Transitional metal bases, correlation

Rates of reaction of transition metal nucleophiles correlate both with oxidation potentials for MLn and with the pKa values of the corresponding acids, HMLn. Therefore, the two parameters, E° and H, in the Edwards equation are not independent parameters. The same result is found for other nucleophiles, if the donor atom is C,N, O, or F. However, for bases with heavier donor atoms, E° and H are not as correlated with each other. For transition metal complexes, soft ligands, L, increase acidity and decrease nucleophilic reactivity. 

The arguments given state that easily oxidized bases will be good nucleophiles toward alkyl halides and also strong bases toward the proton. This statement means that E° and H in the Edwards equation are no longer independent parameters but essentially one and the same property for transition metal bases. For bases where the donor atom is a nonmetal, this correlation is normally not the case. The fluoride ion is a stronger base than the iodide ion but is more difficult to oxidize. Still, examination of bases of the representative elements more closely to see if E° and H are truly independent is worthwhile. Actually E°, the redox potential in water, is not the best parameter to use. E° is measurable only for a few nucleophiles and is complicated by the nature of the products formed. For example, in... 

Two other, closely related, consequences flow from our central proposition. If the d orbitals are little mixed into the bonding orbitals, then, by the same token, the bond orbitals are little mixed into the d. The d electrons are to be seen as being housed in an essentially discrete - we say uncoupled - subset of d orbitals. We shall see in Chapter 4 how this correlates directly with the weakness of the spectral d-d bands. It also follows that, regardless of coordination number or geometry, the separation of the d electrons implies that the configuration is a significant property of Werner-type complexes. Contrast this emphasis on the d" configuration in transition-metal chemistry to the usual position adopted in, say, carbon chemistry where sp, sp and sp hybrids form more useful bases. Put another way, while the 2s... 

Peterson, K.A. and Puzzarini, C. (2005) Systematically convergent basis sets for transition metals. II. Pseudopotential-based correlation consistent basis sets for the group 11 (Cu, Ag, Au) and 12 (Zn, Cd, Hg) elements. Theoretical Chemistry Accounts, 114, 283-296. 

At present, the correlation contains one transition metal complex, Cu(Hfacac)2. The results on this complex are very interesting and somewhat unusual for a transition metal system in that enthalpies have been obtained in a poorly solvating solvent with nonionic donors (52), instead of the t5 ical stability constant study on a metal cation in some highly polar solvent. Data from this latter type of investigation have many practical uses, but are impossible to interpret and understand. The transition metal ion complex we have studied can be incorporated into the E and C scheme using the same base parameters that are used to correlate the enthalpies of formation of all the other Lewis acid-base adducts in the scheme. 

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