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

Abstract

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 (<b>1</b>), 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 <b>1</b> and the alkyl species [(Me₆tren)­MgMe]Br (<b>3</b>) was produced. It was not possible to separate the two compounds to generate a pure sample of <b>3</b>. Reaction between Me₆tren and greater than 4 equiv of MeMgBr formed [(Me₆tren)­MgBr]₂[MgBr₄] (<b>4</b>), an analogue of <b>1</b> with a different counterion. The highly unusual dialkyl Mg compound (Me₆tren)­MgMe₂ (<b>5</b>), which features a κ³-bound Me₆tren ligand, was synthesized through the reaction of Me₂Mg with Me₆tren. The reaction of <b>5</b> with excess phenylacetylene or carbon dioxide yielded (Me₆tren)­Mg­(CCPh)₂ (<b>6</b>) and Mg­(OAc)₂, respectively, while treatment with benzylalcohol, benzylamine, 4-<i>tert</i>-butylcatechol, 4-<i>tert</i>-butylphenol, and aniline all resulted in decomposition. The addition of 1 equiv of 2,6-lutidine·HBAr^F (BAr^F = tetrakis­(3,5-bis­(trifluoromethyl)­phenyl)­borate) to <b>5</b> formed [(Me₆tren)­MgMe]­BAr^F (<b>7</b>), a rare example of a neutral ancillary ligand supported cationic monoalkyl Mg species. Compounds <b>1</b>, <b>4</b>, and <b>5</b> have been crystallographically characterized