28407-51-4

Usage

Chemical Properties

black crystal(s); cluster structure; used as a catalyst [COT88] [ALD94] [ALF95]

Uses

Catalyst for hydrogenation of alkenes, hydroformylations ofalkenes; reducing agent for aldehydes, ketones, and nitro groups; catalyst for carbenoid reactions of diazo compounds

Purification Methods

It slowly loses CO when heated in air, but may be regenerated by heating at 80-200o in the presence of CO at 200atmospheres pressure for 15hours, preferably in the presence of Cu. It forms black crystals which are insoluble in hexane. It has bands at 2073, 2026 and 1800cm-1 in the IR. [Hieber & Lagally Z Anorg Allgem Chem 251 96 1963, Corey & Dahl J Am Chem Soc 85 1202 1963, Doyle et al. Tetrahedron Lett 22 1783 1981.] POISONOUS.

InChI:InChI=1/16CO.6Rh/c16*1-2;;;;;;

Upstream product

• 494804-05-6 dodecacarbonyltetrarhodium⁽⁰⁾ 
• 503-17-3 dimethylacetylene 
• 201230-82-2 carbon monoxide 
• 1333-74-0 hydrogen 
• 106-45-6 para-thiocresol 
• 2384-70-5 dec-2-yne 
• 2384-86-3 4-decyne 
• 2384-85-2 3-decyne 
• 629-05-0 n-octyne 
• 1942-45-6 4-Octyne 
• 629-74-3 hexadec-1-yne 
• 765-03-7 1-dodecyne 
• 931-48-6 2-cyclohexylacetylene 
• 501-65-5 diphenyl acetylene 

Relevant academic research and scientific papers

Synthesis and reactivity of metal-containing monomers 51. Synthesis and molecular structure of the cluster-containing complex [Rh6(CO)14(μ,η2-PPh2CH2 CH=CH2)]

The reaction of Rh6(CO)15MeCN with allyldiphenylphosphine under mild conditions afforded the cluster-containing complex [Rh6(CO)14(μ,η2-PPh2CH 2CH=CH2)]. Its molecular structure was characterized. The resulting complex is an octahedral Rh cluster with ten terminal and four μ3-bridging CO ligands. The average Rh - Rh distance is 2.762(2) A. The unsaturated ligand is additionally coordinated to the metal center (Rh(4) - C(232), 2.37(1) A; and Rh(4) - C(233), 2.32(2) A) to form a π-bond.

Transformation of rhodium carbonyl complexes in hydroformylation of 1-hexene studied from in situ IR spectroscopic data

Rhodium carbonyl complexes that formed from RhCl3 · 4H2O and RhCl3 · 4H2O modified by poly-N,N-dimethyl-N,N-diallylammonium chloride in a methanol - chloroform medium in the hydroformylation of 1-hexene were studied by in situ IR spectroscopy. Along with the rhodium hydrocarbonyl complexes, anionic complexes of the [Rh(CO)2Cl2]- type, whose concentrations and rates of formation in an acidic medium are much higher than those in a basic medium, were shown to be the active centers of hydroformylation. The function of the polycation is the stabilization of the catalytically active mononuclear rhodium complexes.

Spectral resolution of fluxional organometallics. The observation and FTIR characterization of all-terminal [Rh4(CO)12]

In situ FTIR spectroscopy at 1 cm-1 resolution was conducted on n-hexane solutions of the bridged [Rh4(CO)9-(μ-CO) 3] in the interval T = 268-288 K and PT = 0.1-7.0 MPa using either helium or carbon monoxide as dissolved gas. Analysis of the spectral data sets was conducted using band-target entropy minimization (BTEM), in order to recover the pure component spectra. A new spectral pattern was recovered with terminal vibrations at 2075, 2069.8, 2044.6 and 2042 cm -1. The new spectrum is consistent with an all-terminal [Rh 4(CO)12] species with a C3v anticubeoctahedron structure where 2 different [Rh(CO)3] moieties exist, although the presence of some Td structure can not be entirely excluded. The equilibrium between all-terminal [Rh4(CO)12] and the bridged [Rh4(CO)9(μ-CO)3] was determined in the presence of both helium and CO. The equilibrium constant Keq = [Rh4(CO)12]/[Rh4(CO)9-(μ-CO) 3] at 275 K was ca. 0.011 and the determined equilibrium parameters were ΔrG = 12.63 ± 4.8 kJ mol-1, ΔrH = -21.45 ± 2.3 kJ mol-1 and ΔrS = -114.3 ± 8.35 J mol-1 K-1. The free energy indicates a very small difference between the bridged and terminal geometry, and the lower entropy is consistent with a higher symmetry. This finding helps to address a long-standing issue concerning the existence of various [M4(CO)12] symmetries. In a more general context, the present study illustrates the considerable utility of quantitative infrared spectroscopy (occurring on a fast vibrational timescale) combined with sophisticated deconvolution techniques in order to resolve systems which have been demonstrated to be fluxional on the NMR timescale. The Royal Society of Chemistry 2005.

