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The reaclion of the doubly bridged bis(l,l',2,2'-dimethylsilantxliyl)-7,,Ldicyclopentadienyl titanium and zirconium complexes [M{(SiMez)a(7~S-C5H,0,}Mea] (M = Ti (3), Zr (4)) wiih water gave the g-oxo derivatives [{M[(SiMe:,) Ansa=metallocene complexes of tbe early transition metals have received considerable attention in recent years [I]. The presence of a bridging group restricts the mobility of the cyclopentadienyl rings, providing a more rigid system that renders the activation of their C-H bonds more difficult.The bis(dimethylsilanodiyl)dicyclope,mldienyl anio,1 [SiMe: (C~H.~):] z-can be coordinated to met:d centers as a chelatilig or as a bridging group. This lig:md has been successfully used to stabilize Group 4 metal coinplexes in both high and low oxidation states. The chemistry of mononuclear compounds with symmetric and asymmetric rings bridged by an SIR+, fi'agment, and tlleir potential applications as catalysts in stereo-and• Correspomlmg aulhor. t Dedicated Io Professor Rafael Us6n on the occasion of his 7t)ih birthday.2 X-ray diffraction studies, enantioseleclive hydrogenation and i~oiymerization of olet'ins, ha.s been extolsively studied. Chiral an.s'a° metallocenes containing :~ C~ syrnnletrical arrangement of ring substituents have also proved to I~ effective precursors tbr generating Zieglea'~Naua catalysts, which induce isotacticity in the polymerization of propylene and other a-olefins [2,3]. Recently, the syntbeses of similar halo-and alkyl-titanium(IV) derivatives [4], as well as new titanium(Ill) and (II) metallocene comiJlexes [5] containing this ligand as a chelating system have been reported, including some aspects of their chemical behavior. Dinuclear compounds are also well represented [6]. although they are less well-known for Group 4 metals [7] and not many dinuclear derivatives of these metals are known in low oxklation states.We were interested in isoklting and studying the reactivity of cyclopentadienyl Group 4 metal complexes by using the bis(dimethylsilanodiyl)dicyclopentadienyl dianion [(SiMe 2)2(~TLC+I°! 3): ]~'-as a ligand to increase the stereorigidity of the complex. Different mono-and oligo-nuclear transition metal derivatives containing this 0022-328X/96/$15.00

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