Rhodium amination

Rhodium(II) acetate catalyzes C—H insertion, olefin addition, heteroatom-H insertion, and ylide formation of a-diazocarbonyls via a rhodium carbenoid species (144—147). Intramolecular cyclopentane formation via C—H insertion occurs with retention of stereochemistry (143). Chiral rhodium (TT) carboxamides catalyze enantioselective cyclopropanation and intramolecular C—N insertions of CC-diazoketones (148). Other reactions catalyzed by rhodium complexes include double-bond migration (140), hydrogenation of aromatic aldehydes and ketones to hydrocarbons (150), homologation of esters (151), carbonylation of formaldehyde (152) and amines (140), reductive carbonylation of dimethyl ether or methyl acetate to 1,1-diacetoxy ethane (153), decarbonylation of aldehydes (140), water gas shift reaction (69,154), C—C skeletal rearrangements (132,140), oxidation of olefins to ketones (155) and aldehydes (156), and oxidation of substituted anthracenes to anthraquinones (157). Rhodium-catalyzed hydrosilation of olefins, alkynes, carbonyls, alcohols, and imines is facile and may also be accomplished enantioselectively (140). Rhodium complexes are moderately active alkene and alkyne polymerization catalysts (140). In some cases polymer-supported versions of homogeneous rhodium catalysts have improved activity, compared to their homogenous counterparts. This is the case for the conversion of alkenes direcdy to alcohols under oxo conditions by rhodium—amine polymer catalysts... 

Skibsted LH. Photoisomerization of rhodium amine complexes. The deduction of an excited state reaction mechanism. Coord Chem Rev 1989 94 151-79. 

Si 3H CP/MAS-NMR was used to probe interactions of transition metal carbonyl clusters (Ru3H(CO)M, Os2FI(CO)ii, Co(CO)4 ) deposited in the mesoporous aluminosilicate material MCM-41.637 A 29Si MAS-NMR study has been made of rhodium-amine complexes on Si02 surfaces.638 31P CP/MAS-NMR spectroscopy was able to characterise Cu6(TePh)6(PPh2Et)5 clusters in the pores of MCM-41.639... 

The complex m r-[RhCl3(NH3)3j has been reported to have good activity, the best of the rhodium—amine complexes, but it is very insoluble [2]. Rhodium complexes are of interest because of the demonstration of their antibacterial action [7] (see Chapter 9) in structures of type [RhCl2(py)4] , which show, however, only marginal antitumour activity. Conversely, the most antitumour active rhodium species in general show few antibacterial... 

El. Gao, 1999, Rhodium-amine complexes tethered on silica-supported metal catalysts. Highly active catalysts for the hydrogenation of arenes. New J. of Chem. 23, 6,633-640 F.R Hartley, 1985, Supported Metal Complexes, D. Reidel Publ. Co. Dordrecht... 

Some examples of the use of a temporary additional site of coordination have been published. Burk and Feaster have transformed a series of ketones into hydrazones capable of chelating to a rhodium catalyst (Scheme 4.7). Upon coordination, enanti os elective hydrogenation of the hydrazone is feasible, yielding N-aroylhydrazines in up to 97% ee. Finally, the hydrazines were transformed into amines by treatment with Sml2. 

So you can see that to make MDA or MDMA using either NH3 or MeNH2 one is going to have to think of a way to keep them in the fray. Strike s first impulse is to dissolve the amine in a solvent. But what solvent And would the reaction even work in any solvent Rhodium thinks that maybe an aqueous amine solution would work considering the clay is moistened with water anyway. 

Rhodium complexes with oxygen ligands, not nearly as numerous as those with amine and phosphine complexes, do, however, exist. A variety of compounds are known, iucluding [Rh(ox)3] [18307-26-1], [Rh(acac)3] [14284-92-5], the hexaaqua ion [Rh(OH2)3] [16920-31 -3], and Schiff base complexes. Soluble rhodium sulfate, Rh2(804 )3-a H2 0, exists iu a yellow form [15274-75-6], which probably coutaius [Rh(H20)3], and a red form [15274-78-9], which contains coordinated sulfate (125). The stmcture of the soluble nitrate [Rh(N03)3 2H20 [10139-58-9] is also complex (126). Another... 

