Organometallic Compounds MCQ Quiz in తెలుగు - Objective Question with Answer for Organometallic Compounds - ముఫ్త్ [PDF] డౌన్‌లోడ్ కరెన్

Explanation:

• The 1-norbornyl ligand is seen to form a stable complex with transition metal Cobalt through a Co-C bond.
• This can be attributed to the fact that it is bulky and it is less prone to β-Hydrogen elimination reaction.
• The oxidation state of metal cobalt in the complex  is +IV.
• The electronic configuration in the state is 3d⁵.
• It has been experimentally found that the complex is tetrahedral and it norbornyl induces pairing in the system.
• The CFSE of tetrahedral is not that strong to induce electron pairing and no low spin complexes of the first transition series have been identified before this.
• So, the CFSE looks like this:

​

• So, the number of unpaired electrons is one, and the geometry is tetrahedral.

Concept:

Hapticity refers to the number of contiguous atoms in a ligand that directly coordinate to a metal center in a complex. The hapticity of a ligand can vary depending on the temperature and the dynamics of the ligand’s interaction with the metal. In the case of metal complexes with cyclooctatetraene (C₈H₈) ligands, the hapticity can change with temperature, which affects the NMR spectrum:

• Room Temperature: At higher temperatures, ligands like C₈H₈ often exhibit a higher hapticity due to rapid coordination exchange, creating a symmetric environment.

• Low Temperature: At lower temperatures, the hapticity may decrease as the ligand "freezes" into a specific coordination mode, often resulting in an asymmetric environment and multiple peaks in the NMR spectrum.

• NMR Observation: Changes in hapticity are reflected in the NMR spectrum as the number of peaks corresponds to the number of different environments for the hydrogen atoms.

Explanation:

• For the complex Ru(ηⁿ-C₈H₈)(CO)₃, the NMR data shows:
  • At Room Temperature: Only one peak is observed in ¹H NMR, indicating that the C₈H₈ ligand is in a high-symmetry, rapidly exchanging coordination mode, likely η⁸.
  • At Low Temperature: Four peaks are observed, suggesting that the coordination mode has changed to a lower symmetry configuration, likely η⁴.
    • ​
• Thus, the change in hapticity from η⁸ at room temperature to η⁴ at low temperature corresponds to a difference of:
  • 8 - 4 = 4

Conclusion:

The difference in hapticity of the ligand between room temperature and low temperature is: 4 (Option 1).

CONCEPT:

Reaction of \([(η^5−C_5​H_5​)Fe(CO)_2​(C_2​H_5​)]\) with PPh₃

• This reaction follows a mechanism involving migration insertion and ligand substitution, common in organometallic chemistry.
• Migration Insertion: The ethyl group (C₂H₅) migrates from the iron center to one of the CO ligands, forming an acyl group (COC₂H₅). This is a critical step as it alters the bonding environment around the iron and increases the compound's stability and reactivity.
• Ligand Substitution: After the migration of the ethyl group, PPh₃ replaces one of the remaining CO ligands, completing the reaction and forming the final product where both an acyl group and PPh₃ are coordinated to the iron center.

EXPLANATION:

• Initial Complex: The starting material,\([(η^5−C_5​H_5​)Fe(CO)_2​(C_2​H_5​)]\) (commonly referred to as a cyclopentadienyl iron dicarbonyl ethyl complex), consists of an iron atom coordinated to two CO ligands, an ethyl group (C₂H₅), and a Cp ring \((η^5−C_5​H_5​)\). The Cp ring stabilizes the iron center, while the CO ligands and ethyl group complete the coordination sphere of the iron.
• Migration Insertion Mechanism: In this step, the ethyl group migrates from the iron center to one of the CO ligands, converting the CO ligand into an acyl group (COC₂H₅). Migration insertion is a key mechanism in organometallic chemistry where a ligand moves to a neighboring site, typically onto a carbonyl ligand, creating a stronger bond between the carbon and the migrating group. This transformation increases the stability of the complex by forming a more reactive and stabilized acyl group. The acyl group is much more reactive than an ethyl group due to the presence of the electron-withdrawing carbonyl functionality.
• Ligand Substitution by PPh₃: Once the migration occurs and the acyl group is formed, the next step involves the substitution of one of the remaining CO ligands by PPh₃. In this substitution, PPh₃ coordinates to the iron center, displacing one of the carbonyl ligands. Ligand substitution typically proceeds through an associative mechanism, where the incoming ligand (PPh₃) forms a bond with the iron before the CO ligand is displaced. This results in the final product, \([(η^5−C_5​H_5​)Fe(COC_2​H_5​)(CO)(PPh_3​)]\), where the iron is coordinated to the acyl group, one CO ligand, and PPh₃.
• Stabilization and Reactivity: The final product is stabilized due to the presence of the acyl group and PPh₃. Acyl groups are more reactive than alkyl groups due to the presence of the carbonyl group, making the complex more suitable for subsequent chemical reactions. The PPh₃ ligand, being a good electron donor, further stabilizes the iron center by donating electron density, balancing the electron-withdrawing effect of the remaining CO ligand.
•  
• 

