Hafnium-​pyridylamido organometallics: Unusual reactivity of exceptional catalysts for olefin polymerization

Pyridylamido-​Hf(IV)​-​based organometallics have emerged as remarkable catalysts for olefin polymn. having unique properties. Initially reported as the first industrially relevant systems to yield highly isotactic polypropylene with soln.-​process technol., they attracted even greater attention for their propensity of undergoing reversible chain transfer with main element alkyls (such as AlR3 and ZnR2)​, thereby opening the door to novel olefin block copolymers through "chain shuttling" [1]​. In this contribution, we report the results of an integrated NMR and DFT study aimed at understanding the reactivity of hafnium pyridylamido complexes with dialkylzinc and trialkylaluminium species [2]​. In particular, we show that pyridylamido hafnium cations undergo ligand exchange with ZnR2 or AlR3 thus affording unusual heterobimetallic adducts, in which the cyclometallated naphthyl acts a bridge between hafnium and main element. The results of 1H EXSY NMR expt., carried out to investigate the dynamicity of such adducts, are also reported. Finally, we show how the reactivity of the catalyst towards α-​olefins is affected by the presence of ZnR2 or AlEt3.