Bulky cyclopentadienyl ligands

Structure of tBu3C5H3, a prototypical bulky cyclopentadiene.

In the area of organometallic chemistry, a bulky cyclopentadienyl ligand is jargon for a ligand of the type C
5H
5−nR−
n where R is a branched alkyl and n = 3 or 4. Representative examples are the tetraisopropyl derivative C
5HiPr−
4 and the tris(tert-butyl) derivative 1,2,4-C
5H
2tBu−
3. These ligands are so large that their complexes behave differently from the analogues derived from pentamethylcyclopentadienyl, itself a bulky ligand.

General properties of complexes

Because they cannot closely approach the metal, these bulky ligands can stabilize high spin complexes, such as (C5H2tBu3)2Fe2I2. These large ligands stabilize highly unsaturated derivatives such as (C5H2tBu3)2Fe2N2.

Synthesis and reactions

Structure of (tBu3C5H2)2Fe2N2.

The (tert-butyl)cyclopentadiene is prepared by alkylation of cyclopentadiene with tert-butyl bromide in the presence of sodium hydride and dibenzo-18-crown-6.[1] The intermediate in this synthesis is di-tert-butylcyclopentadiene. This compound is conveniently prepared by alkylation of cyclobutadiene with tert-butyl bromide under phase-transfer conditions.[2][1]

Illustrative of the unusual complexes made possible with these bulky ligands is molecular iron nitrido complex (tBu3C5H2)2Fe2N2.[3] In contrast to (C5Me5)2Ir2Cl4, (tBu3C5H2)IrCl2 is monomeric.[4]

Less bulky ligand are of the type C5H3R−2 where R is a branched alkyl. Examples include the di-tert-butyl and related trimethylsilyl derivatives. One such complex is U(C5H3(SiMe3)2)3.[5]

References

  1. ^ a b Reiners, Matthias; Ehrlich, Nico; Walter, Marc D. (2018). "Synthesis of Selected Transition Metal and Main Group Compounds with Synthetic Applications". Inorganic Syntheses. Vol. 37. p. 199. doi:10.1002/9781119477822.ch8. ISBN 978-1-119-47782-2.
  2. ^ Hyster, Todd K. (2015). "1,3-Di-tert-butylcyclopentadiene". Encyclopedia of Reagents for Organic Synthesis. pp. 1–2. doi:10.1002/047084289X.rn01866. ISBN 9780470842898.
  3. ^ Reiners, Matthias; Maekawa, Miyuki; Daniliuc, Constantin G.; Freytag, Matthias; Jones, Peter G.; White, Peter S.; Hohenberger, Johannes; Sutter, Jörg; Meyer, Karsten; Maron, Laurent; Walter, Marc D. (2017). "Reactivity studies on [Cp′Fe(μ-I)]2: Nitrido-, sulfido- and diselenide iron complexes derived from pseudohalide activation". Chemical Science. 8 (5): 4108–4122. doi:10.1039/C7SC00570A. PMC 6099922. PMID 30155215.
  4. ^ Shimogawa, Ryuichi; Takao, Toshiro; Suzuki, Hiroharu (2017). "Half-sandwich Cyclopentadienyl Iridium Dichloride Monomer Cp‡IrCl2 (Cp‡ = 1,2,4-tri-tert-butylcyclopentadienyl)". Chemistry Letters. 46 (2): 197–199. doi:10.1246/cl.160937.
  5. ^ Eralie, Dylan M. T.; Ducilon, John; Gorden, Anne E. V. (2025). "Uranium Chemistry: Identifying the Next Frontiers". Inorganic Chemistry. 64 (2): 767–784. doi:10.1021/acs.inorgchem.4c02173. OSTI 2477795. PMID 39190695.
allikas: http://en.wikipedia.org/wiki/Bulky_cyclopentadienyl_ligands