om0003178_si_001.cif (65.26 kB)

Titanium Complexes of Sterically Demanding Cage-Phosphinimide Ligands

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posted on 16.08.2000, 00:00 by Charles-Antoine Carraz, Douglas W. Stephan
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.