Tris(benzhydryl) and Cationic Bis(benzhydryl) Ln(III) Complexes: Exceptional Thermostability and Catalytic Activity in Olefin Hydroarylation and Hydrobenzylation with Substituted Pyridines

A series of Ln(III) tris(benzhydryl) complexes [( p ‐ t Bu‐C 6 H 4 ) 2 CH] 3 Ln (Ln=La ( 1 ), Nd ( 2 ), Y ( 3 )) were synthesized by the salt metathesis reactions of LnHal 3 (THF) 3.5 (Ln=La, Nd, Hal=Cl; Ln=Y, Hal=I) and [( p ‐ t Bu‐C 6 H 4 ) 2 CH]Na. In 1–3 the benzhydryl ligands are linked with the metal centres in η 4 ‐coordination mode. For diamagnetic complexes 1 and 3 a fluxional behaviour was detected in solution. Complexes 1 – 3 proved to be thermally stable: no decomposition was observed even after heating their solutions in toluene‐d 8 at 140 °C during 72 h. The reactions of 1 and 2 with B(C 6 F 5 ) 3 allowed for the synthesis of base‐free cationic complexes [( p ‐ t Bu‐C 6 H 4 ) 2 CH] 2 Ln[( p ‐ t Bu‐C 6 H 4 ) 2 CHB(C 6 F 5 ) 3 ] (Ln=La ( 4 ), Nd ( 5 )) which adopt the structure of a contact ion pair. Combinations of 1 – 3 and borane ((B(C 6 F 5 ) 3 , [Me 2 NHPh][B(C 6 F 5 ) 4 ], [Ph 3 C][B(C 6 F 5 ) 4 ]) as well as 4 and 5 were found to be highly efficient, regio‐ and chemoselective catalysts for hydroarylation and hydrobenzylation of C=C bonds of a variety of substrates with substituted pyridines. These catalysts enable highly challenging transformations such as hydrobenzylation of 1,1‐disubstituted and internal C=C bonds.