CONCLUSION:

The correct product is \([(η^5−C_5​H_5​)Fe(COC_2​H_5​)(CO)(PPh_3​)]\), formed through the migration of the ethyl group to a CO ligand and subsequent ligand substitution by PPh₃.

The answer is Cr.

Concept:-

• 18-electron rule: This rule states that transition metal complexes are most stable when the metal atom's valence shell contains 18 electrons.
• Extended 18-electron rule (48-electron rule in this case): An adaptation of the 18-electron rule to handle more complex structures like metal clusters.
• Valence electrons: The outer shell electrons involved in forming bonds.
• Electron counting: A key concept in inorganic and organometallic chemistry, used to predict and explain the structure and reactivity of metal complexes.
• Metal Clusters: These are assemblies of metal atoms that have properties intermediate between a molecule and a solid and are often involved in catalysis.

Explanation:-

TVE = 3(M) + 3(6) + 3(4) =48
48 - 18-12 = 3M
18 = 3M

M=6
i,e Cr
Conclusion:-

So, the  metal M is Cr.

Concept:-

Coordination Complexes: These are molecules or polyatomic ions composed of a central atom (usually a metal) surrounded by non-metal atoms or groups of atoms, called ligands, which are linked to the central atom by coordinate covalent bonds.

Monodentate Ligands: Ligands that bind to the central atom at a single point. Examples include the water molecule, the ammonia molecule, and the carbonyl group in this situation.

Fullerenes: A form of carbon, such as C₆₀, in which the atoms form polyhedra rather than sheets (graphite) or closed tubes (nanotubes). Despite consisting of multiple atoms, a fullerene can act as a single ligand within a coordination complex.

Explanation:-

The structure of [W(C60)(CO)5] 

Proposed structure of the C₆₀-W(CO)₅ complex. It is suggested that the metal atom binds to C₁-C₂ atoms between the hexagonal rings in an n² fashion.

So W is connected to 5 carbons of CO and 2 carbons of C60. In total it is 7

Conclusion:-

The number of carbon atoms connected to the metal center in [W(C60)(CO)5] is 7

The correct answer is [PdCl4]2- and CuCl2

Concept:-

Catalysts: A catalyst is a substance that increases the rate of a chemical reaction by lowering the activation energy, but it does not undergo any permanent chemical change in the process. By providing an alternative reaction mechanism with lower activation energy, catalysts increase the rate at which reactions occur. In the Wacker process, palladium (Pd) is used as the catalyst.

Co-catalysts: Co-catalysts, also known as promoters, are substances that enhance the activity of a catalyst. They aren't as efficient as catalysts on their own but can improve the performance of the main catalyst. In the Wacker process, copper (Cu) is used as the co-catalyst.

Wacker Process: The Wacker process is an industrial procedure used to produce ethylene oxide from ethylene using a palladium catalyst and a copper co-catalyst. The actual process is a redox cycle, where palladium(II) reacts with ethylene, gets reduced to palladium(0), which is subsequently re-oxidized to palladium(II) by copper (II).

Redox Reactions: The term 'redox' comes from two concepts within the reaction: 'reduction' and 'oxidation'. Reduction means a gain of electrons, and oxidation means a loss of electrons. In the Wacker process, palladium is first oxidized (loses electrons) and then reduced (gains electrons) with the help of the copper co-catalyst.

