Thermomorphic system catalyst recovery

Thermomorphic solvent mixtures have been tested for hydroformylation of 1-octene and 1-dodecene to determine the ease of product recovery and catalyst recycling. Using both batch and continuous reactors, we demonstrated the efficacy of a biphasic, thermomorphic, system that had the following advantages ... 

While recovery of a polymer-bound catalyst like 115 in a thermomorphic system is quantitative based on the absence of detectable Pd in the nonpolar phase, product yields can often be lowered in the first few cycles. This is illustrated by the data in Table 1 for Heck and Suzuki reactions like Eqs. 51 and 52... 

Dendrimers too can be used in thermomorphic systems. In a report describing dendrimer-bound Pd(0) catalysis [163], Kaneda compared the liq-uid/liquid thermomorphic separation scheme with more established membrane and solvent precipitation procedures. Starting with commercially available third-, fourth-, and fifth-generation poly(propylene imine) dendrimers, the primary amine groups at the periphery were converted into chelating phosphines. The resulting phosphines were in turn allowed to react with Cl2Pd(PhCN)2 to form Pd(II) complexes that were reduced by hydrazine in the presence of triphenylphosphine to form the Pd(0) catalyst 126 (Eq. 63). This catalyst was successfully used in the allylic amination shown in Eq. 64. In this example, solvent precipitation, membrane filtration, and thermomorphic liq-uid/liquid separation were all used to recycle 126. The latter procedure proved to be simplest with the best recovery of active catalyst. 

A second nucleophilic catalyst supported by PtBS is the polymer-bound di-methylaminopyridine analog that was also used in latent biphasic catalysis with the poly(JV-alkylacrylamide) support 129 [131]. This example of a nucleophilic catalyst (133) was used to catalyze formation of a t-Boc derivative of 2,6-di-methylphenol (Eq. 70). In this case, the extent of recovery of the catalyst and the yields of product were directly comparable to those seen with thermomorphic systems. The isolated yield for the first five cycles of this reaction were 34.3, 60.9,82.2,94.6, and 99%. In this case we reused catalyst 133 through 20 cycles. Yields after the first few cycles were essentially quantitative (ca. 93% average for each of 20 cycles). Separation of the polymer from the aqueous ethanol phase was quantitative as judged by either visual observation or UV-visible spectroscopic analysis. 

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