Sanderson, Matthew D. Kamplain, Justin W. Bielawski, Christopher W. Quinone-Annulated N-Heterocyclic Carbene−Transition-Metal Complexes:  Observation of π-Backbonding Using FT-IR Spectroscopy and Cyclic Voltammetry A new N-heterocyclic carbene architecture comprising a 1,4-naphthoquinone annulated to 1,3-dimesitylimidazolylidene (NpQ−NHC) was synthesized in two high yielding steps from commercially available starting materials. The free NpQ−NHC was characterized (solution and solid-state) and was used to synthesize various Rh and Ag complexes that ranged in π-electron density. Enabled by the quinone moiety, the π-systems of these complexes were analyzed using infrared spectroscopy and cyclic voltammetry. In contrast to previous reports, π-backbonding was found to be non-negligible and was directly influenced by the metal's electronic character. Cyclic VoltammetryA;naphthoquinone;NpQ;backbonding;Backbonding;Ag complexes;Rh;annulated;Carbene;cyclic voltammetry;contrast;quinone moiety;material;Enabled;Complexe;dimesitylimidazolylidene;carbene;Spectroscopy;electron;density;solution;spectroscopy 2006-12-27
    https://acs.figshare.com/articles/journal_contribution/Quinone_Annulated_N_Heterocyclic_Carbene_Transition_Metal_Complexes_Observation_of_Backbonding_Using_FT_IR_Spectroscopy_and_Cyclic_Voltammetry/3038632
10.1021/ja067475w.s001