Thermally Stable Cationic Bis(benzhydryl) Complexes of Early Lanthanides (La, Ce, Nd)

A series of base-free Ln(III) tris(benzhydryl) complexes [( p - t Bu-C 6 H 4 ) 2 CH] 3 Ln (Ln = La ( 1 ), Ce ( 2 ), Nd ( 3 )) were synthesized by the salt metathesis reactions of LnCl 3 (THF) 3.5 and [( p - t Bu-C 6 H 4 ) 2 CH]K. Cerium complex 2 similarly to the previously published congeners 1 and 3 features η 4 -type of coordination of benzhydryl ligands. The reactions of equimolar amounts of 1 – 3 and Brønsted acid [NHEt 3 ][B(C 6 H 5 ) 4 ] allowed for the synthesis of cationic bis(alkyl) complexes of large lanthanides [{( p - t Bu-C 6 H 4 ) 2 CH} 2 Ln(TMEDA)][BPh 4 ] (Ln = La ( 4 ), Ce ( 5 ), Nd ( 6 )), which were isolated as separated ion pairs containing one TMEDA molecule coordinated with a Ln ion. In contrast, the reaction of 2 with Lewis acid B(C 6 F 5 ) 3 affords a base-free cationic complex [{( p - t Bu-C 6 H 4 ) 2 CH} 2 Ce][μ-{( p - t Bu-C 6 H 4 ) 2 CH}B(C 6 F 5 ) 3 ] ( 7 ), which adopts the structure of a contact ion pair with μ-η 1:η 6 -bridging benzhydryl ligand. Cationic complexes 4 – 7 proved to be thermally stable: no decomposition was observed even after heating their solutions in toluene at 80 °C for 72 h.