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

The one-pot salt-metathesis reaction of ScCl(3), cyclopentadienyl lithium salts, and allylmagnesium chlorides afforded with ease the corresponding base-free half-sandwich scandium di(eta(3)-allyl) complexes [(C(5)Me(4)SiMe(3))Sc(C(3)H(5))(2)] (1 a), [(C(5)Me(5))Sc(C(3)H(5))(2)] (1 b), and [(C(5)Me(5))Sc(2-MeC(3)H(4))(2)] (1 c) in high yields. Reaction of 1 a with 1 equivalent of [PhNMe(2)H][B(C(6)F(5))(4)] in toluene gave rapidly the N,N-dimethylaniline-coordinated cationic mono(eta(3)-allyl) complex [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(eta(6)-PhNMe(2))][B(C(6)F(5))(4)] (2). The similar reaction of 1 a with [Ph(3)C][B(C(6)F(5))(4)] yielded the analogous toluene-separated ion pair [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(eta(6)-PhMe)][B(C(6)F(5))(4)] (3). When [PhNMe(2)H][BPh(4)] was treated with 1 a, the contact ion pair [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))( mu,eta(6)-Ph)BPh(3)] (4) was obtained. Recrystallization of 2, 3, and 4 in THF yielded the corresponding thf-separated ion pair complexes [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(thf)(2)][B(C(6)F(5))(4)] (5) and [(C(5)Me(4)SiMe(3))Sc(eta(3)-C(3)H(5))(thf)(2)][BPh(4)] (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.