2d

Question 1

how do we increase the rate of the wilkinsons // a catalytic cycle

Answer 1

we need to increase the rate determining step,, which in the wilkinsons example is thehydride migration//insertion?

so for the hydride to move we need to make it more negative,, aka more hydridic.

for these to be more negative we need e- rich ligands connected to the same metal,, to donate some e- desntty!!!

Question 2

what proves that negative hydrides move faster

Answer 2

nmrrr

bc negative hs aka hydrides have a negative chemical shift

Question 3

how do the ligands on a wilkinsons catalyst increase the rate

Answer 3

• if u have an e- rich ligand u increase the rate (OMe)
• if u have an electronegative ligand u decrease electron density on the metal and the hydrides, reduing rate and hydride migration (F)
• if u switch Cl to like Br or I the rate also increases bc I is softer than Cl,, which increases the rate due to soft soft acid base theory. also bc softer can stabilise the reaction intermediates better

Question 4

if I is sm better at increasing rate than Cl bc it can stabilise reaction intermediates,, why doesnt eilkinsons acc use I instead

Answer 4

bc its very insoluble

Question 5

what about the position of ligands decreases rate,, around a benzene

Answer 5

if ur electron rich ligand is hindered rate wont increase,, aka if its ortho.

if ur electron rich ligand isnt hindered aka para,, rate will increase drastically

Question 6

what two catalytic cycles do we learn about

Answer 6

wilkinsons,, where the rds is the hydride insertion // migration onto the alkene.

RuCl2(PPh3)2

Question 7

whats the oxidation state of Ru in RuCl2(PPh3)2

Answer 7

2

Question 8

steps of the RuCl2(PPh3)3 catalytic cycle

Answer 8

RuCl2(PPH3)3S
remove a PPh3 bc its bulky

RuCl2(PPh3)2S
generate HCl

RuCl(H)(PPh3)2S
bind an alkene to it

RuCl(H)(alkene)(PPh3)2S
hydride migration occurs

RuCl(alkyl)(PPh3)2S

H binds to the alkyl and alkane is released

Question 9

the rds in the RuCl2(PPh3)2 reaction is what and how does it occur

Answer 9

H2 binding and releasing an alkane

either by heterolytic cleavage of H2 orrrrrrrrr by oxidative addition // reductive elimination

Question 10

whats the meaning of metathesis

Answer 10

swapping smt

Question 11

metathesis catalysis uses what

Answer 11

metal carbenes

Question 12

what is a metal carbene

Answer 12

a metal directly bonded to a C with 2 substituents on it

Question 13

are carbenes stable by themselves

Answer 13

no

Question 14

how are carbenes stabilised

Answer 14

they sigma bond to the metal

metal pi bonds to them ,, if its a singlet carbene

if its a triplet carbene they both sigma bond and pi bond towards eachother.

Question 15

describe a propene

Answer 15

3 carbons

theres a double bond in there too

Question 16

if we have 2 propenes and metathesis occurs whathappens

Answer 16

u have 2 x 3carbon elements with a double bond

u kinda overlay these double bonds and imagine them just fusing together to form a butene,, and bc of where the double bond is we know its a but-2-ene and an ethylene

Question 17

describe metathesis,, what should we think of

Answer 17

think of the two double bonds overlapping and fusing

then bc theyre overlapping one of the double bonds,, litch just one of the double bonds will float away

Question 18

what does olefin mean

Answer 18

it means alkene

Question 19

what does disproportionation mean

Answer 19

it means metathesis

Question 20

whats cross methathesis

Answer 20

when the two alkenes are different

Question 21

are the rules for cross metathesis the same as olefin normal metathesis

Answer 21

yhhh
u just overlap the double bonds and then get rid of a ethene

but with this u can get a mix of cis and trans products

reactions can favour one config more than the other but normally its a mix

its also a combo of different R groups,, R + R’ gives RR, R’R’ and RR’

Question 22

whats ring closing metathesis // RCM

Answer 22

lets say u have a cyclic molecule but its lowks open and it has 2 double bonds at the endddd

these can undergo metathesis and obvs the double bonds will overlap

the cycliic molecule will then be closed and an ethene will be released

Question 23

whats ROMP

Answer 23

ring open metathesis polymerisation

Question 24

what happens during ROMP girl

Answer 24

ring open,, aka u have a cyclic ring which is obvs gonna open

metathesis come onnn, the double bonds of the cyclic moelcules are gonna overlap and fuse,, then polymerisation bcccc obvs we want a long chain

Question 25

whats ADMET

Answer 25

acyclic diene methathesis for polymerisation aka if u have a moelcule with two double bonds,, metathesis can hsappen and u can form a polymerrr. acyclic dimer soo a straight chain thing,, metathesis so overlapping of bonds to fuse together

Question 26

hiw can we make a polymer

Answer 26

form a cyclic molecule wit ha double bond and do ROMP find an acylic molecule with 2 double bonds aka an acyclic diene and then do metathesis with this to form a polymer

Question 27

when we have a carbene with 2 subs,, how does the orientation of the subs affect whats going on

Answer 27

if the subs are in a line we will get a triplet carbene with 1 e- in 2 p orbitals ,, aka they will have parallel spins if the subs are gauche lowks then the electrons will be paired up and itll be in singlet state,, they act like a donor // line pair

Question 28

whats X-NR2

Answer 28

its a N heterocyclic carbene aka imagine a 5 membered ring with N where the cupcake wrapper will be. the Ns have 1R sticking out of them each and a double bond and the bottom of the cupcake. the lone pair will then be where the icing would be at the top of the cupcake

Question 29

what kind of carbon is the one in a carbene

Answer 29

its a divalent carbon

Question 30

what does a divalent carbon mean

Answer 30

it means that the carbon in carbenes is bonded to 2 R groups it therefore then has 2 electrons left over and these can be a singlet or triplet state

Question 31

whats a metal carbene complex girllll

Answer 31

its LnM=CH-R also known as an alkylidene

Question 32

can metal carbenes undergo metathesis

Answer 32

yes bc they have a double bonddd

Question 33

what can a metal carbene undergo metathesis with

Answer 33

it can undergo metathesis with an alkene

Question 34

metathesis with a metal carbene and an alkene mech

Answer 34

write them one on top of the other then the metal will bond to one of the C of the alkene this will then form a box type transition state (metallacycle,, a cyclic ring with 1 metal and C carbons) this will then break down so thst the metal is now double bonded to one of the alkene R groups and that C

Question 35

whats an alkylidene

Answer 35

a metal carbene aka a metal bonded to a C via double bond LnM=CHR

Question 36

what two different alkylidenes do we have

Answer 36

fischer and schrock

Question 37

describe a fischer alkylidene

Answer 37

fish pie so not similar to a normal pi bond the electrons on the divalent carbon are in the same orbital and form a sigma bond,, the 2 electrons oaired up in the metal are donated to the lumo forming a pi bond the C is partially positive C is sp2 low valent TM aka mid to late 18e- pi acceptor ligands on the metal like CO pi donor groups on the C like OR, NR2, Ph its a neutral 2e- donor

Question 38

describe a schrock alkylidene

Answer 38

u have the carbon in a triplet state. aka the 2 e- are in two diff orbitals and have parallel spins. looks like a pi bond lowks. the two e- matxh up to form q sigma bond and the same thing happens to the pi bond. the C is negatively charged sp2 C high valent aka early TM no pi acceptor liands on the TM (bc C is negative so we want all e- onto C) R groups on C are H or alkyl aka no pi donors its a neutral 2e- donor