Effects of Ancillary Ligands

Table 3. Effect of ancillary ligands on SO2 coordination geometry and infrared frequencies... 

The common properties attributed to helper ligands in improving lanthanide-based detection techniques include enhanced stability, sensitivity, and selectivity. We will start with the effects of ancillary ligands on lanthanide photophysics and then explore the impacts of these ligands on sensor properties (Section II). Other factors influencing stability, such as sterics and oxophilicity, will be summarized in Section III. A brief discussion of future applications will follow (Section IV). 

Wliile investigating the effects of ancillary ligands on the binding of dipicolinate, we developed a binding afBnity by competition (BAG) assay to quantify the binding constant of anal5rte to lanthanide complex (Eq. 3) (102). 

The data in Tables 1-3 probably constitute the most extensive overview available for solution M-H BDE data that have been obtained by a single method. The effect of ancillary ligands on the M-H BDEs in series of related complexes can be studied in some detail. It was pointed out in Section 3.3.1 that the BDEs are remarkably insensitive to certain changes in the ligands. For example, within each of the following groups from Table 1, BDE differences are smaller than 8 kJ moL CpCr(CO)2(L)H (entries 1-4) CpW(CO)2(L)H (entries 12 and 13) Mn(CO)4(L)H (entries 17 and 18) Co(CO)3(L)H (entries 24-26) CpM(CO)3H compared with Cp M(CO)3H (M = Cr, entries 1 and 5 Mo, entries 8 and 9). Similar effects are found in Table 2 less than 5 kJ mol differences within the series CpIr(CO)(L)H+ (entries 32-39) Cp Ir(COD)H+ (entries 41-45) Cp Ir(CO)(L)H+ (entries 46-51, where the dicarbonyl differs somewhat more from the substituted compounds). 

The development of volatile compounds of alkaline-earth metals has attracted attention because of the need for these compounds as precursors for the preparation of thin films by chemical gas phase methods. Hatanpaa and coworkers [200] characterized the effect of ancillary ligands on the structural and thermal properties of several [Mg(thd)2(A)] complexes, in which A is a neutral Lewis-base ligand. They showed that the evaporation processes of diamine adducts contain two overlapping steps, the first step associated with the evaporation of amine and the second with the evaporation of [Mg2(thd)4] dimer. All the complexes containing amines evaporated almost completely, but the complex which contained 1,2-ethanediol, was thermally unstable and decomposed when heated. At temperatures below the dissociation temperature, all adducts of diamines appeared to evaporate intact. 

Table 5.10. Effect of ancillary ligand on arene ring exchange.

Table 8.1.. The effect of ancillary ligand electronic effects on the rate of reductive elimination of benzene from Cp RhtPRjKPhKH).

The Effects of Ancillary Ligands on Metal-Carbon Bond Strengths as Determined by C-H Activation... 

The Effects of Ancillary Ligands rai Metal-Carbon Bond Stiraigths as... 

Several recent studies have begun to uncover the molecular mechanisms of carbon-heteroatom bond-forming reductive elimination from Pd centers. This recent work has addressed such fundamental questions as the electronic requirements of C-X coupling, the effects of ancillary ligands, the influence of solvent and additives, and the relative rates of competing transformations. The future of this field is bright, as there are stiU many outstanding mechanistic questions to be... 

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