Reduction of Nitrogen Oxides by Dimagnesium(I) Compounds.

The dimagnesium(I) reagent [{Mg(NCNDipp)}2] (NCNDipp = [(Dipp)NC(NiPr2)N(Dipp)]-, Dipp = 2,6-diisopropylphenyl) reacts with N2O to give the tetra-magnesium oxide/hyponitrite complex [{(NCNDipp)Mg}(μ-N2O2){Mg(NCNDipp)}2(μ-O){Mg(NCNDipp)}] (1) in yields of up to 60%. The solid-state structure of 1 reveals the cis-N2O22- unit to bridge three [Mg(NCNDipp)]+ cations, while the oxide, O2-, bridges three magnesium centers in a μ3-fashion. The electronic structure of 1 was probed computationally. Dimagnesium(I) reagents, [{Mg(NCNDipp)}2] and [{Mg(BDIDipp)}2] (BDIDipp = [{(Dipp)NC(Me)}2CH]-), are shown to react with N-heterocyclic carbene "adducts" of the NO radical (NHCAr-NO•, NHCAr = (HCNAr)2C:, Ar = Mes, 2,4,6-trimethylphenyl; or Dipp) yielding the corresponding NHC-nitroxyl complexes [(NCNDipp)Mg(κ2-N,O-ON-NHCDipp)] (2) and [(BDIDipp)Mg(κ2-N,O-ON-NHCMes)] (3). These products form via a one electron reduction of the NHCAr-NO• radical by a magnesium(I) center. Magnesium(II) butyl [Mg(BDIDipp)(nBu)(THF)] similarly reacts with NHCDipp-NO•, affording [(BDIDipp)Mg(κ1-O-ON-NHCDipp)(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.