Rhodium complexes, as catalysts

An early attempt to hydroformylate butenediol using a cobalt carbonyl catalyst gave tetrahydro-2-furanmethanol (95), presumably by aHybc rearrangement to 3-butene-l,2-diol before hydroformylation. Later, hydroformylation of butenediol diacetate with a rhodium complex as catalyst gave the acetate of 3-formyl-3-buten-l-ol (96). Hydrogenation in such a system gave 2-methyl-1,4-butanediol (97). 

The use of a catalyst such as cadmium oxide increases the yield of dibasic acids to about 51% of theoretical. The composition of the mixed acids is about 75% C-11 and 25% C-12 dibasic acids (73). Reaction of undecylenic acid with carbon monoxide using a triphenylphosphine—rhodium complex as catalyst gives 11-formylundecanoic acid, which, upon reaction with oxygen in the presence of Co(II) salts, gives 1,12-dodecanedioic acid in 70% yield (74). 

There are currentiy no commercial producers of C-19 dicarboxyhc acids. During the 1970s BASF and Union Camp Corporation offered developmental products, but they were never commercialized (78). The Northern Regional Research Laboratory (NRRL) carried out extensive studies on preparing C-19 dicarboxyhc acids via hydroformylation using both cobalt catalyst and rhodium complexes as catalysts (78). In addition, the NRRL developed a simplified method to prepare 9-(10)-carboxystearic acid in high yields using a palladium catalyst (79). 

This type of hydrodehalogenation has been performed generally in the presence of organic or inorganic bases to neutralize the hydrogen halides formed. Among published results, the use of rhodium complexes as catalysts dominates, but palladium and ruthenium complexes have also been applied on a frequent basis. 

The rhodium-diphosphine catalysts are generally sensitive to oxygen, hence the reactions have to be carried out under strictly inert atmospheric conditions. A decrease in the yield or the enantiomeric excess can be due to a lack of sufficient precaution during the procedure or to the inactivation of the catalyst when exposed to oxygen. However, the reactions using rhodium complexes as catalysts give very good results which correlate well with the published material. 

We (79TH1 81GEP3117363 84USP4588815) and others (87MI1) have studied acetylacetonato and rj -cp-rhodium complexes as catalysts in the pyridine formation [Eq.(l)]. Resin-attached cp-rhodium complexes are also active in the cocyclization of alkynes and nitriles, and the activity is... 

Table 2.5 Asymmetric hydrogenation of indoles using (S,S)-(I ,I )-PhTRAP-rhodium complex as catalyst...

A review of asymmetric hydrogenation of ketones with rhodium complexes as catalysts has been presented.330 A review of the developments in the asymmetric hydrogenation of ketones with ruthenium complexes as homogenous catalysts of hydrogenation, with particular emphasis on the work of Halpern, has been presented.331... 

The directing group promoted C-H activation reaction is applicable to sp C-H bonds adjacent to the nitrogen in alkylamines, as shown in Scheme 5. Alkylation occurred when reaction of 25 with CO and ethylene was conducted in the presence of Ru3(CO)12 as catalyst [11], On the other hand, the use of a rhodium complex as catalyst resulted in C-H carbonylation [12],... 

The idea of applying water-soluble rhodium complexes as catalysts for the hydroformylation reaction [212, 213] was taken up and commercialized by Ruhrchemie AG for the hydroformylation of propene [269]. After only two years of development on the laboratory scale the first plant was erected in 1984, followed by rapid further increases in capacity to more than 600000 tons/year today [214]. An additional unit for the production of n-pentanal from n-butene has been brought onstream in 1995 [271, 294]. 

Bdnnemann and co-workers [22] and others [23] have tried acetylacetonato-and -Cp-rhodium as well as resin-attached / -Cp-rhodium complexes as catalysts in the pyridine synthesis [23]. However, rhodium catalysts are generally less effective than the analogous cobalt systems. 

We come now to photochemical redox processes. Reinvestigation of the photoreaction between cyclohexanone and triethylamine by Schuster and Insogna has removed the necessity to postulate an intermediate triplet excimer of the enone. Selective photoreduction of aldehydes in the presence of a ketone has been achieved using cyclo-octane as H-donor and a rhodium complex as catalyst (Sakura et al.). 

Asymmetric synthesis at a prochiral silicon center in catalytic asymmetric reactions has been effected in the hydrosiiyiation of ketones with dihydrosilanes using rhodium complexes as catalysts . ... 

