With rhodium

This is a chapter written entirely by a chemist named Rhodium (with guest speaker Osmium ). Rhodium is, as far as Strike is concerned, the world s leading underground scientist. Knowledgeable in nearly every aspect of drug chemistry, this chemist has been the savior for many a person that was lost. Here he has contributed some new reactions for your reading pleasure. Radical stuff that you can bet will become the next wave of synthesis protocol. The rest of this chapter is Rhodium s voice.]... 

Turbine inlet temperature. Thermocouple is constructed of platinum-platinum rhodium with the junction enclosed with ceramic insulation. Typically, 9-12 units are required at this stage. 

The pattern of iridium halides resembles rhodium, with the higher oxidation states only represented by fluorides. The instability of iridium(IV) halides, compared with stable complexes IrCl4L2 and the ions IrX (X = Cl, Br, I), though unexpected, finds parallels with other metals, such as plutonium. Preparations of the halides include [19]... 

Acyl chlorides containing an a hydrogen are smoothly converted to alkenes, with loss of HCI and CO, on heating with chlorotris(triphenylphosphine)rhodium, with metallic platinum, or with certain other catalysts. The mechanism probably involves conversion of RCH2CH2COCI to RCH2CH2—RhCO(Ph3P)2Cl2 followed by a concerted syn elimination of Rh and H. See also 14-39 and 19-12. 

Anchored Wilkinson s Catalyst Comparison with the Homogeneous Catalyst and Supported Rhodium with Respect to Reaction Selectivity... 

N) bonding of quinoline to rhodium with loss of complexed MeCN, fol-... 

Asymmetric hydrogenation of a,fi-unsa turated acids.1 2- Aryl-3-methyl-2-bu-tenoic acids (2) undergo highly stereoselective hydrogenation catalyzed by a complex of rhodium with the chiral (aminoalkyl)ferrocenylphosphine (1), but not with... 

A similar pattern has always been discussed for rhodium, with hydri-dotetracarbonylrhodium H-Rh(CO)4 as a real catalyst species. The equilibria between Rh4(CO)i2 and the extremely unstable Rh2(CO)s were measured by high pressure IR and compared to the respective equilibria of cobalt [15,16]. But it was only recently that the missing link in rhodium-catalyzed hydroformylation, the formation of the mononuclear hydridocomplex under high pressure conditions, has been proven. Even the equilibria with the precursor cluster Rh2(CO)8 could be determined quantitatively by special techniques [17]. Recent reviews on active cobalt and rhodium complexes, also ligand-modified, and on methods for the necessary spectroscopic in situ methods are given in [18,19]. 

Of some interest are the different colored crystals resulting from compounding rhodium with the halogens RhF = red, RhCl = red, RhBrj = brown, and Rel = black. 

Scheme 1.5 Silica, alumina and titania surface oxygens behaving as ligands in the M.L.H. Green formalism [9] after reaction of r -tris(allyl)rhodium with a partially dehydroxylated surface [39].

Ni and Co or of oxophilic metals, for example. Re, is still poorly studied the surface-mediated synthesis of bimetallic carbonyl clusters is limited to a few examples the surface-mediated synthesis of metal compounds without carbonyl ligands has just begun with the silica-mediated synthesis of [RhH2(PMe3)4] by treatment of bis (allyl) rhodium with PMe3 followed by H2 [121] the silica-mediated synthesis of tantalum clusters has been investigated recently but the products were not extracted from the surface-for example, treatment of silica physisorbed Ta(CH2Ph)5 in H2 at 523 K for 20 h led to tri-tantalum clusters, as shown by EXAFS spectroscopy [122]. 

The mechanism is well understood, involving complexation of the rhodium with iodine and carbon monoxide, reaction with methyl iodide (formed from the methanol with hydrogen iodide), insertion of CO in the rhodium-carbon bond, and hydrolysis to give product with regeneration of the complex and more hydrogen iodide. 

Rhodium trichloride is prepared by heating rhodium with chlorine gas at... 

A complex of rhodium with a chiral ligand called DIOP... 

The exocyclic C=C double bond has been hydrogenated in 247 with a palladium catalyst <1983JHC45>, and enantioselectively in 248, using rhodium with (R,R)-Me-DuPhos ligand as catalyst <2005JOC1679>. 

An excellent review describing asymmetric transfer hydrogenation has been published156. Many excellent results have been achieved in recent studies of acrylic acid reductions employing the same catalysts of ruthenium or rhodium with a chiral diphosphine as were used in the hydrogen gas process1331157. In this case, however, the most common hydrogen source is the combination of formic acid with an amine. The choice of amine is often critical in the reduction shown in Scheme 30, the use... 

In contrast with the difluorides, the distribution of trifluorides extends to the third series of the transition metals, where iridium and gold trifluorides are fully characterized. In the second series, trifluorides are known for the elements from niobium to rhodium, with the exception of technetium, and in the first series, from titanium to cobalt. All the trifluorides have been characterized structurally, with earlier reports based on X-ray powder-diffraction data, since the compounds were not prepared in single-crystal form until more recently, when high-temperature, crystal-growth techniques became available. 

This possibility of intimate association of rhodium with the aromatic ring suggests further experiments. A logical extension of asymmetric syntheses involving prochir-al reactants is a kinetic resolution with related chiral reactants under similar conditions. In the one case of hydroboration-amination where this has been applied, it has proved to be very effective. The reactant was prepared directly by a Heck reaction on 1,2-dihydronaphthalene, and under the standard conditions of catalytic hydrobora-tion gave >45% of both enantiomerically pure recovered alkene with (after oxidative work-up) the alcohol of opposite hand, mainly as the trans-isomer. This procedure forms a simple and potentially useful route to pharmacologically active substances, demonstrated by the racemic synthesis shown [105] (Scheme 34). 

The correct enantiomer can be synthesized from an achiral starting material by catalytic hydrogenation using a complex of rhodium with a chiral ligand called DIOP. Such an enantioselective synthesis is more efficient than making a racemic mixture, resolving it into enantiomers, and discarding the unwanted enantiomer. 

RhLfl means rhodium with an unspecified number of unspecified ligands. This notation is common in organometallic chemistry when the nature of die carbon-metal bonding Is important, but the precise structure of the metaf complex is not. 

The catalyst is a cationic complex of rhodium with another diphosphine, DIPAMP. DIPAMP s chirality resides in the two stereogcnic phosphorus atoms unlike amines, phosphines are configurationally stable, rather like sulfoxides (which we will discuss in the next chapter). The catalyst imposes chirality on the hydrogenation by coordinating to both the amide group and the double bond of the substrate. Two diastereoisomeric complexes result, since the chiral catalyst can coordinate to either of the enantiotopic faces of the double bond. 

In the 1970s Union Carbide had reported the use of rhodium with promoters such as amines, carboxylates, etc. for the synthesis of ethylene glycol from CO plus H2. Manufacture of ethylene glycol by this route, however, was never commercialized. The mechanism of this reaction is not understood. Both mononuclear and polynuclear (cluster) rhodium carbonyls can be seen by NMR and IR spectroscopy under conditions approximating that of the catalytic reaction. The question as to whether the catalytic intermediates are mononuclear or cluster has not been answered with any certainty so far. 

Potassium Pentabromrhodite, K RhBrg, is obtained by heating finely divided rhodium with potassium bromide in a stream of bromine... 

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