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

Abstract

Abstract Homogeneous catalytic systems based on metallocenes, organoaluminum compounds, and activators proved to be efficient in alkene dimerization, oligomerization, and polymerization reactions. Metal hydrides can act as highly reactive species of these catalytic systems. Despite the large number of experimental and theoretical studies in this field, the effect of the activator on the structure and dynamics of hydride intermediates is an open question. In order to elucidate the dependence of the structure and reactivity of the bimetallic hydride intermediates formed in the systems metal complex – OAC – activator on the nature of the transition metal atom and ligand environment, we used NMR spectroscopy to study reactions of a series of L2MCl2 complexes (M = Hf, Zr; L2 = Cp2, CpMe2, ansa-(Me2C)2Cp2, ansa-Me2CInd2) with HAlBui2 and ММАО-12 activator. As a result, M,Al-bimetallic intermediates containing [L2ZrH3] and [(L2Zr)2H3] type moieties were detected for both hafnium and zirconium complexes with cyclopentadienyl ligands. The [L2ZrH3] type structure predominates in the system based on the ansa-linked bis-indenyl zirconium complex. The detected complexes provide associates with ММАО-12 and, hence, they can act as precursors of active sites determining the alkene dimerization and oligomerization routes.