Synthesis and structural analysis of formamidinate-supported Mg complexes

• Five Mg complexes were synthesized and structurally characterized.
• Products were mononuclear or halide-bridged bimetallic.
• Ligands of increased steric demands produced only monomeric complexes.
• Multiple factors together control the product conformation.
• Formamidinates exhibited a symmetric bidentate chelating (η2) coordination mode.

Reactions of 2-mesitylmagnesium bromide with N,N′-diarylformamidines afforded five Mg compounds [(DPhF)Mg(THF)2]2(μ-Br)2 (1), [D(3,5-Xyl)F]2Mg(THF)2 (2), [D(2,6-Xyl)F]2Mg(THF) (3), [D(2-iPrPh)F]MgBr(THF)3 (4), and [D(2-tBuPh)F]2Mg(THF) (5). Complexes 1, 2 and 4 displayed monomeric octahedral metal centers supported by formamidinates, bromide counter anions, and coordinating THF solvent molecules, while the metal cores in 3 and 5 were five-coordinated and in distorted square-pyramidal geometries. Detailed structural analysis indicated that only dimagnesium or mononuclear complexes were obtained through the use of formamidinate ligands. Ligands of increased steric demands resulted in the formation of monomeric complexes. Solvent molecules and counter anions that can coordinate to the metal cores further regulated the product conformation. Monoanionic formamidinates in the complexes, mostly featuring two nearly identical N–C bonds on the N–C–N backbone upon complexation, exhibited a symmetric bidentate chelating (η2) coordination mode.

Five formamidinate-supported Mg complexes were synthesized and structurally characterized. Three complexes displayed monomeric octahedral metal centers while the metal cores in the other two compounds exhibited distorted square-pyramidal geometries. Multiple factors such as ligand properties, coordinating solvent molecules and halides together participated in governing the product conformation.Figure optionsDownload as PowerPoint slide