Reduction of Nitrogen Oxides by Dimagnesium(I) Compounds

The dimagnesium(I) reagent [{Mg(NCN^Dipp)}₂] (NCN^Dipp = [(Dipp)NC(NⁱPr₂)N(Dipp)]^-, Dipp = 2,6-diisopropylphenyl) reacts with N₂O to give the tetra-magnesium oxide/hyponitrite complex [{(NCN^Dipp)Mg}(μ-N₂O₂){Mg(NCN^Dipp)}₂(μ-O){Mg(NCN^Dipp)}] (1) in yields of up to 60%. The solid-state structure of 1 reveals the cis-N₂O₂^2- unit to bridge three [Mg(NCN^Dipp)]⁺ cations, while the oxide, O^2-, bridges three magnesium centers in a μ₃-fashion. The electronic structure of 1 was probed computationally. Dimagnesium(I) reagents, [{Mg(NCN^Dipp)}₂] and [{Mg(BDI^Dipp)}₂] (BDI^Dipp = [{(Dipp)NC(Me)}₂CH]^-), are shown to react with N-heterocyclic carbene "adducts" of the NO radical (NHC^Ar-NO^•, NHC^Ar = (HCNAr)₂C:, Ar = Mes, 2,4,6-trimethylphenyl; or Dipp) yielding the corresponding NHC-nitroxyl complexes [(NCN^Dipp)Mg(κ²-N,O-ON-NHC^Dipp)] (2) and [(BDI^Dipp)Mg(κ²-N,O-ON-NHC^Mes)] (3). These products form via a one electron reduction of the NHC^Ar-NO^• radical by a magnesium(I) center. Magnesium(II) butyl [Mg(BDI^Dipp)(ⁿBu)(THF)] similarly reacts with NHC^Dipp-NO^•, affording [(BDI^Dipp)Mg(κ¹-O-ON-NHC^Dipp)(THF)] (4) via an electron transfer process that ultimately generates n-octane through an alkyl coupling process. Complexes 2-4 were structurally authenticated in the solid-state and characterized in solution by NMR spectroscopic methods. DFT studies were used to give insight into the electronic structure of complexes 2-4.