C-Cl reductive elimination

The experimentally derived rate law for chlorination is consistent with dinuclear Pd(III) complex 54 being the immediate product of oxidation during catalysis. Complex 54 has one apical chloride ligand and one apical acetate ligand and thus, upon thermolysis, could undergo either C-Cl reductive elimination, to generate 52, or C-O reductive elimination, to generate 55 (Fig. 32). We evaluated and confirmed the kinetic and chemical competence of 54 as an... 

In 2010, we reported a study regarding the role of the dinuclear core during C-Cl reductive elimination from 62, an analog of the dinuclear Pd complexes that have been proposed in catalysis (Fig. 35) [96,119]. Experimental results established that reductive elimination from 62 proceeds without fragmentation of the dinuclear core C-Cl bond formation proceeds from a dinuclear complex. 

The computed electron binding energies of Pda and Pd during the low-energy reductive elimination pathway from A, the computed structure of 62, monotonicaUy decrease during reduction from Pd(lll) (A) to Pd(ll) (D). The observed trends are consistent with simultaneous redox chemistry at both metal centers during C-Cl reductive elimination (Fig. 36). 

Fig. 36 Electron binding energies as a function of reaction progress for C-Cl reductive elimination from dinuclear Pd(in) structure A...

Improving the quality of the leaving group, Z - ArO , in complex 8 by introducing electron-withdrawing substituents to the para-position of an aryloxide ArO leads to a faster C-O reductive elimination kinetics (p-CN > P-CF3 > p-Cl > H > p-Me p-OMe). It was suggested that the energy of the transition state TSd (Fig. 9) and the rate of dissociation of an aryloxide from the Pt center are more... 

In the case of the C sp )-0 elimination reaction shown in Fig. 7, it was established that a dissociation of the carboxylate ligand trans- to the aryl from the starting Pd complexes 13 does occur at temperatures much lower than those required for the C-O reductive elimination reaction. This observation suggests that the reaction might proceed via a cationic intermediate 6 and follow a reaction path shown in Fig. 11 with a solid line. If so, the transition state TSd which corresponds to the carboxylate dissociation is of a noticeably lower energy compared to the TSc corresponding to the R-Z elimination step. A Hammett analysis of the kinetics of the reaction in Fig. 7 showed that increased nucleophilicity of the benzoate /5-XC6H4COO in complexes 13 leads to a faster kinetics (p-OMe > p-Me > H > p-OPh > p-F > p-Cl > p-Ac > P-CF3 > p-CN > P-NO2), a trend opposite to that observed for trimethyl Pt complexes 8 involved in an S iv2-type reaction shown in Fig. 5. As the electronic requirements to the nucleophilicity of Z for the... 

Possibly an oxidative addition of Cl—CCI3, insertion of C=C and reductive elimination, but this could also be a radical chain reaction initiated by the metal. In this case CCl3 would add to the free alkene to give RCH CH2CCl3, which would abstract Cl from another mole of CCI4. If the latter were true, however, we would see crossover, so we can rule out the radical pathway. 

Oxidative addition of the vinyl C-Cl to Pd(0) must be followed by the insertion of the alkyne into the Pd-C bond. Reductive elimination with the Pd-Cl acquired at the oxidative addition step completes the process. Such a Cl-Pd-C reductive elimination to Cl-C is relatively rare. 

Catalyst systems of the type [NiL X + AlEt Xj (where L = PR and X = halide) afford highly active catalysts for olefm dimerisation. However, when complex 11 (Scheme 13.8) is treated with AlEt Cl in the presence of 1-butene, in toluene at 20°C the only products observed were decomposition products, 12,13,14 no butene dimers were obtained [22], At low temperatures (-15°C) and using the complex with 1,3-diiso-propylimidazolin-2-ylidene as the NHC ligand, small amounts of butene dimers were observed. It is apparent from these results that Ni-NHC complexes are capable of olefin dimerisation, however, decomposition of the catalyst via reductive elimination predominates. 

Let us consider the general trends of the reactivity of C-C, C-S, and C-Q (Q = Cl, Br, I) bonds towards oxidative addition and reductive elimination (Scheme 7-25). In many cases, either C-C bond-forming reductive elimination from a metal center (a) or the oxidative addition of a C-Q bond to a low-valent metal center is a thermodynamically favorable process (c). On the other hand, the thermodynamics of the C-S bond oxidative addition and reductive elimination (b) lies in between these two cases. In other words, one could more easily control the reaction course by the modulation of metal, ligand, and reactant Further progress for better understanding of S-X bond activation will be achieved by thorough stoichiometric investigations and computational studies. 

In the low-temperature reaction of 1 with dimethylaluminum chloride insertion into the Al-Cl bond was expected. Instead, insertion into a Al-C bond took place, as concluded from the reaction products. After the insertion process, a reductive elimination step led to the formation of the known aluminum compound 3937 and of an undefined polymer of the composition (Me5C5SiMe)ra.30 This surprising result has initiated further... 

PdCl2-promoted stoichiometric dichlorocarbonylation of acetylene (Eq. 20) is the first example of oxidative carbonylation of an alkyne that appeared in the literature [69,70], and presumably occurs through the mechanism shown in Scheme 13, involving addition of PdC to the triple bond followed by CO insertion, reductive elimination, oxidative addition to the C - Cl bond, further CO insertion and reductive elimination (Scheme 13, path a). 

Again, it proceeds by the standard mechanism for cross-coupling reactions oxidative addition of Pd(0) to the C-Cl bond, transmetallation (can also be viewed as ligand substitution) to give the N-Pd(II)-C compound, and reductive elimination. 

Oxidative addition of Pd(0) to a c/s-dihaloethylene gives an intermediate that can undergo 3-halide elimination. The C-Br or C-I bond is more prone to undergo (3-elimination than the much stronger C-Cl bond. The transmetallation and reductive elimination steps of the Sonogashira coupling have more time to occur when a C-Cl bond is (3 to Pd than when a C-Br or C-I bond is (3 to Pd. 

The reductive elimination has been less studied than the oxidative addition and migratory insertion steps. Forster reported that [Rh(C(0)Me)(CO)l3f decomposed to Acl and [Rh(CO)2l2] in several solvents without any marked dependence of the rate on the solvent. Acl was detected in aprotic media from reaction of Mel with CO in the presence of [Rh(CO)2l2r. However, it was also concluded that oxidative addition of AcX to [Rh(CO)2X2] (X = Cl, Br) was not thermodynamically favorable [34]. 

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