Influence of ring methylation in group 15 tetramethylcyclopentadienyl complexes, M(C5Me4H)nI3-n (M = As, Sb)

Stephen C. Chmely, Timothy P. Hanusa, Arnold L. Rheingold

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Arsenic and antimony triiodide react with 3 equiv of Na[C 5Me4H] in THF to form the yellow tris(tetramethylcyclopentadienyl) derivatives M(C5Me 4H)3 in 61% and 76% yields, respectively. When equimolar amounts of SbI3 and Na[C5Me4H] react in THF, the orange diiodo species Sb(C5Me4H)I2 is produced in 87% yield. The effect on the complexes of the methylated cyclopentadienyl rings varies from minimal to substantial. For example, the properties of the antimony compound Sb(C5Me4H)3 are similar to those of the unsubstituted complex Sb(C5H 5)3; in contrast, As(C5Me4H) 3 and Sb(C5Me4H)I2 are considerably more thermally stable than their parent versions. The complexes are fluxional on the 1H NMR time scale at room temperature. A single-crystal X-ray structure of As(C5Me4H)3 reveals three σ-bound rings with strongly localized bonding. The As-C distances are nearly identical, averaging 2.033(3) Å, and the C-As-C angles range from 96.4° to 109.3°. The antimony structure is similar, with average Sb-C bonds of 2.238(6) Å and C-Sb-C angles from 93.6° to 107.7°. The diiodo complex Sb(C5Me4H)I2 displays an η3-bound ring and forms a coordination polymer in the solid state, with ordering driven by intermolecular I⋯I′ and Me⋯Me′ van der Waals attractions. The structures of As(C 5H5)3, As(C5Me4H) 3, and Sb(C5H5)3 were examined with density functional theory calculations; these indicate that the energy barrier for haptotropic rearrangements is roughly the same in the arsenic compounds, 12-15 kcal mol-1, but is about half that for the antimony complex.

Original languageEnglish (US)
Pages (from-to)5551-5557
Number of pages7
Issue number21
StatePublished - Nov 8 2010

All Science Journal Classification (ASJC) codes

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry


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