Cationic scandium allyl complexes bearing mono(cyclopentadienyl) ligands: Synthesis, novel structural variety, and olefin-polymerization catalysis

The one-pot salt-metathesis reaction of ScCl3, cyclopentadienyl lithium salts, and allylmagnesium chlorides afforded with ease the corresponding base-free half-sandwich scandium di-(eta(3)-allyl) complexes [(C5Me4SiMe3)Sc- (C3H5)(2)] (1a), [(C5Me5)Sc(C3H5)(2)] (1b), and [(C5Me5)Sc(2-MeC3H4)(2)] (1c) in high yields. Reaction of 1a with 1 equivalent of [PhNMe2H][B(C6F5)(4)] in toluene gave rapidly the N,N-dimethylaniline-coordinated cationic mono-(eta(3)-allyl) complex [(C5Me4SiMe3)Sc-(eta(3)-C3H5)(eta(6)-PhNMe2)][B(C6F5)(4)] (2). The similar reaction of 1a with [Ph3C][B-(C6F5)(4)] yielded the analogous toluene-separated ion pair [(C5Me4SiMe3)Sc(eta(3)-C3H5)(eta(6)-PhMe)][B(C6F5)(4)] (3). When [PhNMe2H][BPh4] was treated with 1a, the contact ion pair [(C5Me4SiMe3)Sc- (eta(3)-C3H5)( mu, eta(6)-Ph)BPh3] (4) was obtained. Recrystallization of 2, 3, and 4 in THF yielded the corresponding thf-separated ion pair complexes [(C5Me4SiMe3)Sc(eta(3)-C3H5)(thf)(2)][B-(C6F5)(4)] (5) and [(C5Me4SiMe3)SC(eta(3)- C3H5)(thf)(2)][BPh4] (6). The N,N-dimethylaniline-coordinated cationic scandium allyl complex 2 and the toluene-coordinated analogue 3 showed high activity (activity: 3 > 2) toward the polymerization and copolymerization of isoprene and norbornene to afford random copolymers with a broad range of isoprene content (33-86 mol %). The tight ion pair 4 and the thf-coordinated complexes 5 and 6 showed no activity under the same conditions. These results offer unprecedented insight into the structure-activity relationship of a cationic metal polymerization-catalyst system.