Alkaline earth metal organoamide complexes displaying close Ae-F(C) (Ae = Ca, Mg) interactions

Deacon, Glen B.;Junk, Peter C.;Kelly, Rory P.

Abstract

Protolysis of [Ca{N(SiMe(3))₂)(thf)₂] (thf = tetrahydrofuran) with the N,N-dialkyl-N′-2,3,5,6-tetrafluorophenylethane-1,2-diamines, p-HC₆F₄N(CH₂)₂NR₂ (LᴿH; R = Me or Et), yields [Ca(p-HC₆F₄N(CH₂)₂NR₂ (L(thf)₂], whilst protolysis of di-n-butylmagnesium by the same amines yields [Mg(p-HC₆F₄N(CH₂)₂NR₂ complexes. X-Ray crystal structures show that the calcium derivatives contain eight-coordinate calcium atoms, with tridentate (N,N′,o-F) coordination of the organoamide ligands and cisoid thf donors. It is noteworthy that the Ca–F(C) bond lengths are shorter than the Ca–NR₂ bond lengths. By contrast, magnesium forms centrosymmetric, six-coordinate, homoleptic complexes, in which the Mg–NR₂ bond lengths are shorter than the Mg–F(C) bond lengths. 19F{1H} NMR spectra of the R = Me complexes support retention of Ae–F(C) linkages in solution at low temperatures. Heating the complexes for a prolonged period in C₆D₆ at 80°C showed no evidence of C–F activation reactions.

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Australian Journal of Chemistry

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1445-0038

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CSIRO Publishing

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DOI

10.1071/CH13228