Ruthenocenes

The structure of ferrocene and an MO description of its bonding have already been given (p. 937). The rings are virtually eclipsed as they are in the analogous ruthenocene (light-yellow, mp 199°C) and osmocene (white, mp 229°C). 

Hydrochloric acid in anhydrous methanol (1 4 volume ratio) has been used to desilylate the trimethylsilyl derivatives of ferrocene, ruthenocene, and os-mocene, the rate coefficients (lO5 ) being ferrocene (5.60, 4.08), ruthenocene (261, 182), and osmocene (104, 80.2) for 0.596 M and 0.477 M hydrochloric acid, respectively, (temperature not quoted)690. 

A significant step was made by neutron irradiation of ruthenocene. It was found that 20—25% of the ruthenium activity was recoverable as ruthenocene, and that also considerable rhodium activity was sublimed along with the ruthenocene. The rhodium was identified as being rhodium dicyclopentadienide, produced in high yield by the decay of ruthenocene. 

Synthesis of ruthenocene from fission-product ruthenium isotopes was done by neutron irradiation ofU30g and FeCpj powder mixtures. It was shown that most of the ruthenocene found was actually produced by the decay of a precursor. Subsequent knowledge makes it apparent that the fission product recoils formed a rhodium dicyclopentadienide whose structure was preserved through the decay . The total yield of ruthenocene reached a value of 60% under some experimental conditions and was rarely less than 40%. 

A similar synthesis of ruthenocene was done by neutron irradiation of FeCp2 and RUO2 powders together. The yield of RuCp2 was, however, extremely low (0.01 %)37).38>. K ,... 

Isotope effects in neutron-activated ruthenocene were studied by Harbottle and Zahn . Crystalline samples showed a small ( 10%) effect, but a much larger isotope difference was found in benzene solutions. Frozen solutions were found to be similar to the crystalline samples. 

A very interesting result on ruthenocene showed that when fission product ruthenium was projected into dimeric cyclopentadiene, the yield of ruthenocene was quite low, while when monomeric cyclopentadiene was used, the yield was close to 100%. This was interpreted as involving a thermal reaction between the ruthenium atom and a cyclopentadiene monomer molecule, likely the simple displacement of an acid hydrogen. 

The radiochemistry of ruthenocene has been studied by Baumgartner and Reichold (9) and by Harbottle and Zahn (29). It is found that neutron irradiation of crystalline RuCp2 yields about 10% of the radioactive ruthenium as RuCp2- More specifically, an isotopic difference in the radiochemical yield is found Ru, 9.6 0.1% Ru, 10.7 0.2% and Ru, 9.9 0.2% (29). In liquid solution the isotopic effect is much more pronounced, although the yields are lower. This was suggested by Harbottle as a general principle the greatest isotope effects are associated with the lowest yields. While this principle has not yet been substantiated, it seems reasonable since any thermal reactions which may increase the yields would not likely show any isotope effect. 

In connection with j8-decay synthesis, the synthesis of organometallic compounds as a consequence of nuclear fission must be mentioned 9-11, 13). In this way, for example, a powdered mixture of Fe(CjH5)2 and UsOg gives good yields of ruthenocene (10) and iodoferrocene (9) on fission. 

Haaland A, Nilsson JE (1968) Determination of barriers to internal rotation by electron diffraction. Ferrocene and ruthenocene. Acta Chem Scand 22 2653-2670... 

Ru has a nuclear ground state with spin /g = 5/2 and a first excited state with 4 = 3/2" ". Electric quadrupole perturbation of Ru was first reported by Kistner [110] for Ru02 and ruthenocene this author has also evaluated the ratio of the nuclear quadrupole moments to be QJQ > 3. The sign and magnitude of the individual quadrupole moments are given in Table 7.1 (end of the book). 

Isomer shift and quadmpole splitting of salts, [Ru(C5H5)X] Y (X = Cl, Br Y = PFg and X = I, Y = I3) are larger compared to those of ruthenocene. This indicates direct chemical bonding between Ru and Cl, Br and I and that the Ru ion in each salt is in an oxidation state higher than Ru(II) in ruthenocene... 

