Selenoether macrocyclic chemistry - syntheses and properties of new potentially tridentate and hexadentate Se/O-donor macrocycles

Treatment of O(CH2CH2SeCN)(2) with Na in NH3(1), followed by dropwise addition of a thf solution of o-C6H4(CH2Br)(2) at -40 degrees C leads to formation of three mixed Se/O-donor macrocycles which are separable by column chromatography, the [1 + 1] species L-1, the [2 + 2] ring L-2 and the [3 + 3] ring L-3, of which L-2 is by far the major species. Using the same starting materials, but in a high dilution cyclisation at room temperature with NaBH4 in thf/ EtOH gives exclusively the [1 + 1] ring, L-1. The saturated ring Se/ O-donor macrocycles, L-4 and L-5 are obtained by simultaneous dropwise addition of solutions of O(CH2CH2SeCN)(2) and Br(CH2)(3)Br to NaBH4 suspended in thf/ EtOH. The small tridentate Se2O-donor ring, L-4, is again the dominant product under these conditions (71%), although the more flexible precursors in this reaction also give rise to the larger Se4O2-donor ring, L-5, as a by-product in 8% yield. These compounds are readily separated and purified by column chromatography (ethyl acetate: hexane, 1: 19). The new macrocycles have been characterised by H-1, C-13{H-1} and Se-77{H-1} NMR spectroscopy and mass spectrometry, together with crystal structures of L-1 and L-2. Complexes of L-1 and L-2 with late transition metals (Pd(II), Pt(II), Cu(I) and Ag(I)) are also described.