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)
Revh. Spence et We. Piers, 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), Organometallics, 14(10), 1995, pp. 4617-4624
Alkylation of bis[eta(5)-(2-propenyl)cyclopentadienyl] zirconium dichl
oride, 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 yl)cyelopentadieny
l](tert-butylamino)dimethysilane (Cp(allyl)SiNR) was synthesized in a
one-pot procedure and attached to zirconium via reaction of its dilith
io salt with ZrCl4 . 2THF, producing (Cp(allyl)SiNR)ZrCl2, 4, in 84% y
ield. 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 wh
ich the pendant double bond(s) was hydroborated, giving [eta(5)-C5H4CH
2CH2CH2B(C6F5)(2)]2ZrCl2, 6, and [t-C(4)H(9)NSiMe(2-eta 5)-C5H3CH2CH2C
H2B-(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, r
eacted cleanly with 1 to yield a complex, 8, whose structure was eluci
dated using multinuclear and two-dimensional NMR techniques. In this c
omplex, both benzyl groups on zirconium were observed to transfer to b
oron, giving a cationic zirconium compound stabilized by a coordinated
benzyl group from the counterion [(C6H5CH2)B(C6F5)(2)].