Reduction of Nitrogen Oxides by Dimagnesium(I) Compounds

The dimagnesium(I) reagent [{Mg(NCN^Dipp)}₂] (NCN^Dipp = [(Dipp)NC(N^<i>i</i>Pr₂)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)}] (<b>1</b>) in yields of up to 60%. The solid-state structure of <b>1</b> reveals the <i>cis</i>-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 <b>1</b> 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 (<b>NHC</b>^<b>Ar</b><b>-NO</b>^•, NHC^Ar = (HCNAr)₂C:, Ar = Mes, 2,4,6-trimethylphenyl; or Dipp) yielding the corresponding NHC-nitroxyl complexes [(NCN^Dipp)Mg(κ²-<i>N,O</i>-ON-NHC^Dipp)] (<b>2</b>) and [(BDI^Dipp)Mg(κ²-<i>N,O</i>-ON-NHC^Mes)] (<b>3</b>). These products form via a one electron reduction of the <b>NHC</b>^<b>Ar</b><b>-NO</b>^<b>•</b> radical by a magnesium(I) center. Magnesium(II) butyl [Mg(BDI^Dipp)(^<i>n</i>Bu)(THF)] similarly reacts with <b>NHC</b>^<b>Dipp</b><b>-NO</b>^•, affording [(BDI^Dipp)Mg(κ¹-<i>O</i>-ON-NHC^Dipp)(THF)] (<b>4</b>) via an electron transfer process that ultimately generates <i>n</i>-octane through an alkyl coupling process. Complexes <b>2</b>-<b>4</b> 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 <b>2</b>-<b>4</b>.