Secondary and tertiary amines are preferentially produced when rhodium or palladium are chosen as catalyst. As in Method 3, reforming reactions do not normally compete with the hydrogenation reaction and high selectivities to the desired product are possible. 

Alkali moderation of supported precious metal catalysts reduces secondary amine formation and generation of ammonia (18). Ammonia in the reaction medium inhibits Rh, but not Ru precious metal catalyst. More secondary amine results from use of more polar protic solvents, CH OH > C2H5OH > Lithium hydroxide is the most effective alkah promoter (19), reducing secondary amine formation and hydrogenolysis. The general order of catalyst procUvity toward secondary amine formation is Pt > Pd Ru > Rh (20). Rhodium s catalyst support contribution to secondary amine formation decreases ia the order carbon > alumina > barium carbonate > barium sulfate > calcium carbonate. 

Conditions cited for Rh on alumina hydrogenation of MDA are much less severe, 117 °C and 760 kPA (110 psi) (26). With 550 kPa (80 psi) ammonia partial pressure present ia the hydrogenation of twice-distilled MDA employing 2-propanol solvent at 121°C and 1.3 MPa (190 psi) total pressure, the supported Rh catalyst could be extensively reused (27). Medium pressure (3.9 MPa = 566 psi) and temperature (80°C) hydrogenation usiag iridium yields low trans trans isomer MDCHA (28). Improved selectivity to aUcychc diamine from MDA has been claimed (29) for alumina-supported iridium and rhodium by iatroduciag the tertiary amines l,4-diazabicyclo[2.2.2]octane [280-57-9] and quiaucHdine [100-76-5]. 

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). 

Olefins can be aminomethylated with carbon monoxide [630-08-0] (CO) and amines in the presence of rhodium-based catalysts. Eor example, pipera2ine reacts with cyclohexene [110-83-8] to form W,Af-di-(l-cyclohexylmethyl)-pipera2ine [79952-94-6] (55). 

Most ring syntheses of this type are of modern origin. The cobalt or rhodium carbonyl catalyzed hydrocarboxylation of unsaturated alcohols, amines or amides provides access to tetrahydrofuranones, pyrrolidones or succinimides, although appreciable amounts of the corresponding six-membered heterocycle may also be formed (Scheme 55a) (73JOM(47)28l). Hydrocarboxylation of 4-pentyn-2-ol with nickel carbonyl yields 3-methylenetetrahy-drofuranone (Scheme 55b). Carbonylation of Schiff bases yields 2-arylphthalimidines (Scheme 55c). The hydroformylation of o-nitrostyrene, subsequent reduction of the nitro group and cyclization leads to the formation of skatole (Scheme 55d) (81CC82). 

As already noted (p. 1073), the platinum metals are all isolated from concentrates obtained as anode slimes or converter matte. In the classical process, after ruthenium and osmium have been removed, excess oxidants are removed by boiling, iridium is precipitated as (NH4)2lrCl6 and rhodium as [Rh(NH3)5Cl]Cl2. In alternative solvent extraction processes (p. 1147) [IrClg] " is extracted in organic amines leaving rhodium in the aqueous phase to be precipitated, again, as [Rh(NH3)5Cl]Cl2. In all cases ignition in H2... 

