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

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 alpha-diimine ligands. The magnesium complexes [Mg(CH2Ph){CyN=C(CH2Ph)NCy}](2) (1), [Mg(CH2Ph)-{(PrN)-Pr-i=C(CH2Ph)(NPr)-Pr-i}](2) (2) and the homoleptic [Mg{(BuN)-Bu-t=C(CH2Ph)(NBu)-Bu-t}(2)] (3) (Cy = cyclohexyl, Pr-i = isopropyl, Bu-t = 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 (Dipp(2)DAD) ligand afforded the corresponding homoleptic magnesium complex [Mg{DippN=C(CH2Ph)CH(2)NDipp}(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 Dipp(2)DAD resulting in a monoanionic amido-imino ligand. In a further reaction between 1 and N-aryliminopyrrolyl ligand 2-(2,6-(Pr2C6H3N)-Pr-i-CH)C4H3NH (ImpDipp-H) in 1 : 2 molar ratio, a new magnesium complex [Mg(ImpDipp)(2){CyN=C(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{DippN=C(CH2Ph)CH(2)NDipp}(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{DippN=C(CH2Ph)CH(2)NDipp}(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 singlecrystal X-ray diffraction analysis.