The heteroleptic magnesium complexes [{Ar′OMgBu}2]
1 and [{Ar′OMgN(i-Pr)2}2]
2, where OAr′
= 2,6-di-tert-butylphenoxy, have been prepared and found to be dimeric in the solid state, with tri-coordinate metal centers. Complex 1 utilizes the aryloxide anions as bridging groups whereas the amido anions connect the metals in 2. Addition of THF or TMEDA to hydrocarbon solutions containing 2 results in disproportionation and the exclusive precipitation of the homoleptic, solvated, complexes [Mg(OAr′)2·2THF]
3 or [Mg(OAr′)2·TMEDA]
4. Both 3 and 4 are monomeric in the solid state with tetra-coordinate magnesium centers. Solution NMR spectroscopic studies of 1 and 2 reveal that disproportionation to the homoleptic complexes is promoted in THF-d8 but that the main component still appears to be the heteroleptic species. Dissolution of the unsolvated dimeric complex [Mg(OAr′)2]
5 in THF-d8 results in partial formation of the magnesiate complex [Ar′OMg]+[(Ar′O)3Mg]−10, along with the monomer 3. In contrast, no magnesiate is formed on dissolution of 3 in THF-d8, indicating that magnesiate formation most likely proceeds via unsymmetrical cleavage of the dimer. Ab initio calculations (HF/6-31G*) have been used to investigate the possible structures of the magnesiate species.
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