Question

It has been suggested that there is a similarity between the bonding of \(\mathrm{C}_{2} \mathrm{H}_{4}\) to \(\mathrm{CH}_{2}\) in cyclopropane, \(\mathrm{C}_{3} \mathrm{H}_{6}\), and the Chatt-Duncanson model of the bonding of the \(\mathrm{C}_{2} \mathrm{H}_{4}\) to \(\mathrm{Pt}\) in Zeise's salt. Critically assess this suggestion.

Short answer

While the bonding of \(\mathrm{C}_{2} \mathrm{H}_{4}\) in cyclopropane and Zeise's salt both involve ethene exhibiting planar structures, the nature of the bonds differ. Bonding in cyclopropane is typified by \(sp^{2}\) hybridization and involves resonance, leading to greater delocalization of \(\pi\) electrons than in Zeise's salt. In Zeise's salt, the \(\pi\) electrons of ethene donate into an empty d-orbital of platinum, forming a coordinate bond guided by the Chatt-Duncanson model. Thus, while there are similarities, there are also distinct differences.

Step-by-step solution

Understand the components

First, understand what each component represents. \(\mathrm{C}_{2} \mathrm{H}_{4}\) is the molecular formula for ethene, \(\mathrm{CH}_{2}\) represents a part of a methylene group, and \(\mathrm{C}_{3} \mathrm{H}_{6}\) corresponds to cyclopropane. Zeise's salt is a complex compound with the formula \(\mathrm{K}[PtCl_3(\eta^2-C_2H_4)]·H_2O\). The key part of Zeise's salt being compared here is how ethene (\(\mathrm{C}_{2} \mathrm{H}_{4}\)) bonds to platinum (\(\mathrm{Pt}\)).

Analyze Cyclopropane bonding

Cyclopropane (\(\mathrm{C}_{3} \mathrm{H}_{6}\)) represents a small cyclic alkane where the three carbon atoms form a ring. The \(\mathrm{C}_{2} \mathrm{H}_{4}\) (ethene) molecule presents in the planar form and forms a bond with a \(\mathrm{CH}_{2}\) group. The bond is characterized by \(sp^{2}\) hybridization and involves resonance which is a characteristic feature of cyclic compounds. This form of bonding helps in delocalizing the pi electrons and stabilizes the ring structure.

Analyze Zeise's salt bonding

In Zeise's salt, the ethylene (\(\mathrm{C}_{2} \mathrm{H}_{4}\)) molecule also forms a planar structure and bonds with platinum. It takes place by accepting electron pairs into the empty orbitals of platinum to form a coordinated bond. The concept is explained by the Chatt-Duncanson model, which indicates a metal to olefin bond where the \(pi\) electrons of the olefin (\(\mathrm{C}_{2} \mathrm{H}_{4}\)) donate into an empty metal d-orbital, forming a coordinate bond.

Compare bonding forms

Both the bonding in cyclopropane and Zeise's salt seem to have similar planar formations of the ethene molecule. However, in cyclopropane, the \(\mathrm{CH}_{2}\) uses the \(sp^{2}\) hybrid orbitals to overlap, forming a sigma bond and pi bond with the ethene \(\pi\) electrons. In contrast, the bonding in Zeise's salt involves donation of electron pairs into an empty d-orbital of platinum to form a coordinate bond. The electrons are somewhat delocalized, but not as much as in a cyclic compound like cyclopropane. There are similarities in the interaction, but also clear differences.

Key concepts

Zeise's Salt

Zeise's salt, known by its chemical formula \(\mathrm{K}[\mathrm{PtCl}_3(\eta^2-\mathrm{C}_2\mathrm{H}_4)]\cdot\mathrm{H}_2\mathrm{O},\)is an intriguing example of a coordination compound. It is famous for its unusual structure where ethene (\(\mathrm{C}_2\mathrm{H}_4\)) binds to a platinum center. This complex marks an important historical point in coordination chemistry as it was one of the first to highlight metal-olefin interactions.
The key process in Zeise's salt involves a

• donation of electron density from the \(\pi\)-bond of ethene into an empty \(d\)-orbital of platinum,
• back-donation from filled metal \(d\)-orbitals back into the antibonding \(\pi^*\) orbitals of ethene.

These interactions create a stable metal-olefin bond where electron density is shared between the metal and the ethylene ligand.
The discovery and study of Zeise's salt paved the way for the understanding of transition metal-olefin complexes which are essential in many industrial catalytic processes.

Coordinate Bonding

Coordinate bonding, also known as dative covalent bonding, is a vital concept in chemistry that connects molecules with metals. In this type of bonding, one atom provides both electrons needed to form a bond - a key feature distinguishing it from covalent bonds where electrons are shared equally.
The process of coordinate bonding can be broken down into :

• One atom, the donor, has a lone pair of electrons.
• Another atom, the acceptor, typically a metal, has vacant orbitals to accommodate this lone pair.

For example, in Zeise's salt, ethene donates its \(\pi\) electrons to platinum, forming a coordinate bond. The nature of these bonds means they are often strong and can influence the geometry and reactivity of the compounds they form.
By understanding coordinate bonding, chemists can predict and control how molecules behave in complex systems, allowing the creation of compounds with desired properties.

Cyclopropane Bonding

Cyclopropane (\(\mathrm{C}_3\mathrm{H}_6\)) is a fascinating compound due to its unique bonding characteristics. In this small cyclic molecule, three carbon atoms are bonded into a strained ring structure that challenges traditional understanding of carbon bonding.
Despite being a simple three-carbon ring, cyclopropane involves a complex interplay of:

• \(sp^{2}\) hybridized carbon atoms,
• sigma bonds formed by the overlap of these hybrid orbitals.

Additionally, cyclopropane's bonds exhibit a property called resonance, which allows delocalization of electrons within the ring. This delocalization affords the compound unusual stability despite its significant ring strain.
Though initially appearing similar to planar bonding in coordination complexes like Zeise's salt, cyclopropane's bonding is rooted in organic chemistry principles, focusing on carbon-carbon interactions rather than metal-ligand coordination. This highlights the diverse nature of chemical bonds and the versatility of carbon in forming varying structures.