Reduction of Nitrogen Oxides by Dimagnesium(I) Compounds

The dimagnesium(I) reagent [{Mg(NCN Dipp )} 2 ] (NCN Dipp = [(Dipp)NC(N i Pr 2 )N(Dipp)] −, Dipp = 2,6-diisopropylphenyl) reacts with N 2 O to give the tetra-magnesium oxide/hyponitrite complex [{(NCN Dipp )Mg}(μ-N 2 O 2 ){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 -N 2 O 2 2– unit to bridge three [Mg(NCN Dipp )] + cations, while the oxide, O 2–, bridges three magnesium centers in a μ 3 -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)} 2 CH] − ), are shown to react with N-heterocyclic carbene “adducts” of the NO radical ( NHC Ar –NO •, NHC Ar = (HCNAr) 2 C:, Ar = Mes, 2,4,6-trimethylphenyl; or Dipp) yielding the corresponding NHC-nitroxyl complexes [(NCN Dipp )Mg(κ 2 - N,O -ON–NHC Dipp )] ( 2 ) and [(BDI Dipp )Mg(κ 2 - 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 )( n Bu)(THF)] similarly reacts with NHC Dipp –NO •, affording [(BDI Dipp )Mg(κ 1 - 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 .