494804-05-6Relevant articles and documents
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.
REVERSIBLE SYNTHESES OF MONO-(CYCLOPENTADIENYL)RHODIUM-TRI-RUTHENIUM CLUSTER COMPLEXES AND (η-C5Me5)2Rh2Ru2(CO)7; CRYSTAL AND MOLECULAR STRUCTURES OF CpRhRu32(CO)9, Cp = η-C5H5 OR η-C5Me5 AND (η-C5Me5)Rh2Ru32(CO)9
Lindsell, W. Edward,Knobler, Carolyn B.,Kaesz, Herbert D.
, p. 209 - 228 (2007/10/02)
The mixed metal complexes CpRhRu32(CO)9, (3a: Cp = η-C5H5; 3b: Cp = η-C5Me5) 4b: (η-C5Me5)RhRu34(CO)9, 5: (η-C5Me5)2Rh2Ru2(CO)7) are formed when H2 ia bubbled through solutions of Ru3(CO)12 and the respective CpRh(CO)2 at 70-90 deg C.These are easily disrupted at 25 deg C back into the starting materials under an atmosphere of CO.Using 13CO, the starting materials are obtained with complete 13CO exchange.While CpRh(CO)2 undergoes exchange at 25 deg C with 13CO at atmospheric pressure, Ru3(CO)12 does not, nor does it exchange in the presence of simply an added amount of CpRh(CO)2.Attachment of the CpRh moiety to the Ru3 skeleton as in the products obtained in this work thus leads, under 13CO, to the completely enriched starting materials Ru3(13CO)12 and CpRh(13CO)2.Structures of three new products have been determined using a Picker (FACS-1) four circle automated diffractometer and graphite-monochromatized Mo-Kα radiation.For 3a, 3831 unique reflections with I > 3?(I) were used in the refinement; final discrepancy indices, R = 0.030 and Rw = 0.050.Complex 3a crystallizes in the monoclinic space group P21/n; cell dimensions a 8.1856(5), b 15.0706(10), c 16.3013(12) Angstroem, and β 91.033(1) deg; calculated density 2.49 g cm-1.For 3b, 4801 unique reflections with I > 3?(I) were used in the refinement; final discrepancy indices, R = 0.026 and Rw = 0.042.Complex 3b crystallizes in the monoclinic space group P21/n in a cell having the dimensions of a 8.7580(5), b 14.5578(8), c 19.829(1) Angstroem, and β 97.591(2) deg, calculated density 2.18 g cm-3.For 4b, 6756 unique reflections with I > 3?(I) were used in the refinement; final discrepancy indices, R = 0.030 and Rw = 0.040.Complex 4b crystallizes in the monoclinic space group P21/a; cell dimensions a 17.470(1), b 18.451(1), c 17.200(1) Angstroem, and β 114.684(1) deg; calculated density 2.10 g cm-3.Metal atoms in all three structures were located by direct methods (MULTAN80).All other nonhydrogen atoms were then located by difference maps.Hydrogen atoms bridging various edges of the clusters were located after all hydrogen atoms in the η-C5H5 (= Cp) or η-C5(CH3)5 (= Cp*) groups were refined isotropically in calculated positions.Each of the crystals studied consists of discrete molecules of the complexes, each with a triangle of ruthenium atoms capped by a CpRh or Cp*Rh group.Isomeric structures are observed for 3a and 3b.In the former, a CO group is found bridging between one Ru atom and the Rh atom while one each of two cluster-bound hydrogen atoms bridge two separate edges of the Ru3 triangle.In 3b, both a CO group and one of the cluster-bound hydrogen atoms are found bridging between Rh and two separate Ru atoms of the Ru3 triangle.The remaining cluster-bonded hydrogen atom is found bridging one edge of the Ru3 triangle.In 4b, two of the cluster-bound hydrogen atoms are found (one each) on two edges of the Ru3 triangle.The other two are found bridging each of two of the Ru-Rh bonds.The metal-metal separations ...
