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

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.