Titanium Complexes of Sterically Demanding Cage-Phosphinimide Ligands

The known ligand PPh(C6H4O3Me4) (1) and its analogue PCy(C6H4O3Me4) (2) have been prepared. In the latter synthesis the diphosphine species (PCy)2(C6H2O3Me4) (3) was also isolated as a minor product. Reaction of the cage phosphines 1 and 2 with Me3SiN3 effected oxidation to the corresponding (trimethylsilyl)phosphinimines Me3SiNPR(C6H4O3Me4) (R = Ph (4), Cy (5)). Subsequent reactions afforded the titanium complexes CpTiCl2(NPR(C6H4O3Me4)) (R = Ph (6), Cy (7)) and CpTiMe2(NPR(C6H4O3Me4)) (R = Ph (8), Cy (9)). Preliminary screening for catalytic activity in ethylene polymerization employing either methylalumoxane (MAO) or [Ph3C][B(C6F5)4] as the activator showed minimal catalytic activity. These observations were probed via reactions of these complexes with AlMe3, MAO, or [Ph3C][B(C6F5)4]. Reaction of 8 with AlMe3 gave several products, one of which was fully characterized as the cage-rupture product CpTiMe2(NPCy(C6H4O3Me5)(μ-AlMe2)(AlMe3)) (10). A similar product is inferred by the spectroscopic monitoring of the reaction of 8 with MAO. In contrast, reaction of 2 with AlMe3 resulted only in the formation of the adduct Me3AlPCy(C6H4O3Me4) (11). Structural data are reported for 2, 3, 8, 10, and 11.