Ferrocenyl oxadiazoles

Between the two synthetic schemes, the amidoxime route appears to be the most used and reliable strategy. For instance, oxadiazole systems involved as organometaUic Hgands can be synthesized by precursors already including the complexed metal, such as in the case of ferrocenyl oxadiazoles 18 (2014JOM-C67). The latter is produced from ferrocenyl substituted prop-argyl aldehyde 15 which, after O-functionalization into intermediate 16, undergoes an intramolecular Michael addition into oxadiazoline 17, before elimination of acetaldehyde to yield final product 18 (Scheme 5). 

Oxadiazole 220 bearing a ferrocenyl substituent was reacted with ammonium ethanoate and hydrazine to yield the corresponding 1,2,4-triazoles 221 and 222 in reasonable yield (Scheme 19) <2003JOM(675)1>. 

A number of ferrocene-containing 1,3,4-oxadiazoIes have been prepared. The reaction of ferrocenecarboxhydrazide with triethyl orthoformate gave three products, the principal one being 2-ferro-cenyl-l,3,4-oxadiazole (126 R = H). 76 2-Phenyl-5-ferrocenyl-l,3,4-oxadiazole (126 R = CgH5) and 2,5-diferrocenyl-l,3,4-oxadiazole (126 R = ferrocenyl) were prepared from the appropriate 1,2-diacyl-hydrazines.117 A number of other ferrocenyloxadiazoles, including the bis compound 127, were prepared in a similar manner.117 The oxadi-... 

It should be noted that a number of SPC polymers which contain other heterocycles have been prepared, motivated by their promising optical or electrical properties. Examples include pyridine (65) [123], pyrrole (66) [124], oxadiazole (67) [125], selenophene (68) [126], benzo[2,l,3]thiadiazole (69) [127], benzo[2,l,3]selenadiazole (70) [126], perylene bisimide (71) [128], 1,4-diketo- pyrrolo[3,4-c]pyrrole-l,4-dione (72 and 73) [127,129], and triphenyleamine (74) [127] as part of the polymer backbone by SPC (Figure 19c). Specifically for metal complexation, porphyrin [130], difluoroboraindacene [131], bipyridine [132], phenanthroHne [113], terpyridine [133, 134], and the like [123] were embedded in the backbone. In this context, an interesting report was submitted by Rehahn et al., in which l,l -ferrocenyl units were incorporated into a PPP (Figure 22.20). Due to a low-energy barrier for rotation around the Cp-Fe-Cp axes (Cp = cyclopentadienyl), the obtained polymer 75 was assumed to take randomly coiled conformations [135]. 

---