Formation of rhodium carbonyl thiolate dimers via elimination of dihydrogen; Crystal and molecular structure of [Rh2(CO)4(μ-SC6H4CH3)2]

Reaction of [Rh6(CO)15(NCMe)] with p-thiocresol [(4-Me)C6H4SH] leads to the formation of [Rh2(CO)4(μ-SC6H4CH3)2] as the main product along with a small amount of [Rh6(CO)16]. An approximately 30-fold excess of the thiol is required in order to obtain a good yield of the thiolate-bridged dimer while reaction of [Rh4(CO)12] with an excess of p-thiocresol leads to an apparently clean conversion to the dimeric Rh(I) complex. Mass spectrometric measurements show that the latter reaction involves evolution of H2, and CO evolution is indicated by the retardation of the reaction in CO saturated solution; these results suggest the following reaction stoichiometry: [Rh4(CO)12]+4RSH→2[Rh2(CO)4(μ-SR)2]+2H2+4CO. Kinetic measurements show that the reaction proceeds in three stages which are proposed to involve two rapid pre-equilibria and a final irreversible and relatively slow conversion to the products. The crystal and molecular structure of [Rh2(CO)4(μ2-SC6H4CH3)2] is reported.

Liquid-Phase Reaction of Monosubstituted and Disubstituted Alkynes with Tetrarhodium Dodecacarbonyl under CO and CO/H2 Mixtures. In-Situ IR Spectroscopic Characterization of 20 New Alkyne-Rhodium Complexes

It is well-known that the liquid-phase homogeneous unmodified rhodium-catalyzed hydroformylation of alkenes is irreversibly poisoned by the presence of trace quantities of alkynes. In the present contribution, we examined the reaction of four series of monosubstituted and disubstituted alkynes (20 compounds) with Rh4(CO)12 in n-hexane solvent at 293 K under both (A) 2.0 MPa CO and (B) 2.0 MPa CO and 2.0 MPa H2. The analytic method used was in-situ high-pressure infrared spectroscopy. It was observed that (I) all alkynes used in this study reacted quantitative with Rh4(CO)12 in a matter of hours, (II) the final spectra were not influenced by the presence of hydrogen, (III) the monosubstituted alkynes consistently gave a final product involving six terminal νCO vibrations in the region 2036-2121 cm-1 and two vibrations at ca. 1668 and 1689 cm-1, and (IV) the disubstituted alkynes consistently gave a final spectrum consistent with the superposition of the spectra obtained in III plus a spectrum involving five terminal νCO vibrations in the region 2030-2100 cm-1 and one vibration at ca. 1630 cm-1. These results are consistent with the existence of two primary types of observable species in the final products. Due to the band positions and absorptivities, we tentatively propose that these species are substituted dirhodium carbonyl species, specifically Rh2(CO)6{μ-η1-(CO-HC2R)} for terminal alkynes and Rh2(CO)6{μ-η1-(CO-R1C 2R2)} and Rh2(CO)6{μ-η2-(R1C 2R2)}in the case of disubstituted alkynes. These complexes are the rhodium analogues of well-known dicobalt carbonyl alkyne complexes. It appears that, in the case of terminal alkynes, the dirhodium-alkyne complexes undergo rapid CO insertion under 2.0 MPa CO. In the case of disubstituted alkynes, CO insertion seems more difficult to obtain, and an observable equilibrium is established between the bridged alkyne species and the insertion product. In both cases the final alkyne complexes are stable under CO even in the presence of molecular hydrogen. This is probably the primary reason that trace quantities of alkynes are able to poison the catalytic alkene hydroformylation reaction.

