Syntheses, structures and redox properties of some complexes containing the Os(dppe)Cp* fragment, including [{Os(dppe)Cp*}2(μ-CCCC)]

Abstract

The sequential conversion of [OsBr(cod)Cp*] (9) to [OsBr(dppe)Cp*] (10), [Os(CCH₂)(dppe)Cp*]PF₆ ([11]PF₆), [Os(CCH)(dppe)Cp*] (12), [{Os(dppe)Cp*}₂{μ-(CCH–CHC)}][PF₆]₂ ([13](PF₆)₂) and finally [{Os(dppe)Cp*}₂(μ-CCCC)] (14) has been used to make the third member of the triad [{M(dppe)Cp*}₂(μ-CCCC)] (M = Fe, Ru, Os). The molecular structures of [11]PF₆, 12 and 14, together with those of the related osmium complexes [Os(NCMe)(dppe)Cp*]PF₆ ([15]PF₆) and [Os(CCPh)(dppe)Cp*] (16), have been determined by single-crystal X-ray diffraction studies. Comparison of the redox properties of 14 with those of its iron and ruthenium congeners shows that the first oxidation potential E¹ varies as: Fe ≈ Os < Ru. Whereas the Fe complex has been shown to undergo three sequential 1-electron oxidation processes within conventional electrochemical solvent windows, the Ru and Os compounds undergo no fewer than four sequential oxidation events giving rise to a five-membered series of redox related complexes [{M(dppe)Cp*}₂(μ-C₄)]ⁿ⁺ (n = 0, 1, 2, 3 and 4), the osmium derivatives being obtained at considerably lower potentials than the ruthenium analogues. These results are complimented by DFT and DT DFT calculations.