CHEM 495 TRANSITION METAL CHEMISTRY
– FALL 2001
ANSWERS to Test #1
1. What is the mechanism
for the following catalytic reaction using RhCl(PPh3)3
as the catalyst? What is the other product? Which do you think is formed in
greater yield? Why? (20 points).
Answer:
What is the other
product?
Answer:
Which do you think
is formed in greater yield?
Answer:
1,2,4-tert-butylbenzene
Why?
Answer:
The oxidative addition
reaction occurs at a sterically less hindered C-C bond.
2. What is the oxidation state
and electron count for each of the following? (20 points)
(a) Fe(CO)2(PPh3)4
(b) [Cr(MeCN)2(PMe3)4]2+
(c) [Cr(H)(CO)2(PMe3)4]+
(d) Ru2(O2CMe)4
(e) Ru2(O2CMe)4Cl
Answer:
|
Compound
|
oxidation
state
|
electron
count
|
| Fe(CO)2(PPh3)4 |
0 |
20 (not stable) |
| [Cr(MeCN)2(PMe3)4]2+ |
+2 |
16 |
| [Cr(H)(CO)2(PMe3)4]+ |
0 (H+) or +2 (H-)
|
18 |
| Ru2(O2CMe)4 |
+2 |
16 (Ru=Ru) |
| Ru2(O2CMe)4Cl |
+2 and +3 |
16 |
3. If CO is a two electron donor and NO is a 3 electron donor, what are the
possible formulae of the stable 18e- Cr0 and Fe0
compounds containing just NO and/or CO (10 points).
Answer:
| Cr(CO)6 |
Fe(CO)5 |
| Cr(CO)3(NO)2 |
Fe(CO2(NO)2 |
| Cr(NO)4 |
|
4. What are the possible oxidation
states and structure of a compound with the general formula, RuH4L3
(L = PPh3) ? Which is most likely and why? (Remember electron count,
geometry, ligand field splitting and the types of ligands). (10 points)
|
#
|
Oxidation
state
|
structure
|
|
1
|
0
|
|
|
2
|
2
|
|
|
3
|
4
|
|
Which is most likely and why?
Answer:
Structure 2. This is d6,
octahedral, 18 e- (t2g level filled, stable electron configuration and obeys
Toleman's rule), with p-acid ligands.
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