Susceptibility to catalyst poisoning

Homogeneous catalysts often have the advantages of better catalyst reproduci bility and better selectivity. They are also less susceptible to catalyst poisoning (heterogeneous catalysts are usually poisoned by small amounts of sulfur, often found in rubber stoppers, or by sulfur-containing compounds, such as thiols and sulfides). On the other hand, heterogeneous catalysts are usually easier to separate from the reaction mixture. 

Carbon-phosphorus bonds may also be formed. Chemists at Merck developed a synthesis of either enantiomer of the valuable ligand BINAP 133 from the more easily resolved BINOL 2.612, using a triflate-phosphine coupling reaction (Scheme 2.183). They reasoned that nickel catalysis would be more effective as this metal is harder than palladium and, therefore, less susceptible to catalyst poisoning by the product. BINAP 133 could be obtained with no loss of chirality. They also reported a resolution procedure for BINOL 2.612.224... 

The efficiency and overall performance of a given redox catalyst, as will he seen helow, depend on several factors. Kinetically, reaction (60) on the catalyst surface should he very fast to compete with fast thermal hack-electron-transfer reactions. Also the reaction should he c[uantitative as written. Furthermore, the catalyst should he stable and not susceptible to catalyst poisoning over extensive cycles of the reactions such as (60). 

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