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

This contribution reveals the first synthesis, protonation reactions and skeletal rearrangements of a series of [M(eta(5)-C5R5)(eta(2):eta(2)-bicyclo[3.2.1]octa-2,6-diene or 2,6-bcod)(M=Co, Rh, Ir, R=H, Me)] 1-3 and [Ru(eta(6)-arene)(eta (2):h(2)-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 center dot Et2O or CF3SO3H at low temperature (-80 degrees to -20 degrees C) forms agostic M-H-C structures for [Rh(p-H)(eta(5)-C5R5)(eta(2):h(2)-2,6-bcod)[(+) 5, [Co(mu-H)(h(5)-C5H5)(h(2): h(2)-2,6-bcod)](+) 6 and [Ru(mu-H)(eta(6)-arene)(eta(2):h(2)-2,6-bcod)](+), 7. Similar reactions of 2a, b with the 5d transition metals gave terminal hydride complexes [Ir(H)(eta(5)-C5Me5)(eta(2):h(2)-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 eta(2)-vinyl eta(3)-cyclohexenyl cations 9 - 12, independent of the non-coordinating anions. All metal coordinated eta(2)-vinyl, eta(3)-cyclohexenyl cations were isolated and characterized by H-1 and C-13 NMR spectroscopic methods. The structure of 9b was solved by X-ray crystallographic analysis. Nucleophilic addition of H- to the [Ruthenium(eta(2)-hexamethyl)(eta(2)-vinyl eta(3)-cyclohexenyl)]PF6 cation, 12c resulted in the formation of 5-ethyl-eta(4)-1,3-cyclohexadiene complex, 14c as the isomerized product. (C) 2022 Elsevier B.V. All rights reserved.

Automated summary

This study presents the synthesis, protonation reactions, and skeletal rearrangements of a series of complexes. Protonation of these complexes can lead to the formation of agostic M-H-C structures. The resulting cationic salts can undergo hydride migration and carbon-carbon bond cleavage to generate various cyclohexenyl cations.