Observing a Homogeneous Ziegler Catalyst Precursor at Work: Insertion Reactions into the Zirconium – Carbon Bond of the (Butadiene)ZrCp2/B(C6F5)3 Addition Product

Abstract (Butadiene)zirconocene adds to B(C6F5)3 to form the metallacyclic metallocene–boron betaine system 1, which contains a C–F → Zr interaction. Addition of tert‐butylisocyanide or tert‐butyl‐cyanide leads to cleavage of the zirconium – fluorine linkage and formation of the adducts 4 and 7, respectively. With additional tert‐butylisocyanide, 4 reacts further to yield the corresponding η2‐imino‐acyl betaines 5 and 6 (2 stereoisomers), whereas 7 inserts additional tert‐butyl‐cyanide into the Zr–C bond to give a chiral metallacyclic N‐zirconaketimine complex that is probably stabilized by an internal borate → Zr interaction. Ethene and propene insertion reactions into the Zr ‐ C bond of 1 follow a similar course: the mono‐insertion products 9 and 10, respectively, generated in situ and characterized by NMR spectroscopy at – 35°C in [D8]toluene solution, are chiral and are also stabilized by internal borate → Zr coordination. Complexes 9 and 10 are likely to be intermediates in the formation of active homogeneous Ziegler polymerization catalysts.