Singly NHC-coordinated (aminoboryl)aminoborenium salts react with Na 2 [Fe(CO) 4 ]toyield stable coordination complexes of aminoborylene-stabilized aminoborylenes, which exhibit exceptional s-donor properties.Upon photolytic CO extrusion from the metal center,the diboron ligand adopts anovel h 3 -BBN coordination mode,where bond-strengthening backdonation from the metal center into the vacant B À B porbital is observed. This bonding situation can be alternatively described as aF e-diaminodiborene complex. In ar elated reduction of CAAC-stabilized (aminoboryl)aminoborenium with KC 8 ,t he reduced species can be captured with nucleophiles to form three-coordinate (diaminoboryl)borylenes, where both amino groups have migrated to the distal boron atom. Collectively,t hese reactions illustrate the isomeric flexibility imparted by amino groups on this reduced diboron system, thus opening multiple avenues of novel reactivity. Figure 1. Examples of monovalent boron and diboron species.Supportinginformation and the ORCID identification number for two of the authors of this article can be found under: https://doi.