Heterobi‐ and ‐trimetallic Ion Pairs of Zirconocene‐Based Isoselective Olefin Polymerization Catalysts with AlMe 3

The reactivity towards AlMe 3 of discrete cationic ansa‐zirconocenes 2 a,b that are ubiquitously used in isoselective propylene polymerization and based on [{Ph(H)C(3,6‐ t Bu 2 ‐Flu)(3‐ t Bu‐5‐Et‐Cp)}ZrMe 2 )] {Cp‐Flu} and rac ‐[{Me 2 Si‐(2‐Me‐4‐Ph‐Ind) 2 }ZrMe 2 ] {SBI} was scrutinized. The first example of a structurally characterized Group 4 metallocene AlMe 3 adduct ( 3 b ) is reported. In the presence of excess AlMe 3 , the {SBI}‐based AlMe 3 adduct 3 b undergoes a slow decomposition via CH activation in a bridging methyl unit to yield a new species ( 4 b ) with a trimetallic {Zr(μ‐CH 2 )(μ‐Me)AlMe(μ‐Me)AlMe 2 } core. EXSY NMR data for the process 2 b ⇄ 3 b → 4 b suggest very rapid and reversible binding of an additional AlMe 3 molecule onto AlMe 3 adduct 3 b . The resulting heterotrimetallic species intermediates exchange of methyl groups between different metal centers and slowly undergoes the CH activation reaction towards 4 b .