Rhodium phosphite catalysts

Paul C. J. Kamer, Joost N. H. Reek, and Piet W. N. M. van Leeuwen 

Institiite of Molecular Chemistry. University of Amsterdam. Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands 

The important discovery by Wilkinson [1] that rhodium afforded active and selective hydroformylation catalysts under mild conditions in the presence of triphenylphosphine as a hgand triggered a lot of research on hydroformylation, especially on hgand effects and mechanistic aspects. It is commonly accepted that the mechanism for the cobalt catalyzed hydroformylation as postulated by Heck and Breslow [2] can be apphed to phosphine modified rhodium carbonyl as well. Kinetic studies of the rhodium triphenylphosphine catalyst have shown that the addition of the aUcene to the hydride rhodium complex and/or the hydride migration step is probably rate-limiting [3] (Chapter 4). In most phosphine modified systems an inverse reaction rate dependency on phosphine ligand concentration or carbon monoxide pressure is observed [4]. 

The high catalytic activity of the rhodium bulky phosphite system was also evident in the hydroformylation of 1-alkenes [11,12]. A rhodium complex containing tris(2-ferf-butyl-4-methylphenyl) phosphite (lb) as ligand gave extremely high rates up to 161,000 mol.mol Rh. h in the hydroformylation of 1-octene with moderate selectivity for the linear aldehyde. 

One of the commercial apphcations of bulky phosphites is the production of 3-methylpentane-11,5-diol by hydroformylation of 3-methylbut-3-en-l-01 by Kuraray [17]. Furthermore, they reported the use of bulky phosphite in the hydroformylation of vinyl acetate and 7-octenal, the latter providing an intermediate for the preparation of nonanediol. The high reactivity induced by bulky phosphite hgands has also led to the application of hydroformylation in the functionalization of natural product derivatives that are otherwise hardly reactive. Syntheses of important intermediates to fine-chemicals have been reported by hydroformylation of dihydroluran [18], glucal derivatives [19] and methyl oleate [20] (see also chapter 6 for further details). 

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The first step in the synthesis of nonvolatile plasticizers - which are of increasing importance - is hydroformylation of a long-chain olefin, for which rhodium phosphite catalysts have very useful properties. The current use of sterically hindered phosphites as antioxidants for polyalkenes together with their much simpler... 

Wasserscheid, R. van Hal, Supported Ionic Liquid Phase Catalysis-Heterogenization of Homogeneous Rhodium Phosphite Catalysts in Ionic... 

Asymmetric Hydroformylation with Rhodium-Phosphite Catalysts... 

Ligand metallation. In early transition metal polymerization catalysis often metalation of the ligand occurs leading to inactive catalysts. In late transition metal chemistry the same reactions occur, but now the complexes formed represent a dormant site and catalyst activity can often be restored. Work-up of rhodium-phosphite catalyst solutions after hydroformylation often shows partial formation of metallated species, especially when bulky phosphites are used [50]. Dihydrogen elimination or alkane elimination may lead to the metallated complex. The reaction is reversible for rhodium and thus the metallated species could function as a stabilized form of rhodium during a catalyst recycle. Many metallated phosphite complexes have been reported, but we mention only two, one for triphenyl phosphite and rhodium [51, 52] (see Figure 19) and one for a bulky phosphite and iridium [53]. 

Scheme 5.21 Isomerization-hydroformylation of methyl oleate with different rhodium phosphite catalysts.

Scheme 6.122 Hydroformylation of paraformaldehyde with a rhodium-phosphite catalyst.

Hydroformylation of pure or technical grade methyl oleate was conducted by Monflier and colleagues [40] under the assistance of activated carbon (Nuchar WV-B mesoporous activated carbon with an average pore size of 3.1 nm) as mass transfer promotor (Scheme 7.9). Noteworthy, in comparison to the hydroformylation with a rhodium-phosphite catalyst in toluene [41], impurities of the technical grade feed did not significantly perturb the reaction. Under similar conditions, also other biomass-based substrates such as methyl hnoleate... 

High rhodium or phosphorus leaching with rhodium-phosphite catalysts at reaction temperatures of 80 °C may be attributed to the acid-catalyzed degradation of the organophosphorus ligand - which has a larger partition coefficient in the fluorous phase-by reaction with aldehydes to give polar phosphonates. (Scheme 7.10)... 

In a continuous flow hydroformyiation with a rhodium phosphite catalyst in an SCF-ionic liquid mixture, after two to three runs the activity and regioselectivity... 

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