Unusual activation pathways of amines in the reactions with molybdenum pentachloride

The 1-:-1 molar reactions at room temperature of MoCl5with aliphatic amines were investigated in dichloromethane. Pyrrolidine, diethylamine and dibenzylamine underwent dehydrogenative oxidation when allowed to react with MoCl5; the compounds [MoCl5NCH(CH2)3], 1, and [CH3CHNHEt][MoOCl4], 2, were isolated in moderate to low yields from MoCl5/pyrrolidine and MoCl5/NHEt2, respectively. The chloride-amide complex [MoCl4(NEt2)], 3, was afforded in 65% yield from MoCl5and Et2NSiMe3. The interaction of MoCl5with Me2NSiMe3was accompanied by activation of the solvent, and the complexes [MoCl3(NMe2)(κ2-Me2NCH2NMe2)], 4a, and [MoCl3(NMe)(κ2-Me2NCH2NMe2)], 4b, co-crystallized from the reaction mixture. The reactions of MoCl5with a series of primary amines afforded mixtures of products, and the Mo(vi) chloride imido complexes [MoCl4(NR)]2(R = Cy, 5a;tBu, 5b) were isolated in ca. 40% yield from MoCl5/NH2R (R = Cy,tBu). C-H bond activation may be viable in the reactions of MoCl5with tertiary amines: the compounds [(CH2Ph)2NCHPh]2[MoCl6]·CH2Cl2, 6, and [NHEt3]2[Mo2Cl10], 7, were obtained from MoCl5/tribenzylamine and MoCl5/triethylamine, respectively. Pyrrolidine and tribenzylamine underwent analogous activation pathways when allowed to react with [MoCl3OCH(CF3)2]2in the place of MoCl5. The isolated metal products were characterized by analytical and spectroscopic techniques, in addition the structures of 1, 2, 4, 5a, 6·CH2Cl2and 7 were ascertained by single crystal X-ray diffraction studies. The organic products were identified by NMR and GC-MS after hydrolysis of the reaction mixtures. DFT calculations were carried out in order to assist the IR assignments, and clarify structural and mechanistic aspects.