Rhodium 5 3 + , deuteration

Reduction of the A" -double bond with the rhodium complex is a very slow reaction, but it has been accomplished in 17)S-hydroxyandrost-4-en-3-one (140)d The product, 4a, 5a-d2-androstan-17j3-ol-3-one (141), is a further example of the preferential a-side deuteration in homogeneous solution as contrasted with the )S-face attack with heterogeneous catalysts. [For a more convenient preparation of compound (141) see section V-C.]... 

SO the Sgl mechanism and not the usual arenium ion mechanism is operating. Aromatic rings can also be deuterated by treatment with D2O and a rhodium(III) chloride or platinum catalyst or with CeDs and an alkylaluminum dichloride catalyst," though rearrangements may take place during the latter procedure. Tritium ( H, abbreviated T) can be introduced by treatment with T2O and an alkylaluminum dichloride catalyst. " Tritiation at specific sites (e.g., >90% para in... 

Prior literature indicated that olefins substituted with chiral sulfoxides could indeed be reduced by hydride or hydrogen with modest stereoselectivity, as summarized in Scheme 5.10. Ogura et al. reported that borane reduction of the unsaturated sulfoxide 42 gave product 43 in 87 13 diastereomer ratio and D20 quench of the borane reduction mixture gave the product 43 deuterated at the a-position to the sulfoxide, consistent with the hydroboration mechanism [10a]. In another paper, Price et al. reported diastereoselective hydrogenation of gem-disubstituted olefin rac-44 to 45 with excellent diastereoselectivity using a rhodium catalyst [10b],... 

The coordination of the alkyne to the rhodium catalyst allows the carborhodation of the triple bond to afford the vinylrhodium intermediate 47 (Scheme 14). The rearrangement of this organometallic compound into the 2-(alkenyl)phenylrhodium intermediate 48 is evidenced by one deuterium incorporation resulting from the deuter-iolysis of the Rh-C bond. The addition of the phenylrhodium intermediate 45 must occur before its hydrolysis with water. The 2-(alkenyl)phenylrhodium intermediate 45, generated by the phenylrhodation of an alkyne followed by... 

Analysis of the reaction KIE using monodeuterated sulfamate 106 reinforces the proposed rhodium-nitrene model (Eq. 9). The ratio of H/D products 107/108 is a direct measure of the KIE and has been found to equal 1.5 0.2 by integration of the C NMR spectrum. An equivalent value is obtained for nitrene C-H insertion upon photolysis of a carbamoyl azide, and is taken as evidence for a nonlinear transition state. As noted previously, Muller s use of NsN=lPh with partially deuterated adamantane gives... 

The rhodium-hydride vibration disappears upon deuteration of the complex as the rhodium-deuteride vibration appears in the fingerprint region. The large frequency shift of the highest energy absorption is indicative of a trans-CO geometry [40]. In solution IR, the rhodium hydride vibration and the lowest energy CO vibration overlap, which results in only two absorptions. 

The reversibility of the hydride migration in unmodified rhodium catalysts has been studied intensively by Lazzaroni et al. [56]. Reversible hydride migration will result in aldehydes containing deuterium at the a-carbon, whereas irreversible hydride migration will result in exclusive deuteration of the aldehyde and P-carbon. Mutual reversible alkene coordination and hydride migration ivill result in the formation of deuterated alkenes. Reversible formation of the branched rhodium alkyl will place deuterium at Cl and reversible formation of the linear alkyl complex will provide deuterium at C2 (Scheme 6.4). 

Lazzaroni showed that the reversibility of the hydride migration to coordinated vinyl ethers is highly dependent on the temperature for the unmodified rhodium catalyst (Scheme 6.4, L = CO) [56a]. Both the branched and linear rhodium alkyl intermediates showed considerable P-hydride elimination at 100 °C, as indicated by significant amounts of both alkenes deuterated at Cl or Cl (Figure 6.17). Deuter-... 

Palladium and rhodium form C2D6 as the major initial product with steadily decreasing amounts of the less deuterated species. The values of M for these metals are 4.8 and 5.0, respectively. 

