Lithium aryloxo magnesiates: an examination of ligand size and donor effects

The combination of equimolar amounts of LiOAr and Mg(OAr)2 (OAr=aryloxide) in polar media afforded several lithium aryloxomagnesiates. Factors influencing the structural chemistry of the compounds, such as the degree of ligand bulk, type of Lewis base donors, and crystallization solvent, are examined. Structural characterization reveals a discrete, solvent-separated species, Li(thf)4]Mg(BHT)3].THF (1) (BHT=2,6-tBu2-4-MeC6H2O) and a family of molecular compounds with various Li/Mg stoichimetries, including a 1:1 Li/Mg ratio in LiMg(Odpp)3(thf)2].0.5PhMe (2) (Odpp=2,6-Ph2C6H3O) and Li(Et2O)Mg(Odpp)3].0.5PhMe (3), a 2:1 Li/Mg ratio as in {Li(thf)2}2Mg(OMes)4].2THF (4) (OMes=2,4,6-Me3C6H2O) and {Li(tmeda)}2Mg(m-Odtp)4].0.5Et2O (5) (m-Odtp=3,5-tBu2C6H3O), and a novel 2:3 Li/Mg ratio in {Li(thf)2}2Mg3(m-Odtp)8(thf)2].3THF (6). Two new homometallic magnesium bis(aryloxides), Mg(Odpp)2(thf)2 (7) and Mg(Odpp)2(Et2O)2 (8), are also included for the sake of comparison. The solution behavior of the heterobimetallic compounds in arene and polar solvent is analyzed by 1H NMR spectroscopy.