Activation of carbon-carbon bonds in d9 (Co, Rh, Ir) and d8 (Ru) metal coordinated bicyclo[3.2.1]octa-2,6-diene via agostic M-H-C and M-H interactions

Abstract

This contribution reveals the first synthesis, protonation reactions and skeletal rearrangements of a series of [M(η5-C5R5)(η2:η2-bicyclo[3.2.1]octa-2,6-diene or 2,6-bcod)(M=Co, Rh, Ir, R=H, Me)] 1-3 and [Ru(η6-arene)(η2:h2-bicyclo[3.2.1]octa-2,6-diene)(arene= C6Me6, C6Me4H2, C6H3Me3)] 4 complexes. Monoprotonation of these coordinated bicyclo[3.2.1]octa-2,6-diene or 2,6-bcod complexes, 1,3,4 with super acids such as HPF6 (60% aq), HBF4.Et2O or CF3SO3H at low temperature (-80° to -20 °C) forms agostic M-H-C structures for [Rh(µ-H)(η5-C5R5)(η2:h2-2,6-bcod)]+, 5, [Co(µ-H)(h5-C5H5)(h2: h2-2,6-bcod)]+6 and [Ru(µ-H)(η6-arene)(η2:h2-2,6-bcod)]+, 7. Similar reactions of 2a, b with the 5d transition metals gave terminal hydride complexes [Ir(H)(η5-C5Me5)(η2:h2-2,6-bcod)][PF6] 8a, b as isolable salts at room temperature. Initial products of all these monoprotonated cationic salts 5 - 8, undergo isomerization via hydride migration and subsequent cleavage of carbon-carbon bonds to the corresponding η2-vinyl η3-cyclohexenyl cations 9 - 12, independent of the non-coordinating anions. All metal coordinated η2- vinyl, η3-cyclohexenyl cations were isolated and characterized by 1H and 13C NMR spectroscopic methods. The structure of 9b was solved by X-ray crystallographic analysis. Nucleophilic addition of H− to the [Ruthenium(η6-hexamethyl)(η2-vinyl η3-cyclohexenyl)]PF6 cation, 12c resulted in the formation of 5-ethyl-η4-1,3-cyclohexadiene complex, 14c as the isomerized product.