The majority of studies of asymmetric hydroformylation with rhodium and platinum complexes have made use of DIOP (49) as a ligand. With either the complex [RhCl(CO)(DIOP)] or [RhCl(C2H4)2]2 plus DIOP, styrene was hydroformylated to 2-phenylpropanal with optical yields of only 16%.366 When a-monodeuterostyrene was used as substrate, with DIOP and complex (34) as catalyst, essentially the same optical yield was obtained.367 The same catalyst with non-deuterated styrene under different conditions gave an optical yield of 25%.368... 

Tanaka has recently reviewed the hydrogenation of ketones with an emphasis on the mechanistic aspects of the reaction.233 Numerous references related to this subject can be found in his article. Deuteration of cyclohexanones and an application of NMR spectroscopy to the analysis of deuterated products have revealed that on ruthenium, osmium, iridium, and platinum, deuterium is simply added to adsorbed ketones to give the corresponding alcohols deuterated on the Cl carbon, without any deuterium atom at the C2 and C6 positions, while over palladium and rhodium the C2 and C6 positions are also deuterated.234 A distinct difference between rhodium and palladium is that on rhodium deuterium is incorporated beyond the C2 and C6 positions whereas on palladium the distribution of deuterium is limited to the C2 and C6 carbons.234,235 From these results, together with those on the deuteration of adamantanone,236 it has been concluded that a Tt-oxaallyl species is formed on palladium while deuterium may be propagated by an a, 3 process237 on rhodium via a staggered a, 3-diadsorbed species. 

Chiral methyl chiral lactic acid (5). This labeled molecule, useful for study of stereospecificity of enzymic reactions, has been prepared in a way that allows for synthesis of all 12 possible isomers. One key step is the stereospecific debromination of 1, accomplished by conversion to the vinyl-palladium cr-complex 2 followed by cleavage with CF3COOT to give the tritium-labeled 3. The next step is the catalytic deuteration of 3, accomplished with a rhodium(I) catalyst complexed with the ligands norbornadiene and (R)-l,2-bis(diphenylphosphino)propane. This reaction gives 4 with an optical purity of 81%. The product is hydolyzed to 5, which is obtained optically pure by cr3rstallization. 

The reaction of the terminal borylene [(OC)sM=B=N(SiMe3)2] (M = Cr, W) compounds with [ RhCl(CO)2 2] in deuterated benzene for a few minutes led to formation of a tetranuclear rhodium bis-borylene compound as black crystals 18a. The bis-borylene derivative possesses two fused B-Rh-Rh, dirhodium-borirane rings <2006AGE2132>. Compound 18a was characterized by multinuclear NMR and infrared spectroscopy, elemental analysis and single crystal X-ray diffraction. The B NMR (C6D6) spectrum presents a single signal at 74 ppm, a low frequency shift when compared with similar systems, which normally appear between 98 and 120 ppm. 

Hydrogenation of olefins on a soluble catalyst has been reported recently [61,62]. Tris(triphenylphosphine)rhodium chloride [(Ph3P)3RhCl] will promote homogeneous hydrogenation of reactive double bonds, including the A -bond in Ai -dien"3-ones, where the product of deuteration was the ia,2a-dideutero-compound (17) [62]. The mechanism is not... 

However, the carbonyl of the methoxycarbonyl group may be involved in the formation of an oxallyiic intermediate (23), which affords a path to both syn and anti isomers. A similar structure was proposed by Teratani et al. to explain the distribution of deuterium in the products of deuteration of 2-methylcyclo-hexanone catalyzed by palladium such a structure was not required to explain the results of catalysis by rhodium. ... 

Table XIX presents a selection of the results obtained in a study of the reaction of ethylene with deuterium over rhodium-alumina (31), together with some calculated distributions obtained by the method previously employed. The proportion of deuterated ethylenes in the initial products rises from 30% at —18° to 75% at 110°. In contrast to the behavior of palladium, ethane-dj is the major ethane throughout and hydrogen exchange is significant at all but the lowest temperature studied. The parameters used in the calculations attribute the greatest effect of temperature to the variation of the chance of ethylene desorption, which rises from 25% at —18° to 62% at 110°. The effect of temperature on the chance of alkyl reversal is relatively small. Another resjject in which the reaction over rhodium differs from that over palladium is that the chance of acquisition of deuterium in the hydrogenation steps is higher, and indeed it appears that, as with iridium, molecular deuterium may be substantially responsible for the conversion of ethyl radicals to ethane. E — E, is 3 kcal mole and E, — E, is 4.5 kcal mole. The reaction is first-order in hydrogen and zero in ethylene.

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