Titanium Complexes of Sterically Demanding Cage-Phosphinimide Ligands

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