title: Assessing the reactivity of sodium alkyl-magnesiates towards quinoxaline: single electron transfer (SET) vs. nucleophilic alkylation processes.
abstract: By exploring the reactivity of sodium butyl-magnesiate (1) supported by the bulky chelating silyl(bisamido) ligand {Ph2Si(NAr*)2}(2-) (Ar* = 2,6-iPr2-C6H3) towards Quinoxaline (Qx), the ability of this bimetallic system to effectively promote SET processes has been disclosed. Thus 1 executes the single-electron reduction of Qx affording complex (2) whose structure in the solid state contains two quinaxolyl radical anions Qx˙ stabilised within a dimeric magnesiate framework. Combining multinuclear NMR and EPR measurements with DFT calculations, new insights into the constitution of 2 in solution and its magnetic behaviour have been gained. Further evidence on the SET reactivity of 1 was found when it was reacted with nitroxyl radical TEMPO which furnished contacted ion pair sodium magnesiate [(Ph2Si(NAr*)2)Mg(TEMPO(-))Na(THF)3] (4) where both metals are connected by an alkoxide bridge, resulting from reduction of TEMPO. The role that the different ligands present in 1 can play in these new SET reactions has also been assessed. Using an amination approach, the Bu group in 1 can be replaced by the more basic amide TMP allowing the isolation of (3) which was characterised by multinuclear NMR and X-ray crystallography. (1)H NMR monitoring of the reaction of 3 with Qx showed its conversion to 2, leaving the hydrogen atoms of the heterocycle untouched. Contrastingly, using sodium homoalkyl magnesiate [NaMg(CH2SiMe3)3] (5) led to the chemoselective C2 alkylation of this heterocycle, suggesting that the presence of the steric stabiliser {Ph2Si(NAr*)2}(2-) on the mixed-metal reagent is required in order to facilitate the Qx reduction.
authors.affiliation: WestCHEM, Department of Pure and Applied Chemistry, University of Strathclyde, Glasgow, G1 1XL, UK. eva.hevia@strath.ac.uk.
authors.forename: Zoe
authors.initials: Z
authors.lastname: Livingstone
authors.forename: Alberto
authors.initials: A
authors.lastname: Hernán-Gómez
authors.forename: Sharon E
authors.initials: SE
authors.lastname: Baillie
authors.forename: David R
authors.initials: DR
authors.lastname: Armstrong
authors.forename: Luca M
authors.initials: LM
authors.lastname: Carrella
authors.forename: William
authors.initials: W
authors.lastname: Clegg
authors.forename: Ross W
authors.initials: RW
authors.lastname: Harrington
authors.forename: Alan R
authors.initials: AR
authors.lastname: Kennedy
authors.forename: Eva
authors.initials: E
authors.lastname: Rentschler
authors.forename: Eva
authors.initials: E
authors.lastname: Hevia