Rhodium amine complexes, hydroformylation with

Under mild conditions, hydroformylation of olefins with rhodium carbonyl complexes selectively produces aldehydes. A one-step synthesis of oxo alcohols is possible using monomeric or polymeric amines, such as dimethylbenzylamine or anion exchange resin analog to hydrogenate the aldehyde. The rate of aldehyde hydrogenation passes through a maximum as amine basicity and concentration increase. IR data of the reaction reveal that anionic rhodium carbonyl clusters, normally absent, are formed on addition of amine. Aldehyde hydrogenation is attributed to enhanced hydridic character of a Rh-H intermediate via amine coordination to rhodium. 

Tables Hydroformylation of 1-octene with rhodium and plat-inum-tm complexes supported by amine, arsine and phosphine ligands ...

The atropisomeric dinaphthophosphepins ( )-(35) (R = Me, Ph) can be prepared from 2,2 -dimethyl-l,r-dinaphthyl by lithiation and addition of the respective dichlorophosphine <94TA5ll, 94JOC6363>. The resolutions of ( )-(35) (R = Me, Ph) were accomplished by the method of metal complexation with use of an optically active ortho-metallated palladium(II)-amine complex. The absolute configuration of (S)-(—)-(35) (R = Ph) was determined from the x-ray crystal structure of (36). The optically active phosphepin in conjunction with rhodium(I) is an effective auxiliary for the asymmetric hydroformylation of styrene. 

Karakhanov and coworkers [41] incorporated hydroformylation with methyl-formate in a hydroaminomethylation tandem reaction by using a dual metal catalyst consisting of homogeneous Ru and Rh complexes (Scheme 3.19). In contrast to rhodium, the ruthenium catalyst was used in excess. The transformation is exemplified in the scheme with 1-pentene as substrate. Also, other terminal and internal olefins could be converted with dimethylamine into the corresponding amines. High temperatures enhanced the formation of the desired amines and lowered the degree of olefin hydrogenation. The reaction proceeded also well. 

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. 

A water-soluble hydroformylation catalyst was developed by Xi and co-workers [65]. Third generation PAMAM dendritic ligands, with hydrophilic amine or sulfonic acid end groups, were phosphonated and the rhodium complexes thus formed were found to catalyse efficiently the hydroformylation of 1-octene and styrene, under very mild conditions. Water-soluble dendritic cobalt phthalocyanines that exhibited catalytic activities and oxidised thiols in the presence of oxygen, have been synthesised by Kimura and co-workers [66]. The catalytic activity of the phthalocyanines was influenced by a egation of the catalytic sites that results fi om strong intermolecular cohesive forces. It was proposed that steric isolation, enforced by the addition of a bulky dendritic coaf around the active phthalocyanine unit, could improve the catalytic activity. Acid terminated polyamide dendrimers were coupled to a phthalocyanine core to produce the desired water-soluble cobalt phthalocyanines, which were tested subsequently for catalytic activity and stability. The results obtained showed that the aggregation of phthalocyanines was reduced the catalytic activity was improved and the stability of the catalyst was improved by addition of the dendritic substituents. 

Bidentate ligands were used by Alper and coworkers. The bis(diphenylphospino-methyl)amine ligands were prepared on primary amine-terminated PAMAM dendrons on silica as well as polyamido dendrons on polystyrene via the double Mannich-like reaction with formaldehyde and diphenylphosphine (Scheme 15.36a). " Subsequently, Alper and coworkers subjected the dendronized ligand-decorated supports to complexation with rhodium and palladium precursors in order to prepare active catalysts for a number of important chemical transformations (Scheme 15.36b). Initially, the dendronized rhodium catalysts were tested in the hydroformylation reaction and carbonylative ring expansion of... 

Hydroaminomethylation is a simple, efficient and atom-economic method to synthesize various amines. This one-pot reaction consists of three consecutive steps in the first step a hydroformylation of an olefin is performed followed by the reaction of the resulting aldehyde with a primary or secondary amine to give the corresponding enamine or imine. Lastly, this intermediate is hydrogenated to the desired secondary or tertiary amine (Fig. 11) [33-39]. In most cases rhodium salts or complexes are used as the homogeneous catalyst in the hydroaminomethylation. 

