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.
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
Liu, Guowei,Garland, Marc
, p. 3457 - 3467 (2008/10/08)
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.
