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

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.Michael I. Bruce, Karine Costuas, Thomas Davin, Jean-François Halet, Kathy A. Kramarczuk, Paul J. Low, Brian K. Nicholson, Gary J. Perkins, Rachel L. Roberts, Brian W. Skelton, Mark E. Smith and Allan H. Whit