Rhodium complexes generated from

Virtually quantitative conversions were observed in the hydroformylation of 1-tetradecene with rhodium complexes generated from the lithium salt of tppms or the lithium (sodium) salts of 21 (Table 2 R=Ph n=3,4) and 22 (Table 2) in methanol as solvent.127,334 Catalyst recycling involved evaporation of methanol and addition of water to form a two phase system, separation of the aqueous phase, evaporation to dryness and addition of MeOH. 

A highly enantioselective 1,4-addition of aryltrialkoxysilanes ArSi(OR)3 to a,fi-unsaturated esters and amides RCH=COX (X = OR, NR R") was catalysed by a chiral rhodium complex generated from [(MeCN)2Rh(COD)]BF4 and (S)-BINAP in aqueous dioxane.243... 

Rhodium complexes generated from A-functionalized (S)-proline 3.60 [933, 934, 935] or from methyl 2-pyrrolidone-5-carboxylates 3.61 [936, 937, 938] catalyze the cyclopropanation of alkenes by diazoesters or -ketones. Diastereoisomeric mixtures of Z- and E-cydopropylesters or -ketones are usually formed, but only the Z-esters exhibit an interesting enantioselectivity. However, if intramolecular cyclopropanation of allyl diazoacetates is performed with ligand 3.61, a single isomer is formed with an excellent enantiomeric excess [936,937], The same catalyst also provides satisfactory results in the cyclopropanation of alkynes by menthyl diazoacetate [937, 939] or in the intramolecular insertion of diazoesters into C-H bonds [940]. 

Rhodium complexes generated from the polyethylene glycol)-functionalized phosphine 9 (n = 1, x = 0, R = Me, Bu), which should behave as a nonionic surfactant and be able to induce micelle formation, have been used as catalysts in the hydroformylation of 1-dodecene in an aqueous/organic two-phase system [31]. The conversion of 1-dodecene was 80% and the n/iso ratio 60 40, with no carryover of the rhodium catalyst into the organic phase. The Rh/9 (n = 1, x = 0, R = Me, Bu) catalyst remained active after one recycle step [31],... 

Rhodium complexes generated from the water-insoluble carboxylated surfactant phosphine 17 (n = 3, 5, 7, 9, 11) were used as catalysts in the micellar hydrogenation of a- and cyclic olefins, such as 1-octene, 1-dodecene, and cyclohexene, in the presence of conventional cationic or anionic tensides such as cetyltrimethylammo-nium bromide (CTAB) or SDS and co-solvents, e.g., dimethyl sulfoxide [15], After the reaction the catalyst was separated from the organic products by decantation and recycled without loss in activity. There is a critical relationship between the length of the hydrocarbon chain of the ligand 17 and the length and nature of the added conventional surfactant, for obtaining maximum reactivity. For example,... 

Specific examples of the hydroaminomethylations of olefins with secondary amines are shown in Equations 17.19-17.21. Cyclic and acyclic secondary amines occur in high yield with linear-to-branched ratios exceeding 50 to 1 in most cases when catalyzed by the rhodium complex generated from [Rh(COD)JBF and xantphos. The reaction of pen-tene with piperidine is shown in Equation 17.19. These reactions are also compatible with alcohol (Equation 17.20) and acetal functional groups (Equation 17.21). 

The success of the methodology was extended to other substrates such as a, 3-unsaturated esters and amides by the same group [65]. Enantioselective 1,4-addition of aryltrialkyloxysilanes to the described substrates (Scheme 5.21), catalyzed by a chir2il rhodium complex generated from [Rh(COD)(MeCN)2]2BF,i and (S)-BINAP, was described. Aryl groups can be introduced easily with high enantioselectively at the (3-position of a variety of esters and amides. The enantioselectivity and the chemical yield were affected by the bulkiness of the substituents at the olefin terminal and also by the ester or amide moiety. 

