Big Chemical Encyclopedia

Chemical substances, components, reactions, process design ...

Articles Figures Tables About

Dinuclear intermediate

Recently, a proposal has been put forth that a /raor-addition process may be possible through dinuclear ruthenium intermediates.34 As shown in Scheme 5, reaction of tetraruthenium aggregate A with phenylacetylene results in the fully characterized bridging dinuclear alkenyl complex B. The authors propose a direct /ra .r-dclivcry of hydride through a dinuclear intermediate may be active in the hydrosilylation catalyzed by A, though compound B itself is unreactive to Et3SiH. [Pg.793]

Muetterties has suggested that the dimeric hydride [RhH(P OiPr 3)2]2 catalyzes alkene and alkyne hydrogenation via dinuclear intermediates [91]. However, no kinetic evidence has been reported to prove the integrity of the catalysts during the reactions. On the other hand, studies of the kinetics of the hydrogenation of cyclohexene catalyzed by the heterodinuclear complexes [H(CO) (PPh3)2Ru((u-bim)M(diene)] (M = Rh, Ir bim=2,2 -biimidazolate) suggested that the full catalytic cycle involves dinuclear intermediates [92]. [Pg.30]

Based on the NMR spectroscopic studies and kinetic results of complexes 54 and 55, we conclude that the intermediate structure of these two complexes should be different during the polymerization. A dinuclear intermediate has been proposed for the polymerization initiated by complex 54 as shown in Scheme 9. [Pg.238]

The high lability of bound N2 in [FeII(CN)5N2]3 regenerates the active site, namely the [FeII(CN)5H20]3 ion, which is able to further bind and process hydrazine. A more detailed kinetic study could be warranted for this interesting set of reactions. Some uncertainties still remain as to the nature of the intramolecular electron-transfer rate processes (91). At the employed concentration levels of the complex, the participation of mixtures of mononuclear and dinuclear complexes complicate the spectral evolution. Even the nature of the dinuclear intermediates (cyano- or hydrazino-bridged) could be put into question (probably both are involved, due to the labile interconversion equilibria). The participation of Fe(III) species, either in the mononuclear or dinuclear species, as reactive intermediate precursors of the formation of diazene and N2... [Pg.105]

These copper-mediated reactions very often involve dinuclear intermediates, but detailed mechanistic studies on stoichiometric systems are relatively few. The key features are the formation of p-peroxo or p-superoxo complexes by electron transfer from cop-per(i) to dioxygen. The co-ordinated oxygen may then act as an electrophile to the aromatic ring. A possible mechanism for the ortho-hydroxylation of phenol by dioxygen in the presence of copper catalysts is shown in Fig. 9-29. [Pg.279]

Reaction (4) is an equilibrium reaction and is generally slow at room temperature. The proposed reaction mechanism involves the formation of a stacking dinuclear intermediate (4) that isomerizes through the intermediate (5) to a mixed-ligand dinuclear species (6). Dissociation of 6 forming the mixed-ligand complexes is the rate-limiting step (Scheme 3). Consistent with the proposed mechanism, addition of a base such as a phosphine or an arsine, which is likely to suppress the dissociation of 6, inhibits the reaction. The equilibrium constant is not affected by the presence of an excess base (53). [Pg.278]

The reaction proceeds with Ru3(CO)12 in cyclohexane at 100 C under a CO pressure of 50 bar, after 17 hr the conversion is 85%, corresponding to a catalytic turnover of 825 (49). The isolation of the dinuclear bisoxi-mato complexes Ru2(CO)5(Me2CNO)2(Me2CNOH) (49) and Ru2(CO)4 (Me2CNO)2(Me2CNOH)2 (50) suggests a catalytic cycle involving dinuclear intermediates. [Pg.47]

Bergman has reported that at higher concentrations, the iridium allyl complex Cp Ir(r 3-allyl)H reacts with benzene to give a dinuclear product that has activated benzene. Furthermore, this dinuclear compound undergoes reversible benzene loss indicating that the dinuclear intermediate [Cp>fIr(r 1,r 3-al-lyl)IrCp ] is capable of reacting with aromatic C-H bonds (Eq. 27) [111]. [Pg.38]

The mechanism of the photoaddition of CO to h -C5H5(CO)2Mo(jii-SMe)W(CO)j to break the metal-metal bond and form h -C5H5(CO)3Mo(/a-SMe)W(CO)j also may follow a radical mechanism because W(CO) and (h -C5H5)jM0j(CO)4 are also formed in the photoreaction, although an open dinuclear intermediate similar to that proposed in photosubstitution of (h -C5Hj)2Fe2(CO) (see 13.3.1.1.3) is also possible. [Pg.359]

For the reaction of transition metals with alkaline earth metal complexes, the formation of the dinuclear intermediate is more likely to be rate-limiting. The adjunctive rate constant can be rationalized on the basis of the stability of the metal complex with a ligand fragment (corresponding to a partially dissociated complex), the stability of the initial complex, and the rate of reaction of the incoming metal with the partially dissociated complex (Margerum, 1963 Margerum et al., 1978). [Pg.154]

This mechanism of lead-metal exchange on EDTA is believed to proceed by an associative (Se2) process, with the formation of dinuclear intermediates in which each metal is coordinated to one of the iminodiacetate halves of the EDTA molecule (273). Tanaka et al. (277, 278) showed that the presence of buffer molecules in solution slows the rate of metal exchange by limiting Pb accessibility but proposed that the buffer does not alter the overall mechanism. Consequently, it is necessary to include the kinetics of metal-buffer coordination in calculations in order to produce meaningful rate constants (275, 276, 278, 280). Studies of Pb(ll) exchange with Co -EDTA confirm that both hydrated and monoacetato Pb(II) ions take part in the substitution reaction, but substitution reactions with monoacetato lead complexes occur more slowly than those with hydrated lead ions (280, 281). [Pg.62]

The formation of the dinuclear intermediate and its dissociation to two metal complexes in a concerted pathway suggest a reversible intermolecular exchange of the two ligands. Most of the transmetalation reactions, however, occur smoothly... [Pg.234]

This reaction proceeds via a dinuclear intermediate, as shown in Scheme 5.24. The SnBu3 group of the ortho substituent of the phenyl ligand is able to approach the Cu-Ph bond of another cuprate unit in the eight-membered cyclic dimer structure. Alkyl and phenyl hgand exchange between Sn and Cu centers in both cuprates leads to the introduction of a phenyl group to the Sn center. [Pg.259]


See other pages where Dinuclear intermediate is mentioned: [Pg.111]    [Pg.184]    [Pg.199]    [Pg.180]    [Pg.109]    [Pg.192]    [Pg.381]    [Pg.395]    [Pg.312]    [Pg.359]    [Pg.307]    [Pg.359]    [Pg.1257]    [Pg.149]    [Pg.4815]    [Pg.240]    [Pg.236]    [Pg.337]    [Pg.235]    [Pg.1085]    [Pg.297]    [Pg.478]    [Pg.133]    [Pg.4814]    [Pg.225]    [Pg.565]    [Pg.1257]    [Pg.4711]    [Pg.727]    [Pg.234]    [Pg.244]    [Pg.263]    [Pg.264]   
See also in sourсe #XX -- [ Pg.234 , Pg.244 , Pg.259 , Pg.263 , Pg.264 , Pg.279 , Pg.282 ]




SEARCH



Dinuclear

© 2024 chempedia.info