Mechanism of the catalytic transformation of cyanopyridine isomers into pyridinecarboxamide isomers by magnesium phthalocyanine

Abstract

Three intermediate magnesium phthalocyanine complexes with 2-, 3- and 4-pyridiniecarboxamide, MgPc(2-pyridinecarboxamide), MgPc(3-pyridinecarboxamide) and (MgPc)2(4-pyridinecarboxamide), were obtained during the catalytic transformation of the respective cyanopyridine isomers in presence of magnesium phthalocyanine. These complexes were obtained in the crystalline form and their structures were determined by the X-ray single crystal analysis. In MgPc(2-pyridinecarboxamide) and MgPc(3-pyridinecarboxamide) the Mg centre of MgPc is 4+1 coordinated by the oxygen atom of amide groups of axially coordinated 2- or 3-cyanopyridnine isomers. In the third complex the 4-pyridinecarboxanide acts as an O,N- bridging ligand forming 4+1 O- and N-coordinated (MgPc)2(4-pyridinecarboxamide) supramolecular complex. Owing to the Mg⋯O interaction of the electropositive Mg-centre of MgPc molecule with oxygen atom of amide group of 2- and 3-pyridinecarboxamide axial ligands, the Mg atom is significantly displaced (∼0.5Å) from the plane defined by the four isoindole N atoms of Pc(2-) macrocycle. In the (MgPc)2(4-pyridinecarboxamide) complex the O,N- ligand bridges two MgPc units, therefore the interaction of Mg centre from both MgPc units causes the deviation of the Mg atoms by 0.472(2) and 0.413(2)Å from the N4-plane, respectively for Mg–O-coordinated and Mg–N-coordinated. The interactions of Mg with the axial ligand (Mg⋯O and Mg⋯N) lead a distortion of a planar Pc(2-) macrocycle to the saucer-shape form. Some remarks on the transformation mechanism of the CN group of cyanopyridine isomers into amide group of respective pyridinecarboxamide isomers have been made. The calculated three-dimensional molecular electrostatic potential maps are helpful for understanding the transformation mechanism as well as for better understanding the organisation and the arrangement of the molecules in solid-state (crystal).