Hydroformylation 1,5-cyclooctadiene

Complexes of carbonic or carboxylic acid anions have been used as hydroformylation catalysts for various alkenes. The bicarbonate complex [Rh(H)2(02COH)(PPr 3)2] as catalyst enabled 1-hexene to be converted to aldehydes using paraformaldehyde as source of hydrogen and carbon monoxide in place of the more usual gas mixture.338 The acetate complex [Rh(OAc)CO(PPh3)2] (74) has been shown to effect the selective hydroformylation of cyclic dienes. The cyclohexadienes gave predominantly dialdehydes, whereas 1,3- and 1,5-cyclooctadiene gave the saturated monoaldehydes.339... 

Highly active unmodified rhodium catalysts for the hydroformylation of various olefins in SCCO2 are formed under mild conditions from [(cod)Rh(hfa-cac)] (8 cod = cis,cis-l,5-cyclooctadiene) and a number of other simple rhodium precursors [24]. Especially for internal olefins, the rate of hydroformylation is considerably higher than using the same catalysts in conventional liquid solvents under otherwise identical conditions. A detailed study of the hydroformylation of 1-octene (Scheme 6) using the online GC setup shown in Fig. 3 revealed a network of competing isomerization and hydroformylation when 8 was used without additional modifiers. As a result, the regioselectivity for the desired linear n-aldehyde varied considerably with conversion. At 60% conversion, the product aldehydes contained almost 80% of nonanal, whereas only 58 % linear aldehyde were present in the final product mixture. 

Reetz et al.59 have introduced polypropylenimine (PPI) dendrimers as the core for building phosphine-coated constructs that can complex with Rh(COD) BF4, where COD = 1,5-cyclooctadiene, to instill the desired catalytic character. Hydroformylation of 1-octene with these metallodendrimers was shown to have turnover numbers that were comparable to those of monomeric analogs. It was pointed out that these catalysts could be easily recovered by means of membrane separation technology.60 Gong et al. have used water-soluble, phosphonated dendritic... 

Rhodium catalysts, also important in asymmetric hydrogenation (see Section D.2.5.1.), usually show greater versatility and selectivity in asymmetric hydroformylation than cobalt catalysts. Various rhodium precursors are available, such as Rh203, Rh2(OAc)4, Rh2(C2H4)4Cl2, [Rh(nor-bornadiene)Cl]2 , [Rh(l,5-hexadiene)Cl]2118. [Rh(l,5-cyclooctadiene)Cl]238, [Rh4(CO)12]39, [Rh(CO)2Cl]2106, RhH(CO)(PPh3)33, Rh(allyl)3 139. and [Rh(nbd)2]BF467. 

There are only a few reports on the use of N-heterocyclic carbene complexes in biphasic hydroformylation (160). In one of the successful attempts, a rhodium(I)-NHC complex prepared from bromo( l,5-cyclooctadiene)[l-(2 -hydroxyethyl)-3-methylimidazoline-2-ylidene]rhodium(I) and an amphiphilic block copolymer was used for the hydroformylation of 1-octene in an aqueous-organic biphasic system at 100°C and 5 MPa of H2 CO = 1 1. The reaction rate was high (TOF up to 2360 h ) however, regioselectivity (n iso) was only around 60 40 (161). 

Recently, Breit and coworkers [37] showed an influence of activity and enantioselectivity on the metal catalyst precursor employed in the asymmetric hydroformylation of styrene. [Rh(NBD)2]BF4 (NBD = norbornadiene) or [Rh(OMe)(COD)]2 (COD= 1,5-cyclooctadiene) immediately developed high activity, whereas only with the latter the enantioselectivity could be kept constant. By the application of Rh(acac)(CO)2, a pre-formation time of several hours was... 

Kinetic investigations by Rosales et al. [8] on the hydroformylation of 1-hexene with a catalyst generated from Ir(acac)(COD) (acac = acetylacetonate, COD = 1,5-cyclooctadiene) and an excess of PPh3 indicated several similarities with the Rh-catalyzed reaction (CO/Hj = 1 1, 2.5 bar, 60 °C for Rh and 100 "C for Ir). With both metals, the transfer of the hydride to the olefin was found to be the ratedetermining step. Since under the chosen conditions no hydrogenation product was detected, it was assumed that the CO insertion in the metal-alkyl bond proceeded faster than the reductive ehmination ofthe corresponding alkane from the metal center. 

