Transition-Metal Containing Phase-Transfer Agents and Their Use in Synthesis

3 Transition-Metal Containing Phase-Transfer Agents and Their Use in Synthesis 

The idea that transition-metal complexes can act as PT agents was presented in some early studies of metal-complex-catalyzed reactions under PTC conditions. Lately, several approaches to the design of bifunctional catalysts have been made. Organometallic complexes capable of effecting phase transfer reactions were prepared for the first time in 1982 [192, 193]. Tertiary phosphines containing polyether substituents react with Pd(PhCN)2Cl2 to afford complexes capable of catalyzing the reduction of bromobenzene with NaH suspended in toluene. 

Phosphine-containing crown ethers, combined with [Rh(l,5-cycloocta-diene)Cl]2, promote hydrogenation of alkali-metal cinnamates [194]. It has been also demonstrated that ( 7r-C3H5PdCl)2, in the presence of such crown ethers, catalyzes the reaction of allyl bromide with powdered Nal or KI in benzene [194]. 

Systems containing a transition-metal anion, with a quaternary onium ion as the cation (e. g., [R4N]3 [IrCl6] ), should possess an advantage [198-200]. The bifunctional catalytic properties of such systems were demonstrated in the hydrosilylation of PhC=CH and subsequent PTC reaction with dichlorocarbene 

Scrutiny of the literature data shows that numerous transformations of diverse organic molecules are readily catalyzed by homogeneous metal complexes in two-phase systems. The joint use of transition metals and phase-transfer agents considerably expands the synthetic possibilities of both metal-complex catalysis and PTC. The combination of these two different types of catalysts in many cases leads to higher reaction rates, higher product yields, milder conditions, higher selectivities, and simpler reaction execution and product isolation. Biphasic reactions in the presence of transition-metal complexes and PT agents have been 

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