Question 1

What is [Co(salen)]2 and why is it used in bioinorganic chemistry?

Accepted Answer

[N,N'-Bis(salicylaldehyde)ethylenediimino]cobalt(II), or [Co(salen)]2, is an organometallic complex that models oxygen-transporting metalloproteins like hemoglobin. Synthetic inorganic chemists use molecular species such as [Co(salen)]2 to study how metal complexes reversibly bind O2, helping researchers understand metalloprotein active sites and oxygen transport mechanisms in living organisms.

Question 2

How do the active and inactive forms of [Co(salen)]2 differ structurally?

Accepted Answer

The active form contains a heterodimer where two cobalt centers interact via weak van der Waals forces, creating space for O2 insertion. In the inactive form, cobalt centers form dative bonds with oxygen atoms on adjacent molecules, decreasing spacing. DMSO, a coordinating solvent, can stabilize the O2 adduct in the inactive form by completing the octahedral coordination sphere around each cobalt center.

Question 3

What is the role of DMSO in [Co(salen)]2 oxygen binding?

Accepted Answer

DMSO is a coordinating solvent that stabilizes the O2 adduct by completing the octahedral coordination sphere of each cobalt center in the inactive [Co(salen)]2 form. When O2 coordinates end-on to the two cobalt centers, DMSO facilitates formation of a 2:1 complex. Without DMSO, molecular O2 cannot fit between the cobalt units due to decreased spacing.

Question 4

How is oxygen binding to [Co(salen)]2 a redox reaction?

Accepted Answer

Oxygen binding involves electron transfer: two cobalt centers each lose one electron, while the O2 molecule gains two electrons, forming a peroxide ion (O22-). Oxygen has two unpaired electrons in its π* molecular orbital with a triplet ground state, while [Co(salen)]2 has one unpaired electron. This orbital overlap enables the redox interaction between the complex and molecular oxygen.

Question 5

How can you determine the Co:O2 ratio in the [Co(salen)]2-O2 reaction?

Accepted Answer

The Co:O2 ratio is determined by measuring the volume of O2 consumed in a closed system. Using the ideal gas law with recorded temperature and pressure, the moles of consumed O2 are calculated. Dividing the moles of cobalt in [Co(salen)]2 by the moles of O2 yields the stoichiometric ratio, which typically approaches 2:1 in experimental conditions.

Question 6

Why does adding CHCl3 reverse oxygen binding in [Co(salen)]2?

Accepted Answer

CHCl3 is a non-coordinating solvent that cannot stabilize the O2 adduct. When added to the [Co(salen)]2-O2 complex, CHCl3 decreases DMSO concentration and shifts the reaction equilibrium toward reactants, causing O2 release. This reversibility demonstrates that oxygen binding is equilibrium-dependent on the presence of coordinating solvents like DMSO.

Question 7

What applications do chiral salen complexes have beyond oxygen transport studies?

Accepted Answer

Chiral salen complexes are used in hydrolytic kinetic resolution to separate racemic mixtures, such as epichlorohydrin, which is difficult to produce in enantiopure form. A polystyrene-supported chiral salen ligand selectively hydrolyzes one enantiomer in the presence of water. The polymer-supported catalyst can be filtered and reused, making this approach efficient for producing enantiopure compounds.

Synthese van een zuurstofdragend kobalt(II)-complex

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