Cyclopentadienylindium(I) Explained

Cyclopentadienylindium(I), C₅H₅In, is an organoindium compound containing indium in the +1 oxidation state. Commonly abbreviated to CpIn, it is a cyclopentadienyl complex with a half-sandwich structure.It was the first (1957^[1]) low-valent organoindium compound reported.

Preparation and chemistry

CpIn can be readily prepared by reacting indium(I) chloride with cyclopentadienyllithium:^[2]

InCl + CpLi → CpIn + LiCl

InCp reacts with BF₃, BCl₃, BBr₃, BI₃ and trimethylborane B(CH₃)₃ to form adducts,^[3] e.g.:

CpIn + BF₃ → CpIn·BF₃

In these adducts the bonding of the Cp ligand to the indium atom changes from η⁵ (π complexing) to η¹ (σ bonding).

Salts containing the InX₂⁻ anion containing indium in the +1 oxidation state have been prepared from cyclopentadieneindium; for example:^[4]

CpIn + HCl + N(Et₄)Cl → N(Et₄)InCl₂+ C₅H₆

Structure and bonding

Solid CpIn is polymeric consisting of zigzag chains of alternating indium atoms and C₅H₅ units. Two indium atoms interact with the opposite faces of each C₅H₅⁻ ring, nearly perpendicularly to the ring plane, and two rings interact with each indium atom, forming an angle of about 128°.^[5] In the CpIn monomer present in the vapour phase the indium atom sits on the central axis of the aromatic cyclopentadienyl anion, C₅H₅⁻.

Bonding studies have shown that the aromatic ring electrons of the cyclopentadienyl anion interact with the indium 5s and 5p atomic orbitals, and that the lone pair on the indium atom is a dominant feature.^[6]

Notes and References

1. Metall-cyclopentadienyle des Indiums. Fischer E.O. . Hofmann H.P. . Angew. Chem.. 1957. 69. 20. 639. 10.1002/ange.19570692008 . 1957AngCh..69..639F .
2. A simple synthesis of cyclopentadienylindium(I). Peppe C. . Tuck D.G. . Victoriano L. . J. Chem. Soc., Dalton Trans.. 1981. 69. 12. 2592. 10.1039/DT9810002592.
3. Coordination compounds of indium. XXIII. Adducts of cyclopentadienylindium(I) with boron trihalides or trimethylboron. Contreras J. G. . Tuck D. G. . Inorganic Chemistry. 1973. 12. 11. 2596–2599. 10.1021/ic50129a021.
4. Co-ordination compounds of indium. Part XXXI. Further studies of anionic complexes of indium(I). Habeeb J.J. . Tuck D.G. . J. Chem. Soc., Dalton Trans.. 1976. 10. 866–869. 10.1039/DT9760000866.
5. Synthesis, characterization and structural studies of In(C₅H₄Me) by x-ray diffraction and electron diffraction techniques and a reinvestigation of the crystalline state of In(C₅H₅) by x-ray diffraction studies . Beachley O. T. . Pazik J. C. . Glassman T. E. . Churchill M. R. . Fettinger J.C. . Blom R. . Organometallics . 1988. 7 . 5 . 1051–1059 . 10.1021/om00095a007 .
6. The electronic structure of cyclopentadienylindium. Lin C.S. . Tuck D.G. . Can. J. Chem.. 1982. 60. 6 . 699–702. 10.1139/v82-103.