Activation of metallocene hydride intermediates by methylaluminoxane in alkene dimerization and oligomerization

In order to elucidate the dependence of the structure and reactivity of the bimetallic hydride intermediates formed in the systems metallocene—organoaluminum compound—activator on the nature of the transition metal atom and ligand environment, we used NMR spectroscopy to study reactions of a series of L 2 MCl 2 complexes (M = Hf, Zr; L 2 = Cp 2 , (CpMe) 2 , ansa -(Me 2 C) 2 Cp 2 , ansa -Me 2 CInd 2 ) with HAlBu i 2 and MMAO-12 activator. As a result, M, Al-bimetallic intermediates containing [L 2 MH 3 ] and [(L 2 M) 2 H 3 ] type moieties were detected for both hafnium and zirconium complexes with cyclopentadienyl ligands. The [L 2 ZrH 3 ] type structure predominates in the system based on the ansa -bis-indenyl zirconium complex. The detected complexes provide associates with MMAO-12 [L 2 MH 3 ]·MAO and [(L 2 M) 2 H 3 ]·MAO. The MAO-associated intermediates of the [(L 2 M) 2 H 3 ] type are precursors of the catalytically active sites for alkene dimerization. In the system based on ansa -bis-indenyl zirconium complex, the intermediate of the [L 2 MH 3 ] type affords a set of hydride structures, presumably cationic, which lead to alkene oligomerization.