Synthesis and Structural Characterization of Bis(salicylaldiminato)magnesium Complexes of Varying Aggregation and Coordination State

A series of salicylaldiminato ligands [C6H5N=CHC6H4OH (L-1), 2,6-iPrC(6)H(3)N=CHC6H4OH (L-2), and 2,6-iPrC(6)H(3)N=CH-3,5-tBu(2)C(6)H(2)OH (L-3)] were treated with Bu2Mg in the presence of the appropriate solvent system to yield the crystalline compounds [((L6Mg3)-L-1)center dot thf] (1), [((L2Mg)-L-2 center dot thf)] (2), and [(L2Mg)-L-3] (3). The products were characterized by H-1 and C-13 NMR spectroscopy and single-crystal X-ray diffraction. X-ray crystallographic analysis revealed that 1 adopts a unique trimeric aggregation state consisting of six-coordinate magnesium centers. Substitution of the ligand backbone resulted in the formation of the monomeric species 2 and 3. X-ray crystallographic analyses revealed 2 as a five-coordinate, distorted square-pyramidal magnesium complex and 3 as a four-coordinate, distorted tetrahedral species. Inspection of the metrical parameters in 1-3 indicates a decrease in the Mg-O and Mg-N bond lengths and an increase in the N-Mg-O bite angle with a decreasing coordination number at magnesium.