Unexpected alkyl-substituent exchange during the formation of a cationic bis(zirconocene) complex that contains a planar four-co-ordinate carbon atom
Abstract
Treatment of the alkyl Group 4 metallocene cation reagent [ZrCp2{CH2Si(CH3)3}(THF)]+[BPh4]– 2b with bis(propynyl)zirconocene 1a yielded the cationic dimetallic complex [(ZrCp2)2(µ-η1∶η2-CH3CCCH3){µ-κ2-CCCH2Si(CH3)3}]+ 3d with BPh4– anion. Complex 3d was characterized spectroscopically and by a crystal structure analysis. It contains a planar four-co-ordinate carbon atom, which is stabilized by the interaction with both Group 4 metal centres. Finding the CH2Si(CH3)3 substituent, that originates from the alkylzirconocene reagent, attached at the µ-acetylide ligand in the final product is unusual. A reversible alkynyl carbometallation sequence is proposed to account for the observed selective formation of 3d. Complex 3d reacted with alkyl isocyanides RNC (R = CMe2CH2CMe3, CMe3, or cyclohexyl) by replacement of the µ-η1∶η2-CH3CCCH3 ligand to form the µ-isocyanide complexes [(ZrCp2)2(µ-η1-C∶η2-C,N-RNC){µ-κ2-CCCH2Si(CH3)2}]+ (with BPh4– anion) of which one was characterized by a crystal structure analysis.