The alkoxo compounds [TaCp*Me 3 (OR)] (R ) SiiPr 3 , 1a; 2,6-Me 2 C 6 H 3 , 1b; 2,6-iPr 2 C 6 H 3 , 1c) were obtained by reaction of [TaCp*Me 4 ] with the corresponding alcohol ROH, at room temperature for R ) SiiPr 3 and upon heating at 100 °C over 2 and 3 days for R ) 2,6-Me 2 C 6 H 3 and 2,6-iPr 2 C 6 H 3 , respectively. The alkoxo cations [TaCp*Me 2 (OR)] + (R ) SiiPr 3 , 2a; 2,6-Me 2 C 6 H 3 , 2b; 2,6-iPr 2 C 6 H 3 , 2c) were formed when one of the methyl groups of the neutral trimethyl complexes 1 was dissociated by reaction with 1 equiv of B(C 6 F 5 ) 3 to generate the borate anion [MeB(C 6 F 5 ) 3 ] -(B) and with 1 and 2 equiv of Al(C 6 F 5 ) 3 to give the mononuclear [MeAl(C 6 F 5 ) 3 ] -(Al) and dinuclear [Me{Al(C 6 F 5 ) 3 } 2 ] -(Al2) aluminate anions, respectively. A similar reaction of the neutral compound [TaCp*Me 4 ] with 1 and 2 equiv of Al(C 6 F 5 ) 3 gave salts of the [MeAl(C 6 F 5 ) 3 ] -(Al) and [Me{Al(C 6 F 5 ) 3 } 2 ] -(Al2) anions containing the [TaCp*Me 3 ] + (3) cation. Compounds 1 and [TaCp*Me 4 ] did not show catalytic activity for MMA polymerization when B(C 6 F 5 ) 3 was used as cocatalyst but were active in the presence of Al(C 6 F 5 ) 3 , yielding high molecular weight syndiotactic PMMA.