Cobalt complexes of nitrogen anchored tripodal N-heterocyclic carbene ligand: Coordination chemistry and reactivity study

Cationic cobalt(I) tris-carbene complexe [(TIMENxyl)Co]+ (1) is synthesized by reacting Co(PPh3)3Cl with the nitrogen anchored tripodal N-heterocyclic carbene ligand tris[2-(3-xylenylimidazol-2-ylidene)ethyl]amine (TIMENxyl). Compd. 1 displays diverse reactivity with small mols. 1 reacts with carbon monoxide, dichloromethane, and trimethylsilyl azide to form complexes [(TIMENxyl)Co(CO)]+ (2), [(TIMENxyl)CoCl]+ (3), and [(TIMENxyl)CoN3)]+ (4) resp. Halide-abstraction of 3 in acetonitrile yields complex [(TIMENxyl)Co(CH3CN)]2+ (5). Complexes 1-5 exhibit high-spin electron configurations and are characterized by paramagnetic 1H-NMR, UV-Vis, IR spectroscopy, SQUID magnetization measurement, and X-ray crystallog. Reaction of 1 with dioxygen yields the diamagnetic Co(III) complex [(TIMENxyl)Co(O2)]+ (6). The side-on coordinated dioxygen ligand in 6 is nucleophilic and reacts with electron-deficient unsatd. org. substrates. Reaction of 1 with p-tolyl azide affords a cobalt(III) imido complex [(TIMENxyl)CoNTol)]+ (7). In soln., the imido functionality in 7 migrates into the Co Deg-C(carbene) bond readily in soln. to produce complex [(TIMENxylNTol)Co]2+ (8). The crystal structures of 6 and 8 are detd. [on SciFinder (R)]