Rhodium derivatives stereochemistry

As indicated in the introduction, bis-l,3-diphenylphosphino-propane (dppp) and bis-l,2-diphenylphosphinoethane (dppe) were reacted with tris(triphenylphosphine)rhodium(II) carbonyl hydride in toluene-deuterobenzene solution to derive cis-chelate complex hydroformylation catalysts. These complexes were expectedly non-selective terminal hydroformylation catalysts for 1-butene hydroformylation (see Table I) because of their cis-stereochemistry. They were also somewhat less active due to their specific structural features. The structure of these complexes in solution was studied in detail by P-31 NMR spectroscopy. 

Asymmetric hydrogenation. Procbiral u,/ -unsaturated acids and their derivatives can be hydrogenated with high stereoselectivity by rhodium complexes with 1, such as (BPPM)Rh(COD)Cl and (BPPM)Rh(COD)+ClCV, in which COD = 1,5-eyclooctadiene. The stereoselectivity is dependent in part on the hydrogen pressure, ami the effect can be attenuated by addition of triethylamine, which also increases Ihc optical yield. The stereoselectivity is markedly controlled by the stereochemistry of the double bond.1... 

Chiral catalysts with structures related to rhodium(II) acetate should principally afford optically pure enantiomeric > -lactones from diazoacetates of type 21. As a matter of fact, Doyle et al. have obtained alkoxy-substituted y-lactones 22 in 85-90% ee (eq. (10)) upon using a Rh2X4-catalyst derived from chiral 2-pyrroli-dinones [18], Related results suggest that the catalyst has a rigid stereochemistry throughout the catalytic cycle [19], which conclusion had already been drawn for enantioselective cyclopropanation [20] (cf. Section 3.1.7). 

Bicyclo[6.1.0]nona-2,4,6-triene and the 9-methyl-substituted analog 35 were complexed with (trifluoroacetylacetonato)rhodium(I) [(tfacac)Rh(I)] and selectively hydrogenated to form bicyclo[6.1.0]nona-2,6-diene complexes 37, which upon decomplexation underwent Cope rearrangement to give bicyclo[5.2.0]nona-2,5-dienes 39. The parent compound 38 (R = H) and the u t/-9-methyl derivative rearranged above 0 °C, while the ij n-9-methyl- and the 9,9-dimethyl system 38 (R = Me) require 150°C for this transformation. The stereochemistry of these conversions was investigated with deuterium-labeled analogs. ... 

Finally, carbenoid species can be used as the carbon donor in aldehyde epoxidations. Thus, the rhodium carbenoid derived from the cyclic diazoamide 49 and rhodium(II) acetate reacts stereo selectively with aryl aldehydes to provide spiro-indolooxiranes 50 with Z-stereochemistry. The reaction is believed to proceed via the formation of a carbonyl ylide 51, which undergoes stereospecific thermal conrotatory electrocyclization to form the observed epoxide <04SL639>. 

While copper and iron Lewis acids are the most prominent late transition metal Diels-Alder catalysts, there are reports on the use of other chiral complexes derived from ruthenium [97,98],rhodium [99],andzinc [100] in enantioselective cycloaddition reactions, with variable levels of success. As a comparison study, the reactions of a zinc(II)-bis(oxazoline) catalyst 41 and zinc(II)-pyridylbis(ox-azoline) catalyst 42 were evaluated side-by-side with their copper(II) counterparts (Scheme 34) [101]. The study concluded that zinc(II) Lewis acids catalyzed a few cycloadditions selectively, but, in contrast to the [Cu(f-Bubox)](SbFg)2 complex 31b (Sect. 3.2.1), enantioselectivity was not maintained over a range of temperatures or substitution patterns on the dienophile. An X-ray crystal structure of [Zn(Ph-box)] (01)2 revealed a tetrahedral metal center the absolute stereochemistry of the adduct was consistent with the reaction from that geometry and opposite that obtained with Cu(II) complex 31. 

In this Section, we confine our attention to the complexes where the non-equivalence of the phosphorus atoms derives from the stereochemistry of the complex, rather than from the groups attached to phosphorus within the ligand. The results for some chloro-complexes are given in Table III. The meridianal form of the rhodium(III) complexes has the structure (12), which is of the same symmetry as the... 

To avoid the formation of alkylated products, the reaction was repeated with iV-acylated pyrroles, such that the pyrrole ring would be less electron-rich and less prone to rearomatize. Rhodium(II) acetate catalyzed decomposition of the vinyldiazomethane 4 in the presence of A-carbomethoxy pyrrole results in the formation of the [3+4] annulation product (entry 1, Table 12), and this reaction is applicable to a range of vinylcarbenoid derivatives. The tropanes are formed as the endo isomers, which is the expected stereochemistry for the tandem cyclopropanation/Cope rearrangement sequence. 

Prochiral olefins such as the (Z)-a-acetamidocinnamic acid derivatives, MAC and EAC, bind to the rhodium-DIPAMP catalyst to form the diastereomeric olefin complexes A and A shown in Scheme 15.18. Oxidative addition of dihydrogen to each of the diastereom-ers forms diastereomeric hydride complexes B and B, each of which imdergoes migratory insertion to form alkyl hydride complexes C and C. These complexes then undergo reductive elimination to form the amino acid ester products. The stereochemistry of the organic products can be predicted for the two parallel paths, assuming that the addition of occms to the face of the olefin coordinated to Rh. The N-acetyl-(R)-phenylalanine ester would be produced from the olefin adduct A and the (S)-product from A. ... 

Oxidative addition of alkyl halides to vinylrhodium(i) complexes gives isolable alkylvinylrhodium(m) species (75). Heating the latter gives a tri-substituted olefin whose stereochemistry can be controlled by judicious choice of conditions. Derivation of (76) by addition of rhodium hydride to the acetylene results in an overall conversion of an acetylene into a tri-substituted olefin (Scheme 2). ... 

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