Tris(benzhydryl) and Cationic Bis(benzhydryl) Ln(III) Complexes: Exceptional Thermostability and Catalytic Activity in Olefin Hydroarylation and Hydrobenzylation with Substituted Pyridines
Alexander N. Selikhov, Egor Boronin, Anton V. Cherkasov, Georgy K. Fukin, Andrey S. Shavyrin, Alexander A. Trifonov
Abstract
Abstract 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. magnified image