New effective reagent [Cp2ZrH2 · ClAlEt2]2 for alkene hydrometallation

New bimetallic complex [Cp2ZrH2 · ClAlEt2]2 (1) was synthesized, and its reactivity in hydrometallation reaction with the following alkenes was studied: hept-1-ene, okt-1-ene, α-methylstyrene, (1S)-β-pinene, (+)-camphene. Complex 1 shows the highest reactivity among the other known Al,Zr-bimetallic complexes: [Cp2ZrH2 · ClAlBui2]2 (2), [Cp2ZrH2 · AlEt3]2 (3), [Cp2ZrH2 · AlBui3]2 (4) and [Cp2ZrH2 · HAlBui2] (5) as well as organoaluminium compounds (OAC): iBu2AlH, iBu3Al and iBu2AlCl in presence of Zr catalysts. Chlorine containing complexes 1 and 2 appear to be more effective in alkene hydrometallation, and relative hydrometallation rates are (1S)-β-pinene ⩽ (+)-camphene < α-methylstyrene < oct-1-ene < hept-1-ene. Hydrometallation of (1S)-β-pinene and its subsequent oxidation with I2 run with high diastereoselectivity and yield trans-myrtanol. However, the diastereoselectivity of (+)-camphene hydrometallation is less than that for (1S)-β-pinene, and the reaction gives predominately endo-camphanol.

Graphical abstractNew bimetallic complex [Cp2ZrH2 · ClAlEt2]2 was synthesized, and its reactivity in hydrometallation reaction with the following alkenes was studied: hept-1-ene, okt-1-ene, α-methylstyrene, (1S)-β-pinene, (+)-camphene.Figure optionsDownload full-size imageDownload as PowerPoint slide