The reduction of a cyclic alkyl(amino)carbene (CAAC)‐stabilized organoberyllium chloride yields the first neutral beryllium radical, which was characterized by EPR, IR, and UV/Vis spectroscopy, X‐ray crystallography, and DFT calculations.

The reactions of terminal acetylenes with doubly Lewis base-stabilised diborenes resulted in different outcomes depending on the nature of the ligands at boron and the conformation of the diborene (cyclic...

Durch die Reduktion eines cyclischen Alkyl(amino)carben (CAAC)‐stabilisierten Organoberylliumchlorids konnte das erste neutrale Berylliumradikal erhalten werden, welches durch EPR‐, IR‐ und UV/Vis‐Spektroskopie, Röntgenkristallographie und DFT‐Rechnungen charakterisiert wurde.

Nine different coinage metal (Cu, Ag) π complexes of diborenes with various anionic diborene (aryl, heteroaryl) and metal substituents (Cl, Br, C 6 F 5 , C 2 SiMe 3 ), stabilizing neutral donors (N-heterocyclic carbene = NHC, phosphine), configurations (cis/trans, acyclic/cyclic diborene), and charges (neutral, cationic) were synthesized and characterized by multinuclear NMR spectroscopy and X-ray crystallographic analyses. Their optical properties were investigated by UV−vis absorption and steadystate as well as time-resolved luminescence spectroscopy in solution and the solid state to gain insights into the excited-state behavior of this unusual class of photoactive compounds and to provide structure−property relationships. The structural and electronic modification of the (B�B)•••M motif greatly influences not only the visible light absorption but also the photostability and quantum yields, which can reach high values of up to f = 0.42. The lifetimes are found in the nanosecond regime, providing estimated radiative rate constants over a wide range of k r = 1.3−14 × 10 7 s −1 , indicative of fluorescence. Intersystem crossing (ISC) is sufficiently slow for prompt emission from the S 1 state to be observed, while the spin−orbit coupling in the T 1 state is too weak for phosphorescence to occur at room temperature. ISC can be accelerated, however, by modifying diborene ligand substitution and the coinage metal center, hinting at the potential for exploiting the properties of long-lived triplet excited states of metal diborene complexes in the future.