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)
Cj. Schaverien, 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), Organometallics, 13(1), 1994, pp. 69-82
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 subseque
nt 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) reac
t regiospecifically and irreversibly with 4 to give the mu-n-alkyl spe
cies 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 nonreversibili
ty of olefin insertion. Compounds 4-8 polymerize ethene and are single
-component catalysts for the polymerization of alpha-olefins and nonco
njugated 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 po
ly(methylene-1,3-cyclopentanediyl) rather than promotes cyclization to
methylenecyclopentane. The mu-alkyls 5-8 show diastereotopic alpha-CH
2 resonances, implying idealized C2, rather than C2upsilon geometry, w
hich indicates a mutually transgeometry for the attendant C5Me5 and OA
r ligands. In 6, exchange of the two diastereotopic CalphaH2 hydrogens
by inversion at Y(mu-C(alpha))Y occurs with DELTAG(double dagger) = 1
1.1 +/- 0.5 kcal mol-1 (-25-degrees-C), and tert-butyl group equilibat
ion on the same phenoxide occurs with DELTAG(double dagger) = 9.0 +/-
0.5 kcal mol-1 (-93-degrees-C). The terminal acetylene HC=CSiMe3 react
s 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 g
ive the monomeric acetylide Y(C5Me5)(OAr)C=CSiMe3(THF)2(11). The THF-f
ree analog Y(C5Me5)(OAr)C=CSiMe3 (10) is prepared by reaction of 3 wit
h 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 (1
3). Reaction of 2 with MeLi (1.6 equiv) gives the yttrium trimer [Y(C5
Me5)(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(OA
r)3 (1), 2, Y(C5Me5)2CH(SiMe3)2, Y{CH(SiMe3)213, and Y(C5Me5)2(OAr) ha
ve been determined. From these, group contributions to the Y-89 NMR ch
emical shift were calculated to be -100 ppm for C5Me5, +56 ppm for OAr
, and +298 ppm for CH(SiMe3)2.