POLYMERIZATION OF METHYL-METHACRYLATE WITH ALANE COMPLEXES OF BIVALENT LANTHANIDOCENES

Alane complexes of some bivalent ytterbocenes, L2YbAlH3. NEt3 (L = C5M e5 (IV), 1-SiMe(3)Ind (V), 9-SiMe(3)Flu (VI)) were found to provide st ereospecific polymerization of methyl methacrylate. The apparent activ ities of initiators IV-VI were estimated to be a few times greater tha n those of their monometallic analogues L2Yb . THF (I-III). The polyme rization was shown to proceed via the formation of a catalytically act ive intermediate, L2YbAlH2[OC(OMe)=C(Me)CH2C(Me)(2)(CO2Me)] which was proposed to exist in various forms. At low temperatures the alane frag ment did not disrupt the stereocontrol mechanism originating from the metallocene template. The catalysts IV-VI produced an atactic pMMA at 0 degrees C. (C) 1998 Elsevier Science S.A. All rights reserved.