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‐tBu‐C₆H₄)₂CH]₃Ln (Ln=La (1), Nd (2), Y (3)) were synthesized by the salt metathesis reactions of LnHal₃(THF)_3.5 (Ln=La, Nd, Hal=Cl; Ln=Y, Hal=I) and [(p‐tBu‐C₆H₄)₂CH]Na. In 1–3 the benzhydryl ligands are linked with the metal centres in η⁴‐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‐d₈ at 140 °C during 72 h. The reactions of 1 and 2 with B(C₆F₅)₃ allowed for the synthesis of base‐free cationic complexes [(p‐tBu‐C₆H₄)₂CH]₂Ln[(p‐tBu‐C₆H₄)₂CHB(C₆F₅)₃] (Ln=La (4), Nd (5)) which adopt the structure of a contact ion pair. Combinations of 1–3 and borane ((B(C₆F₅)₃, [Me₂NHPh][B(C₆F₅)₄], [Ph₃C][B(C₆F₅)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.

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