Metal-promoted reactions of 2-cyanopyridine: iron(II), cobalt(II), nickel(II), and copper(II) complexes of O-methylpyridine-2-carboximidate

Abstract

Reaction of 2-cyanopyridine (2-CNpy) with copper(II) chloride in methanol solution can give three different products, viz., [(2-CNpy)₂CuCl₂], (I); [(Mepy)CuCl₂], (II)[Mepy =O-methylpyridine-2-carboximidate]; or [(Mepy)₂(H₂O)₂Cu]Cl₂, (III), (II) and (III) were also prepared directly from O-methylpyridine-2-carboximidate. Methyl 2-picolinate may be obtained in 78% yield from (II); this constitutes a new route to this otherwise difficulty accessible ester. Complexes of O-ethyl- and O-n-butyl-pyridine 2-carboximidates, analogous to (II), were prepared from 2-cyanopyridine with the appropriate alcohol as solvent. [(Mepy)₂Cu](ClO₄)₂, [(Mepy)₂(H₂O)BrNi]Br, [(Mepy)₃Co](ClO₄)₂, [(Mepy)₂CoCl₂], and [(Mepy)CoCl₂],H₂O were prepared from 2-cyanopyridine. [(Mepy)₃Fe](ClO₄)₂,H₂O is low-spin; this result, and the high value of Δ(12,800 cm.^–1) found for [(Mepy)₃Ni](ClO₄)₂, confirm that O-methylpyridine-2-carboximidate is a strong-field ligand of the α-di-imine type. [(np)CuCl₂](np = 2-picolinic acid N-methylamide) and [(np)₃Ni](ClO₄)₂ were prepared and their spectra compared with the isomeric complexes of O-methylpyridine-2-carboximidate. Pyridine 2-carboxamide was obtained in 54% yield via the copper(II)-promoted hydration of 2-cyanopyridine. Spectroscopic, magnetic, and conductimetric results for the complexes are presented and are briefly discussed.