Unusual activation pathways of amines in the reactions with molybdenum pentachloride?

New Journal of Chemistry Pub Date: 2017-05-08 DOI: 10.1039/C6NJ03992H

Abstract

The 1?:?1 molar reactions at room temperature of MoCl5 with aliphatic amines were investigated in dichloromethane. Pyrrolidine, diethylamine and dibenzylamine underwent dehydrogenative oxidation when allowed to react with MoCl5; the compounds [MoCl5{NCH(CH2)3}], 1, and [CH3CH[double bond, length as m-dash]NHEt][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 MoCl5 and Et2NSiMe3. The interaction of MoCl5 with Me2NSiMe3 was 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 MoCl5 with 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 MoCl5 with tertiary amines: the compounds [(CH2Ph)2N[double bond, length as m-dash]CHPh]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 [MoCl3{OCH(CF3)2}]2 in 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·CH2Cl2 and 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.

Graphical abstract: Unusual activation pathways of amines in the reactions with molybdenum pentachloride
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