Cp*ZrMe3 reacts with silica pretreated at 800 degrees C, SiO2-(800) through two pathways: (a) protolysis of a Zr-Me group by surface silanols and (b) transfer of a methyl group to the surface by opening of strained siloxane bridges, in a relative proportion of ca. 9/1, respectively, affording a well-defined surface species [(tSiO) ZrCp*(Me)(2)], 3, but with two different local environments 3a, [( SiO) ZrCp*(Me)(2)][ Si-O-Si ], and the other with 3b, [GRAPHICS] The reaction of the species 3 with B(C6F5)(3) is controlled by this local environment and gives three surface species [( SiO) ZrCp*(Me)](+)[MeB(C6F5)(3)](-) [ Si-O-Si ], 4a (20%), [( SiO) ZrCp*(Me)](+)[(Me)B(C6F5)(3)](-) [ Si-Me], 4b (10%), and [( SiO)(2)ZrCp*](+)[(Me)B(C6F5)(3)](-)[ Si-O-Si ], 5 (70%). On the contrary, the reaction of Cp*Zr(Me)(3), Cp2Zr(Me)(2) with [ SiO-B(C6F5)(3)](-)[HNEt2Ph](+), 6, leads to a unique species [( SiO)B(C6F5)(3)](-)[Cp*Zr(Me)(2)center dot NEt2Ph](+), 7, and [( SiO)ZrCp2](+)[(Me)B(C6F5)(3)](-), 9 respectively. The complexes 4 and 7 are active catalysts in ethylene polymerization at room temperature, 93 and 67 kg PE mol Zr1- atm(-1) bar(-1), respectively, indicating that covalently bounded Zr catalyst 4 is slightly more active than the "floating" cationic catalyst 7.