Similarity with cobalt is also apparent in the affinity of Rh and iH for ammonia and amines. The kinetic inertness of the ammines of Rh has led to the use of several of them in studies of the trans effect (p. 1163) in octahedral complexes, while the ammines of Ir are so stable as to withstand boiling in aqueous alkali. Stable complexes such as [M(C204)3], [M(acac)3] and [M(CN)5] are formed by all three metals. Force constants obtained from the infrared spectra of the hexacyano complexes indicate that the M--C bond strength increases in the order Co < Rh < [r. Like cobalt, rhodium too forms bridged superoxides such as the blue, paramagnetic, fCl(py)4Rh-02-Rh(py)4Cll produced by aerial oxidation of aqueous ethanolic solutions of RhCL and pyridine.In fact it seems likely that many of the species produced by oxidation of aqueous solutions of Rh and presumed to contain the metal in higher oxidation states, are actually superoxides of Rh . ... 

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). 

Catalysts show remarkable product variation in hydrogenation of simple nitriles. Propionitrile, in neutral, nonreactive media, gives on hydrogenation over rhodium-on-carbon high yields of dipropylamine, whereas high yields of tripropylamine arise from palladium or platinum-catalyzed reductions (71). Parallel results were later found for butyronitrile (2S) and valeronitrile (74) but not for long-chain nitriles. Good yields of primary aliphatic amines can be obtained by use of cobalt, nickel, nickel boride, rhodium, or ruthenium in the presence of ammonia (4J 1,67,68,69). 

Noble-metal catalysts can be used under mild conditions. Rhodium 16,24,61,73) has given excellent results. Rhodium seems esp>ecially useful when other catalysts give excessive secondary amine. Ruthenium functions best in aqueous media, but under these conditions it is apt to promote extensive... 

Both amine oxides related to pyridines and aliphatic amine oxides (/25) are easily reduced, the former the more so. Pyridine N-oxide has been reduced over palladium, platinum, rhodium, and ruthenium. The most active was rhodium, but it was nonselective, reducing the ring as well. Palladium is usually the preferred catalyst for this type of reduction and is used by most workers 16,23,84 158) platinum is also effective 100,166,169). Katritzky and Monrol - ) examined carefully the selectivity of reduction over palladium of a... 

Amine complexes are an important class of rhodium(III) complex. Figure 2.44 shows some relationships. 

Secondary amines can be added to certain nonactivated alkenes if palladium(II) complexes are used as catalysts The complexation lowers the electron density of the double bond, facilitating nucleophilic attack. Markovnikov orientation is observed and the addition is anti An intramolecular addition to an alkyne unit in the presence of a palladium compound, generated a tetrahydropyridine, and a related addition to an allene is known.Amines add to allenes in the presence of a catalytic amount of CuBr " or palladium compounds.Molybdenum complexes have also been used in the addition of aniline to alkenes. Reduction of nitro compounds in the presence of rhodium catalysts, in the presence of alkenes, CO and H2, leads to an amine unit adding to the alkene moiety. An intramolecular addition of an amine unit to an alkene to form a pyrrolidine was reported using a lanthanide reagent. 

When the substrate is an allylic alcohol or amine, the addition is generally anti," though the stereoselectivity can be changed to syn by the use of catecholborane and the rhodium complexes mentioned above. Because the mechanism is different, use of this procedure can result in a change in regioselectivity as well, [e.g., styrene PhCH=CH2 gave PhCH(OH)CH3]. ... 

Reduction, carboxyl groups, 56,83 Reduction of a,0-unsaturated p-toluene-sulfonyl-hydrazones to alkenes, 59,42 Reductive alkylation, 56,52 Reductive cleavage, 56, 101 Resolution of amines, 55,80, 83 Rexyn 201,55,4 Rhodium(III) oxide, 57, 1 Ring contraction, 56, 107 Ring expansion of cycloalkanones to cycloalkenones, 59, 113... 

Much research has been carried out into direct amination of aromatic substrates, typified by the direct conversion of benzene to aniline using ammonia and a catalyst. Although there have been many patented routes conversions, are normally low, making them uneconomic. Modem catalysts based on rhodium and iridium, together with nickel oxide (which becomes reduced), have proved more active,and such is the research activity in this area that it is only a matter of time before such processes become widely used. 

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