5c

Question 1

reactions seen in organometallic complexes

Answer 1

• oxidative addition
• reductive elimination
• migratory insertion
• beta hydride elimination

Question 2

whats oxidative addition

Answer 2

a neutral molecule is added to a metal complex
the molecule is split as its added

giving 2 anionic ligands

Question 3

molecules that are normally added via oxidative addition

Answer 3

H2
R-X where X is a halogen

Question 4

what reaction is this: LnM + A-B –> LnM - A and - B

Answer 4

this is oxidative addition as ur adding a neutral moelcule thats lowks non polar

and is its added ur also splitting it to form 2 anionic ligands

Question 5

what happens to the metals os, corrdination and d electrons when oxidative addition occurs

Answer 5

oxidative addition therefore its oxidised,, so the Os increases by 2. OS + 2

the coordination increases by 2 bc the neutral moelcule splits to 2 anionic ligands

the metals d e- -2 bc ur adding to each ligand

Question 6

is the overall charge of the complex when oxidation addition occurs changed

Answer 6

no
the overall charge of the complex doesnt change

the os of M changes but the complex charge doesnt change

Question 7

if the metals de- count in oxidative addition is reduced by 2, what metals are more likely to undergo oxidative addition

Answer 7

nucleophilic metals aka e- rich metals

low in OS !!! bc they need to give 2 e- away in oxidative addition

Question 8

oxidative addition normally occurs in what tyype of complexes

Answer 8

normally occur in complexes with less than 18e- or with 18e- if prior ligand dissociation takes place

bc obvs ur adding 2 ligands so yes

Question 9

what ligands are used in oxidative addition // seen in the complexes

Answer 9

good sigma donors

aka PMe3, H-, R- bc we want the metal to be e- rich

Question 10

what metals are suually seen in oxidative addition

Answer 10

Ni(0) to Ni(2)
Pd(0) to Pd(2)
Rh(1) to Rh(2)
Ir(1) to Ir(2)

Question 11

oxidative addition can go from what to octahedral §

Answer 11

from square planar to octahedral

Question 12

whats the thermodynaic drive for oxidative addition

Answer 12

its going from square planar to octahedral where all e- are in t2g set of orbitals which is very stable

Question 13

oxidative addition has how many mechs it can occur by

Answer 13

3

Question 14

what are the 3 mechs of oxidative addition

Answer 14

concerted addition

sn2

radical chain (hard to exp so we dont)

Question 15

explain concerted oxidative addition

Answer 15

happens with H, R3-Si-H, R-H

its an associative 2 step mechanism:
formation of the sigma bond, breaking of the ligands bond

sigma bond donation from free ligand to empty metal d orbital

at the same time the metal donates e- from the filled d orbitals to the antibonding orbitals of the ligand molecule,, breaking them apart bc they fill up the antibonding orbital

theres 3 centred transition state between the metal and the ligand

leads to a cis isomerrrr not trans

Question 16

describe the sn2 oxidative addition

Answer 16

its sn2 like and occurs with polar ligands like R-X where X is a halogen

e- pairs are added to a and b simultaneously by acting like a lone pair

the TM acts like a nuc and the electrophile is the ligand were adding and breaking up.

inversion of stereochem occurs if theres 3 subs on the C.

metal attacks the C of the ligand and the X is kicked off,, aka a good lg is kicked off,, the lg then comes back and bonds to the Metal directly

Question 17

whats reductive elimination

Answer 17

the opposite of oxidative addition

its where 2 ligands on the metal come together and kick themself off the complex.

aka Ln-M - A - B —> LnM + A-B

oxidation state of metal increases by 2

corrdination number of metal decreases by 2

metals de- count increases by 2

forms a new C-C aka A-B bond

favoured by e- poor // electrophilic M with high oxidation states

can occur in compelxes with 18e- or less than 18e- if prior ligand coordination occurs

ligands used are strong pi accrptors like CO , alkenes, P(OR)3

we want ligands that take e- away from the metal.

Question 18

describe migratory insertion reactions

Answer 18

theyre different from OA or RE

no change in the metals os
the groups migrating must be cis to one another
a vacant coordination site is usually generated

if R has a chiral carbon when its bound to the M,, this doesnt change!! aka retention of config

we use M-X or M-R

basically we have M-R and we insert stuff between these.

if we add an alkene it turns into an alkane between the M and the R

Question 19

migration insettion of M-R and CO

Answer 19

M - CO - R

Question 20

M-R and = for migration insertion

Answer 20

M - C- C - R

Question 21

when is migratory insertion of metal CO useful

Answer 21

its useful in catalysis as a new CC bond is formed

Question 22

what are the 2 types of migratory insertion

Answer 22

u have the dorect attack of incoming CO

aa the CO atatcks the space between the M-R and the R moves onto that CO

or we have migration then insertion,, aka the R migrates onto an original CO,, then a new CO comes and inserts itself into the space made

Question 23

how do we figure out what migration insertion it is

Answer 23

we used 13CO

and we studyied it via reversivble reaction where when u heat it under vac,, the 13CO is removed.

but basically they learnt that it goes via migration thennn insertion hence the name,,

the R group migrates to an OG CO,, then another CO comes and bonds to the site R used to be in

Question 24

rules with migratory insertion of metal CO

Answer 24

CO and R need to be CIS so the R can migrate

Question 25

the rate of migration insertion depends on what

Answer 25

- the M-R bond strength and the ligands

Question 26

strong M-R bond

Answer 26

slow insertion and migration

Question 27

to accelerate migration what can we do

Answer 27

- use super bulky ligands so the migration is favoured as it reduces steric strain - bond a lewis acid to the CO, O so the C is more partially positive,, so the R is more likely to bind to the C - use electron deficient M,, by using pi acceptor ligands or cationic complexes,, to make C more positive in CO - oxidate the metal,, remove some of its e-,, to make it moroe psoitive and enhance the liability of a 17e- species

Question 28

the more delta negative the R,, the what

Answer 28

the more nucleophilic it is and therefore the faster migration we have Et > Me > PhCH2 > vinyl > Ph > PRCH > HOCH2 heteroatoms or H or CF3 dont rlly migrate

Question 29

migratory insertion of alkenes

Answer 29

LnM-R - alkene trnaition state and the u have R at the end of an alkane and a vacant site where the R used to be

Question 30

when we have alkene insertion what can happen

Answer 30

if the alkene isnt symmetric,, it can be added to the M in any C,, and the R can be added onto other ones leading to isomers. kinda,, give sus branced // linear ones 1,2 insertion or 2,1 insertion

Question 31

describe beta hydride elimination

Answer 31

the betas hydrogen goes onto a metal its the reverse of a migration reaction aka the alkane ligand has a beta hdyrogen and the Metal hasa vacant site,, the beta hydriode goes to the M and forms an alkene where it was

Question 32

why is beta hydride reaction elimination so easy

Answer 32

bc its got a low Ea

Question 33

what do we need for a beta hydride elimination to occur

Answer 33

vacant site on the metal beta hydride need a coplanar tranition state between th eH and the alkane alkene thing need the alkene generated to be stable