Pd-X bonds

The broken bonds (boldface=dissociated fragment) BDEs (boldface = recommended data reference in parentheses) Methods (reference in References 

Pd(110, surf.)-PVBA P VB A=A-trans-1-(pyrid-4-yl-vinyl) benzoic acid 19.1 0.7 80.1 + 2.9 STM 1999WEC/BAR 

---

Metal cations can lend electrophilic assistance to weaken the Pd—X bonds in the intermediate R-Pd —X. Either full fission of this bond, leading to the realization of a polar mechanism, or partial polarization, might take place. Soft Lewis acids (the cations of Cu, Ag, Tl) are used most often (see Chapter 9.8 for a discussion of how metal ions act as Lewis-acid catalysts). 

Those interactions mentioned above lead to jr-complexation and oxidative addition, representing two of the several most widely employed routes to organopalladium derivatives along with transmetallation with Pd, hy-dropalladation, and heteropalladation defined as addition of Pd - X bonds to 7r-bonds, where X is any element other than C or H [2],... 

Solvent effects are less dominant in the isomerization of the phosphole complexes than in the isomerizations of the phosphine complexes. Likewise changes in internal bond strengths are more important for the phosphole complexes than for the phosphine complexes. This is because both the Pd-P and Pd-X bonds are stronger and shorter in the phosphole than in the phosphine complexes suggesting that DMPP is both a better a-donor and r-acceptor toward Pd(II) than is Me2PPh. 

The nature of X in 1 (and thus the strength of the Pd-X bond in 5) is clearly an important factor unless the reaction conditions are modified aryl and vinyl tri-... 

Two possible routes are proposed (Scheme 2a), the former ( cationic ) pathway beginning with the dissociation of X from 5 to generate the tricoordinate 14e cationic complex 8 with the accompanying counterion X . Complexation of 2 into the vacant site then gives the 16e species 9, and insertion of 2 into the Pd—R bond followed by reformation of the Pd—X bond gives 6 as desired, with the chiral bidentate ligand having... 

In the donor-acceptor interplay, the Pd(n)-coordinated olefin becomes activated toward attack by nucleophiles (i o-attack). Moreover, the olefin can insert into Pd-C and some other Pd-X bonds (endo-attacVi) (Scheme 2). These... 

Perhaps the most efficient way to ensure the desired regioselectivity is by the choice of electrophile. As stated, neutral palladium(II) halide complexes are typically formed, when aryl and vinyl halides are used, resulting from a strong Pd—X bond, leading to the linear alkene products. In contrast, the poor coordinating abilities of the triflate counterparts readily facilitate the formation of the... 

Table show that for a given complex in a given solvent the kinetic parameters are, as one would expect for a pseudo-octahedral substrate, independent of the nature of the incoming ligand. In protic solvents, the reactivity of [Pd(dien)X]+ decreases in the order X = Q > Br > I this reactivity decrease stems from the variation in activation enthalpies rather than that in activation entropies (Section B of Table 5). These observations suggest an associative type of mechanism with a transition state [Pd(Et4dien)X(soIvent)]+. In such a mechanism the activation enthalpy would be expected to vary according to the respective strengths of the Pd— X bonds being stretched, but as the halide ion...

---