Nonpolar biphasic catalysis

Nonpolar biphasic catalysis Suzuki- and Sonogashira coupling reactions... 

NONPOLAR BIPHASIC CATALYSIS SUZUKI- AND SONOGASHIRA COUPLING REACTIONS... 

Only the biphasic method, specially of aqueous-biphasic catalysis, has provided a fundamental remedy to the problem of stress-free and economical recovery and recycle of homogeneous oxo catalysts [12]. The fact that the catalyst, which still acts homogeneously, is dissolved in water, thus in a polar solvent, and remains dissolved, enables it to be separated from the nonpolar products without problems and with minimal effort after reaction. 

Fig. 5-19. Catalyzed chemical reaction between polar educt A and nonpolar educt B and a reagent in a biphasic solvent system with temperature-dependent mutual miscibility of the polar and nonpolar (fluorous) solvents. A more detailed illustration of the experimental possibilities for catalysis in fluorous solvents is given in reference [890].

The oligomerization reaction is carried out in a polar solvent in which the nickel catalyst is dissolved but the nonpolar products, the a-olefins, are nearly insoluble. Preferred solvents are alkanediols, especially 1,4-butanediol. This was one of the first examples of a biphasic liquid/liquid system to be used in catalysis and is one of the key features of the process. The nickel catalyst is prepared in situ from a nickel salt, e.g., nickel chloride, and a chelating PnO ligand like o-diphenylphosphinobenzoic acid (Structure 1) by reduction with sodium boro-hydride [30, 39]. Suitable ligands are the general type of diorganophosphino acid derivatives (2). 

Phase-transfer catalysis (PTC) is the most widely used method for solving the problem of the mutual insolubility of nonpolar and ionic compounds. Basic principles, synthetic uses, industrial applications of PTC, and its advantages over conventional methods are well documented [1-3]. PTC has become a powerful and widely accepted tool for organic chemists due to its efficiency, simplicity, and cost effectiveness. The main merit of the method is its universality. It may be applied to many types of reactions involving diverse classes of compounds. An important feature of PTC is its computability with other methods for the intensification of biphasic reactions (sonolysis, photolysis, microwaving, etc.) as well as with other types of catalysis, in particular, with transition-metal-complex catalysis. Homogeneous metal-complex catalysis under PTC conditions involves the simul-... 

---