C-H-Bond Activation and Isoprene Polymerization Studies Applying Pentamethylcyclopentadienyl-Supported Rare-Earth-Metal Bis(Tetramethylaluminate) and Dimethyl Complexes.

As previously shown for lutetium and yttrium, 1,2,3,4,5-pentamethylcyclopentadienyl (CMe = Cp*)-bearing rare-earth metal dimethyl half-sandwich complexes [Cp*LnMe] are now also accessible for holmium, dysprosium, and terbium via tetramethylaluminato cleavage of [Cp*Ln(AlMe)] with diethyl ether (Ho, Dy) and tert-butyl methyl ether (TBME) (Tb). C-H-bond activation and ligand redistribution reactions are observed in case of terbium and are dominant for the next larger-sized gadolinium, as evidenced by the formation of mixed methyl/methylidene clusters [(Cp*Ln)(CH)(Me)] and metallocene dimers [Cp*Ln(AlMe)] (Ln = Tb, Gd). Applying TBME as a "cleaving" reagent can result in both TBME deprotonation and ether cleavage, as shown for the formation of the 24-membered macrocycle [(Cp*Gd)(Me)(CHOBu)(AlMe)] or monolanthanum complex [Cp*La(AlMe){MeAl(CH)OBu}] and monoyttrium complex [Cp*Y(AlMe)(MeAlOBu)], respectively.

1,3-Diene Polymerization Promoted by Half-Sandwich Rare-Earth-Metal Dimethyl Complexes: Active Species Clustering and Cationization/Deactivation Processes.

When activated with fluorinated borate cocatalysts the trimetallic complexes [Cp*LnMe ] (Ln=Y, Lu; Cp*=C Me ) promote efficiently the formation of high-cis polybutadiene. Respective polyisoprenes instead bear much less pronounced microstructures, but reveal crosslinked products at lower polymerization temperatures. Varying the amount of cocatalyst, the emerging active species were examined by NMR spectroscopic techniques (incl.