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CM4212 – Main Group
CM4212 – TM OM
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Main Group OM
1. Carbonyl complexes are favorably formed with low valent metal centers.
False
True
Show answer
Carbonyl ligands are good pi-acceptors. Low valent metal centers provide sufficient electron density for favorable pi-backbonding to bound carbonyl ligands.
2. Main group organyls react primarily as ...
Acids
Bases
Electrophiles
Nucleophiles
Show answer
They are essentially "stabilized" carbanions which due to the negative charge react as strong nucleophiles or bases.
3. Which are the most reactive main-group organyls?
organomagnesium compounds
organolithium compounds
organomercury compounds
organozinc compounds
Show answer
Organolithium compounds are the most reactive in this series, because they have the highest bond polarity (most ionic bond-character).
4. What is the bond order of M-Br-M bridges?
1.5
2.0
0.5
1.0
5. Which reaction utilizes Grignard\'s reagent?
Mizoroki-Heck
Suzuki-Miyaura
Negishi
Kumada-Corriu
6. Bridged complexes form due to ...
both electronic and steric reasons.
change in concentration.
steric reasons.
electronic reasons.
Show answer
Bridges only form, when the complex fragments are electronically unsaturated. Electronically saturated complexes do not dimerize, etc. even if their ligands are small.
7. Homoleptic carbonyl complexes exhibit only one CO band.
False
True
Show answer
The number of carbonyl bands depends on the number of unique carbonyl ligands, which in turn is influenced by geometry and symmetry.
8. Aggregation of organolithium compounds occurs preferably in ...
Non-polar, non-protic solvents
Polar, protic solvents
Polar, non-protic solvents
Non-polar, protic solvents
Show answer
Protic solvents decompose organolithium species (acid-base reaction), and polar solvents tend to break higher aggregates apart through coordination to the electron-deficient Li-centers.
9. Which ligands form the most stable bridges between metals?
halido
hydrido
alkoxido
alkyl
Show answer
Alkyl and hydrido bridges are electron-deficient, while alkoxido bridges are sterically less favorable.
10. What is the bond order of M-H-M bridges?
2.0
0.5
1.5
1.0
11. Which reaction utilizes organozinc species?
Kumada-Corriu
Negeshi
Suzuki-Miyaura
Sonogashira
12. Which of the statements is true?
Alkyl bridges are favored over hydrido bridges due to electronic reasons.
Hydrido bridges are favored over alkyl bridges due to electronic reasons.
Hydrido bridges are favored over alkyl bridges due to steric reasons.
Alkyl bridges are favored over hydrido bridges due to steric reasons.
Show answer
Alkyl- and hydrido-bridges are both electron-deficient (3c-2e). They only differ in their sterics, and bridges with smaller ligands (hydrido) are preferred.
13. Which reaction utilizes organoboron species?
Suzuki-Miyaura
Kumada-Corriu
Mizoroki-Heck
Negishi
14. Many main-group organyls are ...
pyrophoric
air stable
moisture sensitive
water soluble
Show answer
Many main-group organyls are very strong bases which exothermically react with water (moisture sensitive). The heat released can ignite them (pyrophoric) and/or the organic solvent they are stored in.
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