Dirhodium complexes

Asymmetric hydrogenation of ketopantolactone (19) in the presence of chiral dirhodium complexes gave (R)-pantolactone (9) in high yield and excellent selectivity (36) (Table 2). 

On the other hand, Doyle et al. have developed methyl 2-oxoimidazolidine-4(carboxylate ligands, containing 2-phenylcyclopropane attached at the 1-iV-acyl site, such as the (4(5),2 (7 ),3 (7 )-HMCPIM) ligand. The resulting dirhodium complex led, for the cyclopropanation of styrene with EDA, to the corresponding cyclopropane with 68% ee and 59% yield, but with almost... 

Formation of the adduct with dirhodium complex [6] has significantly changed the chemical shift of the compounds in which proton transfer occurred, for example, for the adduct of iV-(5-nitrosalicylidene)-2-ami nobutane, the chemical shift was —198.2, which was shielded by of 110 ppm in comparison to that in the starting Schiff base.12 The large signal shift was due to the shift of the proton transfer equilibrium towards NH tautomer. For the adduct of N-(salicylidene)-2-aminobutane, existing in the OH-form, the 15N chemical shift has changed from —87.5 to — 84.6 ppm. 

The position of the proton transfer equilibrium for the Schiff bases being derivatives of rac-2-aminobutane [24] or rac-a-methylbenzylamine [25] and their adducts with dirhodium complex has been estimated in CDCI3 solution on the basis of measurements of deuterium isotope effects on 15N chemical shift.12 It was shown that adduct formation significantly influenced the position of the equilibrium which was manifested by AN(D) values. 

The results of unsymmetrical 7r-acid bidentate ligands, e.g., (81), have in the hydroformylation of ra-octenes was described. The preparation of seven such ligands was described. Thus, [Rh-(acac)(cod)]-catalyzed hydroformylation of ra-octene in the presence of a phosphinite ligand gave 94% ra-nonanal.295 A new upper-rim phosphacalix[4]arene 5,17-bis(diphenylphosphinomethyl)-25,26,27,28-tetrapropoxycalix[4]arene has been prepared. It reacted with [(cod)RhCl]2 to give a dirhodium complex that is an active catalyst for the hydroformylation of 1-octene and styrene.296 Rhodium complexes of [l-propyl-3-methylimidazolium+]2 [PhP(C6H4SO%)2] dissolved in the... 

Perez-Pietro et al. have introduced the dirhodium complex (105) with a unique o/7/io-metalated arylphosphine ligand. The complex is an efficient catalyst for the cyclization of alkenyl diazo ketones (Scheme 7S).288 289... 

Activation of a C-H bond requires a metallocarbenoid of suitable reactivity and electrophilicity.105-115 Most of the early literature on metal-catalyzed carbenoid reactions used copper complexes as the catalysts.46,116 Several chiral complexes with Ce-symmetric ligands have been explored for selective C-H insertion in the last decade.117-127 However, only a few isolated cases have been reported of impressive asymmetric induction in copper-catalyzed C-H insertion reactions.118,124 The scope of carbenoid-induced C-H insertion expanded greatly with the introduction of dirhodium complexes as catalysts. Building on initial findings from achiral catalysts, four types of chiral rhodium(n) complexes have been developed for enantioselective catalysis in C-H activation reactions. They are rhodium(n) carboxylates, rhodium(n) carboxamidates, rhodium(n) phosphates, and < // < -metallated arylphosphine rhodium(n) complexes. 

A mechanism similar to that shown in Scheme 16.2 has also been proposed to rationalize the arene hydrogenation activity of the triply-bridged dirhodium complex L2HRh(/7-H3)RhL2 (L=P(OiPr)3) [14]. 

Reaction of the heterocubane cluster 14 (R = Ph) with (Cp Rhl2)2, a reagent that functions both as a Lewis acid (the metal center) and a Lewis base (the iodide ligands), generates the dirhodium complex 18. Complex 14 also adds to l,l-bis(diphenylphosphinoferrocene) to form the cyclic species 19.8... 

