Reduction of coordinated

For the increase of sensitiveness of the voltamperometric determination Co(II) use o,o -dihydroxysubstituted azodyes (eriochrome red B and calces). The Co(II) determination can be conducted at potential of reduction of coordinating connection of Co(II)-azodye (E = - 0,9V) and directly the Co(II) (E = -1,2V, ammonia buffer solution) ions. The results of reseaixhes show that selectivity of the Co(II) determination in presence the Ni(II) and Pd(II) ions more high with the use of analytical signal at the potential -1,2V. Is it thus succeeded move aside potentials of peaks of reduction of the Ni(II) and Co(II) ions on a background ammoniac buffer solution from AE=0,2V to AE = 0,4-0,5V. The Co(II) determination can be conducted in presence 50-100 multiple surpluses Ni(II). Palladium in these conditions does not prevent to 60 multiple surplus. 

Bis(i7-pentamethylcyclopentadienyl)zirconium was proposed as an intermediate in the permethylzirconocene hydride promoted reduction of coordinated carbon monoxide by Bercaw and co-workers (65,67-69). In hopes of intercepting such an intermediate, CO was allowed to diffuse... 

Coin-cyclam322-324 and Nin-cyclam322 catalyze the electroreduction of nitrate in aqueous electrolytes with good current efficiencies and turnover numbers, giving mixtures of ammonia, nitrite, and hydroxylamine at a variety of electrode materials. Mechanistic investigations suggested the adsorption of electroreduced Co1- and Ni1 cyclam onto the electrode surface,322 and the formation of an oxo-metal bond via reduction of coordinated nitrate.323... 

A variety of redox reagents have been employed to effect both oxidation and reduction of coordinated macrocycles. For example, the... 

In none of the cases discussed above is molecular hydrogen involved. The first report of the stoichiometric reduction of coordinated carbon monoxide by molecular hydrogen is that published by Bercaw et al. (35, 36). They reported that mononuclear carbonyl and hydride complexes of bis(pentamethylcyclopentadienyl)zirconium are capable of promoting stoichiometric H2 reduction of CO to methoxide under mild conditions. Thus, treatment of the dicarbonyl complex (rj5-C5Me5)2Zr(CO)2 with... 

The attack on coordinated carbon monoxide by nucleophiles was first extensively developed in synthetic organometallic chemistry by E. 0. Fischer and his students (6) as discussed by others in this volume, this reaction provides one route to the reduction of coordinated CO and to catalysis of the water gas shift reaction. Those carbonyl groups which are susceptible to attack by nucleophiles are electron deficient, as judged by their high CO stretcing frequencies (7). 

The above observations strongly indicate that O-protonation is an important step in this particular reaction for the reduction of coordinated CO. Recent studies in our laboratory provide other examples of proton induced reduction in metal cluster systems, and an example of proton induced CO reduction has recently been reported by Atwood (44). It thus appears that protons as well as Lewis acids are effective in the bifunctional activation of coordinated CO. 

Reduction of Coordinated CO on CpFe(CO)Conversion of Two CO Ligands to an Alkoxyacetyl Ligand... 

A significant contribution to the catalysis-related problem of stepwise reduction of coordinated carbon monoxide to a metal-attached methylene unit has been reported by Steinmetz and Geoflfroy (300). 

The years 1978 and 1979 have witnessed continuing activity on the catalytic reduction of CO and models for it. Both Casey and Gladysz have established that the neutral formyl complex (C5H5)Re(CO)(NO)(CHO) which they synthesized (59b,c) is the first intermediate in the borohydride reduction of coordinated CO to methyl as reported by Graham and co-workers (55). When the neutral formyl complex is reacted with BH3 THF, the species (C5H5)Re(CO)(NO)(CH3) results. A similar reduction does not occur when H2 is used as the reductant, however (59b). While the previous report by Nesmeyanov et al. (86) of a hydroxymethyl species in the BH4 reduction process is now viewed as incorrect (59b,e), Casey has recently described (59e) unequivocal characterization of this species, and has shown how the formyl complex (C5H5)Re(CO)(NO)(CHO) can lead to its formation as shown in (23a). 

In the first example, Shriver and co-workers have identified each step in the proton induced reduction of coordinated carbon monoxide in [Fe4(CO)l3]2- to methane [Eq. (7)] (77). 