Explanation:-

[PdCl₄]^2- is used as a catalyst during the reaction which transforms to Pd (0). Co-catalyst CuCl₂ is used to convert Pd (0) to Pd (II)

The initial stoichiometric reaction was first reported by Phillips.The net reaction can also be described as follows:

[PdCl₄]^{2 −} + C₂H₄ + H₂O → CH₃CHO + Pd + 2HCl + 2 Cl⁻
This conversion is followed by reactions that regenerate the Pd(II) catalyst:

Pd + 2 CuCl2 + 2 Cl − → [PdCl4]2− + 2 CuCl
2 CuCl + 1/2 O₂ + 2 HCl → 2 CuCl₂ + H₂O

Conclusion:-

So, The catalyst and co-catalyst used in the Wacker process, respectively, are [PdCl4]2- and CuCl2

Concept:-

• The structures of boranes can be classified according to the following scheme:
  • Closo boranes have the formula BnHn2- ions,
  • Nido boranes are formally derived from BnHn4- ions,
  • Arachno boranes are formally derived from BnHn6- ions,
  • Hypho boranes are formally derived from BnHn8- ions,
  • Klado boranes are formally derived from BnHn10- ions.
• The electron-counting schemes can be extended to isoelectronic species such as carboranes.
• The CH+ unit is isoelectronic with BH, many compounds are known in which one or more BH groups have been replaced by CH+ (or by C, which also has the same number of electrons as BH).
• This is Because a carbon atom has the same number of valence electrons as a boron atom plus a hydrogen atom, formally each C should be converted to BH.
• For example-

C2B8H10 → (BH)2B8H10 (C=BH)

B10H12 - 2 H+ = B10H102-

• The classification of the carborane C2B8H10 is therefore closo.
• The CH group of a carborane is isolobal with 15-electron fragments of an octahedron such as Co(CO)3. Similarly, BH, which has 4 valence electrons, is isolobal with 14-electron fragments such as Fe(CO)3 and Co(C5H5)2.
• Shown here are examples of organometallic fragments and their corresponding isolobal BHx fragments

• Using wades rule, the shape of Metallaboranes and Metallacarboranes are given having Closo Structures with the number of skeletal atoms (n). 

Explanation:-

1. C2B4H6Ni(PPh3)2

• For C2B4H6 fragment

C2B4H6 → (BH)2B4H6 (C=BH)

→ B6H8 

B6H8 

= B6H8 - 2 H+ 

= B6H62-

• While the Ni(PPh3)2 fragment is isolobal with the BH fragment as follows,

Ni(PPh3)2 = !0 + 2 × 2

= 14

= BH fragment

• Thus, the formula for C2B4H6Ni(PPh3)2 will be

C2B4H6Ni(PPh3)2 = B6H62- (BH)

= B7H72- (n=7)

• The classification of C2B4H6Ni(PPh3)2 is therefore closo having the number of vertices(n)=7.

• Hence, the shape of C2B4H6Ni(PPh3)2 (number of vertices=7) is Pentagonal bipyramidal.

2. [B9H9NiCp]-

• For [B9H9NiCp]- fragment

B9H₉^- → B9H10

• While the NiCp fragment is isolobal with the BH₂ fragment as follows,

NiCp = 10 + 5

= 15

= BH₂ fragment

• Thus, the formula for [B9H9NiCp]- will be

[B9H9NiCp]-= B9H10 (BH₂)

= B10H12 (n=10)

= B10H10^2- (n=10)

• The classification of the [B9H9NiCp]- is therefore closo having the number of vertices(n)=10.

• Hence, the shape of C2B6H8Pt(PMe2)3 (number of vertices=10) is a Bicapped square antiprism.

Conclusion:-

• Hence, the shape of C2B4H6Ni(PPh3)2 and [B9H9NiCp]- is Pentagonal bipyramidal and Bicapped square antiprism using the wades rule.​ 

The correct answer is Two

Concept:-

• EAN rule:   
• The EAN rule is given by Sidgwick.
• According to the EAN rule, the EAN of metal is equal to the sum of electrons on metal and the electrons donated by the ligands and the EAN is equal to the atomic number of the next noble gas.
• The EAN rule is applicable to organometallic complexes. The rule is similar to the 18 electron rule.
• According to this rule, the sum of valence electrons of transition metals or metal ions is equal to 18.
• The complexes in which the EAN rule is followed are considered stable. The first row of transition metal carbonyls mostly obeys the 18-electron rule. There are many complexes that do not follow the 18 electron rule. 
• The metal carbonyl clusters are classified into two types:     Low nuclearity carbonyl clusters  and High nuclearity carbonyl clusters

Explanation:-

• Calculation of the number of M-M bonds in compounds of Low Nuclearity
• Step 1: Calculate the total number of valence electrons TVE on the central atom in the compound say A which is the total number of valence electrons from the metal, the ligands, and the charge.
• Step 2: Subtract A from n × 18; where n is the number of metal atoms in the compound say it is B.
• So, B = n × 18 - A.
• Step 3: The value of B/2 gives the total number of M-M bonds.
• The value A/n gives the number of electrons per metal.
• In the complex given [(η 5 - C5H5)Mo(CO)2]₂ ^2-  the ligand cyclopentadienyl ligand contributes 5 electrons, carbonyl donates two electrons. Manganese has seven valence electrons, so the value of

A = 5 × 2 + 6 × 2 + 4 × 2 +2 = 32.