As illustrated by the example of dicyclopentadiene, non-conjugated double bonds can be hydroformylated like isolated olefins, but rapid conjugation prior to the hydroformylation may prevent the formation of the expected poly-aldehydes. In the hydroformylation of 1,5-cyclooctadiene with unmodified Co or Rh catalysts, the main product was formyl cyclooctane [88]. In contrast, cycloheptatriene was formylated twice. The amount of triformylcycloheptanes did not exceed 10%. 

Albers et al. [77] analyzed the pressure effect on the hydroformylation of 1- and 4-octene with [Rh(COD)(PPh3)2]BF,j (COD = 1,5-cyclooctadiene) at 70 °C (Table 5.2). As expected, with the terminal olefin as a substrate at low pressure, n- and iso-aldehyde 1 and 2 were formed in the ratio 1.6 1. Because of some isomerization, also the other branched aldehydes 3 and 4 were detected in decreasing amounts. Extremely high syngas pressure of 500 MPa completely suppressed double bond migration, and -nonanal and 2-methyl-octanal were formed in almost equal quantities. This result illustrates nicely the poor ability of the catalyst to discriminate between the 1- and 2-position of the terminal double bond. With 4-octene as a substrate, at low pressure, isomerization also played a significant role. The highest yield of 4-formyl-octane (4), which derives from the C-C bond formation in C4/C5 position of 4-octene, was observed at 500 MPa. Noteworthy, also aldehydes 2 and 3 were obtained. These products require the prior isomerization of 4-octene into the less thermodynamically stable olefins, which accounts for a kinetic control. This result is in contrast to the reaction with 1-octene under the same conditions. 

H2, and amines (piperidine, aniline, or NEtg). In the presence of an amine and syngas (CO/H2 = 1 2), the trigonal bipyramidal complex 3 was formed, irrespective of whether 1,5-cyclooctadiene (COD) complex 1 or dicarbonyl complex 2 was used as a precursor (Scheme 5.91). Complex 3 is a typical hydroformylation precatalyst with detailed description of composition and geometric structure in the literature [27]. The square-planar complex 2 - its structure could be proven by X-ray structural analysis - reacts with H2 to produce the corresponding dihydride 6. Upon oxidative addition of H2 and in the absence of CO, the binu-clear rhodium complex 5 is formed. Under CO, the latter is in equilibrium with the neutral complex 3. Chemical calculations provided evidence that an amine assists in the deprotonation of 6 to produce 3 via an outer-sphere mechanism. 

Hydroformylation of 2,6-dimethyl-l,5-cyclooctadiene in 300g scale under similar conditions gave rise to a mixture of unsaturated and saturated monoaldehydes as well as to the corresponding dialdehyde (Scheme 6.27) [104]. All three compounds, which have been separated by means of a spinning band column distillation, are characterized by different odors. It was suggested to employ them as scent boosters to force the aroma of citrus scents. 

Cyclooctadiene-1,5 is also partly isomerized during the reaction to cyclo6ctadiene-l,3 (VIII). Only the mono-aldehyde (VII) or monool (II) is obtained from (VIII), since conjugated dienes are hydrogenated rapidly to olefins (IX) in the hydroformylation reaction [10, 251]. (VIII) reacts practically quantitively through (IX) to (VII). 

The catalytic properties of l,2-bis(diphenylphosphino)-c/( i( -carborane(12)s (1) were first studied in 1985 by Hart and Owen [33] in the hydrogenation and hydroformylation of 1-hexene, 1,3- and 1,5-cyclooctadiene. The catalyst, [RhCKPPhjXl)], yielded between 70% and 100% at 110°C, under 6 MPa initial hydrogen pressure. Under milder conditions, (40°C, 0.1 MPa) no conversion was... 

When the reaction was promoted by the unmodified catalysts [(cod) Rh(hfacac)] (hfacac = hexafluoroacetylacetonate CF3COCHCOCF3, cod = cyclooctadiene), the superiority of SCCO2 in the hydroformylation rates was demonstrated very well. The modified catalytic systems formed with perfluoroalkyl-substituted triarylphos-phine and triaryl phosphite ligands exhibited higher regioselectivities in scCOj than in conventional solvents. The olefin isomerization is a typical side reaction for phosphite-modified systems in conventional solvents, while it is suppressed effectively in SCCO2. 

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