The approach to polyketide synthesis described in Scheme 5.2 requires the relatively nontrivial synthesis of acid-sensitive enol acetals 1. An alternative can be envisioned wherein hemiacetals derived from homoallylic alcohols and aldehydes undergo dia-stereoselective oxymercuration. Transmetallation to rhodium could then intercept the hydroformylation pathway and lead to formylation to produce aldehydes 2. This proposal has been reduced to practice as shown in Scheme 5.6. For example, Yb(OTf)3-cata-lyzed oxymercuration of the illustrated homoallyhc alcohol provided organomercurial 14 [6]. Rhodium(l)-catalyzed hydroformylation of 14 proved successful, giving aldehyde 15, but was highly dependent on the use of exactly 0.5 equiv of DABCO as an additive [7]. Several other amines and diamines were examined with variation of the stoichiometry and none proved nearly as effective in promoting the reaction. This remarkable effect has been ascribed to the facilitation of transmetallation by formation of a 2 1 R-HgCl DABCO complex and the unique properties of DABCO when both amines are complexed/protonated. 

Both the rhodium and the cobalt complexes catalyze olefin isomerization as well as olefin hydroformylation. In the case of the rhodium(I) catalysts, the amount of isomerization decreases as the ligands are altered in the order CO > NR3 > S > PR3. When homogeneous and supported amine-rhodium complexes were compared, it was found that they both gave similar amounts of isomerization, whereas with the tertiary phosphine complexes the supported catalysts gave rather less olefin isomerization than their homogeneous counterparts (44, 45). 

The group of Van Leeuwen has reported the synthesis of a series of functionalized diphenylphosphines using carbosilane dendrimers as supports. These were applied as ligands for palladium-catalyzed allylic substitution and amination, as well as for rhodium-catalyzed hydroformylation reactions [20,21,44,45]. Carbosilane dendrimers containing two and three carbon atoms between the silicon branching points were used as models in order to investigate the effect of compactness and flexibility of the dendritic ligands on the catalytic performance of their metal complexes. Peripherally phosphine-functionalized carbosilane dendrimers (with both monodentate... 

If higher concentrations of aqueous sodium hydroxide (15%) are used, all of the re-immobilized ligands and the rhodium complex can be extracted into the aqueous phase. This can thus be submitted to the oxidative treatment for Rh recovery according to [34-36]. In this way, 92-95% of the Rh content may be recovered. The amine content of the organic phase was used again by treatment with fresh sulfonated phosphine and sulfuric acid. In the subsequent hydroformylation the same results were actually observed. 

It is also worth mentioning that the multiphase approach has been used as a strategy to avoid undesired consecutive reactions [lla-c] or even to segregate two different and incompatible catalysts in one-pot or in tandem syntheses. In a typical example, Chaudhari et al. described the combination of a hydroformylation step -catalyzed by phosphine-modified rhodium complexes - with the Mannich reaction of the 0x0 aldehydes formed, catalyzed by tertiary amines. Thus the manufacture of methacrolein according to Figure 7 proceeds best in two different phases the organic phase for hydroformylation and the aqueous phase in which the Mannich reaction is achieved (Figure 8) [lid]. 

It seemed interesting to trap the iminium ion intermediate by performing an intramolecular aSH, so we plarmed a CHC/aSH/hydroformylation domino reaction (Scheme 10). This reaction involves an allylsilane present on the amine moiety which, in an acidic medium, reacts with an acyliminium ion derived from the CHC to form a vinyl group. The resulting vinyl double bond must be hydroformylated regioselectively by the rhodium complex present in the reaction medium to lead to a functionalized polycyclic structure. 

In contrast to other areas of hydroformylation chemistry, in dendrimer-based hydroformylation phosphorus ligands play a role not only as ligating groups for rhodium but also as scaffolds with amine- or amino alcohol functionahty [120]. Moreover, nanoparticles, colloids, or mesoporous silica have been used to stabilize unmodified [121] or phosphine (e.g., PPhj, diphenylphosphinophenylsulfonate)-modified rhodium complexes [122]. 

Along with the increasing success of the hydroformylation reaction in industry, the focus of research in HAM shifted to the use of homogeneous cobalt and rhodium complexes. A particularly important contribution came from the Hungarian group of Marko and Bakos [19], who showed that these typical hydroformylation catalysts are also active in the reductive amination of aldehydes. 

Later, Eilbracht et al. developed a related enantioselective domino hydroformylation-aldol reaction catalysed by a rhodium complex in combination with a chiral amine derived from L-proline. In this process, the reaction of acetone with vinylbenzene afforded the corresponding chiral p-hydrojgr ketone in 69% yield, a moderate diastereoselectivity of 74% de, and a high enantioselectivity of 93% ee, as shown in Scheme 7.50. ... 

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