Reactivity of the magnesium phthalocyanine in dry 3,5-lutidine, in 3,5-lutidine/DMSO and in 3,5-lutidine/acetylacetone systems

A Blueprint for the Stabilization of Sub-Valent Alkaline Earth Complexes

The study of sub-valent Group 2 chemistry is a relatively new research field, being established in 2007 with the report of the first Mg(I) dimers. These species are stabilized by the formation of a Mg-Mg covalent bond; however, the extension of this chemistry to heavier alkaline earth (AE) metals has been frustrated by significant synthetic challenges, primarily associated with the instability of heavy AE-AE interactions. Here we present a new blueprint for the stabilization of heavy AE(I) complexes, based upon the reduction of AE(II) precursors with planar coordination geometries. We report the synthesis and structural characterisation of homoleptic trigonal planar AE(II) complexes of the monodentate amides {N(SiMe3 )2 }- and {N(Mes)(SiMe3 )}- . DFT calculations showed that the LUMOs of these complexes all show some d-character for AE = Ca-Ba. DFT analysis of the square planar Sr(II) complex [Sr{N(SiMe3 )2 }(dioxane)2 ]∞ revealed analogous frontier orbital d-character. AE(I) complexes that could be accessed by reduction of these AE(II) precursors were modelled computationally, revealing exergonic formation in all cases. Crucially, NBO calculations show that some d-character is preserved in the SOMO of theoretical AE(I) products upon reduction, showing that d-orbitals could play a crucial role in achieving stable heavy AE(I) complexes.

Water-Involved Hydrogen Bonds in Dimeric Supramolecular Structures of Magnesium and Zinc Phthalocyaninato Complexes

Two dimeric supramolecular structures {MgPc(H2O)·4-methylmorpholine}2-(1) and {ZnPc(H2O)·4-methylmorpholine}2-(2) formed from two molecules of magnesium and zinc aquaphthalocyanines in 4-methylmorpholine solution were revealed by single-crystal X-ray diffraction. Coordinated H2O molecules to the metal center of respective Mg or Zn phthalocyanines oriented face-to-face to form two hydrogen bonds, one of them connecting via O-H···N-azamethine atom to form a dimeric structure in the crystals with ring-to-ring distances of 3.412(3) Å in 1 and 3.403(5) Å in 2, whereas the second hydrogen bonds link the solvent 4-methylpholine molecules to form supramolecular dimeric {MgPc(H2O)·4-methylmorpholine}2-(1) and {ZnPc(H2O)·4-methylmorpholine}2-(2) structures. The interaction of the metal center of MgPc or ZnPc with O atom of the water molecule results its displacement of ∼0.5 Å from the N4-isonodole plane of the phthalocyaninate(2-) macrocycle that adopts a saucer-shape form. To better understand the interactions leading to the existence of the dimeric structures in the crystals, theoretical calculations of dimer stabilization energy composed of two monomers (MgPcH2O and ZnPcH2O), as well as three-dimensional molecular electrostatic potentials, have been performed using the density functional theoretical method. The calculated absorption spectra of both supramolecular monomers and dimers were compared with the experimental ones in 4-methylmorpholine solution. The water axial ligation of MgPc and ZnPc and the formation of the monomeric and dimeric supramolecular structures only slightly change the energy gap between highest occupied molecular orbital and lowest unoccupied molecular orbital levels that is compared with those of the parent MgPc and ZnPc pigments.