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*LnMe2 ]3 (Ln=Y, Lu; Cp*=C5 Me5 ) 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. 1 H DOSY). The occurrence of donor-solvent and thermally induced degradation products of the highly reactive precatalyst [Cp*YMe2 ]3 and derived catalyst species was revealed by the elucidation of methylidene clusters [Cp*3 Y3 Me4 (CH2 )(thf)2 ] and [Cp*6 Y6 Me4 (CH2 )4 ], as well as [(Cp*Y)2 Me2 (N(Me)2 (C6 H4 )]n [B(C6 F5 )4 ]n , implying a multimetallic active species.