Synthesis and structural characterization of magnesium compounds supported by 2,2':6',2″-terpyridine: access to a terminal magnesium azide complex.

Magnesium complexes of 2,2';6',2″-terpyridine (terpy) may be accessed via the reaction of terpy with {Mg[N(SiMe3)2]2}2 to afford (terpy)Mg[N(SiMe3)2]2, from which a series of other (terpy)Mg[N(SiMe3)2]X derivatives are obtained via its reactivity towards Me3SiX (X = Cl, Br, I, N3) and CHX3 (X = Cl, Br, I). The molecular structures of (terpy)Mg[N(SiMe3)2]2 and (terpy)Mg[N(SiMe3)2]X have been determined by single crystal X-ray diffraction, which indicates that whereas (terpy)Mg[N(SiMe3)2]X are best described as possessing a distorted square pyramidal geometry, (terpy)Mg[N(SiMe3)2]2 exhibits a shift towards trigonal bipyramidal. The azide compound (terpy)Mg[N(SiMe3)2]N3 is of particular significance because it is the first example of a neutral magnesium complex that features a terminal azide ligand, and density functional theory calculations on (terpy)Mg[N(SiMe3)2]N3 indicate that the metal azide functionality is highly flexible, with the energy of the molecule varying by only ca. 1 kcal mol-1 over the range of 110° to 140°.