Synthesis, structure, and dynamics of six-membered metallacoronands and metallodendrimers of iron and indium

In the reaction of the N-substituted diethanolamines (H2L1-3) (1-3) with calcium hydride followed by addition of iron(m) or indium(m) chloride, the iron wheels [Fe6Cl6(L-1)(6)] (4) and [Fe6Cl6(L-2)(6)] (6) or indium wheels [In6Cl6(L-1)(6)] (5), [In6Cl6(L-2)(6)] (8) and [In6Cl6(L-3)(6)] (9) were formed in excellent yields. Exchange of the chloride ions of 6 by thiocyanate ions afforded [Fe-6(SCN)(6)(L-2)(6)] (7). Whereas the structures of 4, 5 and 7 were determined unequivocally by single-crystal X-ray analyses, complexes 8 and 9 were characterised by NMR spectroscopy. Contrary to what is normally presumed, the scaffolds of six-membered metallic wheels are not generally rigid, but rather undergo nondissociative topomerisation processes. This was shown by variable temperature (VT) H-1 NMR spectroscopy for the indium wheel [In6Cl6(L-1)(6)] (5) and is highlighted for the enantiotopomerisation of one indium centre {1/6[S-6-5] reversible arrow 1/6[S-6-5']}. The self-assembly of metallic wheels, starting from diethanolamine dendrons, is an efficient strategy for the convergent synthesis of metallodendrimers.