Question 1

Which of the following metal centres is likely to obey 18-electron rule in their organometallic compounds&#10;A) Nb(V)&#10;B) Ru(II)&#10;C) Ir(I)

Accepted Answer

B

Question 2

Identify the correct statement:&#10;A) CO is a weak $\sigma$donor but a good  $\pi$acceptor.&#10;B) C-O bond is stronger when CO is coordinated to an electron-rich metal.&#10;C) Ultraviolet spectroscopy can tell us a lot about M-CO bonding.

Accepted Answer

CO is a weak σ donor but a good π acceptor, which is why it forms strong bonds with metals by back-donation of electron density from the metal to the CO π* orbitals.

Question 3

Identify the best $\pi$acceptor among these phosphines: A) PCl₃ B) P(OEt)₃ C) P(i-Pr)₃

Accepted Answer

PCl₃ is the best F1F1F1S1F1F1F10 acceptor among these phosphines because it has the most electronegative substituents, which withdraw electron density from the phosphorus atom and make it more electrophilic.

Question 4

How many electrons can an allyl ligand donate? A) In $ \eta $¹ bonding mode two electrons with single negative charge, in $ \eta $³ mode three electrons with single negative charge. B) In $ \eta $¹ bonding mode two electrons with single negative charge, in $ \eta $³ mode four electrons with single negative charge. C) In $ \eta $¹ bonding mode one electron with single negative charge, in $ \eta $³ mode three electrons with single negative charge.

Accepted Answer

An allyl ligand can donate two electrons in the η^1 bonding mode and four electrons in the η^3 bonding mode, both with a single negative charge.

Question 5

Which of the following statements outline the similarities between $\eta$ ⁶-benzene and $\eta$ ⁵-cyclopentadienyl ligands?
(i) They are both six electron donors in donor-pair method of electron counting.
(ii) We can consider both to occupy three coordination sites around a metal center.
(iii) They have the same charge.

A) (i) and (ii)
B) (ii) and (iii)
C) All of them are correct.

Accepted Answer

(i) Both benzene and cyclopentadienyl ligands act as six electron donors when using the donor-pair method for electron counting. (ii) Both can occupy three coordination sites around a metal center, reflecting their ability to form η^6 and η^5 complexes, respectively.

Question 6

Which of the following carbonyls should be the easiest to reduce? A) [Fe(CO)₅] B) [Cr(CO)₆] C) [V(CO)₆]

Accepted Answer

The ease of reduction of carbonyl complexes generally increases with the electron density on the metal center. Vanadium (in option C) being less electronegative than iron and chromium, would have a higher electron density on the metal, making its carbonyl complex easier to reduce compared to those of iron and chromium.

Question 7

Identify the correct statement(s):&#10;(i) During an oxidative addition reaction, the oxidation state of the metal increases for two and the coordination number increases for two.&#10;(ii) A characteristic of reductive elimination is a decrease in both oxidation state and coordination number by 2.&#10;(iii) Sigma bond metathesis takes place as side-reaction during oxidative addition.&#10;A) All three&#10;B) (i) and (ii)&#10;C) (ii) and (iii)

Accepted Answer

(i) In an oxidative addition reaction, the oxidation state of the metal indeed increases by two units, and the coordination number also increases by two, as the metal forms bonds with two additional ligands. (ii) In a reductive elimination, the oxidation state of the metal decreases by two units, and the coordination number decreases by two as two ligands are removed from the metal center. (iii) Sigma bond metathesis is not necessarily a side-reaction during oxidative addition; it is a distinct reaction mechanism where a metal-ligand sigma bond and a substrate sigma bond exchange partners without a change in oxidation state or coordination number of the metal.

Question 8

Many metallocenes exhibit fluxionality and undergo internal rotation because:&#10;A) the energy barrier to the interconversion is nonexistent&#10;B) the energy barrier to the interconversion is low&#10;C) the energy barrier to the interconversion is infinite

Accepted Answer

The energy barrier to the interconversion in many metallocenes is low, which allows for fluxionality and internal rotation. This low energy barrier enables the molecules to easily change conformations.

Question 9

Beta hydride elimination is A) a reverse reaction of 1,2-insertion and occurs when the metal has an open coordination site and the organic ligand has hydrogen atoms on second carbon from the metal. B) elimination of two hydride ligands from one metal centre resulting in formation of H₂ and decrease in coordination number. C) elimination of hydrogen atom from the second carbon atom of the organic ligand coordinated to a metal centre using a strong base.

Accepted Answer

Beta-hydride elimination is a reaction where a hydrogen atom on the carbon adjacent (beta position) to the metal-carbon bond is transferred to the metal, leading to the formation of a C-H bond and the elimination of the metal from the organic fragment. This typically occurs when the metal has an open coordination site, allowing for the rearrangement, and the organic ligand has hydrogen atoms on the carbon next to the one directly bonded to the metal.

Question 10

Organometallic complexes of ________ and __________ are used as catalysts in olefin metathesis.&#10;A) Os and Fe&#10;B) Pt and Ir&#10;C) Ru and Mo

Accepted Answer

Ruthenium (Ru) and Molybdenum (Mo) are commonly used as catalysts in olefin metathesis reactions, a type of chemical reaction used in organic synthesis and polymer chemistry.

Deck 22: D-Metal Organometallic Chemistry