Reductive elimination electronic effects

They demonstrated that electron-deficient R groups and electron-rich R substituents at S accelerated the reductive elimination. They proposed 123 (Lj = DPPE, R = Ph, R = Ar) as a transition state, where R acts as an electrophile and thiolate as a nucleophile. The Hammet plot for the reductive elimination showed that the resonance effect of the substituent in R determines the inductive effect of the R group, and the effect in SR showed an acceptable linear relationship with the standard o-values. The relative rate for sulfide elimination as a function of the hybrid valence configuration of the carbon center bonded to palladium followed the trend sp > sp spl... 

More recently, reductive elimination of aryl ethers has been reported from complexes that lack the activating substituent on the palladium-bound aryl group (Equation (55)). These complexes contain sterically hindered phosphine ligands, and these results demonstrate how steric effects of the dative ligand can overcome the electronic constraints of the reaction.112,113 Reductive elimination of oxygen heterocycles upon oxidation of nickel oxametallacycles has also been reported, but yields of the organic product were lower than they were for oxidatively induced reductive eliminations of alkylamines from nickel(II) mentioned above 215-217... 

When the steric repulsion between a cis bidentate and two substituents R and CN increases in a series of bidentate phosphine complexes of palladium, the rate of reductive elimination of R-CN increases by several orders of magnitude [16], Actually, the steric effect and electronic effect are related and careful variation of only one property at a time is needed to distinguish between the two. 

The transfer of iodine to the organic substrate represents a formal reductive elimination at tellurium(lV) to give tellurium(ll) as well as oxidation of the alkene. In a series of diaryltellurium(lV) diiodides, iodination of organic substrates is accelerated by electron-withdrawing substituents and is slowed by electron-donating substituents, which is consistent with the substituent effects one would expect for... 

The Ni-R group is considered to be polarized as NP -R ", whereas the reductive elimination produces electrically neutral R-R. Consequently the reductive elimination is accompanied by partial migration of electrons from R to Ni, which is enhanced by coordination of the 71-acid to Ni. The coordination of the electron-withdrawing olefin to Ni accelerates the reductive elimination by a factor of 10 or larger [16]. This situation is similar to the enhancement effect of electron-withdrawing substituent on acid dissociation [17] ... 

The controlling factor of the reductive elimination on Pd(R)(C=CR )Lm (Eq. 5) may be different from that observed with the nickel complex. However, participation of a similar activation process by coordination of electron-with-drawing RX and R C=CH is conceivable. The Pd(R)(C=CR )Lm-type complex can be isolated, and it has been shown that isolated Pd(R)(C=CR )Lm undergoes the reductive elimination exhibited in Eq. 5 [8]. The reductive elimination seems to be enhanced by addition of Cul. Cul may interact with the Pd complex, and an acceleration effect of Lewis acids on the reductive elimination reaction of NiR2(bpy) has been shown [22]. The X-ray crystallographic structure of an isolated Pd(R)(C=CR )Lm (R=C6H4Me-p R =C6H5) has been determined [8]. 

The introduction of fluorine atoms in a molecule can be used to modify the processes and the rates of metabolism of the drug, in order to extend the plasma half-life or avoid the formation of toxic metabolites. Due to the properties of the fluorine atom, in particular its electronic effects, it may interact differently during the biotransformation steps, according to the type of processes involved (oxidative, reductive, hydrolytic, etc), which allow the clearance of the exogen molecule (i.e., the elimination of the active substance from the organism). 

The Pd-catalysed intermolecular reaction of aryl bromides containing electron-withdrawing substituents with a wide variety of alcohols including MeOH, 2-propanol, benzyl alcohol and i-butyl alcohol gives the aryl ethers 416 under milder conditions than uncatalysed reactions. Bidentate ligands such as BINAP and DPPF (XLIX) are effective [206,207]. The aryl Pd alkoxide 417 was isolated as an intermediate, and the formation of the aryl ethers 418 by reductive elimination of 417 was confirmed. 

The key butenolide needed by Buszek, for his synthesis of (—)-octalactin A, had already been prepared by Godefroi and Chittenden and coworkers some years earlier (Scheme 13.4).9 Their pathway to 10 provides it in excellent overall yield, in three straightforward steps from l-ascorbic acid. The first step entails stereospecific hydrogenation of the double bond to obtain L-gulono-1,4-lactone 13. Reduction occurs exclusively from the sterically less-encumbered ot face of the alkene in this reaction. Tetraol 13 was then converted to the 2,6-dibromide 14 with HBr and acetic anhydride in acetic acid. Selective dehalogenation of 14 with sodium bisulfite finally procured 10. It is likely that the electron-withdrawing effect of the carbonyl in 14 preferentially weakens the adjacent C—Br bond, making this halide more susceptible to reductive elimination under these reaction conditions. 

Two studies have been conducted that outline the effects of ligand steric and electronic properties on the relative rates for reductive elimination of amine and P-hydrogen elimination from amides. One study focused on the amination chemistry catalyzed by P(o-C6H4Me)3 palladium complexes [111], while the second focused on the chemistry catalyzed by complexes containing chelating ligands [88]. 

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