Chelating diamide complexes of titanium:: new catalyst precursors for the highly active and living polymerization of α-olefins

The reaction of RHN(CH2)(3)NHR (1a,b) (a, R = 2,6-(Pr2C6H3)-Pr-i; b, R = 2,6-Me2C6H3) with 2 equiv of BuLi followed by 2 equiv of ClSiMe3 yields the silylated diamines R(Me3Si)N(CH2)(3)N(SiMe3)R (3a,b). The reaction of 3a,b with TiCl4 yields the dichloride complexes [RN(CH2)(3)NR]TiCl2 (4a,b) and two equiv of ClSiMe3. An X-ray study of 4a (P2(1)/n, a = 9.771(1) Angstrom, b = 14.189(1) Angstrom, c = 21.081(2) Angstrom, beta = 96.27(1)degrees, V = 2905.2(5) Angstrom(3), Z = 4, T = 25 degrees C, R = 0.0701, R-w = 0.1495) revealed a distorted tetrahedral geometry about titanium with the aryl groups lying perpendicular to the TiN2-plane. Compounds 4a,b react with 2 equiv of MeMgBr to give the dimethyl derivatives [RN(CH2)(3)NR]TiMe2 (5a,b). An X-ray study of 5b (P2(1)2(1)2(1), a = 8.0955(10) Angstrom, b = 15.288(4) Angstrom, c = 16.909(3) Angstrom, V = 2092.8(7) Angstrom(3), Z = 4, T = 23 degrees C, R = 0.0759, R-w = 0.1458) again revealed a distorted tetrahedral geometry about titanium with titanium-methyl bond lengths of 2.100(9) Angstrom and 2.077(9) Angstrom. These titanium dimethyl complexes are active catalysts for the polymerization of 1-hexene, when activated with methylaluminoxane (MAO). Activities up to 350,000 g of poly(1-hexene)/mmol catalyst h were obtained in neat 1-hexene. These systems actively engage in chain transfer to aluminum. Equimolar amounts of 5a or 5b and B(C6F5)(3) catalyze the living aspecific polymerization 1-hexene. Polydispersities (M-w/M-n) as low as 1.05 were measured. Highly active living systems are obtained when 5a is activated with {Ph3C}(+)[B(C6F5)(4)](-). A primary insertion mode (1,2 insertion) has been assigned based on both the initiation of the polymer chain and its purposeful termination with iodine. (C) 1998 Elsevier Science B.V.