Cation-induced structural variations in the alkali metal derivatives of 2-trimethylsilylaminopyridine: synthesis and X-ray structures of complexes for all five metals Li–Cs with 12-crown-4

Abstract

The secondary amine 2-trimethylsilylaminopyridine [PyN(H)SiMe₃] 1 was synthesised by mono-lithiation of 2-aminopyridine and subsequent reaction with Me₃SiCl. The compound is readily metallated by BuⁿLi in ethereal solvent, in the presence of the macrocyclic polyether 12-crown-4 (12C4), to afford the lithium secondary amide complex [Li(PyNSiMe₃)(12C4)] 2, in which the amide ligand binds through both the amido and pyridyl nitrogen centres. Metathesis of 2 with Bu^tONa yields the unusual ‘ate’ solvent-separated ion pair complex [Na(12C4)₂][Na(PyNSiMe₃)₂(THF)]·(THF) 3. Metathesis of 2 with ROM [R = Bu^t, M = K; R = CH₃CH₂CH₂CH₂C(CH₂CH₃)HCH₂, M = Rb] yields the two bridged dimers [{K(PyNSiMe₃)(12C4)}₂]·2PhMe 4 and [{Rb(PyNSiMe₃)(12C4)}₂] 5. In both 4 and 5 the amido and pyridyl nitrogens bridge between metal centres. Room temperature metathesis of 2 with CH₃CH₂CH₂CH₂C(CH₂CH₃)HCH₂OCs yields the polymeric [{Cs(PyNH)(12C4)}_∞] 6 containing tetranuclear cluster units, with concomitant cleavage of the N–Si bond. Such cleavage is prevented by low temperature synthesis, yielding the bridged dimer complex [{Cs(PyNSiMe₃)(12C4)}₂]·PhMe 7. The compounds have been characterised by multinuclear NMR spectroscopy, CHN microanalysis and (for 2–7) X-ray crystallography.