ALKOXIDES AS ANCILLARY LIGANDS IN ORGANOLANTHANIDE CHEMISTRY - SYNTHESIS, REACTIVITY, ALPHA-OLEFIN AND DIENE POLYMERIZATION BY [Y(C5ME5)(OC6H3(T)BU2)(MU-H)]2

Terminal olefins H2C=CHR (R = H, Me, n-Bu) react regiospecifically and irreversibly with mu-H dimer [Y(C5Me5)(OAr)(mu-H)]2 (1) to give the m u-n-alkyl species trans-[Y(C5Me5)(OAr)]2(mu-H) (mu-CH2CH2R) (R = H (2) ,Me (3),n-Bu (4)) respectively. Reaction of [Y(C5Me5)(OAr)(mu-D)]2 (4- D) (prepared from (C5Me5)Y(OAr)CH(SiMe3)2 and D2) With propene yields selectively only trans-[Y(C5Me5)(OAr)]2(mu-D)(mu-CH2CHDMe) (4-D), conf irming the non-reversibility of olefin insertion. Compounds 1-4 polyme rize ethene and are single-component catalysts for the polymerization of alpha-olefins and non-conjugated dienes. Dissolution of 1 in neat 1 -hexene (to give 4 in situ) results in slow polymerization to yield po ly( 1-hexene) with M(w) = 15700, M(w)/M(n) = 1.67. 1 cyclopolymerizes neat 1,5-hexadiene to poly(methylene-1,3-cyclopentane), rather than cy clization to methylenecyclopentane.