Five N, N'-diarylformamidines with symmetric or asymmetric substituents on the phenyl groups were synthesized and fully characterized. Formamidines without bulky substituents exhibited fluxionality in solution, which was proved by a single set of signal in 1H NMR. In contrast, two sets of signals were observed for formamidines with bulky substituents in the ortho positions, indicating two major conformers (E and Z) co-existing in solution. In solid state, strong stability for E conformers was gained from a pair of H bonds between two ligands facing each other. The phenomenon was observed for all ligands but N, N'-bis(2,6-dimethylphenyl)formamidine, whose Z conformers were connected through H bonds from both sides of a ligand and an infinite chain structure formed in solid state.Metallation of the formamidines with diethylzinc and mesitylmagnesium bromide produced ten complexes in a variety of geometries, indicating a rich diversity in geometry for the formamidine family as coordination ligands. Among these complexes, three bimetallic complexes contains metal atoms close in distance. In each dizinc complex, two formamidinates (deprotonated formamidines) spanned over the two Zn atoms and brought them together, while in the dimagnesium complex, the two Mg atoms were bridged by two bromides, resulting in a Mg2Br2 cubic core. Four of the rest complexes are monometallic complexes whereas the last three complexes contain polymetallic cores in special orientations.

Synthesis and characterization of formamidines and their Zn and Mg complexes

248th National Meeting (2014)

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