Substituted silastannatetrahydro-s-indacenes as cyclopentadienyl transfer agents in the synthesis of silanediyl-bridged zirconocene complexes

The substituted silastannatetrahydro-s-indacenes meso-Me(2)Si(t-BuC(5)H(3))(2)SnMe(2), meso-Me(2)Si(Me(2)C(5)H(2))(2)SnMe(2), and meso-Me(2)Si(Me-i-PrC5H2)(2)SnMe(2), prepared from the corresponding silanediyl-bridged dicyclopentadienide dilithium salts by reaction with Me(2)SnCl(2), were structurally characterized by X-ray diffraction and by H-1-NMR in solution. These cyclic stannanediyl compounds react with ZrCl4 to give selectively the meso diastereomers of the ansa-zirconocene complexes Me(2)Si(3-t-BuC(5)H(3))(2)ZrCl2, Me(2)Si(2,4-Me(2)C(5)H(2))(2)ZrCl2, and Me(2)Si(2-Me-4-i-PrC5H2)(2)ZrCl2, respectively. Reaction of Me(2)Si(2-Me-4-t-BuC(5)H(2)(-) Li+)(2) with Me(2)SnCl(2) gives, instead of Me(2)Si(Me-t-BuC(5)H(2))(2)SnMe(2), the distannyl derivative Me(2)Si(2-Me-4-t-BuC(5)H(2)-1-SnMe(2)Cl)(2). This compound reacts with ZrCl4 to give a 1:1 mixture of the rac and meso isomers of Me(2)Si(2-Me-4-t-BuC(5)H(2))(2)ZrCl2. Ring-opened, racemic distannyl compounds are formed also from meso-Me(2)Si(t-BuC(5)H(3))(2)SnMe(2), meso-Me(2)Si(Me(2)C(5)H(2))(2)SnMe(2), and meso-Me(2)Si(Me-i-PrC5H2)(2)SnMe(2) with excess Me(2)SnCl(2). Competition between Me(2)SnCl(2) and Zr centers for reaction with stannylcyclopentadiene units appears to limit the overall stereoselectivity of the ansa-zirconocene complex formation.