2,6-Diiminopyridine complexes of group 2 metals: synthesis, characterisation and redox behaviour

摘要

Treatment of the 2,6-diiminopyridine, NC5H3{C(Ph)-N(Dip)}(2)-2,6 ((Ph)Dimpy, Dip = 2,6-diisopropylphenyl) with [MgI2(OEt2)(2)] gives the adduct complex [((Ph)Dimpy)MgI2] in which the (Ph)Dimpy ligand is neutral. This complex can be singly reduced by KC8 or a magnesium(i) complex to give [((Ph)Dimpy)MgI], in which (Ph)Dimpy acts as a radical anion. Double reduction of [((Ph)Dimpy)MgI2] in diethyl ether yields [((Ph)Dimpy)Mg(OEt2)], in which the magnesium centre is ligated by dianionic [(Ph)Dimpy](2-). [((Ph)Dimpy)Mg(OEt2)] can alternatively be prepared by the simple, high yielding reaction between (Ph)Dimpy and activated magnesium. A comproportionation reaction occurs between [((Ph)Dimpy)MgI2] and [((Ph)Dimpy)Mg(OEt2)], leading to the quantitative formation of [((Ph)Dimpy)MgI]. The heavier group 2 metal dimeric complexes [{((Ph)Dimpy)M}(2)] (M = Ca, Sr, Ba) can be similarly accessed by reaction of (Ph)Dimpy with the activated metal, or by KC8 reduction of in situ generated [((Ph)Dimpy)MI2] (M = Ca, Sr). All prepared complexes have been characterised by X-ray crystallography and NMR spectroscopy. Electrochemical investigations into the complexes incorporating [(Ph)Dimpy](2-) ligands reveal that they can undergo quasi-reversible 1- and 2-electron reduction processes, quasi-reversible 1-electron oxidations, and largely irreversible 2-electron oxidation events. These studies suggest that the compounds hold promise as soluble reducing agents in organic and inorganic synthesis.