Jon

Question 1

what is dissociative mechanism for ligand association by Tollen’s rule

Answer 1

18e- to 16e- intermediate, to 18e- product

Question 2

what are steric constraints?

Answer 2

vacant coordination sites and if the reacting groups are in the right place

Question 3

what are electronic constraints?

Answer 3

oxidation state and 18e- rule

Question 4

what structures favour 16e-?

Answer 4

sq planar d8

Question 5

compare atom efficiency of ACH and Lucite ALPHA processes

what does each process form?

Answer 5

ACH = 87%

Lucite ALPHA = 99.9%

forms methylmethacrylate

Question 6

what is an agostic intermediate?

Answer 6

a C-H bond stabilises itself and the metal centre (Pd) by entering the metal d-orbital

Question 7

mechanism for decomposition of alkoxide?

what is alkoxide?

Answer 7

beta hydride elimination

alcohol minus the alcohol proton so just O-

Question 8

Explain how the cone angle will affect L/b ratio

Answer 8

l/b ratio = linear/branched ratio

bulkier groups/ligands on the metal will give more steric hindrance, a smaller cone angle so the complex reacts linearly (anti-markovnikov insertion)

cone angle will be bigger for less bulky groups

if the groups are very bulky then they may not coordinate at all giving a lower l/b ratio

Question 9

how do you do the 18e- rule?

Answer 9

total no of e- from all of the ligands (normally 2e- per ligand)

+ no. of de- from the metal centre

if a double metal centre then divide the total no. of e- by 2

Question 10

what does Co + PR3 make?

Answer 10

alcohol

Question 11

what does Rh + PR3 make?

Answer 11

aldehyde

Question 12

what does H being more hydric mean?

Answer 12

more likely to attack the aldehyde and form an alcohol

Question 13

how does PPh3 affect the hydricity of H?

Answer 13

makes the H more hydric bc of the Ph groups making the PPh3 ligand more basic, this weakens the C-O and M-C bonds (M=metal) in the CO ligands

Question 14

what is the mechanism when the oxidation state of a metal has increased by 1?

Answer 14

homolytic addition = adding 1 H2 across a metal-metal bond

Question 15

what is creation of a vacant site?

Answer 15

when one L leaves so the complex is now 16e- ready for another one

Question 16

what is an olefin?

Answer 16

an alkene

Question 17

what is conversion from alkene to metal alkyl?

Answer 17

the added alkene ligand takes the H from the metal centre and now there is a vacancy from where the H was (16e- complex)

Question 18

what is beta hydride elimination?

Answer 18

the reverse of alkene (olefin) insertion (Rh complex)

when the one alkane ligand become an alkene and H again, e- count 16e- to 18e-

Question 19

what can happen with olefin isomerisation?

Answer 19

the double bond from the ALKENE can move

Question 20

what happens with methyl migration/CO insertion?

Answer 20

another phosphine is added to the complex FIRST (18e-) then a CO joins the alkyl ligand already on the complex

Question 21

what is the result of oxidative addition of H2 to Rh complexes?

Answer 21

increases the oxidation state of the metal by 2 so decrease no. of d e- by 2

so 2 new H ligands can be added and complex is 18e- now

Question 22

how is oxidative addition reversible?

Answer 22

reductive elimination: 2 CIS ligands removed from metal, so oxidation state decrease by 2

so metal d count decrease by 2 (18 to 16)

Question 23

how does an electron donating L affect pi-back donation?

Answer 23

1) increases it
2) Co-CO bond is stronger so CO loss is less likely
3) eqm to left
4) lower reaction rate
5) ligand less readily lost so vacant site not formed

Question 24

what techniques can isolate catalytic precursors and intermediates?

Answer 24

mass spec, CHN, x-ray if stable

Question 25

what are classical mechanisms of hydrogenation?

Answer 25

1) metal dihydride
2) oxidative addition w/ H2
3) olefin coordination in 1st coordination sphere
4) olefin insertion
5) reductive elimination of alkane
6) oxidative addition of H2

Question 26

what are the non-classical mechanisms of hydrogenation?

Answer 26

1) metal mono-hydride or di-hydride
2) transfer hydride from the metal and a proton from somewhere else
3) H sources from alcohol/formate/H2
4) transfer hydrogenation - alcohol reduction to ketone, MH and H+
5) substrate not always directly bound to metal
6) H transfer in 1st or 2nd coordination sphere