Cobaltocene synthesis

In 1970, the synthesis of the orange-red sandwich cation 1 from cobaltocene and PhBCl2 (1) marked a further starting point in the chemistry of boron metal compounds. The presence of a planar benzenoid C5H5B ligand moiety in 1 was deduced from XH and UB NMR data (1). This was made ironclad by two X-ray structure determinations which revealed typical centrosymmetric sandwich structures for the 19-e complexes Co(C5H5BOMe)2 (6) (21,22) and Co(C5H5BMe)2 (7) (22) as shown in Fig. 1. 

Bora-2,5-cyclohexadienes have a much greater synthetic potential than is apparent from the examples given so far. This may be exemplified by two recent reactions. Reductive complex formation in the system Co(acac)3/COD/25/Mg/THF affords complex 51 via the organotin route (77) while an earlier synthesis used the cobaltocene route (60). Ni(COD)2 very cleanly forms the (Tj3-l,4,5-cyclooctenyl)nickel complex 52 (29). 

Several preparations of silylated cyclopentadienylmetal complexes involve the formation of a triorganosilylcyclopentadienyl anion (by treatment of a silylated cyclopentadiene with an alkali metal in tetrahy-drofuran or by metalation with n-butyllithium), followed by reaction with metal chlorides. This type of reaction has been used for the synthesis of silylated ferrocenes (41, 43, 58, 83, 84, 103, 107, 116, 135, 142, 171, 172), cobaltocenes (135), nickelocene (135), titanium cyclopen-tadienyls (46, 145), and cyclopentadienylmanganese tricarbonyl (30) [Eqs. (19) and (20)]. It is remarkable that Si—C5H6 bonds are not... 

Asymmetrical, Mixed Bisporphyrinates - The synthetic paths (paths — f, — j, k) preclude an easy synthesis of heterobimetallic complexes like RuOs(OEP)2. Such complexes were obtained in pure forms by stepwise metallation of H2(DPB) to RuOs(DPB) [232]. Separation of a mixture of [Ru(OEP)]2, [Ru(OETAP)]2, and Ru2(OETAPXOEP) was achieved by stepwise oxidation of these bis-metalloporphyrins using AgBF4 in toluene when first [Ru(OEP)]2BF4 and then [Ru2(OETAP)(OEP)]BF4 precipitated. The latter was then reduced with cobaltocene to give pure Ru2(OETAP)(OEP) [233]. 

Reactions of the (Tj5-C5Hs)cobaIt-olefin complexes (26) prepared according to Eqs. (25) and (26) with alkali metals (Li, Na, K) in the presence of olefins lead to the elimination of the second C5H5 ligand from the cobalt (Scheme 5). Complexes 27a and 27b, or the mixed complex 27c are obtained in high yields [Eq. (28)]. The syntheses of the pure complexes 27a and 27b do not, of course, require the isolation of intermediates 26a and 26b. As mentioned previously, synthesis is readily achieved from cobaltocene (24) by reaction with either stoichiometric amounts or excess alkali metal in the presence of COD or ethylene [Eq. (24)]. The alkali metal cyclopentadienides which are formed are easily separated from the cobalt complexes and can be used for the synthesis of cobaltocene (51) [Scheme 5 Eq. (29)]. 

Examples of preparation of copolymers are scarce. Mun et al. [81, 82] showed that the binary system of cobaltocene/ bis(ethylacetoacetato) copper (II) effectively initiates the living radical polymerizaton of MMA at 25 °C in acetonitrile. The polymerization activity of this initiator system was markedly affected by the solvent used. The synthesis of PMMA-b-PS copolymers with molecular weights reaching 700000 was successfully attempted by adding styrene to the living PMMA. The yield of the copolymers reached 80% when the MMA polymerization was carried out for three days. The same team [91] also synthesized PS-b-PMMA copolymers from the polymerization of MMA with polystyrene obtained in the presence of reduced nickel/halide systems. The yields range from 84 to 91% depending on the halide complex used. 

