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

The Me2Si-bridged ansa-Cp/amido half-metallocene, [Me2Si((5)-Me4C5)((NBu)-Bu-t)]TiCl2, 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. Me4C5HSi(Me)(CH2CH=CH2)-NH(C(R)(R')CH=CH2) (R, R' = H or methyl; Me4C5H = tetramethylcyclopentadienyl) was susceptible to ring closure metathesis (RCM) when treated with Schrock's Mo-catalyst to afford -Si(Me4C5H)(Me)CH2CH=CHC(R)(R')NH- containing a six-membered ring framework. Using the precursors and the products of RCM, various CGC derivatives, i.e., [-Si((5)-Me4C5)(Me)CH2CH=CHC(R)(H)N-]TiMe2 (13, R = H; 15, R = Me), [-Si((5)-Me4C5)(Me)CH2CH2CH2CH2N]TiMe2 (14), [((5)-Me4C5)Si(Me)(CH2CH=CH2)NCH2CH=CH2]TiMe2 (16), [((5)-Me4C5)Si (Me)(CH=CH2)NCH2CH=CH2]TiMe2 (17), and [((5)-Me4C5)Si(Me)(CH2CH3)NCH2CH2CH3]TiMe2 (18), were prepared. The catalytic activity of the newly prepared complexes was lower than that of CGC when activated with [Ph3C][B(C6F5)(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/[Ph3C][B(C6F5)(4)]/[iBu(2)Al](2)O was comparable to that of CGC/[Ph3C][B(C6F5)(4)]/iBu(3)Al (4.7 and 5.0 x 10(6) g/mol-Ti, respectively). Advantageously, the newly prepared complexes produced higher molecular weight poly(ethylene-co-1-octene)s than CGC.