Boosting the π‐Acceptor Property of Mesoionic Carbenes by Carbonylation with Carbon Monoxide
Arne Merschel, Yury V. Vishnevskiy, Beate Neumann, Hans‐Georg Stammler, Rajendra S. Ghadwal
Abstract
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‐ i Pr 2 C 6 H 3 ; Ar = Ph, DMP (4‐Me 2 NC 6 H 4 ), Bp (4‐PhC 6 H 4 )) to yield ( E )‐ethene‐1,2‐bis(olate) (i.e. − O−C=C−O − = CO en ) bridged mesoionic carbene (iMIC) lithium compounds CO en ‐[(iMIC)Li] 2 (CO en ‐[iMIC] 2 = [ArC{(Dipp)NC} 2 (CO)] 2 ) in quantitative yields. CO en ‐[(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 CuCl 2 ), and AgCl to afford the dinuclear compounds CO on ‐[(iMIC)E] 2 (E = Se, CuCl, AgCl) featuring a 1,2‐dione bridged neutral bis‐iMIC (i.e. CO on ‐[iMIC] 2 = [ArC{(Dipp)NC} 2 (C=O)] 2 ). CO en ‐[(iMIC)Li] 2 undergo redox‐neutral salt metathesis reactions with LiAlH 4 and (Et 2 O) 2 BeBr 2 and afford CO en ‐[(iMIC)AlH 2 ] 2 and CO en ‐[(iMIC)BeBr] 2 , in which the dianionic CO en ‐moiety remains intact. All compounds have been characterized by NMR spectroscopy, mass spectrometry, and X‐ray diffraction. Stereoelectronic properties of CO on ‐[iMIC] 2 are quantified by experimental and theoretical methods.