Water soluble polymeric ligands in aqueous hydroformylation

8 Water soluble polymeric ligands in aqueous hydroformylation 

Soluble polymers are often used as carriers of catalytic units [119] and the idea has also been applied in the field of aqueous organometallic hydroformylations. In this case, of course, the polymers are water-soluble, and are designed to retain the catalytically active complexes (mainly of 

The phosphinated ligands 135 and 136 prepared from poly(acrylic acid) and from poly(ethyleneimine), respectively, gave active hydroformylation catalysts in reaction with [Rh(acac)(CO)2]. Under the conditions of Table 4.6 low conversions were observed in aqueous/organic biphasic systems, due to the low solubility of 1-octene. Addition of a surfactant (SDS) or an organic co-solvent (MeOH) led to dramatic increases in the yield of aldehydes, revealing the high intrinsic activity of the catalyst [120], 

Proteins are water-soluble biopolymers with a huge number of potential donor atoms and coordination sites which could make them useful carriers of metal complex catalysts. Indeed, a few successful attempts can be found in the literature [139] but often the interaction of proteins and metal complexes lead to a loss of catalytic activity [140]. This was not the case with human serum albumin (HSA) which formed a stable and active catalytically active complex with [Rh(acac)(CO)2]. In the hydroformylation of 1-octene and styrene the selectivity towards aldehydes was excellent, moreover styrene reacted with high regioselectivity (b/1 = 19). The activity 

It seems worth pointing out, that 137 and human serum albumin contain no pendant phosphines and the donor atoms in the complexes formed with rhodium can be only O (137) or O, N and perhaps S (HSA), which are not the most suitable for stabilizing low oxidation state metal ions. Still these macroligands gave active and stable catalysts with rhodium, which shows that perhaps in the high local concentration provided by the polymer even these hard donor atoms are able to save the metal ion against hydrolysis or other deterioration. 

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