what do catalysts do
lower the Ea of reactions
what dont catalysts do
they dont change the thermodynamics of the rea or pro
aka in a reaction energy diagram,, the energy of the rea and products dont change
if we strain a compound what can happen
it moves the whole reaction into higher energy,, aka it thermodynamically changes the rea and pro,, to get closer to the activation energy which also speeds up the reaction
whats bad about homogenous catalysts
theyre in the same phase as the reactants which means its hard to separate them out
its super spenny
acrtivity is high which is good
very sensitive to conditions
what does a wilkinsons catalyst do
it performs catalytic hydrogenation of alkenes ,, the ones that are easiest to reduce
whats hydrogen
a reducing agent
alkene + H2 gives what
an alkane
H2 is equal to what
H-H
and H sigma H with an electron pair in the cloud
H2 can split in 3 diff ways
homolytic scission: forms H* and H*
heterolytic scission : forms H- and H+
2H+ and 2e-
what type of a catalyst is wilkinsons
its a homogenous catalyst
a hydrogenation catalyst
describe wilkinsons catalyst
Rh(1) metal
PPh3
PPh3
PPh3
Cl
16e- , d8 electrons square planar
is WC sterically hindered
yes its very sterically hindered
ketone + H2 and WC
no reaction
bc WC is very selective
if u have a cyclic molecule with a ketone and 2 alkene bonds embedded in it when it reacts with WC what happens
any alkenes conjugated wirh the ketone dont get reduced
only the most easily reuced alkene gets reduced
aka the lone one instead of the one conjugated with something else.
what do catalysts aim to increase
they aim to increase the rate of th RDS
they want the rds to occur faster bc this is the most important step
whats the catalytic cyucle for WC
- ligand dissociation
- concerted oxidative addition
- olefin association
hydride migration to the corrdinated olefin aka onto the alkene - reductive elimination
the photo for the catalytic cycle of WC
WC (1) + H2 homolytically gets added to form Oh 18e- complex Rh(3)
we lose a PPh3 ligand and gain a S ligand
we then add an alkene and this takes the place of the solvent ligand
the rds then occurs and hydride insertion occurs where one of the Hs will move onto one of the C’s
we also then regain the solvent ligand so we have an Oh complex with an akylide ligand
reductive elimination then occurs and the alkene becomes an alkane ,, cis alkane
and were left with a square planar S,L,L,Cl Rh. we then lose L and gain S and it occurd again
then oxidative addition to get the Hs back on it
when we say solvent ligand what do we mean
ethanol or benzene and ethanol mixture
the more sterically bulky the C=C is the what
the lower the rate
aka the longer it takes
aka R=R is bulky
ketone isnt as bulky
=R and cycloalkene are less bulky
