Correlations oxidative addition

From the foregoing, however, it should not be concluded that the approach of Mango and Schachtschneider is appropriate for the understanding of the metathesis reaction. The main difficulty is the supposition that the metathesis is a concerted reaction. If the reaction is not concerted, it makes no sense, of course, to correlate directly the orbitals of the reactants with those of the products. Recently, non-concertedness has been proved probable for several similar reactions, which were formerly believed to be concerted. For instance, Cassar et al. (84) demonstrated that the Rh catalyzed valence isomerization of cubane to sj/w-tricyclooctadiene proceeds stepwise. They concluded that a metallocyclic intermediate is formed via an oxidative addition mechanism ... 

For the related [CpIr(PH3)(CH3)]+ system, four basis sets were used. Basis set one (BS1) is the same as the ones described above for Ir and P, but the C and H are described as D95. Basis set two (BS2) is the Stuttgart relativistic, small core ECP basis set (49) augmented with a polarization function for Ir, and Dunning s correlation consistent double-zeta basis set with polarization function (50) for P, C and H. Basis set three (BS3) is the same as BS1 except the d-orbital of Ir was described by further splitting into triple-zeta (111) from a previous double-zeta (21) description and augmented with a f-polarization function (51). Basis set four (BS4) is the same as BS2 for Ir, P, and most of the C and H, but the C and H atoms involved in the oxidative addition were described with Dunning s correlation consistent triple-zeta basis set with polarization. 

This trend is also observed in palladium chemistry where the general order for oxidative addition often correlates with that of nucleophilic substitution. Not only are 2-, 4- and 6-chloropyrimidines viable substrates for Pd-catalyzed reactions, but 4- and 6-chloropyrimidines react more readily than 2-chloropyrimidines. 

The Eastman group clearly described how this was due to promotion of reaction of intermediate Acl with MeOAc, (Eq. (12)). The HP NMR experiments described above show a good correlation between activity in Mel/MeOAc exchange and promotional activity in catalytic carbonylation. At the same time, the model studies of r promotion of oxidative addition suggest that the formation of Acl may also be accelerated under process conditions (Eq. (48)). Thus, F salts can contribute to accelerating both steps that can be rate controlling in the carbonylation of MeOAc to AC2O. 

Figure 4. Correlation of relative rates of oxidative addition of Ni[P(C6H5)3 3 to substituted aromatic halides with a constants (Id, 22)...

Fig. 2.54 presents a two-dimensional carbon-proton shift correlation of D-lactose after mutarotational equilibration (40% a-, 60% / -D-lactose in deuterium oxide), demonstrating the good resolution of overlapping proton resonances between 3.6 and 4 ppm by means of the larger frequency dispersion of carbon-13 shifts in the second dimension. The assignment known for one nucleus - carbon-13 in this case - can be used to analyze the crowded resonances of the other nucleus. This is the significance of the two-dimensional CH shift correlation, in addition to the identification of CH bonds. For practical evaluation, the contour plot shown in Fig. 2.54(b) proves to be more useful than the stacked representation (Fig. 2.54(a)). In the case of D-lactose, selective proton decoupling between 3.6 and 4 ppm would not afford results of similiar quality. 

Tratnyek and Hoigne (1994) investigated 25 substituted phenoxide anions for QSARs that can be used to predict rate constants for the reaction of additional phenolic compounds oxidized by chlorine dioxide (OCIO). Correlating oxidation rates of phenols in aqueous solution is complicated by the dissociation of the phenolic hydroxyl group. The undissociated phenol and the phenoxide anion react as independent species and exhibit very different properties. The correlation analysis should be performed on the two sets of rate constants separately. 

Table LXVI shows the correlation coefficients obtained for the hard and soft types. The existence of two clay populations limits the meaning of correlations found for the combined data (Hinckley, 1961). In both groups K20 and mica and K20 and Fe203 are positively correlated. In addition, for the soft type there is a positive correlation between Fe203 and mica and negative correlations between mica and books, and Fe203 and books. These interrelations suggest, but do not prove, that books are derived from the mica and that much of the K20 and Fe203 may be present in the mica or that a leaching process that altered the mica and removed its interlayer K20 also removed the iron regardless of where it occurred (pyrite, anatase, iron oxides, etc.).

FIGURE 6.8 The state correlations in the VBSCDs of oxidative—additions of (a) a carbenoid reagent into a C—H bond, and (b) a transition metal complex into a C—X bond. 

These oxidative—addition reactions have been treated extensively by Su et al. (29-31), using the VBSCD model. In all cases, a good correlation was obtained between the computed barriers of the reaction and the respective AEst quantities (which enter into the expression of G), including the relative reactivity of carbenoids, and of PtL2 versus PdL2 (29-31). Another treatment led to the same reactivity patterns for C—F bond activation reactions by Rh(PR3)2X and Ir(PR3)2X d8 complexes, which are isolobal to carbenoids (30). A similar extended correlation was found recently for C—Cl activation by d10-PdL2 (32), and is dealt with in Exercise 6.9. 

Density functional theory modeling of the group IX CpM(CO) intermediates correlates the activation barrier to oxidative addition of a C H bond to the singlet-triplet splitting, AEst, of the 16 electron intermediate. Smaller values of AEst are observed with the lower transition metals in agreement with the ease of oxidative addition. ... 

H, Me). Inclusion of relativistic effects was found to be important for results on the model to agree with experiment. For R = H, the calculated transition state was calculated to be close to the reactants, while for R = Me, the transition state is product-like. Both the ethyl and propyl products show an agostic interaction with a -hydrogen. A second study used DFT methods to explore the oxidative addition of the C-F bond in fluoromethane to unsaturated Rh(I) species modeled by Rh(X)(PH3)2 (R = H, Me, Cl). The activation barrier was found to correlate with the magnitude of the singlet-triplet splitting and to be lowered by the presence of r-donor ligands. ... 

The acyliron(0) complex (102) has been isolated and subjected to the same nucleophilic displacement (or equivalently oxidative addition) with excellent correlation (Scheme 39). The same species is also readily available from acid chlorides (i.e. formation of 103), but the overall process has not been widely used in the synthesis of ketones (Scheme 40). The final step of the process, a reductive elimination of acyliron(II) complex (104) or (105), is quite rapid and it has not been possible to isolate and identify the presumed intermediates in this case (Scheme 41). Since the oxidative addition of the acyliron complex with the alkyl halide is extremely mild, the corresponding ketone formed in the reaction is not subject to attack by organometallic reagents and no tertiary tdcohol is formed. 

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