Rhodium/BIPHEPHOS

Recently, we reported that the rhodium/BIPHEPHOS-catalyzed hydroformylation of trans-4-octene (Scheme 6) provides an interesting approach for the synthesis of n-nonanal [23]. In this context trans-4-octene can also be seen as a model substance for hydroformylation of internally unsaturated fatty acid esters. This could open up access to the use of renewable resources for the synthesis of valuable n-aldehydes. 

Behr, A., Obst, D., Schulte, C., and Schosser, T. (2003) Highly selective tandem isomerization-hydroformylation reaction of trans-4-octene to n-nonanal with rhodium-BIPHEPHOS catalysis. J, Mol, Catal, A-Chem, 206, 179-184. 

The hydroformylation step made use of a rhodium/ Biphephos catalyst and proceeded in a high chemoselectivity (96%) and regioselectivity (94% linear). The reaction required a low catalytic loading of 4000 1 (substrate/ catalyst) and mild conditions (80°C, 3 bar). The overall synthesis was much more efficient than the previously... 

Propylene carbonate is a good solvent of the rhodium precursor [Rh(acac) (00)2] and the phosphite ligand BIPHEPHOS and can thus be used as the catalyst phase in the investigation of the isomerizing hydroformylation of trans-4-octene to n-nonanal in a biphasic system [24]. As already mentioned, the reaction products can be extracted with the hydrocarbon dodecane. Instead of an additional extraction after the catalytic reaction, we carried out in-situ extraction experiments, where the products are separated from the catalytic propylene carbonate phase while the reaction is still in progress. Conversion of 96% and selectivity of 72% was achieved under comparably mild conditions (p(CO/H2) = 10 bar, T = 125 °C, 4 h, substrate/Rh = 200 1). 

The combination of rhodium dicarbonyl acetylacetonate complex (Rh(acac)(CO)2) and a diphosphite ligand, (2,2 -bis[(biphenyl-2,2 -dioxy)phosphinoxy]-3,3 -di-/i t/-butyl-5,5 -dimethoxy-l,T-biphenyl (BIPHEPHOS), is an excellent catalyst system for the linear-selective hydroformylation of a wide range of alkenes. This catalyst system has been successfully applied to the cyclohydrocarbonylation reactions of alkenamides and alkenylamines, which are employed as key steps for the syntheses of piperidine,indolizidine, and pyrrolizidine alkaloids. ... 

Stereoselectivity in hydroformylation reactions, as a result of the supporting ligand set (e.g. large bite angle diphosphines or chiral diphosphines) or by stereocontrol of the substrate has also been discussed by Breit. Rhodium complexes supported by large bite angle diphosphines such as bisbi, biphephos and xantphos, shown in Scheme 10, are now well-established... 

The first investigations concerning the hydroformylation of fatty compounds were accomplished by Ucciani and co-workers with cobalt catalysts such as cobalt bislaurate and dicobalt octacarbonyl [29]. Later, Frankel and co-workers found that the cobalt-catalyzed hydroformylation of methyl oleate also leads to the corresponding fatty alcohols [30]. In recent investigations on the hydroformylation of fatty compounds, the preferred catalyst is based on rhodium. For instance, the hydroformylation of methyl oleate catalyzed by [Rh(acac)(CO)2]/biphephos yields an isomeric mixture of formylstearic add methyl esters [31]. 

Highly regioselective hydroformylation of functionalized alkenes has been studied. The rhodium complex with BIPHEPHOS efficiently catalyzes the regioselective hydroformylation of a variety of functionalized terminal alkenes, giving the corresponding aldehydes (Scheme 2-3). ... 

A mixture of substrate 63 (40 mg 0.22 mmol), rhodium(lI) acetate dimer (1.0 mg, 2.2 mmol), and BIPHEPHOS (3.5 mg, 4.4 mmol) in deoxygenated benzene (5 mL) were placed in a autoclave that was then pressurized to 400 psi of CO/H2 gas (1 1 molar ratio). After heating at 100 °C for 72 h, the autoclave was allowed to cool to room temperature and the solvent was removed under reduced pressure. Purification of the cmde mixture on silica gel using ethyl acetate and light petroleum gave 64a and 64b. ... 

However, a zwitterionic rhodium complex Rh 7P(OPh)3 mainly provides the formyl diene 200, together with the nonconjugated unsaturated aldehyde 201 as by product. This phosphite provides similar yields to BIPHEPHOS, which, however, gives a more active catalyst. 

Sometimes, also polynuclear clusters such as Rh4(CO)j2 or Rh6(CO)26 were submitted to the formation of rhodium catalysts [18]. Metallic rhodium embedded in inorganic materials (carbon, AI2O3) was tested for mini-plant manufacturing. In this context, the frequently phosphorus ligands [PPhj, P(OPh)3] were added with the intention to detach rhodium from the heterogeneous layer (activated rhodium catalyst = ARC) [19, 20] More recently, ligand (Xantphos, PPhj, BIPHEPHOS)-modified or unmodified rhodium(O) nanoparticles were used as catalyst precursors for solventless hydroformylation [21]. It is assumed that under the reaction conditions these metal nanoparticles decompose and merge into soluble mononuclear Rh species, which in turn catalyze the hydroformylation. 

Isomeric pentenes, hexenes, and octenes have been used frequently in academic research to study the properties of new catalytic systems [38, 39]. Kragl and coworkers [40] have screened the hydroformylation of a series of terminal olefins (1-pentene until 1-dodecene) with a rhodium catalyst based on BIPHEPHOS and achieved excellent n-regioselectivities and TOFs (turnover frequencies) between 1895 and 8200 h (Scheme 4.7). 

In a subsequent study in the year 2015, the effect of different metals with BIPHEPHOS as a ligand on the same transformation was investigated [59]. Unexpectedly, under nonoptimized hydroformylation conditions, the relevant iridium catalyst exhibited only 5 times lower reactivity than the rhodium system. But the latter allowed slightly better control of the distribution of internal olefins. Ruthenium and palladium catalysts performed significantly worse. 

Some rhodium catalysts for hydroformylation of epoxides have been claimed by Union Carbide and Shell (Scheme 6.106) [17]. By the use of phosphites (e.g., Alkanox 240, BIPHEPHOS) or phosphine-modified rhodium catalysts, the selectivity was enhanced and the reaction temperature could be lowered. Noteworthy, occasionally a higher partial pressure of Hg in the syngas mixture with a total pressure of 90 bar was employed. 

We subjected this compound to rhodium catalyzed hydroformylation using the BIPHEPHOS ligand, which guarantees the predominant formation of the unbranched aldehyde. (28, 29) Hydroformylation, allylboration and the second hydroformylation proceeded cleanly to furnish the piperidinol derivative 57 in 73% yield. The latter compound was found to exist as a mixture of the lactoi and the aldehyde form. (25)... 

Another short synthesis of ( )-9a-ep(-quinolizidine 195C (rat-2318), by Mann and coworkers, is worth mentioning in view of its use of a Hnear hydroformylation of a homoallylamine (cyclohydrocarbonylation) to constmct the piperidine ring (Scheme 296). ° A three-component aza-Hosomi—Sakurai reaction between allyltrimethylsilane, butanal, and O-benzylurethane catalyzed by boron trifluoride was used to form the protected homoallylamine ( )-2319. The cyclohydrocarbonylation was then performed with a biphephos/rhodium(I) catalytic system in methanol, yielding the piperidine-containing hemiaminal 2320 in 84% yield. This... 

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