Palladium ratio

The most significant PGM deposit in the United States is at Stillwater, Montana, where PGMs are mined as the primary product. The grade has been estimated as between 13 and 22 g/1, having a platinum—palladium ratio of 1 3.5. The first ore was extracted from Stillwater in 1987 and full production of 1000 t/d was reached in 1990. 

Other tetradentate thiophene diamine ligands have been previously involved in the palladium-catalysed test reaction by Kim et al., in 2004. Prepared from (i ,i )-l,2-diaminocyclohexane, these ligands were proved to be very efficient in terms of enantioselectivity in this reaction since an enantioselectivity of up to 98% ee was observed when the ligand/palladium ratio was 4/1 (Scheme 1.61). 

The effects of tin/palladium ratio, temperatnre, pressnre, and recycling were studied and correlated with catalyst characterization. The catalysts were characterized by chemisorption titrations, in situ X-Ray Diffraction (XRD), and Electron Spectroscopy for Chemical Analysis (ESCA). Chemisorption studies with hydrogen sulfide show lack of adsorption at higher Sn/Pd ratios. Carbon monoxide chemisorption indicates an increase in adsorption with increasing palladium concentration. One form of palladium is transformed to a new phase at 140°C by measurement of in situ variable temperature XRD. ESCA studies of the catalysts show that the presence of tin concentration increases the surface palladium concentration. ESCA data also indicates that recycled catalysts show no palladium sulfide formation at the surface but palladium cyanide is present. 

The mechanistic suggestion depicted on Scheme 5.4 may be tme in an excess of phosphine ligands, and in fact, the [phosphine]/[palladium] ratio has a pronounced influence on the rate and selectivity of the reactions. However, it has also been demonstrated [20,58] that the palladium(It)-phosphine complexes used as catalyst precursors are reduced to Pd(0) in the... 

Practical hydroxycarbonylation of olefins is usually carried out with palladium catalysts and requires rather elevated temperatures. Pd/TPPTS [36-39], Pd/TPPMS [40] and Pd/sulfonated XANTHPHOS (51) were all applied for this purpose. In general, TOF-s of several hundred h can be observed under the conditions of Scheme 5.11, and with propene the concentration ratio of linear and branched acids is around l/b=1.3-1.4 [36,38]. At elevated temperatures and at low phosphine/palladium ratios precipitation of palladium black can be observed. It is known, that the highly reactive [Pd(TPPTS)3] forms easily under CO from a Pd(II) catalyst precursor and TPPTS [37], and that in the presence of acids it is in a fast equilibrium with [PdH(TPPTS)3] [39] ... 

In line with the above mechanism, catalyst deactivation by formation of palladium black can be retarded by increasing the [P]/[Pd] ratio, however, only on the expense of the reaction rate. Bidentate phosphines form stronger chelate complexes than TPPMS which may allow at working with lower phosphine to palladium ratios. Indeed, the palladium complex of sulfonated XANTPHOS (51) proved to be an effective and selective catalyst for hydroxycarbonylation of propene, although at [51]/[Pd] < 2 formation of palladium black was still observed. The catalyst was selective towards the formation of butyric acid, with 1/b = 65/35 [41]. 

The solution of hydrogen in palladium must be considered as a different type of alloy system, because the hydrogen cannot replace palladium in the lattice structure. The fall in susceptibility to zero at a hydrogen-palladium ratio of 0.55 suggests that all the electrons of the hydrogen atoms enter the 4d palladium levels (11). 

To obtain useful yields for this reaction, a ligand-to-palladium ratio of 7 1 was needed to maintain catalyst stability. 

It appears from Figures 5 and 6 that there may be a platinum palladium ratio at constant metals concentration which gives optimum... 

X-ray spectra (1) were made of the surfaces of two similar catalysts (Figure 10). Both catalysts contained 0.05 wt % total metals with a platinum palladium ratio of 2.5 1.0. They were made in the same way... 

Of great importance proved to be the ratio of the phosphine to the palladium-compound as shown in Figure 22. At the phosphorus/palladium ratio of 3 1 a maximum of yield and selectivity of the 6-lactone was observed, whereas an excess of phosphine blocked the free coordination sites of the catalytic intermediate. At ratios lower than 2 1 yield and selectivity decrease evidently thus proving that a Tittle excess of ligand is needed to form the catalytic active species. 

Other parameters of the palladium(n)-catalysed benzofuran synthesis were explored. Ultimately, it was found that the ideal system employed a 2 1 ligand/palladium ratio (10mol% Pd(OAc)2 and 20mol% ethyl nicotinate) and a substoichiometric amount (20mol%) of NaOAc at 100 °C. With this system in hand, a variety of substituted benzo-furans were accessed (Figure 9.7). The reaction was limited to electron-rich aryl systems the palladation event required a sufficiently nucleophilic arene in order to occur. The aryl subunit, however, tolerated an array of alkyl and alkoxy substitution patterns within the... 

Hi) The best ligand/palladium ratio appear to be 2-3 when considering the selectivity in isocyanate. 

Table 7.4 Palladium-catalysed cyanation of P-bromostyrene (148) effect of palladium source and phosphorous to palladium ratio on the isolated yield of cinnamonitrile (149)...

The effect of increasing the ligand concentration on the cyanation reaction was also investigated, in order to find the optimum ligand-to-palladium ratio for stabilisation of an active catalytic species (Table 7.4). 

Although silver to palladium ratios of 3 1, 4 1, and 6 1 are commonly used in hybrid apphcations, thrifted versions utilizing Pd contents less than 5% have been shown to have good leach resistance in 62% Sn-36% Pb-2% Ag solders. Table 8.4 compares properties of various Ag Pd ratios. These materials meet the requirements of high-conductivity materials needed for circuits with higher speeds and densities. Similar performance can be met by small additions of platinum to silver (1 100). The leach resistance of a 1 % Pt addition is shown to be equivalent to a 10 percent Pd addition with minimum effect on conductivity. However, Ag migration such as dendritic growth and diffusion into resistors or capacitors when used as a termination material is stUl an issue with only minor Pd or E t additions. 

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