Synthesis, structures, and properties of strained spirocyclic [1]Sila- and [1]germaferrocenophanes and tetraferrocenylsilane

The spirocyclic [1]ferrocenophanes [Fe(eta-C5H4)(2)](2)E (3, E = Si; 4, E = Ge) and Fe(eta-C5H4)(2)-Si(CH2)(3) (5) have been prepared by the reaction of Fe(eta-C5H4Li)(2) . TMEDA (TMEDA = tetramethylethylenediamine) with SiCl4, GeCl4, and Cl2Si(CH2)(3), respectively. Single-crystal X-ray diffraction studies of 3-5 revealed that the molecules possess highly strained structures with tilt angles between the planes of the cyclopentadienyl rings of 19.4(2), 19.1(5), and 20.61(8)degrees, respectively. The Fe---Fe distances in 3 and 4 are 5.314(1) and 5.518(4) Angstrom, and evidence for metal-metal interactions in the form of substantial redox coupling (Delta E-1/2 = 0.37 V for 3 and 0.25 V for 4) is present in the cyclic voltammograms of these species. For structural comparison, the tetraferrocenylsilane [(eta-C5H5)Fe(eta-C5H4)](4)Si (6) was prepared and was characterized by single-crystal X-ray diffraction. Cyclic voltammetry of 6 showed four reversible oxidation waves with E-1/2 values of -0.03 to +0.39 V versus ferrocene; Delta E-1/2 values of 0.10-0.18 V were indicative of significant metal-metal interactions. The results of Mossbauer, IR, and Raman studies of compounds 3, 4, and 6 are also discussed.