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Synthesis and Reactivity of Magnesium Complexes Supported by Tris(2-dimethylaminoethyl)amine (Me6tren)

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journal contribution
posted on 13.05.2013, 00:00 by Louise M. Guard, Nilay Hazari
The reaction of tris­(2-dimethylaminoethyl)­amine (Me6tren) with Grignard reagents and related Mg precursors has been investigated. Treating Me6tren with 2 equiv of PhMgBr in diethyl ether resulted in the formation of [(Me6tren)­MgBr]Br (1), in which Me6tren is bound in a κ4 fashion. This is the first example of a Mg complex containing Me6tren or a related tris­(aminoethyl)­amine ligand. In contrast, when MeMgBr was treated with either 1 or 2 equiv of Me6tren, a mixture containing 1 and the alkyl species [(Me6tren)­MgMe]Br (3) was produced. It was not possible to separate the two compounds to generate a pure sample of 3. Reaction between Me6tren and greater than 4 equiv of MeMgBr formed [(Me6tren)­MgBr]2[MgBr4] (4), an analogue of 1 with a different counterion. The highly unusual dialkyl Mg compound (Me6tren)­MgMe2 (5), which features a κ3-bound Me6tren ligand, was synthesized through the reaction of Me2Mg with Me6tren. The reaction of 5 with excess phenylacetylene or carbon dioxide yielded (Me6tren)­Mg­(CCPh)2 (6) and Mg­(OAc)2, respectively, while treatment with benzylalcohol, benzylamine, 4-tert-butylcatechol, 4-tert-butylphenol, and aniline all resulted in decomposition. The addition of 1 equiv of 2,6-lutidine·HBArF (BArF = tetrakis­(3,5-bis­(trifluoromethyl)­phenyl)­borate) to 5 formed [(Me6tren)­MgMe]­BArF (7), a rare example of a neutral ancillary ligand supported cationic monoalkyl Mg species. Compounds 1, 4, and 5 have been crystallographically characterized.