TOWARD ONE-COMPONENT GROUP-4 HOMOGENEOUS ZIEGLER-NATTA OLEFIN POLYMERIZATION CATALYSTS - HYDROBORATION OF ZIRCONIUM BISALKYLS WITH PENDANT 2-PROPENYL GROUPS USING [(C6F5)(2)BH](2)

Alkylation of bis[eta(5)-(2-propenyl)cyclopentadienyl] zirconium dichloride, 2, with CH3Li, KCH2C6H5, or LiCH(2)SiMe(3) led to the bisalkyl derivatives 3a-c (R = CH3, a; CH2C6H5, b; CH(2)SiMe(3), c), which were isolated as > 95% pure yellow oils. The new ligand [2-(2-propenyl)cyelopentadienyl](tert-butylamino)dimethysilane (Cp(allyl)SiNR) was synthesized in a one-pot procedure and attached to zirconium via reaction of its dilithio salt with ZrCl4 . 2THF, producing (Cp(allyl)SiNR)ZrCl2, 4, in 84% yield. Alkylation with the above reagents yielded alkyl derivatives 5a-c (R = CH3, a; CH2C6H5, b; CH(2)SiMe(3), c) again as > 95% pure yellow oils. Reactions of dichlorides 2 and 4 with the electrophilic borane [(C6F5)(2)BH](n), 1, proceeded smoothly to the expected products in which the pendant double bond(s) was hydroborated, giving [eta(5)-C5H4CH2CH2CH2B(C6F5)(2)]2ZrCl2, 6, and [t-C(4)H(9)NSiMe(2-eta 5)-C5H3CH2CH2CH2B-(C6F5)(2)]ZrCl2, 7. Attempts to alkylate these compounds met with failure. Similarly, hydroborations of most of the alkyl derivatives 3a-c and 5a-c were not clean by virtue of the availability of alternate reaction pathways from hydroboration. Bisbenzyl complex 5b, however, reacted cleanly with 1 to yield a complex, 8, whose structure was elucidated using multinuclear and two-dimensional NMR techniques. In this complex, both benzyl groups on zirconium were observed to transfer to boron, giving a cationic zirconium compound stabilized by a coordinated benzyl group from the counterion [(C6H5CH2)B(C6F5)(2)].