Ruthenocene reactions

Reactions of dilithioferrocene and dilithioruthenocene with N4P4F8 were found to yield a mixture of 1,3- and 1,5-ansa-substituted derivatives. Separation of the ferrocenyl derivatives was achieved by liquid chromatography, but only the 1,5-isomer was obtained in the pure form from the ruthenocene reaction 98, 99). The 1,5-transannular substituted compound of ruthenocene, when further reacted with 1 mol of 1,1 -dilithiated ruthenocene yielded a bis-l,5-diansa-substituted compound. 

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. 

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. 

Ruthenocene has been prepared in 20% yields by reaction of cyclopentadienylmagnesium bromide with ruthenium(III) acetyl-acetonate.8 More recently,4 the compound has been made in 43-52% yield by treatment of sodium cyclopentadienide with ruthenium trichloride in tetrahydrofuran or 1,2-dimethoxyethane. 

Ruthenocene is an example of a stable x-bonded organometallic compound which undergoes substitution reactions similar to those displayed by ferrocene. Because ruthenocene has heretofore been relatively unavailable, its chemistry has not been extensively studied. 

While metallocenes are usually acetylated with acid halides, acid anhydrides, or carboxylic acids, a number of other acylating agents have been reported. The reaction of ferrocene with various isocyanates and aluminum chlorides leads to N-substituted ferrocenecarboxamides (IX) (89). Use of ruthenocene in place of ferrocene leads to analogous results (88). The preparation of V-phenyl-ferrocenecarboxamide from phenyl isocyanate in this manner has been used as a proof of structure for the product obtained from the Beckmann rearrangement of benzoylferrocene oxime (124). 

In a more detailed study of this reaction, Rausch, Vogel, and Rosenberg determined optimum conditions for the synthesis of either XXVII or XXVIII (90). Ruthenocene has also been mercurated using glacial acetic acid as the solvent, but pure products could not be separated (88). 

Various oxidation and reduction reactions of substituted metallocenes have already been discussed. A large number of substituted metallocenes have been oxidized chronopotentiometrically at a platinum foil in acetonitrile solution (39, 46). Electron-withdrawing substituents decrease the ease of oxidation, while electron-donating substituents increase the ease of oxidation with respect to the parent metallocenes. A plot of chronopotentiometric quarter-wave potentials, El, vs. Hammett para-sigma constants shows a definite linear relationship. The Ei s for ruthenocene and osmocene indicate these metallocenes are more difficultly oxidized than ferrocene, in agreement with earlier qualitative observations (18). 

The dicyclopentadienyl metal compounds undergo Friedel-Crafts alkylation and acylation, sulfonation, metalation, arylation, and formyla-tion in the case of ferrocene, dicyclopentadienyl ruthenium, and dicyclopentadienyl osmium, whereas the others are unstable to such reactions ( ). Competition experiments (128) gave the order of electrophilic reactivity as ferrocene > ruthenocene > osmocene and the reverse for nucleophilic substitution of the first two by n-butyl lithium. A similar rate sequence applies to the acid-catalysed cleavage of the cyclopentadienyl silicon bonds in trimethylsilylferrocene and related compounds (129), a process known to occur by electrophilic substitution for aryl-silicon bonds (130). 

The characteristic thermal reaction of these compounds is decarbonylation and new examples include the formation of the ruthenocene compounds 158 by FVP of 157 at 640 °C85, and the decarbonylation of the cyclopentenone 159 to give the synthetically... 

Alkyl-substituted ruthenocenes, preparation, 6, 635-636 Alkyl sulfonates, cross coupling, and Grignard reactions, 9, 44 Alkyltantalum imido complexes, as catalysts, 5, 193 Alkyl tellurides... 

Aza complexes, with mono-Cp Ti(IV), 4, 417 Aza-crown-substituted ruthenocenes, preparation, 6, 635-636 Aza-Diels-Alder reactions, via silver catalysts, 9, 567... 

Grignard additions, 9, 66 radical addition of zincs, 2, 401 zinc-containing reagent additions, 2, 398 Nitroolefins, enantioselective conjugate additions, 10, 382 (Nitrophenylthio)osmocenes, preparation, 6, 634 (Nitrophenylthio)ruthenocenes, preparation, 6, 634 Nitropyridines, reductive aminocarbonylation, 11, 543 Nitroso aldol reaction... 

