The novel versatile Co(I) tris-carbene complex [(TIMENxyl)Co]Cl (1) (TIMEN = (tris[2-(3-aryl-2,3-dihydro-1H-imidazol-2-ylidene)ethyl]amine)) reacts with CO, 1-electron oxidizers such as CH2Cl2, and O2 to yield the Co complexes [(TIMENxyl)Co(CO)]Cl (2), [(TIMENxyl)Co(Cl)]Cl (3), and peroxo species [(TIMENxyl)Co(O2)](BPh4) (5). All new complexes were fully characterized by 1H NMR, UV/visible, and IR spectroscopy as well as superconducting quantum interference device (SQUID) magnetization measurements and single-crystal x-ray crystallog. The nucleophilic character of the eta2-bound dioxygen ligand in 5 was confirmed by d. functional theory (DFT) studies and allows for oxygen-transfer reactions with electron-deficient org. substrates, such as benzoyl chloride. [on SciFinder (R)]