Structural characterization of the 1-metallo-2-t-butyl-1,2-dihydropyridyl rubidium and caesium complexes

With recent reports of alkali metal amides used in homogeneous catalytic chemistry where the reactivity down group one is dependent on the metal identity, esoteric rubidium and caesium amides are finding new admirers amongst chemists who usually study lithium, sodium, and potassium utility amides. Here, as a forerunner to their exploitation in catalysis, we report the X-ray crystallographic and NMR solution structures of the 1-metallo-2-t- butyl-1,2-dihydropyridyl (DHP) complexes of rubidium and caesium, thereby completing the homologous alkali metal series. Crystallized as monosolvated {[Rb(tBuDHP)center dot THF]2}infinity and hemisolvated {[Cs(tBuDHP)]2 center dot THF}infinity, both form spectacular supramolecular structures. While each shares a plethora of metallo-n-contacts with the DHP anion, their subunits differ. The former dimerizes in a 'slipped' fashion via interactions between the symmetrically-equivalent Rb centres and the n-system of the adjacent DHP ring, but the latter has distinct Cs centres within its dinuclear subunit, with one Cs engaging in sigma-bonding to two tBuDHP anions, whereas the other Cs binds in a more side-on fashion to the n-system of the ring.