Synthesis, structure and reactivity study of magnesium amidinato complexes derived from carbodiimides and N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-butadiene ligands

Abstract

We report an amidinato ligand-supported series of magnesium complexes obtained from the insertion of a magnesium–carbon bond into a carbon–nitrogen double bond of different carbodiimides and α-diimine ligands. The magnesium complexes [Mg(CH₂Ph){CyNC(CH₂Ph)NCy}]₂ (1), [Mg(CH₂Ph){ⁱPrNC(CH₂Ph)NⁱPr}]₂ (2) and the homoleptic [Mg{^tBuNC(CH₂Ph)N^tBu}₂] (3) (Cy = cyclohexyl, ⁱPr = isopropyl, ^tBu = tert-butyl) were prepared by the reaction of dibenzyl magnesium [Mg(CH₂Ph)₂(Et₂O)₂] with the respective carbodiimides either in 1 : 1 or 1 : 2 molar ratio in toluene. The analogous reaction of [Mg(CH₂Ph)₂(Et₂O)₂] with the N,N′-bis(2,6-diisopropylphenyl)-1,4-diaza-1,3-butadiene (Dipp₂DAD) ligand afforded the corresponding homoleptic magnesium complex [Mg{DippNC(CH₂Ph)CH₂NDipp}₂] (4) (Dipp = 2,6 diisopropylphenyl) in good yield. The solid-state structures of magnesium complexes 1–4 were confirmed by single-crystal X-ray diffraction analysis. It was observed that in each case, a magnesium–carbon bond was inserted into the carbon–nitrogen double bond of either carbodiimides or Dipp₂DAD resulting in a monoanionic amido–imino ligand. In a further reaction between 1 and N-aryliminopyrrolyl ligand 2-(2,6-ⁱPr₂C₆H₃NCH)C₄H₃NH (ImpDipp-H) in 1 : 2 molar ratio, a new magnesium complex [Mg(ImpDipp)₂{CyNC(CH₂Ph)NHCy}] (5), with one amidinato and two aryliminopyrrolyl ligands in the coordination sphere, was obtained in good yield. In contrast, the homoleptic magnesium complex 4 reacted with one equivalent of N-aryliminopyrrolyl ligand (ImpDipp-H) to produce another mixed ligated magnesium complex [Mg{DippNC(CH₂Ph)CH₂NDipp}(ImpDipp)] (6), with a benzylated DAD ligand and aryliminopyrrolyl ligands in the coordination sphere. Further reaction of complex 4 with benzyl alcohol (PhCH₂OH) afforded the third mixed ligated magnesium complex [Mg{DippNC(CH₂Ph)CH₂NDipp}(OCH₂Ph)₂] (7) in very good yield. The magnesium complexes 5–7 were characterised using standard analytical/spectroscopic techniques and their solid-state structures were established by single-crystal X-ray diffraction analysis.