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Being valuable precursors in the production of adhesives, lubricants, and other high-performance synthetic compounds, alkene dimers and oligomers can be obtained using homogeneous zirconocene catalytic systems. Further advances in such systems require precise control of their activity and chemoselectivity, increasing both the purity and yield of the products. This relies on the process mechanism usually built around the consideration of the hydride complexes as active intermediates in the alkene di- and oligomerization; however, the majority of studies lack the direct evidence of their involvement. Parallel studies on a well-known Cp2ZrCl2-AlR3 or HAlBui2 and a novel [Cp2ZrH2]2-ClAlR2 (R = Me, Et, Bui) systems activated by methylaluminoxane (MMAO-12) have shown a deep similarity both in the catalytic performance and intermediate composition. As a result of the NMR studies, among all the intermediates considered, we proved that new Zr,Zr- hydride complexes having the type x[Cp2ZrH2∙Cp2ZrHCl∙ClAlR2]∙yMAO appear to be specifically responsible for the alkene dimerization with high yield.

The zirconocene complexes L2ZrCl2 (L = C5H5, C5H4Me, Ind, C5Me5; L2 = rac-Me2C­(2-Me-4-But-C5H2)2, meso-Me2C­(2-Me-4-But-C5H2)2, rac-Me2C­(3-But-C5H3)2, rac-Me2C­(Ind)2, rac-Me2Si­(Ind)2, and rac- C2H4(Ind)2) were tested as catalysts in alkene hydroalumination by the isobutylalanes XAlBui 2 (X = H, Cl, Bui). A low-temperature NMR spectroscopy study on the structure and dynamics of Zr,Al intermediates formed in the L2ZrCl2–XAlBui 2 systems showed that the intra- and intermolecular exchange in the bimetallic clusters, controlled by the steric factor of the η5 ligand and organoaluminum compound nature, determines the activity of the whole catalytic system.

The mechanism of intermediate formation in the reaction of HAlBu i 2 with Cp 2 ZrCl 2 has been studied by DFT calculations. Stationary points have been localized on the potential energy surface of the reaction; enthalpy has been calculated for each of them at T ) 203 K. It was shown that the thermodynamically probable way of the process includes formation of a bridge bimetallic complex [Cp 2 ZrCl 2 • HAlBu i 2 ], which with dissociation gives Cp 2 ZrHCl. The subsequent coordination of Cp 2 ZrHCl with HAlBu i 2 provides the intermediate [Cp 2 ZrHCl • HAlBu i 2 ], which dimerizes into an experimentally observed complex [Cp 2 ZrH 2 • ClAlBu i 2 ] 2 . The competing stage of [Cp 2 ZrHCl • HAlBu i 2 ] interaction with HAlBu i 2 yields complex [Cp 2 ZrH 2 • ClAlBu i 2 • HAlBu i 2 ], which shows low activity in the olefin hydrometalation. As a result, the scheme of the intermediates' formations and transformations in the reaction of HAlBu i 2 with Cp 2 ZrCl 2 was proposed.

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