Chem 400

Inorganic Chemistry

Practice Exam 3

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(please print)

1. Show all the steps (i.e., draw the catalytic cycle) for the Monsanto acetic acid synthesis. Include a detailed description of the processes taking place and point out the rate determining step. (10 points)

MeOH + CO → MeCO2H

Two interrelated cycles:

IVV

IRh

I CO

CO

Me

I

CORh

II

I

O

CO

CORh

IOC

I

OI

HI H2O

MeOH MeI

RhCO

I CO

I

O

I

O

OH

I

II

III

VI

-

-

-

-

I: MeOH is converted to MeI, rate determining step, critical for whole process; II: MeI enters the Rh-cycle, oxidative addition to the 16-electron complex cis-[Rh(CO)2I2]; III: methyl migration to form 5 coordinate, 18 electron species (dimer at 253 K, solvated monomer above 273 K); IV: addition of CO, formation of octahedral 18-e- complex; V: elimination of MeC(O)I, enters left handed cycle; VI: formation of acetic acid.

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2. [Co(NH3)6]2+ has absorption bands at 9,000 and 21,100 cm-1. Calculate ∆0 and B for this ion, using the attached Tanabe-Sugano Diagram. Hint: The 4T1g → 4A2g transition in this complex is too weak to be observed. (10 points)

[Co(NH3)6]2+, d7. ν2/ ν1 = 2.34 at ∆0/B = 11 From the Tanabe-Sugano diagram at ∆0 = 11 ν1: E/B = 10 E = 10 B = 9000 cm-1 B = 900 cm-1

ν2: E/B = 22.5 E = 22.5 B B = 21,100 cm-1 B = 938 cm-1

Average B = 920 cm-1 ∆0 = 10,120 cm-1

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3. State the types of isomerism that may be exhibited by the following complexes, and draw structures of the isomers. (4 points each)

a. [Co(en)2(ox)]+ optical isomers

NCo

N O

N

O

N

+

NCo

O N

N

O

N

+

b. [Cr(ox)2(H2O)2]- trans isomer, cis isomer with two optical isomers

OCr

O O

O

OH2

OH2

-

OCr

O O

OH2

O

OH2

-

H2OCr

O O

O

O

OH2

-

c. [Co(en)(NH3)2Cl2]2+

may have trans-Cl, trans-NH3, or both sets mutually cis and for the latter, there are also optical isomers.

NCo

N NH3

NH3

Cl

ClN

CoN Cl

Cl

NH3

NH3

+ +

NCo

N NH3

Cl

Cl

NH3

ClCo

H3N N

N

Cl

NH3

+ +

d. [PtCl2(PPh3)2] cis- and trans-isomers

Cl Pt

PPh3

PPh3

Cl Cl Pt

PPh3

Cl

PPh3

e. [Co(en)3]3+

optical isomers

NCo

N N

N

N

NN

CoN N

N

N

N

3+ 3+

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4. Describe the bonding in (η4-C4H4)Fe(CO)3 (i.e., develop MO diagrams for both the C4H4 fragment and the Fe(CO)3 fragment). Explain why the complex is diamagnetic. (10 points)

FeOC CO

CO

ψ1

ψ2 ψ3

ψ4

EMO

dxz dyz

pzdz2

EMO

The Fe(CO)3 unit provides 2 electrons and the C4H4 ligand has 4π-electrons. Match fragment orbitals by looking at their symmetry: the Fe pzdz2 hybrid overlaps with ψ1 of the organic ligand, and the Fe dxz and dyz orbitals overlap with ψ2 and ψ3 of the ligand. Orbital ψ4 becomes non-bonding in (η4-C4H4)Fe(CO)3. In the complex, there are 3 bonding MOs involving Fe-C4H4 character and the 6 electrons fully occupy there MOs – electrons are paired and the complex is diamagnetic.

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5. Give likely products for the following reactions. Do not forget to assign stereochemistry where appropriate. (2 points each)

a. Fe(H2O)6

3+ + SCN- → [Fe(H2O)5(SCN-N]2+ + H2O b. [(C2H4)PtCl3]- + NH3 → trans-[(C2H4)PtCl2(NH3)] + Cl- c. cis-[RhCl4(H2O)2]- + H2O → fac-[RhCl3(H2O)3] + Cl- d. NiCl2 + 2C3H5MgBr → (η3-C3H5)2Ni + 2 MgBrCl e. (η5-Cp)2(CH3)Ta=CH2 + Al(CH3)3 → (η5-Cp)2(CH3)Ta+CH2Al-(CH3)3 6. Give chemical names for the following compounds or ions: (2 points each) a. [ReH9]2-

nonahydridorhenate(VII) b. Rb[AgF4] rubidium tetrafluoroargentate(III) b. Na[AlCl4] sodium hexachloroaluminate(III) d. [Ag(NH3)2][BF4] diamminesilver(I) tetrafluoroborate(III) e. [Mn(CN)6]4-

hexacyanomanganate(II)

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7. Carbonic anhydrase II is present in red blood cells and catalyzes the reversible hydration of CO2:

H2O + CO2 ↔ [HCO3]- + H+

Based on the schematic representation of the active site in human carbonic anhydrase II (CAII) given below, develop a detailed catalytic cycle for the hydration of CO2 catalyzed by CAII. (10 points):

N

NH

N

NH

N NHZn2+

OH

Mechanism:

(His)N Zn

N(His)N(His)

O O

OH

(His)N Zn

N(His)N(His)

OH

O

O

OC

O

(His)N Zn

N(His)N(His)

OH

2+ 2+ 2+

HCO3-

H2O

(His)N Zn

N(His)N(His)

OH H

(His)N Zn

N(His)N(His)

OHCO2

2+ 2+

H+ transferred to His not in active site.

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8. At low temperature and pressure a gas-phase reaction can occur between iron atoms and toluene. The product A, a rather unstable sandwich compound, reacts with ethylene to give compound B. Compound B decomposes at room temperature to liberate ethylene; at –20 ºC it reacts with P(OCH3)3 to give Fe(toluene)[P(OCH3)3]2, C. Suggest structures for compounds A, B, and C. (10 points)

Fe

A B C

Fe Fe(H3CO)3P P(OCH3)3

9. Determine the number of valence electrons in each of the following compounds.

Hint: Not all of the compounds obey the 18-electron rule! (2 points each) a. Fe(CO)5 Fe 8 e-

5 Co 10 e-

18 e-

b. [Rh(bipy)2Cl]+ Rh 9 e-

2 bipy 8 e-

Cl 1 e-

+ -1 e-

17 e-

c. [HFe(CO)4]- Fe 8 e-

H 1 e-

4 CO 8 e-

- 1 e-

18 e-

d. RhCl(H)2(η2-C2H4)(PPh3)2 Rh 9 e-

Cl 1 e-

2 H 2 e-

η2-C2H4 2 e-

2 PPh3 4 e-

18 e-

e. Fe2(CO)9 2 Fe 16 e-

9 CO 18 e-

Fe-Fe 2 e-

36 e- → 18 e- per Fe

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