Rhodium complexes alumina

A complex naturally occurring amino acid 5-hydroxypiperazic acid (5HyPip) 100 was prepared by a multistep procedure that included Diels-Alder addition of 2,4-pentadienoic acid to phthalazinedione 83a as a first step (Scheme 24). Adduct 97 was esterified and oxidized with mercuric acetate to 98, which on hydrogenation over rhodium on alumina and subsequent hydrolysis provided a mixture of enantiomers from which the required enantiomer 99 was obtained by resolution with quinine. Its hydrazinolysis provided 100 [71JCS(C)514 77H119],... 

The electronic and IR spectra of [Rh(N02)6] are consistent with the expected RhNg chromo-phore, and while ligand field bands were not observed, CT absorbances occur at 317 and 275 nm. Arylazo oximes (N—N) form [Rh(N—N)j] complexes with Rh in which the arylazo oxime acts as a bidentate ligand (five-membered rings 57). Reaction of Rh(N03)3-3H20 with the appropriate arylazo oxime in ethanol at pH 4 (with CO," used to adjust pH) leads to a precipitate offac-and ier-[Rh(N—N),]. The geometric isomers can be separated on alumina, and H NMR showed that approximately equivalent amounts of the fac and mer isomers formed (for R = Me or Pr and Ar = Ph). This represents an unexpected (and unexplained) enhancement of the population of the fac isomer, as statistically, a fac/mer ratio of 1 /3 would be expected only the mer form was detected for [Co(N—N)3]. These rhodium complexes all display intense absorption bands near 480 and 320 nm, which are presumed to be intraligand bands. ... 

PAMAM itself was used as a multivalent macromolecular ligand, probably due to its multiple amino groups, in order to complex and immobilize metal ions, complexes, and nanoparticles with catalytic capabilities. Thus, Kawi and coworkers used PAMAM-on-silica and PAMAM-on-alumina templates to immobilize Rh(l) complexes as hydroformy-lation catalysts. Passivation of the silica OH sites outside the pores of SBA-15 silica resulted in a tighter binding of rhodium complexes inside the pores and led to a series of catalysts that displayed a positive dendritic effect up to the second PAMAM generation." Sreekumar and Krishnan used PAMAM on polystyrene to complex Mn(ll) precursors and catalyze the oxidation of secondary alcohols." " ... 

The most widely used method for adding the elements of hydrogen to carbon-carbon double bonds is catalytic hydrogenation. Except for very sterically hindered alkenes, this reaction usually proceeds rapidly and cleanly. The most common catalysts are various forms of transition metals, particularly platinum, palladium, rhodium, ruthenium, and nickel. Both the metals as finely dispersed solids or adsorbed on inert supports such as carbon or alumina (heterogeneous catalysts) and certain soluble complexes of these metals (homogeneous catalysts) exhibit catalytic activity. Depending upon conditions and catalyst, other functional groups are also subject to reduction under these conditions. 

Complex 7-AI2O3/PTA/ (/< ./< )-(Mc-DuPHOS)Rh(COD) 1 (1) was prepared and tested in the hydrogenation of the prochiral substrate methyl-2-acetamidoacrylate (MAA). After full conversion, the products were separated from the catalyst and analyzed for Rh and W content and product selectivity. The catalyst was re-used three times. Analytical results show no rhodium leaching is observed. Complex 1 maintains its activity and selectivity in each successive run. The first three runs show tungsten (W) leaching but after that no more W is detectable. The leached W comes from the excess of PTA on alumina. The selectivity of both tethered and non-tethered forms gave the product in 94% ee. 

The stmctural complexity and biological activity of the cyathane family of diterpenes has stimulated considerable interest from synthetic chemists, as reflected in the number and diversity of approaches reported thus far [42]. Our own strategy for cyathane synthesis is based on a rhodium-catalyzed [5+2] cycloaddition. The precursor for this reaction was fashioned ultimately from commercially available and inexpensive (S)-(-)-limonene. Treatment of the ketone 139 with 5 mol% [RhCl(CO)2]2 in 1,2-dichloro-ethane gave cycloadduct 140 (Scheme 13.14) in 90% yield and in analytically pure form after simple filtration through a plug of neutral alumina [43]. 

III,C, isomerization often accompanies hydroformylation. It has, however, been found that [(PhCN)2PdCl2] absorbed onto silica gel is 100 times more active for the isomerization of a-olefins, such as 1-heptene, than is the same complex alone (116). This implies some specific role for the silica gel. Attempts to use rhodium(III) chloride absorbed onto silica gel, alumina, activated charcoal, and diatomaceous earth as a-olefin isomerization catalysts showed that all these catalysts were unstable even at room temperature (100). 

An ab initio method has been employed to study the mechanism of the thermal isomerization of buta-1,2-diene to buta-1,3-diene. The results of the study have indicated619 that the transformation proceeds in a stepwise manner via a radical intermediate. Experimental free energies of activation for the bond shift in halocyclooctatetraenes have been reported and analyzed by using ab initio MO calculations.620 The isomerization of hexene using a dihydridorhodium complex in dimethyl sulfoxide has been reported,621 and it has been suggested622 that the Pd(II)-catalysed homogeneous isomerization of hexenes proceeds by way of zr-allylic intermediates. A study has been made623 of alkene isomerization catalysed by the rhodium /-phosphine-tin dichloride dimeric complex, and the double-bond isomerization of olefinic amines over potassium amide loaded on alumina has been described.624... 

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