For similar results using cobaltocene as a catalyst precursor, see Y. Wakatsuki and H. Yamazaki, Synthesis, 1976, 26. 

Perfluoronapthalene appears to form a charge transfer complex with cobaltocene but no further C-F activation is detected [74]. The crystal structure of a ruby-colored ferrocene-perfluorophenanthrene molecular complex has recently been reported [75]. The presence of only one tertiary C-F bond is required for reactivity in this system as illustrated by the synthesis of perfluorotoluene from perfluoromethylcyclohexane under similar conditions. 

Chromium corroles have been isolated as 6-coordinate Cr(III) and 5-coordinate Cr(IV/V/VI) oxo, nitrido, and imido complexes. The synthesis of Cr(tpfc)(py)2 (py = pyridine), which is oxidized to (oxo)Cr(tpfc) on standing in aerated solution, was reported in 2001 [78]. Cr(tfpc)(0) could be reduced by cobaltocene to give... 

Unsupported Floating Metal Cluster Catalysts The term floating catalyst implies the incorporation of a catalyst precursor in the form of a vapor into the reaction chamber, where it decomposes and generates the active catalyst under reaction conditions (76). It was employed by Sen, Govindaraj, and Rao (77) in 1997 to prepare carbon nanotubes by decomposition of ferrocene, cobaltocene, and nickelocene under reductive conditions. In this case, the precursor provides both the carbon and the metal to catalyze the synthesis reaction, but later, benzene or hexane was added to the ferrocene precursor to improve the carbon yield (78). 

Dioctyltin diisooctylthioglycollate catalyst, PU two-pack coatings Dibutyltin bis (laurylmercaptide) catalyst, PU elastomers Ferric acetylacetonate N-Hydroxyethy I pi perazi ne catalyst, purified terephthalic acid polyesters Manganese acetate (ous) catalyst, PVC suspension polymerization Lauroyl peroxide catalyst, pyridine synthesis Cobaltocene... 

Cobaltocene cations, Coi y -CsHsjJ, can serve as templates for the synthesis of molecular sieves as metallocenium inclusion compounds [268, 269]. 

Cuadrado and co-workers have also been active in the synthesis of den-drimers containing ferrocene and cobaltocene moieties (241-244). The synthesis of propylenimine-based dendrimers with up to five generations and 64 peripheral ferrocenyl moieties underwent reversible oxidation processes at.Bi = 0.59 V (241,242). The guest-host relationship of some low generation dendrimers with cy-clodextrins was examined (241). Silicon-based ferrocenyl dendrimers possessing electrochemical communication between the iron centers were also synthesized (243). 

The organocobalt catalysed synthesis of substituted pyridines from alk-l-enes and nitriles (Equation 22) has been extended further by the discovery that the leaction is catalysed by cobaltocene, Co(i7 -05145)2, a more easily obtained complex than earlier catalysts.Acetylene reacts with substituted nitriles to give 2-sub-stituted pyridines in up to 60% yield, whereas mono-substituted acetylenes react to give mixtures of 2,4,6- and 2,3,6-trisubstituted pyridines in moderate yield. 

In the 1970s, Carraher reported the synthesis of a number of cobaltocenium based polymers. Titanium, zirconium, and hafiiium polyesters were synthesized via reaction of the dicyclopentadienyhnetal dichloride complexes with disodium dicarboxylates of cobaltocenium in either aqueous or organic solvents. For example, the synthesis of a polymer (135) that contains cobaltocene and titanocene units in the backbone is shown in Scheme 35. ... 

Finally, a dendrimer containing 243 ferrocenyl units at the periphery was synthesized by ferrocenylsilation of an allyl terminated dendrimer. This macromolecule could be oxidized to the corresponding stable ferrocenium dendrimer and reversibly reduced back to the neutral complex. Cuadrado and coworkers have also been active in the synthesis of dendrimers containing ferrocene and cobaltocene moi-... 

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