Rhodium cationic chiral

In the first step the prochiral alkene entity coordinates to the cationic chiral rhodium centre with either one of the two enantiotopic faces (due to the asymmetry in the diphosphine ligand) which leads to the formation of two possible structures. Only one diastereoisomer of the intermediate alkene adduct is shown on Fig. 6.22 the second diastereoisomer can be easily imagined by taking the... 

Figure 6 A cationic chiral rhodium complex with NMe2 groups added to the BDPP ligand. The amine groups can be protonated to give a complex with a net charge of 5-I-. The protonated complex can be supported on the acid form of a cation-exchange resin...

The chiral bidentate amino-arsine 35 has been used to form chiral rhodium cationic species and the mixed arsine-phosphines Ph2As(CH2)2 or sPPhj have found extensive... 

Chauvin et al. reported the asymmetric hydrogenation of acetamidocinnamic acid to (S)-phenylalanine with a cationic chiral rhodium catalyst in [C4-mim][SbF6] ionic liquid, more recently the 2-arylacryhc acid has been produced with a reasonable 64% yield using a chiral ruthenium catalysts in [C4-mim][BF4] ionic hquids. Palladium catalysts immobilized in an ionic liquid-polymer gel membrane containing either [C2-mim][CF3S03] or [C2-mim][BF4] have also been reported as catalysts for heterogeneous hydrogenation reactions. 

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... 

Hayashi, T. Matsumoto, Y. Ito, Y. Asymmetric Hydroboration of Styrenes Catalyzed by Cationic Chiral Phosphine-Rhodium (I) Complexes. Tetrahedron Asymmetry 1991,2,601-612. 

Hayashi, T. Matsumoto, Y Ito, Y. 1991. Asymmetric hydroboration of styrenes catalyzed by cationic chiral phosphine-rhodium(I) complexes. Tetrahedron Asymm. 2 601-612. 

Cationic rhodium(I)/chiral biaryl bisphosphine complexes are suitable for the enantioselective [2-I-2-1-2] cycloaddition reactions between electron-rich alkynes and electron-deficient unsaturated compounds (alkynes, nitriles, and isocyanates). Alkynylcarbonyl compounds, alkynylphosphonates, and alkynylphosphine oxides are the best-suited electron-deficient unsaturated compounds for these catalysts. These complexes are also able to catalyze the highly enantioselective synthesis of axially chiral anilides and bezamides. 

Pamies O, Net G, Widhalm M et al (1999) Rhodium cationic complexes using macrocyclic diphosphines as chiral ligands application in asymmetric hydroformylation. J Organomet Chem 587 136-143... 

Based on these preliminary findings, related couplings to pyruvates and iminoacetates were explored as a means of accessing a-hydroxy acids and a-amino acids, respectively. It was found that hydrogenation of 1,3-enynes in the presence of pyruvates using chirally modified cationic rhodium catalysts delivers optically enriched a-hydroxy esters [102]. However, chemical yields were found to improve upon aging of the solvent 1,2-dichloroethane (DCE), which led to the hypothesis that adventitious HC1 may promote re-... 

Enantioselective variants of the rhodium-catalyzed reductive cydization reaction using both cationic and neutral complexes have been reported. When 5 mol % of [Rh(cod)2]2 SbF6 was reacted with 129a, MeEt2SiH, and chiral ligand 163 a 76% yield of 154a was achieved with 88% ee (Scheme 33) [97]. Other substrates gave 50-75% chemical yields and 77-89% ee [97,98]. 

Chiral thioureas have been synthesized and used as ligands for the asymmetric hydroformylation of styrene catalyzed by rhodium(I) complexes. The best results were obtained with /V-phenyl-TV -OS )-(l-phenylethyl)thiourea associated with a cationic rhodium(I) precursor, and asymmetric induction of 40% was then achieved.387,388 Chiral polyether-phosphite ligands derived from (5)-binaphthol were prepared and combined with [Rh(cod)2]BF4. These systems showed high activity, chemo- and regio-selectivity for the catalytic enantioselective hydroformylation of styrene in thermoregulated phase-transfer conditions. Ee values of up to 25% were obtained and recycling was possible without loss of enantioselectivity.389... 

An extensive array of chiral phosphine ligands has been tested for the asymmetric rhodium-catalyzed hydroboration of aryl-substituted alkenes. It is well known that cationic Rh complexes bearing chelating phosphine ligands (e.g., dppf) result in Markovnikoff addition of HBcat to vinylarenes to afford branched boryl compounds. These can then be oxidized through to the corresponding chiral alcohol (11) (Equation (5)) ... 

Supported cationic rhodium(I) phosphine complexes, chiral at a men-thyl moiety, effected hydrogenation of ketones, but the 2-butanol produced from methylethylketone was optically inactive (348). Polystyrene-or silica gel-supported DIOP systems, however, are particularly effective for production of optically active alcohols (up to 60% ee) via asymmetric hydrosilylation of ketones (10, 284, 296, 366, 368 see also Section III, A,4). 

A solitary report of enantioselective hydrosilylative cyclization appears in the literature.64 Here, a variety of 1,6-enyne substrates are cyclized in good yields and enantioselectivities, using chirally modified cationic rhodium... 

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