Monomeric Tetraalkylaluminates of Divalent Ytterbium Stabilized by a Bulky Tris(pyrazolyl)borate Ligand

Mononuclear heterobimetallic complexes (TptBu,Me)Yb(AlR4) (R = Me, Et) were obtained in high yields according to a silylamide elimination protocol employing (TptBu,Me)Yb[N(SiMe3)2] and AlR3. The solid-state structures revealed κ3-coordinated TptBu,Me ligands and η2-coordinated [AlR4] moieties, with additional Yb···H agostic interactions from the bridging methyl and methylene groups of the [AlR4] ligands. These agostic interactions however are not strong enough to maintain a rigid structure in solution. 1H NMR spectroscopy showed a highly fluxional ligand environment with only one set of signals for both TptBu,Me and [AlR4] ligands at temperatures down to −80 °C.