BORON-SILICON EXCHANGE-REACTIONS OF BORON TRIHALIDES WITH TRIMETHYLSILYL-SUBSTITUTED METALLOCENES

The reaction of (eta(5)-C(5)H(4)SiMe(3))(2)Fe With excess BCl3 in CH2C l2 at -78 degrees C affords a mixture of metathesis product (eta(5)-C5 H4BCl2)(2)Fe and an isomer, [eta(5)-1,3-C5H3(BCl2)(2)]Fe(eta(5)-C5H5). In contrast, BCl3 does not react appreciably with trimethylsilyl-subs tituted group 4 metallocenes below 80 degrees C. When (eta(5)-C(5)H(4) SiMe(3))(2)MCl(2) (M = Ti, Zr) is treated with excess BBr3 in CH2Cl2 a t 80 degrees C for several days, one methyl group is selectively cleav ed from each trimethylsilyl substituent to afford (eta(5)-C(5)H(4)SiMe (2)Br)(2)MBr(2) (M = Ti, Zr) in useful yields. Exposure of crystalline samples of these bromodimethylsilyl-substituted group 4 metallocene d ibromides to ambient atmosphere for several days results in selective, quantitative hydrolysis to afford the disiloxane-linked ansa-metalloc ene dibromides, [(eta(5)-C(5)H(4)SiMe(2))(2)O]MBr(2). Two other bromod imethylsilyl-substituted metallocenes, (eta(5)-C(5)H(4)SiMe(2)Br)(eta( 5)-C(5)Me(5))MBr(2) and [eta(5)-1,3-C5H3(SiMe(2)Br)(2)](2)ZrBr2 are al so prepared by treatment of the corresponding trimethylsilyl-substitut ed precursors with boron tribromide. The latter tetrasubstituted compl ex is hydrolyzed by ambient atmosphere to afford a metallocene with tw o tetramethyldisiloxane bridges.