Rhodium ions

Table 3.12 surveys current industrial applications of enantioselective homogeneous catalysis in fine chemicals production. Most chiral catalyst in Table 3.12 have chiral phosphine ligands (see Fig. 3.54). The DIP AMP ligand, which is used in the production of L-Dopa, one of the first chiral syntheses, possesses phosphorus chirality, (see also Section 4.5.8.1) A number of commercial processes use the BINAP ligand, which has axial chirality. The PNNP ligand, on the other hand, has its chirality centred on the a-phenethyl groups two atoms removed from the phosphorus atoms, which bind to the rhodium ion. Nevertheless, good enantio.selectivity is obtained with this catalyst in the synthesis of L-phenylalanine. 

A somewhat unusual copper catalyst, namely a zeolite in which at least 25% of its rhodium ions had been exchanged by Cu(II), was active in decomposition of ethyl diazoacetate at room temperature 372). In the absence of appropriate reaction partners, diethyl maleate and diethyl fumarate were the major products. The selectivity was a function of the zeolite activation temperature, but the maleate prevailed in all cases. Contrary to the copper salt-catalyzed carbene dimer formation 365), the maleate fumarate ratio was found to be relatively constant at various catalyst concentrations. When Cu(II) was reduced to Cu(I), an improved catalytic activity was observed. 

The major resonances suggest that complexation of two Rhodium ions by the tetraphosphine ligand 4 occurs in the same manner as binding of one rhodium by the diphosphine Josiphos ligand 3 (see Fig. 2). While the minor resonances observed... 

Rhodium, incorporated in the silver halide grains, decreases sensitivity and increases contrast. This action has been attributed to depression of latent image formation because of deep electron trapping by the trivalent rhodium ion (183-185). Eachus and Graves (184) showed that rhodium, probably as a complex, acts as a deep trap for electrons at room temperature. Weiss and associates (186) concluded that the rhodium salts introduce deep traps for both electrons and holes. Monte Carlo simulation showed that the photographic properties could be accounted for in this way over a wide range of exposure times. 

Oxidative addition of RX to bis[dicarbonylrhodium(I)] porphyrins [317] (see Eq. 28) or monorhodium(I) porphyrins (Scheme 3, path m) also produces (T-bonded complexes. The organic substrates RX include aldehydes, anhydrides, aryl or acyl, arylcarbonyl, or ethoxycarbonylmethyl halides, cyclopropyl ketones [62] or highly strained cyclopropanes [318]. The fate of the second rhodium ion formulated as [Rh(CO)2]+ in Eq. (28) was not investigated. 

The ethylene groups are thus lost stepwise much like the carbonyl groups in metal carbonyls. The relative abundance of the molecular ion in the mass spectrum of CsHsRh EU is only about 10% of that of the strongest rhodium ion CsH5Rh+ similar to the relative abundance of the molecular ions in similar metal carbonyl derivatives. 

RhCl(PPh3) 3 The chlorine radical (Cl ) accepts an electron from rhodium metal (electronic configuration Ad1,5s2) to give Cl and Rh+. The chloride ion then donates two electrons to the rhodium ion to form a dative or a coordinate bond. Each PPh3 donates a lone pair of electrons on the phosphorus atom to the rhodium ion. The total number of electrons around rhodium is therefore 8 + 2 + 3X2=16, and the oxidation state of rhodium is obviously 1 +. The other way of counting is to take the nine electrons of rhodium and add one electron for the chlorine radical and six for the three neutral phosphine ligands. This also gives the same electron count of 16. 

In methyl acetate carbonylation the plot of rate against the concentration of lithium iodide has a small positive intercept. Do you expect it to be the same for two different rhodium ion concentrations ... 

There seem to be very few complexes in which there are two rhodium ions in different oxidation states. The best-authenticated examples are the [RhH2(PR3)2]2 complexes (R = NMe2, PfOPr1 ]. The dimethylamino complex has been shown to have the structure (129) and contains both rhodium(I) and rhodium(III).1287 The other example is provided by the [Rh(02CMe)2]+ ion in [Rh(02CMe)2]2C104. This ion retains the classic lantern structure of the rhodium(II) carboxylato complexes, but the salt contains both rhodium(II) and rhodium(III).1288... 

The systems used at TsKX) °C did not show a decrease of aetivity up to six cycles. This stability suggests that there is not any migration of rhodium ions from the inorganic matrix to the solution. 

Chloroformamide and iodoformamide compounds, by direct interaction between a palladium carbamoyl complex and CI2 or I2 have been recently reported by us [12b, 13]. As far as the mechanism of catalysis under more drastic temperature conditions is concerned, in which our materials lose rhodium ions, the aniline synthesis could still occur through the above mechanism carried out by Rh " " ions eluted in solution. 

In the complex Cp Rhm(PyS)2 (PyS = pyridine-2-thiolato), one PyS ligand is bound to the rhodium ion in an A-monodentate mode, while the other ligand chelates to the metal in an TVA -bidentate mode. In this complex, the thiol thione tautomerism occurs in solution at ambient temperature, so its NMR spectra are solvent-dependent (00ICA(299) 100). 

A 2002 paper reported the synthesis of a Rh(I) complex with the N22-picolyl-substituted derivative of H3tpfc [188]. This structurally unusual metallocorrole, Rh(N22-picolyl-Htpfc)(CO)(PPh3), features an out-of-plane Rh displacement of 1.51 A, compared with a displacement from the -plane of 0.2763(5) A in the Rh(III) complex Rh(tpfc)(PPh3). The rhodium ion is bound to the N23 and... 

The authors established directly the time scale for activation of C-H bonds in solutions at room temperature by monitoring the C-H bond activation reaction in the nanosecond regime with infrared detection. In the first stage of the process, loss of one carbon monoxide ligand (reaction VI-7 —- VI-8 in Scheme VI.6) substantially reduces back-bonding from the rhodium ion and increases the electron density at the metal center. Formed after the solvation stage, complex VI-9 traverses a 4.2 kcai nriol barrier (A = 5.0 x lo s ) and forms the -pCTp complex VI-10 which is more reactive toward C-H oxidative addition. 

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