Group 4 Dimethylmetallocenes: Improved Synthesis and Reactivity Studies

Group 4 dimethylmetallocenes are catalyst precursors for the methylmetallocenium/borate catalyst systems for
olefin polymerization, and they are usually prepared by methylation (with MeMgCl or MeLi) of the parent
metallocene dichlorides. We describe here a simpler preparation of a series of bisindenyldimethylmetallocenes
carried out by reacting the π-ligand with a 2-fold excess of MeLi, and then MtCl4 (Mt = Ti, Zr, Hf). This simple,
one-pot method produces the dimethylated complexes in higher overall yield, and saves on reaction time and
solvents. Ind2MtMe2 (1, Mt = Ti; 2a, Mt = Zr; 3, Mt = Hf), (4,7-Me2Ind)2ZrMe2 (4), rac/meso-[C2H4(Ind)2]ZrMe2 (5), meso-[C2H4(4,7-Me2Ind)2]ZrMe2 (m-6a), and meso-[C2H4(4,7-Me2Ind)2]HfMe2 (m-7a) have been
prepared in 40−80% isolated yields. 2a reacts with 1−4 equiv of t-BuOH to give the mono-tert-butoxy derivative
2b, Ind2ZrMe(O-t-Bu), while reaction with 2 equiv of C6F5OH cleanly affords Ind2Zr(OC6F5)2 (2c). Analogously,
in the presence of 2 equiv of t-BuOH, m-6a gives meso-[C2H4(4,7-Me2Ind)2]ZrMe(O-t-Bu) (m-6b) with replacement
of the outward methyl group only, as established by NMR analysis; meso-[C2H4(4,7-Me2Ind)2]Zr(OC6F5)2 (m-6c) is obtained by reaction with 2 equiv of C6F5OH. The molecular structures of m-6a and m-6c are also described.