Dynamic NMR studies of 1,1′,2,2′-bis(1,2,3-trithia-[3])ferrocenophane and some mixed sulphur/selenium-bridged derivatives

Abstract

The doubly trisulphur-bridged metallocene compound, 1,1′,2,2′-bis(1,2,3-trithia-[3])ferrocenophane 1 exists in solution as a mixture of chair—chair and chair—boat diastereomers arising from the orientations of the trisulphur linkages. Dynamic NMR studies have shown that the energies of the two bridge reversal processes, chair—boat to chair—chair and chair—boat to boat—chair, are, in terms of Δ G‡ (298.15 K) data, 93.9 and 89.0 kJ mol −1 respectively. These values are compared with data obtained for the singly trichalcogen-bridged metallocenophanes, and the mechanism of bridge reversal is discussed. Relative populations of the two diastereomers were strongly solvent dependent, with the less abundant chair-boat conformer more favoured in polar solvents. An NMR analysis of the products resulting from conversion of the doubly -trisulphur-bridged compound, 1, to SSeS-bridged species, namely 1,1′,2,2′-(1,2,3-trithia-[3])(1,3-dithia, 2-selena-[3])ferrocenophane 2 and 1,1′,2,2′-bis(1,3-dithia,2-selena-[3])ferrocenophane 3 identified each compound and its individual diastereomers.