Synthesis and reactivity of [2]ferrocenophanes containing C–Pb and C–Zr bridges

The synthesis, characterization and reactivity of novel carbometalla[2]ferrocenophanes (η-C5Me4)Fe(η-C5H4)CH2ER2 (14) and (15) (E = Pb, R = Ph or E = Zr, R = (η-C5H5)) are reported. Compounds 14 and 15 were prepared by the reaction of the dilithiated species (η-C5Me4)Fe(η-C5H4Li)CH2Li · xTMEDA with the appropriate dichlorodiorganoplumbane or dichlorozirconocene in low yields (ca. 20%). The Pb species 14 was characterized by 1H and 13C NMR, and MS, however it could not be cleanly separated from pentamethylferrocene. Moreover, it was found that the C–Pb bonds of 14 underwent facile cleavage, and under ambient light or at room temperature, 14 decomposed to Pb2Ph6 and pentamethylferrocene. Compound 15, on the other hand, was stable and readily purified; this species was characterized by 1H and 13C NMR, UV–Vis, MS, and elemental analysis. Single crystal X-ray diffraction studies of this compound revealed the presence of a moderate degree of ring-tilt with a value of α = −5.5(2)° (a negative value is used to denote tilting away from the bridging elements), and a potentially moderate degree of strain due to a large β(Zr) of 31.6(1)° (angle between Cp′(Fe) plane and ipso-Cp′–Zr bond). Attempted thermal ring-opening polymerization (ROP) of 15 resulted only in decomposition and attempted transition metal-catalyzed and photolytic ROP were also unsuccessful. The reaction of 15 with HCl · Et2O resulted in cleavage of the C–Zr bonds, and led to the formation of pentamethylferrocene.

Graphical abstractThe synthesis and reactivity of a carboplumba[2]ferrocenophane and a carbozircona[2]ferrocenophane are reported and X-ray characterization of the latter species demonstrated moderate tilting away from the bridging elements. Attempts to induce ring-opening polymerization were unsuccessful, however these compounds underwent stoichiometric ring-opening reactions.Figure optionsDownload full-size imageDownload as PowerPoint slide