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the "individuality" of molar paramagnetic solvent shifts.

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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 TMSC1 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 Mel. 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 (l,3-(TMS)2Cp)Fe(CO)2Li in THF.

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