Rare Earth Metal Alkyl Complexes with Methyl-Substituted Triazacyclononane-amide Ligands:  Ligand Variation and Ethylene Polymerization Catalysis

Abstract

A series of rare earth metal dialkyl complexes was prepared with the general formula [Me 2 TACN-(B)-NR]M(CH 2 SiMe 3 ) 2 (TACN ) 1,4,7-triazacyclononane, B ) (CH 2 ) 2 , SiMe 2 ; R ) tBu, secBu, nBu; M ) Sc, Y, Nd, La). For M ) Sc, mixed monoalkyl-monochloro complexes were also accessible. Selected examples of these complexes were structurally characterized and show the metal in a distorted octahedral environment. With Lewis or Brønsted acid activators the dialkyl compounds can be converted to the corresponding monoalkyl cations, which were characterized by NMR spectroscopy. Comparative testing in catalytic ethylene polymerization showed that the catalyst activity is most strongly influenced by the metal ionic radius, but that variations in the ligand backbone and substitution pattern do influence other factors, such as polymer molecular weight and catalyst stability. Catalysts with the intermediately sized rare earth metal yttrium generally showed the highest activity, but some of these catalysts produce polyethylene with broad molecular weight distributions, suggesting multisite behavior. Hypothetically this could be caused by intermolecular ligand scrambling processes. Evidence that these may occur was found in the isolation of the "half-flyover" bimetallic yttrium complex {[η 3 :η 1 -[Me 2 TACN(CH 2 ) 2 NtBu]Y-(CH 2 SiMe 3 )}{η 3 :µ-η 1 -[Me 2 TACN(CH 2 ) 2 NtBu]Y(CH 2 SiMe 3 ) 3 .

Compositional Insights and Valorization Pathways for Carbonaceous Material Deposited During Bio‐Oil Thermal Treatment

“…Novel applications for instance comprise silylamides as supporting ligands for complexes with metal–metal single and multiple bonds 3,4. Moreover, the use of functionalized silylamide ligands bearing additional donor groups has opened new perspectives in coordination chemistry in particular concerning the stabilization of transition metal dinitrogen complexes5 and lanthanoid metal alkyl complexes 6. In 2004 Passarelli et al reported on zirconium complexes with functionalized silylamide ligands of the type [Me 2 Si(NCH 2 CH 2 X) 2 ] 2– and [Me 2 Si(NCH 2 CH 2 CH 2 X) 2 ] 2– with X = NMe 2 or OMe 7.…”

N-Containing Ligands as Universal Coordination Environments for Rare-Earth Alkyl and Bis(alkyl) Complexes

“…Hessen et al reported the synthesis of a series of bis(alkyl) rare-earth complexes 524-538 containing 9-membered macrocyclic triazacyclononanes (TACN) with various substituents at the nitrogen atoms ( Fig. 43) [186][187][188][189].…”

Use of Tetradentate Monoanionic Ligands for Stabilizing Reactive Metal Complexes

“…[39] An alternative functionalized TACN ligand comes from Hessens group, who focused on the examination of an amido tether linked by either an ethyl or a dimethylsilyl bridge to the TACN moiety. [40][41][42][43] Through protonolysis reactions between HL g/h (HL g…”