Rhodocene

Rhodocene
Skeletal structure of the staggered conformation of rhodocene
Names
IUPAC name
Rhodocene
Other names
  • bis(cyclopentadienyl)rhodium(II)
  • dicyclopentadienylrhodium
  • rhodium(II) cyclopentadienide
Identifiers
3D model (JSmol)
ChemSpider
  • InChI=1S/2C5H5.Rh/c2*1-2-4-5-3-1;/h2*1-5H;/q2*-1;+2 checkY
    Key: IWAKCRNSZSPDTB-UHFFFAOYSA-N checkY
  • InChI=1/2C5H5.Rh/c2*1-2-4-5-3-1;/h2*1-5H;/q2*-1;+2
    Key: IWAKCRNSZSPDTB-UHFFFAOYAC
  • [cH-]1cccc1.[cH-]1cccc1.[Rh+2]
Properties
C10H10Rh
Molar mass 233.095 g·mol−1
Appearance yellow solid (dimer)[1]
Melting point 174 °C (345 °F; 447 K) with decomposition (dimer)[1]
Related compounds
Related compounds
 ferrocene, cobaltocene, iridocene, bis(benzene)chromium
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
☒N verify (what is checkY☒N ?)

Rhodocene is a chemical compound with the formula [Rh(C5H5)2]. Each molecule contains an atom of rhodium bound between two planar aromatic systems of five carbon atoms known as cyclopentadienyl rings in a sandwich arrangement. It is an organometallic compound as it has (haptic) covalent rhodium–carbon bonds.[2] The [Rh(C5H5)2] radical is found above 150 °C (302 °F) or when trapped by cooling to liquid nitrogen temperatures (−196 °C [−321 °F]). At room temperature, pairs of these radicals join via their cyclopentadienyl rings to form a dimer, a yellow solid.[1][3][4]

The history of organometallic chemistry includes the 19th-century discoveries of Zeise's salt[5][6][7] and nickel tetracarbonyl.[2] These compounds posed a challenge to chemists as the compounds did not fit with existing chemical bonding models. A further challenge arose with the discovery of ferrocene,[8] the iron analogue of rhodocene and the first of the class of compounds now known as metallocenes.[9] Ferrocene was found to be unusually chemically stable,[10] as were analogous chemical structures including rhodocenium, the unipositive cation of rhodocene[Note 1] and its cobalt and iridium counterparts.[11] The study of organometallic species including these ultimately led to the development of new bonding models that explained their formation and stability.[12][13] Work on sandwich compounds, including the rhodocenium-rhodocene system, earned Geoffrey Wilkinson and Ernst Otto Fischer the 1973 Nobel Prize for Chemistry.[14][15]

Owing to their stability and relative ease of preparation, rhodocenium salts are the usual starting material for preparing rhodocene and substituted rhodocenes, all of which are unstable. The original synthesis used a cyclopentadienyl anion and tris(acetylacetonato)rhodium(III);[11] numerous other approaches have since been reported, including gas-phase redox transmetalation[16] and using half-sandwich precursors.[17] Octaphenylrhodocene (a derivative with eight phenyl groups attached) was the first substituted rhodocene to be isolated at room temperature, though it decomposes rapidly in air. X-ray crystallography confirmed that octaphenylrhodocene has a sandwich structure with a staggered conformation.[18] Unlike cobaltocene, which has become a useful one-electron reducing agent in research,[19] no rhodocene derivative yet discovered is stable enough for such applications.

Biomedical researchers have examined the applications of rhodium compounds and their derivatives in medicine[20] and reported one potential application for a rhodocene derivative as a radiopharmaceutical to treat small cancers.[21][22] Rhodocene derivatives are used to synthesise linked metallocenes so that metal–metal interactions can be studied;[23] potential applications of these derivatives include molecular electronics and research into the mechanisms of catalysis.[24]

  1. ^ a b c d e f Cite error: The named reference El_Murr_1979 was invoked but never defined (see the help page).
  2. ^ a b Cite error: The named reference Crabtree was invoked but never defined (see the help page).
  3. ^ Cite error: The named reference Fischer_1966 was invoked but never defined (see the help page).
  4. ^ Cite error: The named reference Keller_1967 was invoked but never defined (see the help page).
  5. ^ Cite error: The named reference Zeise discovery was invoked but never defined (see the help page).
  6. ^ Cite error: The named reference Zeise review was invoked but never defined (see the help page).
  7. ^ Cite error: The named reference DCW 1 was invoked but never defined (see the help page).
  8. ^ Cite error: The named reference Hoffman was invoked but never defined (see the help page).
  9. ^ Cite error: The named reference FerroceneHistory was invoked but never defined (see the help page).
  10. ^ Cite error: The named reference Pauson_Kealy was invoked but never defined (see the help page).
  11. ^ a b c Cite error: The named reference JACS_1953 was invoked but never defined (see the help page).
  12. ^ Cite error: The named reference Dewar-Chatt-Duncanson was invoked but never defined (see the help page).
  13. ^ Cite error: The named reference ferrocene bonding was invoked but never defined (see the help page).
  14. ^ Cite error: The named reference Nobel Prize was invoked but never defined (see the help page).
  15. ^ Cite error: The named reference New Scientist Nobel Prize was invoked but never defined (see the help page).
  16. ^ Cite error: The named reference JACS_1982 was invoked but never defined (see the help page).
  17. ^ Cite error: The named reference He_PhD was invoked but never defined (see the help page).
  18. ^ Cite error: The named reference Collins_1995 was invoked but never defined (see the help page).
  19. ^ Cite error: The named reference cobaltocenium was invoked but never defined (see the help page).
  20. ^ Cite error: The named reference Rh in medicine was invoked but never defined (see the help page).
  21. ^ Cite error: The named reference Wenzel was invoked but never defined (see the help page).
  22. ^ Cite error: The named reference organ distrib was invoked but never defined (see the help page).
  23. ^ Cite error: The named reference linked metallocenes was invoked but never defined (see the help page).
  24. ^ Cite error: The named reference Wagner_2006 was invoked but never defined (see the help page).


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