Effect of Anionic Ligands

Table I. Effect of Anionic Ligands on Activity of MoX2(NO)2L2-Derived Disproportionation Catalysts...

Observed effects of anionic ligands on J(PtP) coupling constants... 

SCHEME 24.31 Effect of anionic ligand structure on CDC between 28 and 1,3-dimethoxybenzene. 

The above substitution effects appear to be independent of the nature of the ligand (16) since the benzyl compounds behave similarly, Table XI. It would appear from these observations that the introduction of anionic ligand would be sufficient to increase activity of transition metal alkyl compounds for polymerization. This, however, is probably an oversimplifica-... 

There are no mechanistic details known from intermediates of copper, like we have seen in the studies on metathesis, where both metal alkylidene complexes and metallacyclobutanes that are active catalysts have been isolated and characterised. The copper catalyst must fulfil two roles, first it must decompose the diazo compound in the carbene and dinitrogen and secondly it must transfer the carbene fragment to an alkene. Copper carbene species, if involved, must be rather unstable, but yet in view of the enantioselective effect of the ligands on copper, clearly the carbene fragment must be coordinated to copper. It is generally believed that the copper carbene complex is rather a copper carbenoid complex, as the highly reactive species has reactivities very similar to free carbenes. It has not the character of a metal-alkylidene complex that we have encountered on the left-hand-side of the periodic table in metathesis (Chapter 16). Carbene-copper species have been observed in situ (in a neutral copper species containing an iminophosphanamide as the anion), but they are still very rare [9],... 

Amazingly, there is no systematic cis effect of the ligand L trans to carbon monoxide in the carbonylosmium(II) porphyrins Os(OEP)CO(L) [30a-30g], (Table 10). In the nitrosyl derivatives, Os(OEP)NO(L), the anionic ligand Le exerts only a small effect (Table 11) the wavelengths of the a-bands increase in the series [31c] < [3Id] <... 

The effect of anion binding on k is not nearly as great. The data in Fig. 6 show that for both metals, there is less than a 50% decrease in the thermal ET rate constant between hybrids containing neutral and anionic ligands. 

The fundamental examples of this class of complexes, for example, cyanides, nitrates, thiocyanate, and the isocyanato derivatives are well known, and with the exception of the interesting, strong labilizing effect of the latter, which leads to fast decarbonylation to [Re2(/r-NCO)2(CO)8], they do not have a special chemistry and are sometimes difficult to prepare. In any case, these difficulties have been removed by the use of Re(CO)5FBF3, which readily reacts with these types of anionic ligands to form the corresponding Re complexes. A few structural analogs of (14) and (15), Re(ER2)(CO)5,... 

When chloride was added to the system either as sodium chloride (Table I, lines 3a and b) or as palladium chloride (lines 4r-6) a drastic change in the reaction path occurred. The source of the halide is unimportant apparently a rapid scrambling of anionic ligands occurs during the preparation of the solutions prior to olefin addition (c/., Table I, lines 3a and 4a). However, in the presence of chloride, temperature effects become pronounced. In all cases, the higher reaction temperatures greatly favor I-substitution, so much so that it was possible to reverse completely... 

The study of such a large number of carriers allowed for the elucidation of the effect of both the amount of carrier in the membrane, as well as the effect of the ligand nature on the observed selectivities. It was thus concluded that the selectivity was influenced by the size of the constituent R groups, suggesting steric hindrance in the penta-coordination of the corresponding ionophores by analyte anions. 

The chemistry of AP" in soil solutions is complicated by the fact that soluble inorganic and organic ligands form complexes with AP". Since many of these complexes are soluble, the effect of the ligands is to increase the concentration of total soluble Al. A case in point is the fluoride anion, which strongly complexes with AP". The first step of complexation between AP" and F" is written... 

Figure 4.10 shows the accelerating effect of various ligands in PO anionic polymerisation [14, 53]. 

Figure 4.10 The effect of various ligands on the PO consumption rate in anionic PO polymerisation. Temperature 110 °C Pressure 0.4 MPa catalyst concentration 0.0056 mol/1 NMP N-methyl pyrolidone...

---