Oxidation of cyclic amines by molybdenum(II) and tungsten(II) halocarbonyls, [M(CO)4X2]2 (M = Mo, W; X = Cl, Br)

Abstract

The molybdenum(II) and tungsten(II) halocarbonyls, [M(CO)₄X₂]₂ (M = Mo, W; X = Cl, Br) react with a large excess of the nitrogen bases, 1-methylpyrrolidine, 1-methylpiperidine, 1-ethylpiperidine and 2-ethylpiperidine to give aminecarbonyl complexes of the type M(CO)₃L₃ (L= alkylamine). Excess piperidine reacts with the tungsten halocarbonyls, [W(CO)₄X₂]₂ (X = Cl, Br), to give the trans isomer of the complex, W(CO)₃(C₅H₁₁N)₃. The halogens were recovered as the amminium salts, amine, HX. The oxidized amine dimerized to form a yellow product which was recovered as an oily liquid but in very small amounts. However, in the reaction between Mo(CO)₄Br₂ and 1-ethylpiperidine, a  yellow crystalline solid, with a melting point of 224 ^oC was recovered in sufficient amounts for elemental analysis, melting point and spectral data. Its mass spectrum showed a molecular ion peak at m⁺/z = 222, a clear evidence that the oxidized amine dimerizes. The cyclic dibasic amine piperazine, C₄H₁₀N₂ is not, however, oxidized by these halocarbonyls but rather it reacts by substituting some CO groups to form products of the type, M(CO)₃(C₄H₁₀N₂)₂X₂ (M = Mo, W; X = Cl, Br).  Products were characterized by elemental analysis, IR, UV, ¹H NMR and mass spectrometry.

KEY WORDS: Molybdenum(II), Tungsten(II), Ammines, Halocarbonyls

Bull. Chem. Soc. Ethiop. 2013, 27(2), 233-239

DOI: http://dx.doi.org/10.4314/bcse.v27i2.8