title: Rare-earth metal bis(tetramethylaluminate) complexes supported by a sterically crowded triazenido ligand.
abstract: Complexes [NNN]Ln(AlMe(4))(2) (Ln = Y, La, Nd, Lu) bearing the sterically demanding aryl-substituted triazenido ligand [(Tph)(2)N(3)] (Tph = [2-(2,4,6-iPr(3)C(6)H(2))C(6)H(4)]) can be obtained from homoleptic complexes Ln(AlMe(4))(3) in moderate yields, both via protonolysis with [(Tph)(2)N(3)]H and a salt metathesis reaction pathway utilizing [(Tph)(2)N(3)]K. In the solid state the Y and Lu derivatives are isostructural, with both tetramethylaluminate groups coordinated in an eta(2) fashion, while one of the [AlMe(4)] ligands of the Nd derivative features a distorted eta(2) coordination mode. Due to the high affinity of the triazenido ligand toward the more Lewis-acidic and harder aluminium cation compared to the softer rare-earth metal centres, ligand redistribution is observed in solution and formation of byproduct [(Tph)(2)N(3)]AlMe(2) is prominent. While the monoanionic triazenido ligand coordinates the rare-earth metal centres in an asymmetrical syn/anti fashion, it adopts an almost symmetric syn/syn configuration in the aluminium complex. Attempts were also made to produce putative dimethyl complexes {[(Tph)(2)N(3)]LnMe(2)} (Ln = Y, Lu) via cleavage of the aluminate moieties with diethyl ether. Furthermore, the intrinsic redistribution reactions are proposed to affect the performance of complexes [(Tph)(2)N(3)]Ln(AlMe(4))(2) in isoprene polymerization.
authors.affiliation: Department of Chemistry, University of Bergen, Allégaten 41, 5007, Bergen, Norway.
authors.forename: Rannveig
authors.initials: R
authors.lastname: Litlabø
authors.forename: Hyui Sul
authors.initials: HS
authors.lastname: Lee
authors.forename: Mark
authors.initials: M
authors.lastname: Niemeyer
authors.forename: Karl W
authors.initials: KW
authors.lastname: Törnroos
authors.forename: Reiner
authors.initials: R
authors.lastname: Anwander