Conversion of alkanenitriles to amidines and carboxylic acids mediated by a cobalt(II)–ketoxime system

Abstract

The conversion of sterically unhindered organonitriles RCN (R = Me, Et, n-Pr, n-Bu) into the corresponding amidines RC(NH)NH₂, isolated as the nitrate salts, and carboxylic acids RCO₂H proceeds in the appropriate nitrile as solvent in the presence of Co(NO₃)₂·6H₂O or the cobalt(II) complex trans-[Co(MeCN)₂(H₂O)₄](NO₃)₂ and a ketoxime R′₂CNOH (R′₂ = Me₂ or C₅H₁₀) but does not proceed at all with either the cobalt compound or the ketoxime taken alone. The amidinium nitrates were characterized by C, H, N elemental analyses, FAB⁺-MS, IR, ¹H and ¹³C{¹H} NMR spectroscopies and the structures of RC(NH₂)NH₂⁺NO₃⁻ (R = Et, n-Pr, n-Bu) were determined by X-ray crystallography, while the carboxylic acids were identified by GC and ¹H and ¹³C{¹H} NMR spectroscopies. The reaction proceeds differently with sterically hindered organonitriles, e.g.i-PrCN and t-BuCN, and—instead of amidinium salts—ammonium nitrate and the appropriate carboxylic acids were identified. The structure of trans-[Co(MeCN)₂(H₂O)₄](NO₃)₂, which is anticipated to be an intermediate in the reaction of Co(NO₃)₂·6H₂O, was determined by X-ray diffractometry.