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

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

2tBu−
3. These ligands are so large that their complexes behave differently from the pentamethylcyclopentadienyl analogues. Because they cannot closely approach the metal, these bulky ligands stabilize high spin complexes, such as (C5H2tBu3)2Fe2I2. These large ligands stabilize highly unsaturated derivatives such as (C5H2tBu3)2Fe2N2.

## Synthesis and reactions[edit]

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]

## References[edit]

1. ^ a b Reiners, Matthias; Ehrlich, Nico; Walter, Marc D. (2018). "Synthesis of 1,3,5-Tri-tert-Butylcyclopenta-1,3-diene and Its Metal Complexes Na{1,2,4-(Me3C)3C5H2} and Mg{η5-1,2,4-(Me3C)3C5H2)2". Inorganic Syntheses. 37: 199. doi:10.1002/9781119477822.ch8.
2. ^ Hyster, Todd K. (2015). "1,3-Di-tert-butylcyclopentadiene". Encyclopedia of Reagents for Organic Synthesis: 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.

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Organometallic chemistry

Principles|

* Crystal field theory
* Ligand field theory
* 18-electron rule
* d electron count
* Polyhedral skeletal electron pair theory
* Isolobal principle
* π backbonding
* Dewar–Chatt–Duncanson model
* Hapticity
* spin states
* Agostic interaction
* Metal–ligand multiple bond

Reactions|

* Oxidative addition / reductive elimination
* Migratory insertion
* β-hydride elimination
* Transmetalation
* Carbometalation

Types of compounds|

* Gilman reagents
* Grignard reagents
* Cyclopentadienyl complexes
* Transition metal indenyl complexes
* Transition metal fullerene complexes
* Metallocenes
* Metal tetranorbornyls
* Sandwich compounds
* Half sandwich compounds
* Transition metal acyl complexes
* Transition metal carbene complexes
* Transition metal carbyne complexes
* Transition metal alkene complexes
* Transition metal alkyne complexes
* Transition-metal allyl complexes
* Transition metal carbides

Applications|

* Carbonylation
* Cativa process
* Grignard reaction
* Monsanto process
* Olefin metathesis
* Shell higher olefin process
* Ziegler–Natta process

Related branches of chemistry|

* Organic chemistry
* Inorganic chemistry
* Bioinorganic chemistry

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