Preparation of “Constrained Geometry” Titanium Complexes of [1,2]Azasilinane Framework for Ethylene/1-Octene Copolymerization

The Me(2)Si-bridged ansa-Cp/amido half-metallocene, [Me(2)Si(η(5)-Me(4)C(5))(N(t)Bu)]TiCl(2), termed a “constrained-geometry catalyst (CGC)”, is a representative homogeneous Ziegler catalyst. CGC derivatives with the [1,2]azasilinane framework, in which the amide alkyl substituent is joined by the Si-bridge, were prepared, and the catalytic performances of these species was studied. Me(4)C(5)HSi(Me)(CH(2)CH=CH(2))-NH(C(R)(R’)CH=CH(2)) (R, R’ = H or methyl; Me(4)C(5)H = tetramethylcyclopentadienyl) was susceptible to ring closure metathesis (RCM) when treated with Schrock’s Mo-catalyst to afford -Si(Me(4)C(5)H)(Me)CH(2)CH=CHC(R)(R’)NH- containing a six-membered ring framework. Using the precursors and the products of RCM, various CGC derivatives, i.e., [-Si(η(5)-Me(4)C(5))(Me)CH(2)CH=CHC(R)(H)N-]TiMe(2) (13, R = H; 15, R = Me), [-Si(η(5)-Me(4)C(5))(Me)CH(2)CH(2)CH(2)CH(2)N]TiMe(2) (14), [(η(5)-Me(4)C(5))Si(Me)(CH(2)CH=CH(2))NCH(2)CH=CH(2)]TiMe(2) (16), [(η(5)-Me(4)C(5))Si (Me)(CH=CH(2))NCH(2)CH=CH(2)]TiMe(2) (17), and [(η(5)-Me(4)C(5))Si(Me)(CH(2)CH(3))NCH(2)CH(2)CH(3)]TiMe(2) (18), were prepared. The catalytic activity of the newly prepared complexes was lower than that of CGC when activated with [Ph(3)C][B(C(6)F(5))(4)]/iBu(3)Al. However, the catalytic activity of these species was improved by using tetrabutylaluminoxane ([iBu(2)Al](2)O) instead of iBu(3)Al and the activity of 14/[Ph(3)C][B(C(6)F(5))(4)]/[iBu(2)Al](2)O was comparable to that of CGC/[Ph(3)C][B(C(6)F(5))(4)]/iBu(3)Al (4.7 and 5.0 × 10(6) g/mol-Ti, respectively). Advantageously, the newly prepared complexes produced higher molecular weight poly(ethylene-co-1-octene)s than CGC.