Formation of elastomeric polypropylene promoted by the dynamic complexes [TiCl2{N(PPh2)(2)}(2)] and [Zr(NPhPPh2)(4)]

The homoleptic phosphinoamide complex [Zr(NPhPPh2)(4)] (1) and the bisamido complex [TiCl2(N(PPh2)(2)}(2)] (2) were prepared from ZrCl4 and four equiv alents of LiNPhPPh2 and from TiCl4 and one equivalent of [Li(THF)N(PPh2)(2) ](2). In the solid state, the four NPhPPh2 ligands in 1 exhibit eta(2) coor dination. The ZrN4P4 fragment is highly symmetrical and almost of D-2 symme try. Hence, the complex is chiral, and the two enantiomers cocrystallize in the asymmetric unit. In solution, 1 exhibits signals for the six-coordinat e complex [Zr(eta(2)-NPhPPh2)(2)(eta(1)-NPhPPh2)(2)]. In the presence of me thylalumoxane (MAO), 1 and 2 are active catalysts for the formation of high -molecular-weight elastomeric polypropylene. The formation of elastomeric p olypropylene is a consequence of an epimerization mechanism of the last-ins erted monomer, indicating no detachment of the growing polymer chain from t he metal center during this process. Fractionation studies of all the elast omeric polymers show no atactic fractions. As corroboration for this mechan ism, we have shown that these complexes are active catalysts for the isomer ization and oligomerization of 1-octene, as well as for the rapid isomeriza tion of allylbenzene to trans-methylstyrene. (C) 2000 Elsevier Science S.A. All rights reserved.