Fig. 20. Schematic drawing of dirhodium complexes of terphenylcarboxylate ligands.95...

The reorientation takes place during the oxidation of the dirhodium complex [(triphos)Rh( -Cl)(/ -f/2,7/2-C2H2)(triphos)]Cl, the molecular structure of which is illustrated in Figure 22a, to the derivative [(triphos)Rh( -Cl)2( - /1, /1-C2H2)Rh(triphos)]2+ (the crystal structure of such dication could not be obtained, but that of the related species [(triphos)Rh(iu-Cl)(/i-OH)(/i- /1, 1-C2H2)Rh(triphos)]2+ is shown in Figure 22b).19... 

A spectroscopic study of Claus blue, with comparisons to the much better characterized (180) ion [Rh2(0H)2(H20)n(/u,-02)]3+, was thus undertaken (181). By the use of UV-vis, ESR, and IR/Raman spectroscopies, as well as magnetic susceptibility measurements and voltamme-tric studies, it was determined that Claus blue solutions actually contain superoxo-dirhodium complexes, and not RhO2- ions. The su-peroxo bridge does not, however, derive from dioxygen, but from oxidation of coordinated hydroxide. Finally, Claus blue solutions were demonstrated to be good starting materials for the preparation of superoxo-dirhodium carboxylate complexes, which could be isolated and characterized. 

Analogous ligand exchange reaction of cis- and Pww-Feist s esters with the dirhodium complex [/i-ClRh(ethylene)2]2 in pentane gave the corresponding Feist s esters rf-complexes [/(-ClRhL, (L = cF, tF) (equation 310). Further reaction of the latter complex [p-ClRhL2]2 (L = tF) with cyclopentadienylthallium (CpTl) in CH2C12 afforded the monorhodium complex CpRh(tF)2, and reaction with a mixture of both CpTl and dirhodium... 

In contrast, addition of HBF4-OEt2 to the dirhodium complex (33) affords the //-i/, i -vinyl complex (47), probably via initial attack on the Rh-Rh bond (61) ... 

Optically active sulfonimidamides react with benzylic and allylic methylene groups to give the formal product of nitrene CH insertion.75 The reaction is catalysed by dirhodium complexes and delivers rather mixed results, both de and yield being (g) substrate dependent. The authors finish the transformation by removing the sulfonim-idamide by reduction to leave a benzylic or allylic amine. 

In preparation of di-p-methylenebis(methyl-pentamethylcyclopentadienyl)dirhodium complexes by aerobic oxidation of a solution of the halocomplex and methyllithium or trimethylaluminium in ether—benzene, the reaction mixture occasionally ignited and burned violently. Full precautions and a working scale below 1 mmol are recommended. 

Hydrometallation, enynes, 10, 331 Hydroperoxides, via zinc reagents, 9, 105 Hydrophobic amino acids, via zinc compounds, 9, 97 Hydroselenido ligands, in dirhodium complexes, 7, 147 Hydrosilanes... 

When mixed with equimolar amounts of the dirhodium complex 22, the enantiomers of mesoionic 1,2,3,4-oxatriazoles 19-21 can be differentiated by proton NMR <2003MRC315>. The negatively charged exocyclic nitrogen atom provides the binding site to the rhodium complex <2003MRC921>. 

Chiral dirhodium complex 87 (see Section 7.04.2.4) catalyzes the diastereo- and enantioselective insertion of phenyldiazoacetate 251 into 1,2,3,6-tetrahydropyridine 252 to give predominantly the erythro 6-substituted-l,2,3,6-tetrahydropyridine 253 with high enantiomeric selectivity. The threo-isomex 254 is a minor product and was formed with much lower selectivity (Equation 24) <1999JA6509, 2001TL3149>. 

In contrast, doubly silylene-bridged dirhodium complexes reversibly catch two molecules of H2 at room temperature to form the complexes with two jU-T/2-HSiR2 ligands [Eq. (27)).42... 

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