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

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