Barium tetraalkylaluminate complexes supported by the super-bulky hydrotris(pyrazolyl)borate ligand

A heteroleptic barium aminobenzyl complex [(Tp Ad,iPr )Ba( o -CH 2 C 6 H 4 -NMe 2 )] ( 1 ) was obtained in excellent yield from a simple one-pot reaction. Treatment of [(Tp Ad,iPr )Ba( o -CH 2 C 6 H 4 -NMe 2 )] ( 1 ) with two equivalents of AlR 3 (R = Me, Et) led to the formation of barium tetraalkylaluminate complexes [(Tp Ad,iPr )Ba(AlR 4 )] n (R = Me, n = 2, 2 ; R = Et, n = 1, 3 ) as dimers or monomers in the solid state. The Tp Ad,iPr ligand-free peralkylated barium complex [Ba(AlEt 4 ) 2 ] n was isolated by the addition of ten equivalents of AlEt 3 under the same conditions. The donor-induced aluminate cleavage is not applicable when donor solvents are added to complexes 2 and 3 . In the solution of complexes 2 and 3 , the alkylaluminate moieties and Tp Ad,iPr ligands show a rapid fluxional behavior in [D 8 ]toluene solution over the temperature range of −70 to 25 °C, without any significant decoalescence of the corresponding proton signals. Treatment of [(Tp Ad,iPr )Ba( o -CH 2 C 6 H 4 -NMe 2 )] with two equivalents of AIR 3 affords [(Tp Ad,iPr )Ba(AlR 4 )] n (R = Me, n = 2; R = Et, n = 1).