CHIRAL LANTHANOCENE DERIVATIVES CONTAINING 2 LINKED AMIDO-CYCLOPENTADIENYL LIGANDS - HETEROBIMETALLIC STRUCTURE AND LACTONE POLYMERIZATION ACTIVITY

Reaction of 2 equiv of dilithium amido-cyclopentadienide Li-2(C5R4SiMe 2NCH2CH2X) (C5R4 = C5Me4, C(5)H(3)tBu; X = OMe, NMe2) with anhydrous L nCl(3) (Ln = Y, Lu) gave C-2-symmetric complexes of the type Li[Ln(eta (5):eta(1)-C5R4SiMe2NCH2CH2X)(2)] containing a heterobimetallic core. The molecular structure of Li[Y(eta(5):eta(1)-C5Me4SiMe2NCH2CH2OMe)(2) ] was determined by single-crystal X-ray structural analysis, which sh owed it to exhibit both a pseudotetrahedral yttrium as well as a tetra hedral lithium center. In accordance with a formal 20-electron configu ration at the rare earth metal center Ln, the amido-nitrogen atoms are shown to be pyramidalized. In the case of eta(5):eta(1)-C(5)H(3)tBuSi Me(2)NCH(2)CH(2)X)(2)], mixtures of the two diastereomers in relative ratios depending on the reaction time are formed. The (R,S)-diastereom er is the kinetic product that rearranges to the thermodynamically pre ferred C-2-symmetric (R,R)-diastereomer in donor solvents such as THF. The molecular structures of diastereomerically pure ta(5):eta(1)-C(5) H(3)tBuSiMe(2)NCH(2)CH(2)OMe)(2)] and ):eta(1)-C(5)H(3)tBuSiMe(2)NCH(2 )CH(2)NMe(2))(2)], as determined by single-crystal X-ray structural an alyses, confirm the significantly different steric congestion. All het erobimetallic complexes were shown to be active in the ring-opening po lymerization of epsilon-caprolactone. The poly(epsilon-caprolactone)s obtained are of high molecular weight (M-n > 30 000) and moderate poly dispersity (M-w/M-n < 2.0) and are produced by the action of the nucle ophilic amido-nitrogen atom.