Solvent dependence of the solid-state structures of salicylaldiminate magnesium amide complexes

Abstract

There are challenges in using magnesium coordination complexes as reagents owing to their tendency to adopt varying aggregation states in solution and thus impacting the reactivity of the complexes. Many magnesium complexes are prone to ligand redistributionviaSchlenk equilibrium due to the ionic character within the metal–ligand interactions. The role of the supporting ligand is often crucial for providing stability to the heteroleptic complex. Strategies to minimize ligand redistribution in alkaline earth metal complexes could include using a supporting ligand with tunable sterics and electronics to influence the degree of association to the metal atom. Magnesium bis(hexamethyldisilazide) was reacted with salicylaldimines [1L=N-(2,6-diisopropylphenyl)salicylaldimine and2L= 3,5-di-tert-butyl-N-(2,6-diisopropylphenyl)salicylaldimine] in either nondonor (toluene) or donor solvents [tetrahydrofuran (THF) or pyridine]. The structures of the magnesium complexes were studied in the solid stateviaX-ray diffraction. In the nondonor solvent,i.e.toluene, the heteroleptic complex bis{μ-2-[(2,6-diisopropylphenyl)iminomethyl]phenolato}-κ3N,O:O;κ3O:N,O-bis[(hexamethyldisilazido-κN)magnesium(II)], [Mg2(C19H22NO)2(C6H18NSi2)2] or [1LMgN(SiMe3)2]2, (1), was favored, while in the donor solvent,i.e.pyridine (pyr), the formation of the homoleptic complex {2,4-di-tert-butyl-6-[(2,6-diisopropylphenyl)iminomethyl]phenolato-κ2N,O}bis(pyridine-κN)magnesium(II) toluene monosolvate, [Mg(C27H38NO)2(C5H5N)2]·C5H5N or [{2L2Mg2(pyr)2}·pyr], (2), predominated. Heteroleptic complex (1) was crystallized from toluene, while homoleptic complexes (2) and the previously reported [1L2Mg·THF] [Quinqueet al.(2011).Eur. J. Inorg. Chem.pp. 3321–3326] were crystallized from pyridine and THF, respectively. These studies support solvent-dependent ligand redistribution in solution.In-situ1H NMR experiments were carried out to further probe the solution behavior of these systems.