Open ruthenocenes have been obtained by reaction of hydrated ruthenium trichloride with methylated pentadienes in ethanol in the presence of zinc dust... 

Using the 2-chloro-imidazole annulated Cp ligand, deprotonation of the Cp end and reaction with a suitable Cp Ru precursor forms the appropriate annulated ruthenocene that can in turn be reacted with a palladium(O) source to form the dinuclear Ru/Pd complex (see Figure 4.61). 

The resulting Ru/Pd complex was then used in the Suzuki cross-coupling reaction of phenylboronic acid with p-benzoic acid (94%),p-bromophenol (83%) andp-bromoanisole (82%) in a 10% aqueous solution of acetonitrile in an effort to show that the ruthenocene annulation does not make catalysis impossible. 

The common metathesis reactions for the preparation of metallocenes, treating a metal salt MX2 with NaCp, are hampered in the case of ruthenium by the lack of suitable Ru salts. (Rul2 is commercially available, but is still not commonly used in the synthesis of rathenocene.) Thus, ruthenocene has been obtained from Ru(acac)3 and NaCp in very low yield and later from RuCb and NaCp in 50-60% yield. It has now become apparent that alkene polymers, in particular [Ru(nbd)Cl2]x, but also [Ru(cod)Cl2]x and hydrazine derivatives (Section 3.1), can serve as Ru precursors. Equally successful in many cases is reductive complexation of cyclopentadiene in ethanol in the presence of Zn (Section 3.2), which furnishes the metallocene in about 80% yield. Decamethylruthenocene (82) was first obtained by the Zn reduction route in 20% yield, but can now be prepared conveniently from halide complexes [Cp RuCl2]2 or [Cp RuCl]4, a common method for the preparation of symmetrical and unsymmetrical sandwich compounds of ruthenium featuring one alkyl-substituted ligand. 

As mentioned above, ruthenocene is susceptible to electrophilic substitution in a manner similar to ferrocene. Thus, common reactions for activated aromatics, such as acylation (RCOCFAICI3), sulfonation (SO3 in dioxane), aminomethylation (CH2(NMe2)2), Vilsmeier-Haack formy-lation (DMF/POCI3), arylation via diazonium salts, as well... 

This type of sandwich complex, first reported with iron as the central metal, has now become widespread with ruthenium as well. Early routes to ruthenium complexes were modeled on iron chemistry, and used the AICI3-catalyzed exchange of a cyclopentadienyl ligand for an arene in ruthenocene, or reaction of CpRu(CO)2Cl with AlCb/arene. These methods are less successful with ruthenium than with iron, however, owing to the greater stability of ruthenocene. A mixture of arene, pentamethylcyclopentadiene, and RuCls in the Zn reduction method gives good yields of the mixed-sandwich cations. A... 

Ruthenium has played a central role in the development of 30 valence electron triple-decker cations of the iron group. These compounds were first prepared by Rybinskaya eto/., through reaction of a 12 valence electron [CpRu]+ fragment with a metallocene. The well-known photofragmentation of [CpFe(arene)]+ was used to generate [FeCp]+, which was then complexed to ruthenocene in situ. The stmcture of the triple-decker shows three exactly parallel rings, two of them (one outer and the inner) echpsed and... 

Ruthenocene and osmocene are obtained in good yields from TlCp and [M(COD)Cl2], Several mixed-ligand ruthenocene derivatives are prepared from [Ru(Cp -r )Cl2]2 (Table 7). The latter is derived from the reaction of RuCl3-nH20 and Cp H in refluxing ethanoP ". Similar conditions with added PMCj give Ru(Cp - )Cl(PMe3)2. 

The reaction of 1,3-diboroles 4, LiMe and [ (C5Me5)RuCl 4] leads to the violet, highly air-sensitive Ru sandwich complexes 1810. The compounds 17 and 18 are derived from ferrocene and ruthenocene by formal replacement of two CH groups for B-R units. Therefore the complexes should have only 16 valence electrons (VE). However, the electronic structure of the iron compound 17, studied by EH-MO theory, exhibits a unique bonding The electron density of two B-C c orbitals participates in the bonding by... 

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