounds of the type CpFe(CO)₂SiMe₂R with n-BuLi or LDA results in migration of the silyl group from iron to the Cp ligand. Crossover experiments show the reaction to be intramolecular, and a mechanism involving deprotonation of the Cp ligand followed by silyl group migration utilizing a silicon d orbital is presented. A ring-deprotonated species cannot be observed or trapped, but an independent experiment with CpFe(CO)₂Me shows that compounds of this type can be deprotonated. Treatment of CpFe(CO)₂Me with LDA followed by TMSCl gives (TMSCp)Fe(CO)₂Me (TMS = Me₃Si) which is also the product of a migration sequence involving treating CpFe(CO)₂SiMe₃ with n-BuLi followed by MeI. The regiochemistry of silyl group migration to a substituted Cp ligand is found to be affected by the size of the substituent. Both 1,2- and 1,3-disubstituted products are obtained when the substituent is methyl, while only a 1,3-disubstituted product is obtained when the substituent is trimethylsilyl or dimethylphenylsilyl. Several anions of the type (RMe₂SiCp)Fe(CO)₂Li are characterized by IR spectroscopy. Only carbonyl-bridged ion pairs are present in a solution of (1,3-(TMS)₂Cp)Fe(CO)₂Li in THF.