The control of the absolute stereochemistry of the newly generated stereogenic centre has been targeted at first by Wender who investigated the use of cationic rhodium complexes generated from [Rh(nbd)Cl]2, AgSbFg and (/ )-BINAP under... 

Rhodium catalysts have also been used with increasing frequency for the allylic etherification of aliphatic alcohols. The chiral 7r-allylrhodium complexes generated from asymmetric ring-opening (ARO) reactions have been shown to react with both aromatic and aliphatic alcohols (Equation (46)).185-188 Mechanistic studies have shown that the reaction proceeds by an oxidative addition of Rh(i) into the oxabicyclic alkene system with retention of configuration, as directed by coordination of the oxygen atom, and subsequent SN2 addition of the oxygen nucleophile. 

Electrophilic carbene complexes generated from diazoalkanes and rhodium or copper salts can undergo 0-H insertion reactions and S-alkylations. These highly electrophilic carbene complexes can, moreover, also undergo intramolecular rearrangements. These reactions are characteristic of acceptor-substituted carbene complexes and will be treated in Section 4.2. 

Metal-catalyzed [4 + 2 + 2] cyclotrimerizations of either heteroatom-containing enyne 62 with 1,3-butadiene (Eq. 17) [42] or heteroatom-containing dienyne 64 with an alkyne (Eq. 18) [43] are effected by cationic rhodium complexes generated in situ from a chlo-rorhodium complex modified with silver salts. These processes afford eight-membered ring products 63 and 65, respectively. In both processes, the nature and amount of the silver salt profoundly affect the outcomes. 

A coordinatively unsaturated rhodium(I) complex generated from 10 reacts with biphenylene to give C-H inserted complex 11 as the kinetic product. Complex 11 is then thermally converted to the C-C inserted complex 12 [27]. This re-... 

The addition of a diazocarbonyl compound to an alkene with metal catalysis is an effective method for the formation of cyclopropanes, as discussed above. However, direct addition to aldehydes, ketones or imines is normally poor. Epoxide or aziridine formation can be promoted by trapping the carbene with a sulfide to give an intermediate sulfur ylide, which then adds to the aldehyde or imine. For example, addition of tetrahydrothiophene to the rhodium carbenoid generated from phenyldiazomethane gave the ylide 131, which adds to benzaldehyde to give the trans epoxide 132 in high yield (4.104). On formation of the epoxide, the sulfide is released and hence the sulfide (and the rhodium complex) can be used in substoichiometric amounts. 

Figure 1 quite clearly demonstrates that the bimetallic complexes generated from the dicationic precursor 5r have considerably lower electron densities on the rhodium atoms, as indicated by the 100 cm higher vco stretching frequencies, relative to the electron-rich neutral bimetallic hydrido-carbonyl species formed from the reaction of 8r with H2/CO. 

Notably, an independently synthesized air-stable rhodium complex derived from preligand 24 was shown to be catalytically competent furthermore, spectroscopic data indicated the formahon of complex 28. Therefore, a mechanism was proposed that proceeded via an in situ generation of the corresponding phosphinite, with subsequent cyclometallation. 

In contrast, iridium complexes of phosphoramidite ligands catalyze the enantiose-lective formation of the branched allyUc substitution products with high enantiomeric excess. Takeuchi and Helmchen " - - - reported that iridium complexes, hke rhodium complexes, generate the chiral, branched product from reactions of mono-substituted aUylic acetates and carbonates with carbon and nitrogen nucleophiles (Equations 20.45-20.47). 

Besides rhodium catalysts, palladium complex also can catalyze the addition of aryltrialkoxysilanes to a,(3-unsaturated carbonyl compounds (ketones, aldehydes) and nitroalkenes (Scheme 60).146 The addition of equimolar amounts of SbCl3 and tetrabutylammonium fluoride (TBAF) was necessary for this reaction to proceed smoothly. The arylpalladium complex, generated by the transmetallation from a putative hypercoordinate silicon compound, was considered to be the catalytically active species. 

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