Unmodified Rhodium-Catalyzed Hydroformylation of Alkenes Using Tetrarhodium Dodecacarbonyl. The Infrared Characterization of 15 Acyl Rhodium Tetracarbonyl Intermediates

The homogeneous catalytic hydroformylation of 20 alkenes was studied, starting with Rh4(CO)12 as catalyst precursor in n-hexane as solvent, using high-pressure in-situ infrared spectroscopy as the analytical tool. Five categories of alkenes were studied, namely, cycloalkenes (cyclopentene, cycloheptene, cyclooctene, and norbornene), symmetric internal linear alkenes (3-hexene, 4-octene, and 5-decene), terminal alkenes (1-hexene, 1-octene, 1-decene, 1-dodecene, and 1-tetradecene), methylene cycloalkanes (methylene cyclopropane, methylene cyclobutane, methylene cyclopentane, and methylene cyclohexane), and branched alkenes (2-methyl-2-butene, 2-methyl-2-pentene, 2-methyl-2-heptene, and 2,3-dimethyl-2-butene). The typical reaction conditions were T = 293 K, PH2 = 2.0 MPa (0.018 mol fraction), PCO = 2.0 MPa (0.033 mol fraction), [alkene]0 = 0.1-0.02 mol fraction, and [Rh4(CO)12]0 = 6.6 × 10-5 mol fraction. In each experiment, with the exception of those involving methylene cyclopropane and the branched alkenes, the precursor Rh4(CO)12 was converted in good yield to the corresponding observable mononuclear acyl rhodium tetracarbonyl intermediate RCORh(CO)4. Due to the spectral characteristics, the intermediate RCORh(CO)4 is assigned a trigonal bipyrimidal geometry in all cases with Cs symmetry, with the acyl group taking an axial position. Under the present conditions, the cycloalkenes result in one acyl complex, the symmetric internal linear alkenes result in two acyl stereoisomers, the terminal alkenes result in three acyl complexes (two are stereoisomers), and the methylene cycloalkanes result in two acyl complexes. The first four categories of alkenes gave rise to slightly different spectral wavenumbers and relative intensities for the complexes, namely, cycloalkenes {2109 (0.41), 2063 (0.46), 2037 (0.72), 2019 (1.0), 1699 cm-1 (0.16)}, symmetric internal linear alkenes {2108 (0.43), 2061 (0.45), 2037 (0.84), 2019 (1.0), 1693 cm-1 (0.12)}, terminal alkenes {2110 (0.35), 2064 (0.46), 2038 (0.72), 2020 (1.0), 1703 cm-1 (0.16)}, and methylene cycloalkanes {2110 (0.33), 2064 (0.46), 2038 (0.72), 2020 (1.0), 1704 cm-1 (0.24)}. Finally, the approximate turnover frequencies (TOF) for each system were also calculated. It was found that the TOFs vary from 0.04 to 0.11 min-1 between alkene categories. Thus, to a first approximation, the primary differences in rates of hydroformylation are due to the conversion of Rh4(CO)12 and not TOFs. This answers a long-standing question concerning hydroformylation rates.

Synthesis and X-ray powder diffraction characterization of (OC)2RhCl2Rh(cod) (cod = cycloocta-1,4-diene)

In order to elucidate the nature and the structure of the elusive (OC)2Rh(Ph3SiO)2Rh(COd) (cod) = cycloocta-1,5-diene) complex, an important model compound for surface catalysis, (OC)2RhCl2Rh(cod) has been synthesized, and structurally characterized by ab initio X-ray powder diffraction. Crystals of (OC)2RhCl2Rh(cod) are monoclinic, space group P21/c, a = 6.659(1), b = 12.274(1) and c = 16.096(1) A, β= 92.176(5)°, Z = 4, ρcalc = 2.209 g cm-3. The structure has been solved, from powder diffraction data only, by Patterson and Fourier-difference methods and has been ultimately refined, by the Rietveld method, down to Rp = 0.116 and Rwp = 0.154 for 4050 data points collected in the 12-93° (2θ) range. The molecule contains two square-planar rhodium atoms, one bearing two terminal carbonyls and the other bound to the chelating cod fragment, and two chlorine atoms bridging the Rh...Rh vector. The Rh2Cl2 core is markedly non-planar, the dihedral angle about the Cl...Cl hinge being 135.4(6)°.