Thermoregulated phase-transfer catalysis, however, could be successfully put into effect for the hydroformylation of higher olefins in aqueous/organic two-phase media [11], As shown in Table 2, various olefins have been converted to the corresponding aldehydes in the presence of nonionic phosphine-modified rhodium complexes as catalysts. An average turnover frequency (TOF) of 250 h-1 for 1-do-decene and 470 Ir1 for styrene have been achieved. Even the hydroformylation of oleyl alcohol, an extremely hydrophobic internal olefin, would give a yield of 72% aldehyde [19]. In comparison, no reaction occurred if Rh/TPPTS complex was used as the catalyst under the same conditions. 

The addition of an aldehyde group across an aUcene is a hydroacylation reaction. Whilst there is no hydrogen gas needed for these reactions, the process has some similarity to hydroformylation from a synthetic viewpoint, hence its mention in this chapter. In common with hydroformylations, catalytic asymmetric hydroacylations utilise enantiomerically pure rhodium complexes as catalysts. To date the catalytic asymmetric hydroacylation of alkenes has only been achieved in an intramolecular sense. 4-Substituted pentenal (2.213) and 3,4-disubstituted... 

In the presence of rhodium complexes as catalysts, the initial divinyltetramethylsiloxane, divinyldimethylsilane and divinyltetramethyldisilazane undergo condensation predominantly to dimeric and trimeric general products, ring closure of which then yields the respective cyclocarbosiloxane [32], cyclocarbosilane [21] and cyclocarbosilazane [21] with exocyclic methylenes (see Fig. 2 for the formulas). 

The dehydrogenation of alcohols is thermodynamically more favorable when the hydrogen released is consumed for olefin hydrogenation, as was observed for soluble rhodium complexes as catalysts [13,14]. 

Axially chiral biaryls are an important class of molecules for both biologically active compounds and chiral ligands (78-80). The most common approach to obtain biaryls is by aryl coupling followed by resolution of the racemic product to afford enantiopure biaryls. Even though enantioselective partial intramolecular cyclotrimerization of diyne with alkynes (81,82) or nitriles (83) were developed with various transitional metals, it was difficult to carry out complete intermolecular reaction. Using a cationic chiral rhodium complex as catalyst, a regioselective intermolecular cross-cyclotrimerization of alkynes 72 and 73 for... 

In connection with the catalytic hydrosilylation, asymmetric alcoholysis of dihydrosilanes in the presence of chiral rhodium complexes as catalysts deserves to be described. 

Hydrogenation with a chiral rhodium complex as catalyst affords stereoselective products as shown in eq. (18.33). When the racemate of the raw material is hydrogenated in 54% conversion, the R isomer, which is less reactive, is obtained in 84% purity, and when the racemate is hydrogenated in 70% conversion, pure R isomer is obtained. HCOOH/NEts is used as the hydrogen source. The reaction shown in eq. (18.33) is the reverse reaction of that shown in Scheme 18.2 which is the hydrogenation of carbon dioxide [67]. 

Benzoic acids are convenient entry points for this chemistry as they can be converted in a one-pot reaction into an O-methyl hydroxamates [81] This reaction has been developed using rhodium complexes as catalysts and O-methyl hydroxamates as the substrates along with an internal alkyne [81]... 

Pd(OAc)2 in AcOH at 120 C for 2 h] (62) were not suited for this preparation. However, the compound 131 was obtained in 74-85% yield when the reaction was carried out in die presence of sodium hydrogoi carlwnaie and chloranil as an oxidizing agent in an aprotic solvent, such as 1,2-dkhloroethane or 1,2,4-trichlorobenzene. Asymmetric reduction in the presence of a rhodium-complex as catalyst afforded the 4-bromotryptophan 133 (Scheme 51). 

Fiorini M, Giongo GM. Aminophosphine-rhodium complexes as catalysts in asymmetric hydrogenation. The dependence of the enantioselectivity on the structure of the chiral ligands. J. Mol. Catal. 1979 5(4) 303-310. 

Thus, the comprehensive investigations above demonstrate that a variety of multicyclic compounds with quaternary stereogenic centres can be obtained from this class of dien-ynes, depending on the length of the tethering chain as well as on the substituents of the unsaturated functions. The efficiency of cationic Tol-BEM-AP/Rhodium complexes as catalysts for many reactions of this class has been assessed. 

---