Scheme 2. Initial stages in the reduction of coordinated dinitrogen.

Dialkylhydrazido(2-) complexes have also been shown to be crucial intermediates in the electrochemical reduction of coordinated dinitrogen to substituted hydrazines (273). Finally a chromium(III) hydra-zido(2-) species has been proposed as an intermediate in the chro-mium(II) reduction of nitroamine (192). 

The mechanism is complicated by the possibility of anti-syn-isomerization and by n - a-rearrangements (it - r 3-allyl Act - r 1 -allyl). In the case of C2-unsubstituted dienes such as BD the syn-form is thermodynamically favored [646,647] whereas the anti-isomer is kinetically favored [648]. If monomer insertion is faster than the anti-syn-rearrangement the formation of the czs- 1,4-polymer is favored. A higher trans- 1,4-content is obtained if monomer insertion is slow compared to anti-syn-isomerization. Thus, the microstructure of the polymer (czs-1,4- and frazzs-1,4-structures) is a result of the ratio of the relative rates of monomer insertion and anti-syn-isomerization. As a consequence of these considerations an influence of monomer concentration on cis/trans-content of BR can be predicted as demonstrated by Sabirov et al. [649]. A reduction of monomer concentration results in a lower rate of monomer insertion and yields a higher trans-1,4-content. On the other hand the czs-1,4-content increases with increasing monomer concentration. These theoretical considerations were experimentally verified by Dolgoplosk et al. and Iovu et al. [133,650,651]. Furthermore, an increase of the polymerization temperature favors the formation of the kinetically controlled product and results in a higher cis- 1,4-content [486]. l,2-poly(butadiene) can be formed from the anti- as well as from the syn-isomer. In both cases 2,1-insertion occurs [486]. By the addition of electron donors the number of vacant coordination sites at the metal center is reduced. The reduction of coordination sites for BD results in the formation of the 1,2-polymer. In summary, the microstructure of poly(diene) depends on steric factors on the metal site, monomer concentration and temperature. 

Reduction of coordinated nitrile to the parent amine can be accomplished with NaBH4 in slightly... 

K[Co(N2)(PMe3)3] and [Mg(THF)4][Co(N2)(PMe3)3]2 are unstable in non-polar solvents giving rise to the paramagnetic [Co(N2)(PMe3)3] intermediate, and ultimately to Co, [Co(PMe3)4] and N2 (equation 79).410 Structures are available (Table 35). Although the reduction of coordinated N2 has not yet been demonstrated in these systems, end-on coordination occurs with the above cations... 

A reduction of coordinated CO with rj CpjNbHj gave C -Cj species [15]. Using r-BU] All in the presence of(r Cp) ZrCl2 carbon monoxide was reduced to alcohols [16). 

Figure 4. Examples of low-temperature limit of rate constant of solid-state chamical reactions obtained in different laboratories of the USSR, United States, Canada, and Japan (1) formaldehyde polymerization chain growth (USSR, 1973 [56]) (2) reduction of coordination Fe-CO bond in heme group of mioglobin broken by laser pulse (United States, 1975 [65]) (3) H-atom transfer between neighboring radical pairs in y-irradiated dimethylglyoxime crystal (Japan, 1977, [72], (4, 5) H-atom abstraction by methyl radicals from neighboring molecules of glassy methanol matrix (4) and ethanol matrix (5) (Canada, United States, 1977 [11, 78]) (6) H-atom transfer under sterically hampered isomerization of aryl radicals (United States, 1978 [73]) (7) C-C bond formation in cyclopentadienyl biradicals (United States, 1979 [111]) (8) chain hydrobromination of ethylene (USSR, 1978 [119]) (9) chain chlorination of ethylene (USSR, 1986 [122]) (10) organic radical chlorination by molecular chlorine (USSR, 1980 [124,125]) (11) photochemical transfer of H atoms in doped monocrystals of fluorene (B. Prass, Y. P. Colpa, and D. Stehlik, J. Chem. Phys., in press.).

An important reaction of NO gas, catalyzed by transition metal surfaces, is reduction with hydrogen to give ammonia. As a consequence, a great deal of effort has been directed into studying the reduction of coordinated nitrosyl ligands. 

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