5d Flashcards
describe how we form a hydride using a hydride elimination reaction
u have a metal attached to an alkyl chain ligand
and its when the beta hydrogen is removed to form an alkene between the alpha and beta carbons on the alkyl chain.
long n1 means what
ur bonding through one atom only ,, aka ur general M- CH3
M - ethene
M - phenyl
they all bond via 2 e- and form a sigma donation bond
we treat them all as if theyre R- : 2e- ligands
theres no backbonding
make via metathesis : what happens
u make a M- R bond by having a L-M-Cl
aka metal centre with ligands and a Cl ligand etc
u then react it with R-Li which acts as a nucleophile and SN2’s the Cl off,, replacing it with the R group.
the LiCl precipitates and so must be in an organic solvent such as TFD,, ether or hexane etc
what tupe of alkyls are not stable
the ones with a beta hydrogen … bc the beta hydrogen is removed to give an alkene
what alkyls are stable
the ones without a beta hydrogen
whats a beta hydrogen
okay so the C connected to the Metal is the alpha,, ,the beta one is the one after it,, if this carbon has a H its called a beta H
and if an alkyl ligand has this,, its unstable.
describe an alkene,, what orbitals it has and how it can be used as a longn2 ligand
it can be orthogonal to the metal.
it can do this bc it has:
- one sigma cc bond
- one pi bond
the e- in the pi bond can be used for the sigma donation to the metal (2e-)
and bc this is coming from the pi orbital,, it counts as the 2 carbons not being independent,, bc the e- are both of theirs.
this means that backbonding occurs into the empty cc pi* orbital!! which are also shared by both carbons
whats cool about the sigma donation and pi cackbonding in alkenes
theyre similar and balanced
one is not better than the other
when u have an alkene as a liggand and backbonding occurs,, what can happen to the molecule
greater backbonding can cause the hydrogens to be pushed away from the metal
obvs bb also weakens the cc double bond,, lowering its IR stretching frequency.
how do u draw a metal and alkene ligand complex
the bond connecting them and the double bond are orthogonal
as the bb causes the C=C bond to weaken ,, what can happen
the double bond can break,, forming 2 different single bonds!!!
the metal will be independently bonded to 2 carbon atoms.
the 2 carbon atoms are the carbons involved in the alkene before it broke
whats a bis(longn1)alkyl interaction
when ur metal is bonded to 2 individual carbon atoms after the alkene broke due to backbonding
when bonds break due to backbonding,, what remains the same in both complexes and what changes
the total e- count stays the same
the OS of the metal increases by 2!! bc u backbond 2e-
what about alkynessss,, how do they react with metals,, what orbitals do they have and what orbitals do they use
- alkynes have 1 sigma bond
- alkynes have 2 different pi bonds,, facing in diff planes.
they use their pi bonds for sigma donation
the metal then backbonds into their ??????
due to alkynes having a triple bond,, meaning they have 1 sigma and 2 pi bonds ,, what does that let them do
bc they have 2 sets of pi bonds that face in different directions
they can sigma bond to 2 different metals if they wanted to!!!
they can give 2e- in 2 bonds to 2 diff metals
or give 2e- to a single metal
what properties of alkenes and alkynes can u vary to affect their ligating ability
their steric and electronic properties
aka an alkene with 2 strongly ewg (esters) ,, u have a very good pi acceptor ligand
better than pph3
do we treat non conjugated alkenes as 2 separate alkenes
yes!!
u treat them as 2 separate alkenes bc theyre not conjugated by just connected via alkyl chains
what can nonconjugated alkenes bind to
they can bind to the same metal!!!
like a chelate effect
what efffect is seen when a nonconjugated alkene binds to the same metal
when 2 double bonds in the same molecule bind to the same metal u get a chelate effect
this adds stabilisation!!!!!
we treat each alkene as a how many e- donor
we treat alkenes as 2e- donors
whats a butadiene
an alkene with 2 double bonds
u have the cis and trans version
are butadienes conjugated or not conjugated
theyre conjugated
whats is the diff between a conjugated and non conjugated double bond
u cant treat conjugated alkenes as if theyre different.
u treat them as if theyre the same bonds.
butadiene has how many pi electrons
4 pi electrons!!
so u draw the butadiene with the nodes and everything. and u have the energy line for each one,, 4e- means u fill up the first 2 drawings.
butadiene complete explanation
u have no nodes on the bottom // lower energy one.
and the lower p orbitals are all in phase : aka fully bonding and these interact with the dz^2 d orbital. they do sigma donation from the pi system to the dz^2 orbital.
then u have the diagram with one node i nthe middle,, if u acc think about if u have the dzy d orbital which is the tall one,, and this one also accepts e- from the diene. this one is a sigma and pi donor!!!
u then have the drawing with 2 nodes and this one uses the dzx orbital which also interacts with the diene. the dzx backbonds into the diene with 2 nodes
u then have the highest energy oen with 3 nodes,, this one interacts with the dxy.d orbital and this forms delta backbonding!!!! this is the flat d orbital
zxy cartesian coordinates
z up
y to the left
x in and out
describe what happens to the structure of butadiene due to backbonding etc
the double bonds get longer and the CC middle bond gets shorter.
why doesnt the delta backbonding occur for dienes
bc its extremely high in energy!!!
meaning its hard to populate
