28407-51-4Relevant articles and documents
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)]
Pomogailo,Chuev,Dzhardimalieva,Yarmolenko,Makhaev,Aldoshin,Pomogailo
, p. 1174 - 1177 (1999)
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.
Spectral resolution of fluxional organometallics. The observation and FTIR characterization of all-terminal [Rh4(CO)12]
Allian, Ayman D.,Garland, Marc
, p. 1957 - 1965 (2007/10/03)
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.
Unmodified Rhodium-Catalyzed Hydroformylation of Alkenes Using Tetrarhodium Dodecacarbonyl. The Infrared Characterization of 15 Acyl Rhodium Tetracarbonyl Intermediates
Liu, Guowei,Volken, Romeo,Garland, Marc
, p. 3429 - 3436 (2008/10/08)
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.
