Rhodium complexes infrared spectra

Van t Blik et al. [3] exposed a highly dispersed 0.57 wt% RI1/AI2O3 catalyst (H/M=1.7) to CO at room temperature and measured a CO uptake of 1.9 molecules of CO per Rh atom. Binding energies for the Rh 3ds/2 XPS peak increased from 307.5 eV for the reduced catalyst under H2 to 308.7 eV for the catalyst under CO. The latter value equals that of the [Rh+(CO)2Cl]2 complex, in which rhodium occurs as a Rh+ ion. The infrared spectrum of the Rh/Al203 catalyst under CO showed exclusively the gem-dicarbonyl peaks at 2095 and 2023 cm-1. All results point to the presence of rhodium in Rh+(CO)2 entities. However, how can a rhodium particle accommodate so much CO ... 

Rhodium complex was loaded onto the quatemised polymer support by the reaction with [Rh(CO)2I]2 in hexane (Eq 2). The resulting polymer beads or films showed the characteristic yellow colour of [Rh(CO)2I2] . An infrared spectrum of the powdered beads (KBr disk) showed two weak v(CO) absorptions of similar intensity at 2056 and 1984 cm 1, consistent with the presence of the cis-dicarbonyl complex, [Rh(CO)2I2]" (2059, 1988 cm 1 in CH2C12). Spectra of a much higher quality and intensity were obtained from polymer films loaded with rhodium complex. These observations of polymer supported [Rh(CO),I,r match those reported in the original study of Drago et al. 

The infrared spectrum (C6H6 solution) shows inr H at 2070 cm.-1 and vco at 1930 cm.-1. The H n.m.r. spectrum in CDCls shows the aromatic protons at 3.0r and the CH3 protons at 7. 66t in the ratio of 50 3 as calculated for 1 mole of toluene in the complex the Ir—H resonance is observed at 20.7r as a quartet, Jp h = 22 Hz. The unsolvated complex has been shown to be isomorphous with the rhodium analog which has a trigonal bipyramidal structure with the phosphine ligands at equatorial positions.8... 

Hydridotetrakis(triphenylphosphine)rhodium(I) forms yellow microcrystals which melt at 145-147° in air and at 154—156° in a capillary sealed under nitrogen. The infrared spectrum shows a band at 2156 (m) cm.-1 attributable to v(RhH). The complex is soluble in benzene, chloroform, and dichloromethane. 

Nitrosyltris(triphenylphosphine)rhodium forms bright crimson-red microcrystals. It softens at 96°, then melts with decomposition at 160° in air sealed under nitrogen it melts at 205-206°. The infrared spectrum shows a peak at 1610 cm.-1 (vs) attributed to v(NO). The complex is soluble in dichloromethane, chloroform, and benzene. 

Treatment of aqueous solutions of bis(ethylenediamine)dichloro-rhodium(III) with sodium borohydride give solutions which the proton magnetic resonance spectrum shows to contain an Rh—H complex (t 31 p.p.m., J Rh—h 31 c.p.s.). Also, the infrared spectrum of the precipitated tetraphenyl boronate shows a band at 2100 cm-1 assigned to an Rh—H stretch. 

Under syn gas pressure the rhodium acac precursors were converted to the catalytically active hydride complexes HRh(CO)2(L-L). The complexes are generally assmned to have a trigonal bipyramidal structure and two isomeric structures of these complexes are possible, containing the diphosphite coordinated in a bisequatorial (ee) or an equatorial-apical (ea) fashion. The structure of the complexes can be elucidated by (high pressure) IR and NMR data (Table 3). In the carbonyl region of the infrared spectrum the vibrations of the ee and ea complex can be easily distinguished. The ee complexes typically show absorptions around 20 15 and 2075 cm [24, 26,... 

Kinetic studies produced some surprising results. The rate of carbonylation is independent not only of the concentration of methanol but also of the pressure of carbon monoxide. The reaction, however, is first order in each of the species rhodium and iodide (rate a [Rh][I ]). Bands at 2064 and 1984cm in the infrared spectrum, which correspond to the known ion [Rh(C0)2l2] shift to 2062 and 1711 cm" on addition of methyl iodide. The band at 1711 cm" suggests the formation of an acetyl complex by methyl migration (p. 225). Under... 

The structure assigned to (XXVII) is primarily based on its infrared spectrum and that of the analogous deuteride. Such hydrido complexes are probably intermediates in the pol rmerization of terminal acetylenes by transition metal complexes 91). In this regard it is significant that phenyl-acetylene forms an oligomer in the presence of a catalytic amount of the rhodium complex RhCl(CO)(PPh3)2 32). Rhodium remains chemically bound to this poorly characterized oligomer. 

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