Preparation and structures of 6- and 7-coordinate salen-type zirconium complexes and their catalytic properties for oligomerization of ethylene

Abstract

A series of salen-type zirconium complexes of the general formula LZrCl 2 (L = N, N′-ethylenebis(salicylideneiminate), 3a; N, N′-ethylenebis(3,5-di- tert-butylsalicylideneiminate), 3b; N, N′-ethylenebis(5-methoxysalicylideneiminate), 3c; N, N′-ethylenebis(5-chlorosalicylideneiminate), 3d; N, N′-ethylenebis(5-nitrosalicylideneiminate), 3e; N, N′- o-phenylenebis(salicylideneiminate), 4a; N, N′- o-phenylenebis(3,5-di- tert-butylsalicylideneiminate), 4b; N, N′- o-phenylenebis(5-methoxysalicylideneiminate), 4c; N, N′- o-phenylenebis(5-chloro-salicylideneiminate), 4d) were prepared. The crystal structures of 6- and 7-coordinate zirconium complexes 4b and [ 4b · OCMe 2] were determined by X-ray crystallography, which reveals that a salen-type zirconium complex possesses a labile coordination site on the Zr center with a relatively stable framework and that the coordination and the dissociation of O-donor molecules occur readily at this site. The catalytic properties of 3( a– e) and 4( a– d) were studied for ethylene oligomerization in combination with Et 2AlCl as co-catalyst. Complex 3c featuring a methoxy-substituted salen ligand displayed higher activity than its analogous precursors having chloro and nitro groups as substituents. The catalytic reactions by 3( a– e) and 4( a– d) gave C 4–C 10 olefins and low-carbon linear α-olefins in good selectivity.