Ferrocenes and Enyl complexes Flashcards
What is the aromatic cyclic anion formed when a proton is removed from cyclopentadiene?
Cyclopentadienide.
Describe the typical electron count for ferrocene and its relevance to the 18-electron rule.
Ferrocene typically adheres to the 18-electron rule, with its structure involving 18 valence electrons distributed across bonding and antibonding orbitals.
How are cyclopentadienyl complexes synthesized?
By reacting sodium with cyclopentadiene under heat, then combining the result with a metal chloride.
Explain the interaction of metal d orbitals with cyclopentadienide ligands using molecular orbital theory.
Metal d orbitals, specifically dz2, show minimal overlap with the center of the Cp ring, while dxz and dyz orbitals have significant bonding interactions with Cp π-orbitals.
What characterizes a sandwich compound?
A sandwich compound typically involves a metal layered between two aromatic rings, such as in ferrocene, with 12 electrons filling 6 ligand to metal bonding orbitals.
How does the ExacTech pen meter utilize ferrocene?
The ExacTech pen meter uses ferrocene as an electron transfer agent for measuring blood glucose levels in diabetics.
Describe the ferrocene reaction involving Ph2PCl and AlCl3.
Ferrocene reacts with Ph2PCl and AlCl3 to form a complex by electrophilic attack, highlighting its ability to participate in organometallic reactions.
What type of ligand is cyclopentadienide and how many π-electrons does it donate?
Cyclopentadienide is an aromatic ligand that donates 6 π-electrons.
True or False: Cyclopentadienide complexes always result in high-spin configurations.
False. They can vary between high and low spin configurations depending on the metal and the electronic environment.
What changes occur in the molecular orbital diagram of a cyclopentadienyl metal complex during oxidation or reduction?
During oxidation, electrons are removed from the highest occupied molecular orbitals (HOMO), while reduction involves adding electrons to the lowest unoccupied molecular orbitals (LUMO).
Which orbital shows the least overlap in a metallocene like ferrocene according to the MO diagram?
The dz2 orbital shows the least overlap, due to its orientation relative to the Cp ring’s π-orbital.
Describe the role of ligand-to-metal bonding orbitals in metallocenes.
These orbitals facilitate the transfer of electrons from the ligand’s π system to the metal’s d orbitals, crucial for bonding and stability in metallocenes.
How is manganocene’s colour related to its electronic structure?
Manganocene’s colour arises from a charge transfer transition, likely involving electron movement between ligand-based and metal-based orbitals.
How does cobaltocene act as a reducing agent?
Cobaltocene donates electrons readily, making it an effective reducing agent. This property is attributed to its ability to lose electrons from a weakly anti-bonding LUMO.
Co(II) - d7 becomes Co(III) - d6: more stable configuration as now 18e- (not 19e-)
What is the significance of the HOMO and LUMO in ferrocene?
In ferrocene, the HOMO (highest occupied molecular orbital) can easily lose electrons, while the LUMO (lowest unoccupied molecular orbital) can gain electrons, important for redox reactions.
How does the reactivity at the metal differ from the reactivity at the ring in arenes?
Reactivity at the metal in arenes typically involves coordination and redox processes, whereas reactivity at the ring might involve electrophilic substitution or other organic transformations.
What is the outcome of SN2 attack on vinyl halide in metal-enyl complexes?
The SN2 attack results in the displacement of the halide and the formation of a σ-allyl complex, hapticity of 1
- often undergoes isomerization to a more stable π-allyl form. (Losing CO)
- metal is oxidised by 2 (SN2 attack is by metal)
Pi-allyl isomer is formally a 4e- donor - hapticity of 3
Describe the process and outcome of hydride abstraction in enyl complexes.
Hydride abstraction involves the transfer of 2 e- from the metal to the cyclohexadienyl ligand, losing H-.
- increasing the metal’s oxidation state by 2.
How is an enyl complex synthesized through proton abstraction?
Proton abstraction involves removing a proton from an alkene ligand to form a negatively charged enyl ligand.
- Metal’s oxidation state remains unchanged
- Electron count is unchanged
What is the outcome when cyclopentadienide complexes are protonated?
Protonation typically leads to the generation of hydrogenated derivatives of the complex, altering the electron density and potentially the reactivity of the complex.
What is the structural significance of the MO diagrams featuring dz2 and e1g orbitals in cyclopentadienyl complexes?
The dz2 orbital shows minimal overlap with the Cp ring, contributing little to bonding. In contrast, e1g orbitals (dxz, dyz) show significant overlap and contribute substantially to the bonding in these complexes.
What is the specific example of a reaction involving the synthesis of cyclopentadienyl complexes?
The synthesis of cyclopentadienyl complexes typically involves the reaction of cyclopentadiene with sodium (Na) under heat to form sodium cyclopentadienide, followed by its reaction with a metal chloride like FeCl2 to produce ferrocene.
Provide an example of a reaction where ferrocene undergoes electrophilic substitution.
Ferrocene reacts with acetyl chloride and AlCl3 to form acetylferrocene, an example of a Friedel-Crafts acylation, showcasing ferrocene’s susceptibility to electrophilic aromatic substitution.
What is an example of a metal complex that undergoes ligand protonation?
An example includes the protonation of a cobaltocene (CoCp2) to form cobaltocenium [(Cp)2Co]+ by proton donors such as H2SO4, illustrating changes in the oxidation state and the ligand’s electron density.
Explain a specific example of isomerization in metal-enyl complexes.
Following an SN2 attack and formation of a σ-allyl complex, isomerization can occur where the allyl group rearranges from a less stable σ-bound state to a more stable π-bound configuration, typically observed in complexes such as π-allyl nickel complexes.
