Hydroformylation with rhodium

Table 8.5. Hydroformylation with rhodium phosphite and phosphine catalysts...

Hydroformylation with Rhodium Catalysts at High Pressure, cis-Butene. The 150-ml autoclave was charged with 0.231 gram of HRh(CO)-(P< 3)3 and 0.504 gram of ( — )-DIOP, evacuated and cooled. 10 grams of cw-butene in 70 ml of mesitylene were introduced by suction. The gas mixture was then admitted to 84 atm (room temperature). The autoclave was heated for 22 hrs at 95°C. The aldehyde was separated from the reaction solution by rectification 4.5 grams of ( + )(S)-2-methylbutanal, [ ]D25 + 2.85° (neat) were obtained. The purity, checked by GLC (20% PPG on Chromosorb G, 2 m X 1/8 inch, 90°C), was higher than 99%. 

The majority of studies of asymmetric hydroformylation with rhodium and platinum complexes have made use of DIOP (49) as a ligand. With either the complex [RhCl(CO)(DIOP)] or [RhCl(C2H4)2]2 plus DIOP, styrene was hydroformylated to 2-phenylpropanal with optical yields of only 16%.366 When a-monodeuterostyrene was used as substrate, with DIOP and complex (34) as catalyst, essentially the same optical yield was obtained.367 The same catalyst with non-deuterated styrene under different conditions gave an optical yield of 25%.368... 

The above results were reviewed in 1974 (5). Since then the main advances in the field have been the achievement of asymmetric hydro-carbalkoxylation (see Scheme I, X = -OR) using palladium catalysts in the presence of (-)DIOP (6), the use of other diphosphines as asymmetric ligands in hydroformylation by rhodium (7), and the achievement of the platinum-catalyzed asymmetric hydroformylation (8, 9). Further work in the field of asymmetric hydroformylation with rhodium catalysts has been directed mainly towards improving optical yields using different asymmetric ligands (10), while only very few efforts were devoted to asymmetric hydroformylation catalyzed by cobalt or other metals (11, 12) and it will be discussed in a modified form in this chapter. 

The best optical yields obtained in the hydroformylation are comparable with the highest yield obtained in hydroalkoxycarbonylation using Pd catalysts. In Table 15 the results obtained in hydroformylation with rhodium or platinum catalysts are compared with those obtained in hydroalkoxycarbonylation using identical substrates and identical optically active ligand 9). 

The catalytic cycle and the catalytic intermediates for the rhodium-plus-phosphine-based process are shown in Fig. 5.1. It is important to note that hydroformylation with rhodium can also be effected in the absence of phosphine. In such a situation CO acts as the main ligand (i.e., in Fig. 5.1, L = CO). The mechanistic implications of this is discussed later (Section 5.2.4). 

Yildiz-Unveren, H.H. and Schomacker, R. (2005) Hydroformylation with rhodium phosphine-modified catalyst in a microemulsion comparison of organic and aqueous systems for styrene, cyclohexene and l,4-diacetoxy-2-butene. Catal. Lett., 102, 83. 

A novel chiral ligand type for asymmetric hydroformylation with rhodium and platinum complexes11 125,1 54,156 is the hydroxyproline derived (2S,4>S)-l-(/err-butoxycarbonyl)-4-(diphenylphosphino)-2-[(diphenylphosphino)methyl]pyrrolidine [(-)-BPPM]2-6. As with other diphosphane systems, modifications of BPPM by exchange of either one or both of the different diphenylphosphane groups with dibenzophosphole (DBP) units [BPPM-2DBP, BPPM-4DBP and BPPM-(DBP)2] have been studied158. 

Amino acid derived chiral aminophosphane phosphinites (AMPP) such as Ephos, Proliphos, Glyphos and others1 " 128,195 constitute another new type of chiral phosphane ligand used in asymmetric hydroformylation with rhodium complexes 127,128 and platinum salts113. 

Asymmetric Hydroformylation with Rhodium-Phosphite Catalysts... 

The mechanisms of hydroformylation with rhodium and cobalt catalysts have been studied in detail and are very similar. We have already learnt that for cobalt the active catalyst precursor is [HCo(CO)4] in the case of the modified rhodium catalyst it is the complex [HRh(CO)(PPh3)3]. 

The 6 4 mixture of endo- and exo-bicycloheptenealdehyde [263], obtained from the Diels-Alder reaction [262] of acrolein with cyclopenta-diene, was hydroformylated with rhodium catalyst [254]. 

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