Redox-Switchable Behavior of Transition-Metal Complexes Supported by Amino-Decorated N-Heterocyclic Carbenes.

The coordination chemistry of the N-heterocyclic carbene ligand IMes ^(NMe2)2 , derived from the well-known IMes ligand by substitution of the carbenic heterocycle with two dimethylamino groups, was investigated with d ⁶ [Mn(I), Fe(II)], d ⁸ [Rh(I)], and d ¹⁰ [Cu(I)] transition-metal centers. The redox behavior of the resulting organometallic complexes was studied through a combined experimental/theoretical study, involving electrochemistry, EPR spectroscopy, and DFT calculations. While the complexes [CuCl(IMes ^(NMe2)2 )], [RhCl(COD)(IMes ^(NMe2)2 )], and [FeCp(CO) ₂ (IMes ^(NMe2)2 )](BF ₄ ) exhibit two oxidation waves, the first oxidation wave is fully reversible but only for the first complex the second oxidation wave is reversible. The mono-oxidation event for these complexes occurs on the NHC ligand, with a spin density mainly located on the diaminoethylene NHC-backbone, and has a dramatic effect on the donating properties of the NHC ligand. Conversely, as the Mn(I) center in the complex [MnCp(CO) ₂ ((IMes ^(NMe2)2 )] is easily oxidizable, the latter complex is first oxidized on the metal center to form the corresponding cationic Mn(II) complex, and the NHC ligand is oxidized in a second reversible oxidation wave.