Chemical implantation of Group 4 cations on silica via cyclopentadienyl-and N,N-dialkylcarbamato derivatives

Chemical implantation of Group 4 cations [Ti(III), Ti(IV), Zr(IV), Hf(IV)] has been carried out under mild conditions by the reaction of polycyclopentadienyl- (MCp(n); M = Ti, n = 3, 4; M = Zr, Hf, n = 4), mixed cyclopentadienyl/N,N-dialkylcarbamato (ML(x)(O(2)CNEt(2))(y); M = Ti, L = Cp, C(5)Me(5) (Cp*), x = 2, y = 1; M = Hf, L = Cp, x = 1, y = 3), and N,N-dialkylcarbamato (M(O(2)CNR(2))(n), M = Ti, n = 3, R = (i)Pr; M = Ti, Hf, n = 4, R = Et; M = Zr, n = 4, R = iPr) derivatives, with the silanol groups of amorphous silica. Cyclopentadiene/pentamethylcyclopentadiene and/or carbon dioxide and the secondary amine are released in the process. The amount of implanted cations depends on the metal and on the ligands, the pentamethylcyclopentadienyl complex being less reactive than the unsubstituted congener. The starting complexes and the final products have been characterized by EPR or by (13)C CP-MAS NMR spectroscopy.