Chem 400
Inorganic Chemistry
Practice Exam 3
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KEY
Name _________________________________________________________
(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:
-
Me
I
MeOH
CO
CO
I
II
MeI
Rh
I
III
I
CO
I
HI
-
O
I
Rh
H2O
I
Rh
I
CO
-
CO
I
VI
O
OH
O
V
I
I
OC
I
Rh
O
-
IV
CO
CO
I
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.
1
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
B = 9000 cm-1
ν1: E/B = 10
E = 10
ν2: E/B = 22.5
E = 22.5 B B = 21,100 cm-1
Average B = 920 cm-1
∆0 = 10,120 cm-1
2
B = 900 cm-1
B = 938 cm-1
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
+
O
N
Co
N
O
O
N
N
N
N
[Cr(ox)2(H2O)2]trans isomer, cis isomer with two optical isomers
-
OH2
O
Cr
O
O
O
O
O
O
O
Cr
H2O
OH2
-
O
OH2
O
[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.
N
Co
N
Cl
+
N
NH3
N
N
Cl
Co
Co
N
Cl
NH3
NH3
[PtCl2(PPh3)2]
cis- and trans-isomers
Cl
Pt
Cl
PPh3
Cl
PPh3
Pt
PPh3
Cl
[Co(en)3]3+
optical isomers
3+
N
N
Co
N
N
3+
N
N
N
N
N
N
Co
N
N
3
+
Cl
+
NH3
NH3
PPh3
e.
O
Cr
OH2
Cl
d.
-
O
OH2
c.
N
Co
N
b.
+
O
+
Cl
NH3
H3N
Cl
Cl
Co
N
N
NH3
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)
EMO
EMO
pzdz2
ψ4
dxz
ψ3
ψ2
dyz
ψ1
OC
Fe
CO
CO
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.
4
5. Give likely products for the following reactions. Do not forget to assign
stereochemistry where appropriate. (2 points each)
a.
Fe(H2O)63+ + 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.
b.
b.
[ReH9]2-
Rb[AgF4]
Na[AlCl4]
nonahydridorhenate(VII)
rubidium tetrafluoroargentate(III)
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):
H
O
Zn2+
N
N
N
H
NH
N
NH
Mechanism:
H
O
C
H
Zn
H
O
O
(His)N
O
O
2+
Zn
(His)N
2+
N(His)
N(His)
O
O
N(His)
N(His)
O
O
2+ Zn
(His)N
N(His)
N(His)
H2O
CO2
H
H
O
O
(His)N
Zn
2+
N(His)
N(His)
H+ transferred
to His not in
active site.
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(His)N
Zn
H
HCO3-
2+
N(His)
N(His)
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
Fe
A
(H3CO)3P
Fe
P(OCH3)3
C
B
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 e5 Co 10 e18 e-
b. [Rh(bipy)2Cl]+
Rh
2 bipy
Cl
+
c. [HFe(CO)4]-
9 e8 e1 e-1 e17 e-
Fe 8 eH 1 e4 CO 8 e1 e18 ed. RhCl(H)2(η2-C2H4)(PPh3)2
Rh
9 eCl
1 e2H
2 eη2-C2H4
2 e2 PPh3
4 e18 ee. Fe2(CO)9
2 Fe 16 e9 CO 18 eFe-Fe 2 e36 e- → 18 e- per Fe
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