Synthesis, characterization, and structural study of sterically hindered magnesium alkoxide and siloxide compounds

A series of sterically hindered Mg(OR)2, [OR=OC(CH3)(C6H5)2 (DPE), and OSi(C6H5)3 (TPS)] were synthesized from the reaction of Mg(Bu)2 with 2 HOR in a variety of solvents. The resultant products were crystallographically characterized as Mg3(μ3-DPE)(μ-DPE)3(DPE)2 (1), Mg[(μ-TPS)2Mg(TPS)]2 (2), [Mg(μ-DPE)(DPE)(solv)]2 (solv=THF, 3; py, 4), and [Mg(TPS)2(solv)]2 (solv=THF, 5; py, 6). For 1, the three metal centers are in a triangular arrangement and are bound by a single μ3-DPE, three μ-DPE, and two terminal DPE ligands. Two of the three Mg cations are tetrahedrally (Td) coordinated while the remaining metal center adopts a trigonal pyramidal geometry. In contrast, 2 displays a more linear arrangement of the Mg centers supported by four μ-TPS and two terminal TPS ligands. Two of the Mg cations adopt trigonal planar arrangements while the remaining central Mg exhibits a distorted Td geometry. For the dinuclear complexes (3–6), each metal possesses a Td geometry satisfied by two μ-OR, one terminal OR, and one coordinated solvent. 1H NMR characterization indicates that 1 is likely fluxional in solution while 2–5 remain intact in solution and 6 is disrupted by pyridine to yielding a monomer.