Amine with rhodium

Intramolecular C-H Amination with Rhodium(II) Catalysts 391 Tab. 17.2 Rhodium-catalyzed insertion of sulfamates. 

A synthesis of optically active citroneUal uses myrcene (7), which is produced from P-piaene. Reaction of diethylamine with myrcene gives A/,A/-diethylgeranyl- and nerylamines. Treatment of the aHyUc amines with a homogeneous chiral rhodium catalyst causes isomerization and also induces asymmetry to give the chiral enamines, which can be readily hydrolyzed to (+)-citroneUal (151). 

Plaiinum was more efficient lhan rhodium in ihese experimenis. These catalysts give excellent yields of tertiary amines in reductive alkylation of aliphatic secondary amines with ketones ( 6). 

Allyl groups attached directly to amine or amide nitrogen can be removed by isomerization and hydrolysis.228 These reactions are analogous to those used to cleave allylic ethers (see p. 266). Catalysts that have been found to be effective include Wilkinson s catalyst,229 other rhodium catalysts,230 and iron pentacarbonyl.45 Treatment of /V-allyl amines with Pd(PPh3)4 and (V,(V -dimethylbarbi Lurie acid also cleaves the allyl group.231... 

Prochiral imines can be hydrogenated to the corresponding amines with extremely high enan-tioselectivities in H20/ethyl ethanoate biphasic systems, using Rh1 complexes of sulfonated phosphines 342 The cationic rhodium complex [Rh(NBD)(131)]+ was an active catalyst for hydrogenation of 2-ethanamido-propenoic acid in aqueous solution.343... 

After the initial demonstration of stoichiometric nucleophilic attack on 7i-allyl ligands, catalytic allylic substitution reactions were pursued. In 1970, groups from Union Carbide [3, 4], Shell Oil [5], and Toray Industries [6] published or patented examples of catalytic allylic substitution. All three groups reported allylic amination with palladium catalysts. The Toray Industries report also demonstrated the exchange of aryl ether and ester leaving groups, and the patent from Shell Oil includes catalysts based on rhodium and platinum. 

The stereoselective construction of nitrogen heterocycles remains a topic of intense synthetic interest [39]. Evans and Robinson described the combination of the stereospecific aUylic amination with ring-closing metathesis as a strategy for the constmction of mono- and disubstituted azacycles, which they demonstrated with the stereospecific construction of cis- and tra s-2,5-disubstituted pyrrolines [40]. Furthermore, this approach provided an ideal system for the determination of whether the enantiospecific rhodium-catalyzed aUyhc amination with an enantiomerically enriched nucleophile experiences a matched and a mismatched reaction manifold. 

Under mild conditions, hydroformylation of olefins with rhodium carbonyl complexes selectively produces aldehydes. A one-step synthesis of oxo alcohols is possible using monomeric or polymeric amines, such as dimethylbenzylamine or anion exchange resin analog to hydrogenate the aldehyde. The rate of aldehyde hydrogenation passes through a maximum as amine basicity and concentration increase. IR data of the reaction reveal that anionic rhodium carbonyl clusters, normally absent, are formed on addition of amine. Aldehyde hydrogenation is attributed to enhanced hydridic character of a Rh-H intermediate via amine coordination to rhodium. 

With rhodium trichloride, the only species observed in solution were Rh2(CO)4Cl2 and HC1 gas. As noted in Table I, no hydroformylation occurred in this reaction mixture. When the carbonyl chloride dimer was used as starting material, the clusters, Rh4(CO)i2 and Rh6(CO)i6, formed along with the anion, Rh(CO)2Cl2. Aldehyde, but no alcohol, was produced. These IR data are in good agreement with earlier reports on amine-free systems (16), and they support the contention that a chloride-free carbonyl (or carbonyl hydride) is the active hydroformylation catalyst. 

As shown in Figure 3, a positive p-value (+0.92) was observed in the hydrogenation of substituted benzaldehydes, giving strong support to the postulation by Heil and Marko that the rate determining step in the formation of alcohol (Mechanism 2) is the hydride addition step. It is therefore suggested that coordination of amine to rhodium increases the hydridic character of the Rh-H bond, much the same as is postulated in cobalt-tributylphosphine complexation (20). The differing effect of amine on rhodium (promoter) and on cobalt (inhibitor) is attributed to the more hydridic nature of a Rh-H bond as compared with the very protonic HCo(CO)4. Addition of amines to HCo(CO)4 results in formation of inactive species similar to I. 

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