ALKOXIDES AS ANCILLARY LIGANDS IN ORGANOLANTHANIDE CHEMISTRY - SYNTHESIS OF, REACTIVITY OF, AND OLEFIN POLYMERIZATION BY THE MU-HYDRIDE-MU-ALKYL COMPOUNDS [Y(C5ME5)(OC6H3TBU2)]2(MU-H)(MU-ALKYL)

Reaction of Y(C5Me5)(OAr)2 (2; OAr = 0-2,6-C6H3tBu2) with MCH(SiMe3)2 (M = Li, K) affords Y (C5Me5) (OAr){CH(SiMe3)21 (3), which on subsequent hydrogenation (20 bar, 25-degrees-C) gives the mu-H dimer [Y(C5Me5)(OAr)(mu-H)]2 (4). Terminal olefins H2C=CHR (R = H, Me, Et, n-Bu) react regiospecifically and irreversibly with 4 to give the mu-n-alkyl species trans-[Y(C5Me5)(OAr)]2(mu-H)(mu-CH2CH2R) (R = H (5), Me (6), Et (7), n-Bu (8)), respectively. Reaction of [Y(C5Me5)(OAr)(mu-D)]2 (4-D) (prepared from 3 and D2) with propene yields selectively only trans-[Y(C5Me5)(OAr)]2(mu-D)(mu-CH2CHDMe) (6-D), confirming the nonreversibility of olefin insertion. Compounds 4-8 polymerize ethene and are single-component catalysts for the polymerization of alpha-olefins and nonconjugated dienes. Dissolution of 4 in neat 1-hexene (to give 8 in situ) results in slow polymerization to yield poly(1-hexene) with M(w) = 15 700 and M(w)/M(n) = 1.67. 4 cyclopolymerizes neat 1,5-hexadiene to poly(methylene-1,3-cyclopentanediyl) rather than promotes cyclization to methylenecyclopentane. The mu-alkyls 5-8 show diastereotopic alpha-CH2 resonances, implying idealized C2, rather than C2upsilon geometry, which indicates a mutually transgeometry for the attendant C5Me5 and OAr ligands. In 6, exchange of the two diastereotopic CalphaH2 hydrogens by inversion at Y(mu-C(alpha))Y occurs with DELTAG(double dagger) = 11.1 +/- 0.5 kcal mol-1 (-25-degrees-C), and tert-butyl group equilibation on the same phenoxide occurs with DELTAG(double dagger) = 9.0 +/- 0.5 kcal mol-1 (-93-degrees-C). The terminal acetylene HC=CSiMe3 reacts with 4 to give the mu-acetylide [Y(C5Me5)(OAr)]2(mu-H)(mu-C=CSiMe3) (9). 9 reacts with excess HC=CSiMe3, only in the presence of THF, to give the monomeric acetylide Y(C5Me5)(OAr)C=CSiMe3(THF)2(11). The THF-free analog Y(C5Me5)(OAr)C=CSiMe3 (10) is prepared by reaction of 3 with excess HC=CSiMe3. Treatment of 2 with MeLi (1 equiv) affords the bis(mu-Me) species [Y(C5Me5)(OAr)(mu-Me)]2 (12), which is cleaved by THF, in contrast to the mu-H species 4, to give Y(C5Me5)(OAr)(Me)(THF)2 (13). Reaction of 2 with MeLi (1.6 equiv) gives the yttrium trimer [Y(C5Me5)(mu-Me)2]3 (14). 14 undergoes metathesis with LiOC6H3tBu2 to give 12. Y-89 NMR spectroscopy is a potentially useful diagnostic probe of ligand environment. The Y-89 NMR chemical shifts (all in C6D6) of Y(OAr)3 (1), 2, Y(C5Me5)2CH(SiMe3)2, Y{CH(SiMe3)213, and Y(C5Me5)2(OAr) have been determined. From these, group contributions to the Y-89 NMR chemical shift were calculated to be -100 ppm for C5Me5, +56 ppm for OAr, and +298 ppm for CH(SiMe3)2.