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 MtCl 4 (Mt = Ti, Zr, Hf). This simple, one-pot method produces the dimethylated complexes in higher overall yield, and saves on reaction time and solvents. Ind 2MtMe 2 (1, Mt = Ti; 2a, Mt = Zr; 3, Mt = Hf), (4,7-Me 2Ind) 2ZrMe 2 (4), rac/meso-[C 2H 4(Ind) 2]ZrMe 2 (5), meso-[C 2H 4(4,7-Me 2Ind) 2] ZrMe 2 (m-6a), and meso-[C 2H 4 (4,7-Me 2Ind) 2]HfMe 2 (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, Ind 2ZrMe(O-t-Bu), while reaction with 2 equiv of C 6F 5OH cleanly affords Ind 2Zr(OC 6F 5) 2 (2c). Analogously, in the presence of 2 equiv of t-BuOH, m-6a gives meso-[C 2H 4 (4,7-Me 2Ind) 2]ZrMe(O-t-Bu) (m-6b) with replacement of the outward methyl group only, as established by NMR analysis; meso-[C 2H 4 (4,7-Me 2Ind) 2]Zr (OC 6F 5) 2 (m6c) is obtained by reaction with 2 equiv of C 6F 5OH. The molecular structures of m-6a and m-6c are also described.