The value of B = 2 × 18 - 32 = 36 - 32 = 4.

The value of B/2 = 4/2 = 2.

Conclusion:-

Hence, the number of Mo-Mo bonds is two.

Concept:

• Wade’s rules are used to predict the shape of borane clusters by calculating the total number of skeletal electron pairs (SEP) available for cluster bonding. This rule also helps to predict the shape of transition metal polyhedral complexes.

→When applying Wade’s rules these rules are followed:

• Calculate the total number of valence electrons from the chemical formula, i.e., 3 electrons per B, 4 electrons per C, and 1 electron per H.
• A cluster with 4n+2 electrons has a closo structure.
• A cluster with 4n+4 electrons has a nido structure.
• A cluster with 4n+6 electrons has an arachno structure.
• A cluster with 4n+8 electrons has an hypho structure.

Explanation:-

• Total number of valence electrons for \(\rm Bi^{3+}_5\) 

= 5 × 5 - 3

= 22

• Hence, it follows the (4n + 2) rule, for n = 5
• Thus, \(\rm Bi^{3+}_5\) has a close structure.
• On addition of 2 electrons, the total number of valence electrons for it become

​= 22 + 2

= 24

• Hence, now it follows the (4n + 4) rule, for n = 5 
• The geometry will be Nido/

Conclusion:-

• Hence, the Addition of two electrons to the bismuth cluster \(\rm Bi^{3+}_5\) results in a change in structure type from closo to nido.
• Correct option is (a)

Concept: 

EAN rule:-

• EAN stands for an effective atomic number.
• This rule was given by SIDGWICK.
• According to the EAN rule, the EAN of metal is equal to the sum of electrons of metal and the electrons donated by ligands and EAN is equal to the atomic no. of the next noble gas.
• This concept explains the stability and the possibility of complex compound formation. According to this concept, only that complex compound can be formed that will attain the noble gas configuration. 
• This rule is applicable to organometallic compounds.
• The EAN rule is similar to the 18 e^- rule.
• The transition element on the left side of the periodic table  (Examples are Scandium, Titanium, etc) don't follow this rule because they have fewer valence electrons and to fulfill the EAN rule more ligands need to be attached to give electrons which will increase coordination number greater than 6 which is not possible and create a steric hindrance. Examples are Scandium, Titanium, etc.
• Examples of complex obeying EAN rule:  Cr(CO)₆  
  • The contribution from chromium is 6 electrons (4s¹ 3d⁵)
  • Carbonyl is a neutral ligand and it always contributes 2 electrons.
  • EAN =6 + 2 × 6 = 18

Explanation: 

1) V(CO)3 (\({\eta ^2}\)- C5H8)(R2C = CR2) 

• The contribution from vanadium is 5 electrons (4s² 3d³)
• Carbonyl is a neutral ligand and it always contributes 2 electrons. 
• The contribution from (\({\eta ^2}\) - C5H8) is 2 electrons because it is the coordinate bond between metal and a double bond.
• Similarly, R₂C = CR₂ contributes 2 electrons from the double bond.

​

EAN = 5+( 2 ×  3) +2 +2 =15 

Hence it doesn't obey EAN rule.

2)  Co(CO)3 (\({\eta ^2}\) - C5H8)

• The contribution from cobalt is 9 electrons (4s² 3d⁷)
• Carbonyl (CO) contributes 2 electrons.
• The contribution from (\({\eta ^2}\) - C5H8) is 2 electrons because it is the coordinate bond between metal and a double bond.

​

​EAN = 9 +(2 × 3) +2 =17

Hence it doesn't obey the EAN rule.

3) Fe(\({\eta ^1}\)- C5H5)(\({\eta ^2}\) -C5H5)(CO)3

• The contribution from iron is 8 electrons 4s² 3d⁶
• Carbonyl contributes 2 electrons.
• Contribution from (\({\eta ^2}\) -C5H5 is 2 electrons.
• The contribution from the σ bond in (\({\eta ^1}\) - C5H5) is 1 electron.

​

• The contribution from chromium is 6 electrons (4s1 3d5)
• Carbonyl contributes 2 electrons.
•  The contribution from benzene (\({\eta ^6}\)- C6H6) is 6 electrons.

​