Webb Organometallic Reaction Steps

Question 1

What are the two ligand exchange mechanisms

Answer 1

associative and dissociative

Question 2

What is the trans effect

Answer 2

strong sigma donor or pi acceptor ligand accelerates substitution of a ligand in the trans position

Question 3

Trans influence: what bonds involved? what control is used?

Answer 3

sigma bonds, thermodynamic

Question 4

Trans effect: what bonds involved? what control is used?

Answer 4

pi bonds, kinetic control

Question 5

If the metal to T sigma bond is strong, how strong is the metal to X bond?

Answer 5

weak

Question 6

what effects do steric have on substitution reactions?

Answer 6

crowding at reaction centre inhibits associative, facilitates dissociative

Question 7

how do electron rich ligands effect the rate of oxidative addition?

Answer 7

increase

Question 8

high or low initial oxidation state favourable for oxidative addition?

Answer 8

low

Question 9

How does H2 react with d8 and d10 complexes?

Answer 9

oxidative addition - cis

Question 10

what is sigma-bond metathesis

Answer 10

when two bonds break and two bonds formed at the same time

Question 11

difference between insertion and migration?

Answer 11

insertion sticks in-between a metal and another ligand // whereas a migration sticks on the end of another metal-ligand bond

Question 12

how would you prove that something has migrated instead of inserted?

Answer 12

add heat and inserted bonds break the end off

Question 13

would a bulky solvent increase or decrease reactivity of insertion?

Answer 13

decrease rate

Question 14

what is a condition of migratory CO de-insertion?

Answer 14

vacant site must be cis to acyl fragments

Question 15

how would you suppress B-hydrogen elimination?

Answer 15

maintain coordinative saturation, stabilisation of metal alkyl through choice of metal (early TM + Ln), steric hindrance

Question 16

reactivity trends of migratory insertion

Answer 16

X and Y must be cis; new X-Y and M-Y must be more stable than M-X and M-Y - otherwise reverse will occur; bulky ligands undergo insertions more rapidly; reactivity diminishes down a group

Question 17

what favours reductive elimination?

Answer 17

electron deficient metal, presence of bulky groups, thermodynamically stable product

Question 18

for reductive elimination, which is faster trans or cis?

Answer 18

cis

Question 19

would electron deficiency favour or disfavour reductive elimination?

Answer 19

favour

Question 20

what is the difference between syn and anti addition?

Answer 20

syn is inner sphere (reaction takes place including the M) anti is outer sphere (reaction doesn’t directly touch M)