Boosting the π‐Acceptor Property of Mesoionic Carbenes by Carbonylation with Carbon Monoxide

Abstract

We report the room temperature dimerization of carbon monoxide mediated by C4/C5‐vicinal anionic dicarbenes Li(ADC) (ADC = ArC{(Dipp)NC}2; Dipp = 2,6‐iPr2C6H3; Ar = Ph, DMP (4‐Me2NC6H4), Bp (4‐PhC6H4)) to yield (E)‐ethene‐1,2‐bis(olate) (i.e. –O–C=C–O– = COen) bridged mesoionic carbene (iMIC) lithium compounds (COen‐[(iMIC)Li]2) (COen‐[iMIC]2 = [ArC{(Dipp)NC}2­(CO)]2) in quantitative yields. COen‐[(iMIC)Li]2 are highly colored stable solids, exhibit a strikingly small HOMO‐LUMO energy gap, and readily undergo 2e‐oxidations with selenium, CuCl (or CuCl2), and AgCl to afford the dinuclear compounds COon‐[(iMIC)E]2 (E = Se, CuCl, AgCl) featuring a 1,2‐dione bridged neutral bis‐iMIC (COon‐[iMIC]2 = {ArC{(Dipp)NC}2(C=O)). COen‐[(iMIC)Li]2 undergo redox‐neutral salt metathesis reactions with LiAlH4 and (Et2O)2BeBr2 and afford COen‐[(iMIC)AlH2]2 and COen‐[(iMIC)BeBr]2, in which the dianionic COen‐moiety remains intact. All compounds have been characterized by NMR spectroscopy, mass spectrometry, and X‐ray diffraction. Stereoelectronic properties of COon‐[iMIC]2 are quantified by experimental and theoretical methods.