Rare-Earth-Metal Allyl Complexes Supported by the [2-(N,N-Dimethylamino)ethyl]tetramethylcyclopentadienyl Ligand: Structural Characterization, Reactivity, and Isoprene Polymerization

Abstract

Rare-earth-metal half-sandwich allyl complexes bearing an amino-functionalized cyclopentadienyl ligand (CpNMe2 = 1-[2-(N,N-dimethylamino)ethyl]-2,3,4,5-tetramethylcyclopentadienyl) were synthesized in a two-step salt-metathesis reaction. Treatment of LnCl3(THF)x with LiCpNMe2, followed by an in situ reaction with the Grignard reagent C3H5MgCl, generated the bis(allyl) half-sandwich complexes CpNMe2Ln(η3-C3H5)2 only for the smaller rare-earth metals (Ln = Y, Ho, Lu) in good yields (82–88%). In case of the larger neodymium, the dimeric mono(allyl) chlorido half-sandwich complex [CpNMe2Nd(η3-C3H5)(μ-Cl)]2 was obtained in 68% yield. All complexes show moderate to high activity in isoprene polymerization upon cationization with organoborates [Ph3C][B(C6F5)4] and [PhNMe2H][B(C6F5)4], the yttrium, holmium, and neodymium metal centers yielding mainly 3,4-microstructures (maximum 79%). Addition of 10 equiv of AlMe3 to the catalyst systems CpNMe2Ln(η3-C3H5)2 (Ln = Y, Ho)/[PhNMe2H][B(C6F5)4] and [CpNMe2Nd(η3-C3H5)(μ...