Weak donor

Additionally, MO calculations indicate the lowest energy orientation occurs with the three strongest trans-influence ligands (two hydrides and a PPh3) in a facial configuration. Calculations on compounds IrX(CO)(PR3)2 indicates that weak donors X and strong 7r-acceptors PR3 favour addition in the XIrCO plane [134, 135],... 

A relatively strong organization of an electron donor by an acceptor is typically indicated by experimental values of KEUA or KC f> > 10 M-1. For intermediate values of the formation constant, i.e., 1 < KE A < 10 m, the donor/acceptor organization is considered to be weak.17 Finally, at the limit of very weak donor/acceptor organizations with KEDA 1, the lifetime of the EDA complex can be on the order of a molecular collision these are referred to as contact charge-transfer complexes.18... 

Ligand Preferences. The LVC s are electron rich and in order to exist in stable compounds they require ligands, such as CO, that are weak donors and good tt acceptors. On the other hand the HVC clusters are not attractive to such ligands nor do they require them for stability. In this respect, there is a direct parallel to mononuclear compounds where M° prefers CO, RNC or similarly ir-acidic ligands while the Mn+ (n = 2-4) ions do not generally form CO complexes. 

Many ligands of this category offer the prospect of inducing axial metal-ion coordination even for those cases where the pendant arms incorporate weak donor functions. Coordination will be enhanced simply because the donors are held near to the metal and hence their effective ... 

Coordination of [(t-C4H9)2P(=Se)I] with molecular iodine furnishes a 1 1 adduct that crystallises as cyclic dimer in the solid state (Figure 46).57 From each I2 molecule within the structure, one atom acts as acceptor towards selenium, and the other one becomes very weak donor towards the iodine atom bonded to phosphorus. This compound fulfills the requirements of a soft-soft base pair . As in the structure of the parent donor molecule [(t-C4Hg)2P(=Se)I],... 

Although satisfactory for weak donor-acceptor Interactions, this model does not hold in the case of strong charge transfer such as happens in some disubstltuted benzene derivatives. A simple additive assumption falls short of the experimental values for the three nitroanllines in the para, ortho and meta positions (14). Discrepancies between an additivity assumption and experimental values are seen to Increase with the degree of conjugation Induced by the substituent relative locations. 

It could be shown (Fig. 2) that the Li+ ion in DMSO is coordinated by four solvent molecules. y-Butyrolactone was found to be a convenient diluent in this kind of study. Contrary to DMSO (DN — 29.8), it is a rather weak donor (DN = 18.0) which appreciably dissolves alkali metal salts. Its interaction with DMSO is much weaker than that between DMSO and a metal cation. By plotting the chemical shift of the 7Li NMR signal vs. 

In contrast to the strong and bulky DMSO nucleophile, the small HCN molecule is a weak donor compared to water (vide supra) and can be easily replaced by H20. HCN on the one hand is a water-like solvent, without much application because of its toxicity. On the other hand, it is employed as a simplified model to perform quantum chemical studies on CH3CN. Our calculations corroborated the experimental work that the first coordination sphere around Li+ consists of four tightly bound CH3CN and HCN... 

A similar picture is revealed for the octadienediyl-Ni11 complex involved in the C12-cyclotrimer reaction channel.110 In the ri p1 species, 2b, 3b, r 2-butadiene preferably occupies the fourth position around Ni11, while the coordination of butadiene is unfavorable at the AG surface for the bis(r 3) species 4b. The predominant configurations are 2b and 4b, while bis(r(1) species represent isomers lying at much higher energies. The bis(r 3) species 4b is favorable by 5.6 kcal mol-1 (AG) relative to 2b, which is due to the limited ability of the weak donor butadiene to electronically stabilize the p ri C1) coordination mode. 

The basicity of the donors, which is proportional to the p/ a values, becomes a measure of the relative donor strength. Thus, diglyme (pK.d 4) is a weak donor, while Bu3PO (pKa 0) is a strong donor. 

For example, when a relatively weak donor, such as alcohol, was used,... 

The effect of donors on the catalyst activity can be explained by assuming that the dimeric complex is not an active catalyst (Cramer s kinetics indicate a monomeric Rh species as active catalyst see Section II,B,2) and that 14 with a free coordination site for ethylene is the active catalyst, while 15 with both coordination sites occupied by donors is catalytically inactive. When D is a weak donor, such as ketone or ether (see Fig. 5d), the reaction rate increases, slowly reaching a maximum and leveling off at the maximum as the concentration of the donor is increased. It can be speculated that these donors interact with the catalyst only to the extent that they break up the dimer 8 to form 14, but that... 

Bare metal cations will seek out any source of electrons, but these are relatively inert ions such as Cr+, Mn+, and Ag+. Many metal ions will bond with very weak donors such as Xe. 

Since the identification of bona-fide hydrogen bonds in solid state studies is often a controversial issue, in particular in the cases involving weak donors [10]... 

Recent attempts to unify the polarity scales of solvents (for non-specific interactions) are of great interest in rationalizing the medium effects166. Generally, the spectroscopic properties of appropriate substances are used to check the solvating ability of solvents. 4-Nitroaniline is a useful indicator for estimating solvent polarity because it is an electron acceptor molecule which presents incomplete complexation with weak donor solvents167. 

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