Third, metallocene units, such as ferrocene or ruthenocene, have been linked to phosphazene cyclic trimers or tetramers and these were polymerized and substituted to give polymers of the type mentioned previously (41). Polyphosphazenes with ferrocenyl groups can be doped with iodine to form weak semiconductors. Polymer chains that bear both ruthenocenyl and ferrocenyl side groups are prospective electrode mediator systems. 

Matsue et al. [43] attempted to study the molecular rocket reaction in a ruthenocene-/ -cyclodextrin inclusion compound using the I00Ru y, p) "raTc reaction. They noticed a parallel relationship between chemical processes and nuclear-recoil-induced processes in the non-included ruthenocene compound, as shown in Fig. 9. In the nuclear-recoil-induced processes no dimerization can be observed because of the extremely low concentration of the product, whereas in the chemical processes dimerization is possible, as demonstrated by Apostolidis et al. [48]. When ruthenocene included in /J-cyclodextrin is irradiated with y-rays, a part of the ruthenocene molecule is converted to [TcCp2-] which escapes from the jS-cyclodextrin cavity. The [TcCp2] rocket thus produced can attack neighboring inclusion compounds so as to extract the enclosed ruthenocene molecules and abstract H or Cp (Cp cyclopentadienyl radical). This process is shown schematically in Fig. 10. 

Metallocenes. — With the exception of the 4d6 system, ruthenocene, Ru(Cp)2, all the metallocenes for which adequate electronic spectra are available belong to the first transition series. For the 3d series metallocenes (and 1,1 dimethylmetallocenes) are known as neutral, Af(Cp)2, species for the elements from vanadium to nickel inclusive, whilst the cationic, M(Cp)2+, systems are found for chromium, iron, cobalt, and nickel, these being described generically as metallicenium salts. A number of substituted ferricenium species have also been reported and studied, including the 1,1 dimethyl derivative, but few spectro-... 

In ruthenocene it also proved possible at 77 K to resolve the broad band containing the 12+ -> 1n, and 1Z+ -+ x4> transitions, but as for Fe(Cp)2 only one spin-forbidden d-d band, assigned as shown in Table 11, could be found, despite a spin-orbit coupling constant of the order of 1 kK. Note that although the 3I1 (on S4), 34 (o2 tr 5 3), and 3II (o2 n 6 3) levels are predicted (81) to be split by , %, and 31, respectively, abnormally large band widths would not be anticipated since only one component of each triplet level is capable of mixing with the nearby singlet states. 

While these disadvantages are severe, electron impact determinations play a useful role in suggesting the pattern of variation in bond enthalpy contributions in molecules which have not been studied by conventional thermochemical techniques. A few examples of this are shown in Table 11. Electron impact measurements also indicate that D (Ru-Cp) in ruthenocene is ca. 100 kJ mol-1 greater than D (Fe-Cp) in ferrocene82). 

It would also be interesting to check the ability of the ruthenocene acrylonitrile cation-radical to rotate around the ethylene bond Ruthenocenyl is weaker than ferrocenyl as a donor substituent (Laus et al. 2005). The particular property of rotating around the ethylenic bond in cation-radicals is a method of elucidating an electronic structure. 

The silanol complex 57 exhibits a Si H M agostic interaction characterized by a /(Si-H) of 41 Hz and a Si-H distance of 1.70(7) It would be incautious to interpret such a low value of the Si-H coupling in terms of a significant Si-H bond activation, because the Si-H bond forms rather acute angles with the Si-C and Si-Si bonds (about 82 and 101°, respectively) and thus must have a considerable p character on silicon, which should contribute to the decrease of /(Si-H). The silanol ligand is -coordinate to ruthenium and the Ru-Si bond of 2.441(3) A is not exceptional, but the Si(SiMe3)3 deviates from the silanol plane by 19.0°, probably as a result of the Si-H interaction. Deprotonation of 57 by strong bases affords a neutral ruthenocene-like product. 

Ruthenium reacts with cyclopentadiene in ether to form a sandwich complex, a yellow crystalline compound, bis(cyclopentadiene) ruthenium(0), also known as ruthenocene. 

---