Synthesis and structural characterisation of mixed alkalimetal-magnesium mixed ligand alkyl-amido ate complexes

Andrikopoulos, Prokopis C. and Armstrong, D.R. and Kennedy, A.R. and Mulvey, R.E. and O'Hara, C.T. and Rowlings, Rene and Weatherstone, Susan (2007) Synthesis and structural characterisation of mixed alkalimetal-magnesium mixed ligand alkyl-amido ate complexes. Inorganica Chimica Acta, 360 (4). pp. 1370-1375. ISSN 0020-1693

Abstract

Using two different reaction methodologies, two alkali metal–magnesium alkyl bis(amide) complexes were synthesised. First the lithium magnesiate LiMg{μ-N(SiMe3)2}2(tBu) (1) was prepared by combining equimolar quantities of tBuLi and Mg{N(SiMe3)2}2 in hydrocarbon solvent. An X-ray crystallographic study revealed that the asymmetric unit of 1 has a dinuclear arrangement, based on a planar Li–N–Mg–N four-membered ring. As a result of the presence of intermolecular agostic interactions between the Li centre of one asymmetric unit and a methyl group which is resident on the terminal tert-butyl group of another, 1 is polymeric in the solid-state. Second the sodium magnesiate NaMg{μ-N(SiMe3)2}2(tBu) · (OEt2) (2) was prepared by reacting two molar equivalents of Na{N(SiMe3)2} with one molar equivalent of tBuMgCl in hydrocarbon/diethyl ether solution. X-ray crystallographic analysis revealed that the asymmetric unit of 2 consisted of a dinuclear molecular arrangement. As expected it is not polymeric due to the coordination of the Lewis basic ether. Stabilizing intramolecular agostic NaC bonds are observed (where C is a methyl group resident on a Si atom).

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