Formation of anionic carbonylrhodium complexes from Wilkinson's complexes under conditions of hydroformylation of formaldehyde

The compositions and the dynamics of transformations of carbonylrhodium complexes formed from Wilkinson's complexes, RhCl(PPh3)3, dissolved in mesitylene-N,N-dimethylacetamide (DMAA) mixtures in which the DMAA concentration varied from 0 to 100 percent, in an atmosphere of synthesis gas (pCO+H2 = 6 MPa, T = 373 K) were investigated in situ by IR spectroscopy.The anion complexes, - (x = 1, 2; y = 1, 0) and -, which are the centers of formaldehyde hydrofomylation, are produced in noticeable quantities when 100 percent DMAA is used as a solvent.Separate steps of the formation of anionic complexes from RhCl(PPh3)3 have been identified.Under the conditions of hydroformylation of formaldehyde, CH2O participates in the formation of the anionic complexes along with DMAA.

Rhodium carbonyl cluster chemistry under high pressure of carbon monoxide and hydrogen. 3. Synthesis, characterization, and reactivity of HRh(CO)4

The fragmentation of Rh4(CO)12 in dodecane solutions under 1241-1379 atm of carbon monoxide at 5-12°C has been established by high-pressure infrared spectroscopy to give Rh2(CO)8. Noticeable spectral changes are caused by the introduction of small amounts of hydrogen (1542 atm, CO:H2 = 4.5:1). Fourier subtraction of the spectra of these two species left bands at 2070 (m), 2039 (vs), and 2008 (w) cm-1. By analogy to the spectra previously observed for HIr(CO)4 and HCo(CO)4 this pattern is assigned to HRh(CO)4, a species that has eluded previous attempts of detection. The reaction of [M(CO)4]- (M = Co, Rh, Ir) with protonic acids in tetraglyme-toluene under high pressure of carbon monoxide resulted in the formation of HM(CO)4 (M = Co, Rh, Ir), with the reaction having been readily detected in the case of iridium with phosphoric acid (Ir:P = 0.38:4.12), while a stronger acid such as sulfuric acid was required for cobalt (Co:S = 0.95:29.9) and rhodium (Rh:S = 0.90:29.4) for the detection of a similar reaction. These results suggest that the proton affinity of these ions varies as [Ir(CO)4]- > [Co(CO)4]- > [Rh(CO)4]-. The differences in the acid strength of the corresponding conjugate acids, HM(CO)4 (M = Co, Rh, Ir), was determined under high pressures of CO-H2 by reaction with amines of different basicities such as N-methylmorpholine (pK(water, 25°C) = 7.4) and N,N-dimethylaniline (pK(water, 25°C) = 4.8) after formation of the tetracarbonylmetal hydrides, in situ. HIr(CO)4 is not deprotonated in a detectable fashion by N-methylmorpholine (Ir:N = 1:10), while HCo(CO)4 is deprotonated by this amine (Co:N = 2.4:1.0) but not by N,N-dimethylaniline (Co:N = 2.4:3.0). By contrast HRh(CO)4 readily undergoes deprotonation with this amine (Rh:N, = 2.7:1.0). These results correspond to the following trend in Br?nsted acidity: HRh(CO)4 > HCo(CO)4 > HIr(CO)4.

RHODIUM CARBONYL COMPLEXES WITH TROPOLONES, SALICYLALDEHYDE AND SALICYLALDIMINE SCHIFF BASES

The preparation and properties of rhodium complexes of the general formulae Rh(A)(CO)2 and Rh(A)(CO)L (A=tropolone (trop), Me-trop, i-Pr-trop, salicylaldehyde (sal) are described.The coordinated salicylaldehyde moiety of (Y2=COD, (CO)2, (CO)PPh3) complexes react with primary amines to yield Rh(sal=NR)Y2 derivatives.Rh(sal=NMe)(CO)2 can be formed by addition of salicylaldehyde to the solution obtained by refluxing RhCl3*xH2O with dimethylformamide.