Synthesis of an ansa-Zirconocene via a Novel S4 -Symmetric Spirobis(silastannaindacene) Compound.

A stereoselective reaction of Sn(NMe2 )4 with the silyl-bridged bis(cyclopentadienyl) derivative 1 generates the novel spiro compound 2, in which two C2 -symmetric six-membered rings of opposite configuration are joined at a tin center: One ring is R,R-, and the other S,S-configured. Subsequent reaction with two equivalents of ZrCl4 affords, by stereoselective Sn/Zr exchange, exclusively the C2 -symmetric isomer of the ansa-zirconocene rac-3.