Scheme 1. Diborane or silane-mediated deoxygenation of co-axial uranyl dications to form the new tetracations [OUOUO]⁴⁺2, 3, and 5, with either trans,-cis- (for boron) or trans,-trans- (for silicon) geometry, and the further deoxygenation of 3 to afford the UOU-containing 4.