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){CyN[double bond, length as m-dash]C(CH2Ph)NCy}]2 (), [Mg(CH2Ph){(i)PrN[double bond, length as m-dash]C(CH2Ph)N(i)Pr}]2 () and the homoleptic [Mg{(t)BuN[double bond, length as m-dash]C(CH2Ph)N(t)Bu}2] () (Cy = cyclohexyl, (i)Pr = isopropyl, (t)Bu = 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{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}2] () (Dipp = 2,6 diisopropylphenyl) in good yield. The solid-state structures of magnesium complexes 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 and N-aryliminopyrrolyl ligand 2-(2,6-(i)Pr2C6H3N[double bond, length as m-dash]CH)C4H3NH (ImpDipp-H) in 1 : 2 molar ratio, a new magnesium complex [Mg(ImpDipp)2{CyN[double bond, length as m-dash]C(CH2Ph)NHCy}] (), with one amidinato and two aryliminopyrrolyl ligands in the coordination sphere, was obtained in good yield. In contrast, the homoleptic magnesium complex reacted with one equivalent of N-aryliminopyrrolyl ligand (ImpDipp-H) to produce another mixed ligated magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}(ImpDipp)] (), with a benzylated DAD ligand and aryliminopyrrolyl ligands in the coordination sphere. Further reaction of complex with benzyl alcohol (PhCH2OH) afforded the third mixed ligated magnesium complex [Mg{DippN[double bond, length as m-dash]C(CH2Ph)CH2NDipp}(OCH2Ph)2] () in very good yield. The magnesium complexes were characterised using standard analytical/spectroscopic techniques and their solid-state structures were established by single-crystal X-ray diffraction analysis.
Highlights
Even though organomagnesium halides of the type RMgX were discovered in 1900 by Victor Grignard, the relevance of these compounds is significant even today in organic and organometallic synthesis.[1]
The new magnesium complexes 1–3 were characterised using standard analytical and spectroscopic techniques, and the solid-state structures of all three magnesium complexes were established by single-crystal X-ray diffraction analysis
The singlet resonance that appeared at δ 3.70 and 3.40 ppm can be assigned to benzylic protons attached to the carbon atom of amidinato ligands
Summary
Even though organomagnesium halides of the type RMgX were discovered in 1900 by Victor Grignard, the relevance of these compounds is significant even today in organic and organometallic synthesis.[1]. In the 1H NMR spectra of homoleptic magnesium complex 3, the sharp singlet at 3.71 ppm corresponds to the resonance of four benzylic protons of –CH2Ph groups attached to the amidinato ligand backbone whereas the other sharp singlet at δ 1.01 ppm can be assigned to the 36 methyl protons CH3 present in four tert-butyl groups. We observed a resonance signal at δ 173.5 ppm for (–N–C(CH2Ph)vN–) carbon in the 13C{1H} NMR spectra of 3 which corresponds to those for complexes 1 and 2.
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