Rare-earth metal bis(tetramethylaluminate) complexes supported by a sterically crowded triazenido ligand

摘要

Complexes [NNN]Ln(AlMe_4)_2 (Ln = Y, La, Nd, Lu) bearing the sterically demanding aryl-substituted triazenido ligand [(Tph) _2N_3] (Tph = [2-(2,4,6-iPr_3C_6H _2)C_6H_4]) can be obtained from homoleptic complexes Ln(AlMe_4)_3 in moderate yields, both via protonolysis with [(Tph)_2N_3]H and a salt metathesis reaction pathway utilizing [(Tph)_2N_3]K. In the solid state the Y and Lu derivatives are isostructural, with both tetramethylaluminate groups coordinated in an η~2 fashion, while one of the [AlMe _4] ligands of the Nd derivative features a distorted η~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)_2N_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)_2N_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)_2N_3]Ln(AlMe _4)_2 in isoprene polymerization.