title: Anodic preparation of [Re2Cp2(CO)6]2+: a dimeric dication that provides the powerful one-electron oxidant [ReCp(CO)3]+.
abstract: The half-sandwich piano-stool compounds Re(eta5-C5R5)(CO)3 (1, R = H; or 2, R = Me) are oxidized to the corresponding 17-electron Re(II) cations at glassy carbon anodes in CH2Cl2/[NBu4][B(C6F5)4]. Despite the very strongly positive E1/2 values of the couples (1.16 V for 1/1+ and 0.91 V for 2/2+ vs ferrocene/ferrocenium), the radical cations are persistent in this medium and exist in equilibrium with the corresponding dimeric dications, which may be cathodically reduced back to the neutral starting material. DFT calculations show that the dimer of 1+ achieves its stability through formation of a single long (almost 3.3 A) Re-Re bond made possible when the HOMO in 1 is rehybridized away from the metal in the one-electron oxidation process. The pure salts [1][B(C6F5)4]2 and [2][B(C6F5)4]2 were isolated by preparative anodic electrochemistry. The former may be used for storage of the very strong one-electron oxidant 1+, which was used to prepare a number of oxidation products as their [B(C6F5)4]- salts.
authors.affiliation: Department of Chemistry, University of Vermont, Burlington, Vermont 05405, USA.
authors.forename: Daesung
authors.initials: D
authors.lastname: Chong
authors.forename: Ayman
authors.initials: A
authors.lastname: Nafady
authors.forename: Paulo Jorge
authors.initials: PJ
authors.lastname: Costa
authors.forename: Maria José
authors.initials: MJ
authors.lastname: Calhorda
authors.forename: William E
authors.initials: WE
authors.lastname: Geiger