4d Flashcards
if u have a complex with 2 isomers,, 1 more symmetric than the other,, what one will we predict has more IR abs bands
the less symmetric one will have more IR abs bands!!!
more symmetry = less abs bands
3 ways we can synthesise metal carbonyls
direct combination
reductive carbonylation
ligand replacement
ways of synthesising metal carbonyls: direct combination
give examples
Ni + 4CO –> Ni(CO)4
Fe + 5CO –> Fe(CO)5
only these 2 metals allow us to directly combine them with CO
ways of synthesising metal carbonyls: reductive carbonylation
ReO2 + 17CO –> Re2(CO)10 + 7CO2
aka we have a salt and add CO to get a neutral metal + CO2.
ways of synthesising metal carbonyls: ligand replacement
CO displaces other ligands and takes their place in complexes
what counts as a phosphine ligand
litch anything with P being the donor part with the lone pair!!
the R chains dont matter but theres always 3 of them
describe why phosphine is crazy
super toxic
super smelly
spontaneously fammable
what shape // geometry does a phosphine ligand have
it has tetrahedral geometry
lone pair and the 3R chains
when a phosphine ligand forms a sigma donation bond,, how many e- are donated
the lone pair,, aka,, 2 e-
describe the phosphine M bonds and everything that happens with it
the P: is used for the sigma donation
the metal has a filled d orbital that donates e- into the P-C sigma* orbital!!!!!!!!
for backbonding!!!!
what orbitals do Phosphine ligands accept the electrons from pi backbonding into
they accept them into the P-C sigma** orbital!!
not the P’s d orbital,, this is incorrect.
we still draw the backbonding as a p type orbital tho
what about phosphine ligands is good when making complexes
theres a huge variety of phosphine ligands with diff sizes and diff sigma donor abilities,,, meaning we can pick which one we want to use and predict how this is gonna alter our complexxxx
what about phosphine ligands can we use to customise things
- the phosphine ligands size: aka their tolman cone angle,, larger angles prevent many ligands from being bonded to the metal!! bc they take us smt space.
- its electric properties aka its sigma donor abilities
how can we analyse the sigma donor abilities of a phosphine ligand
based on the 3 R groups its bonded to
if theyre electron withdrawing due to being electronegative,,, the P will be §+ while the R is §- : this weakens the sigma donor abilities of the ligand and theresfore strengthens the pi* backbonding interaction
if theyre electron donative via inductive effect,, this makes the p §- which increases its sigma donor bond,, and therefore weakens its pi* backbonding acceptor abilities.
relationship between sigma donation and pi* backbonding
the better a ligand is at sigma donation,, the weaker it is at accepting pi* backbonding
theyre inversely proportional.
when theyre worse as sigma donor bonds,, theyre better at acception pi* backbonding abilities.
are phosphines or carbonyls better at sigma donor bonds
phosphines are all better at sigma donor bonds accept for the PF3 phosphine ligands.
the M-P bond with phsophine ligands is affected and determined by what
its determined by the metals identity and the identity of the ligands
if the metal is e- rich,, it probs wont want a good sigma donor ligand
if the metal is e- poor it probs will want a good sigma bond donor
e- poor metal will form a stronger MP bond with a good sigma donor ligand
e- rich metal will form a stronger MP bond with a good pi* backbonding acceptor ligand
what can we use to identify phosphine ligands etc
31P NMR
shows diff environments,,, shows coupling constants etcccc
can show OS of metals,, ligand coordination environments and bond strengths
what is a phosphine ligand
any ligand wiht a P as the 2e- donor atom
normally has 3 R groups attached to it
the type of R group it is doesnt matter
a 2e- ligand can displace what
a 2e- ligand can displace other 2e- ligands
a hydrogen directlyy bonded to a metal is called what
a hydride
bc its H-
how many e- does a H-,, aka hydrode have
2e-
bonding of hydrides,, what orbital does it have
it has a 1s orbital
which gives us a pure sigma bond
can u have bridging Hydrides
yesss
H- bridging multiple metals
u overlap its s orbital with other orbitals
MH IR stretch occurs wheree
2250 - 1700cm-1
NMR shift of hydrides
0 –> -50ppm
hydrides are very well shielded
whats a dihydrogen complex
where u have the ethene bond type thing.
like u have the Metal bonded to the bond that sits between 2H atoms.
in dihydrogen,, where do the e- come from
the 2e- come from the H-H bond!!!
aka the sigma donation comes from the 2e- in the dihydrogen bond.
theyre orthogonal to eachother in a diagram.
dihydrogen bonding explanation
its the in phase overlap of the 2 1s orbitals
if the dihydrogen is made up of the in phase overlap of the 2 hydrogen 1s orbitals, what does that mean
that there also the out of phase 1s orbital overlap
this is where the backbonding occurs.
aka the 2e- from the sigma bond donate to the Metal,, and the metals d electrons donate via backbonding into the out of phase combo of 1s orbitals.
backbonding itno dihydrogen causes what
it causes the HH bond to weaken
it causes the HM bond to strengthen
this occurs until the dihydrogen turns into dihydride: Metal is bonded to 2 separate hydrogens!!
what are the dihydrogen hydrogens
theyre n2-H2
meaning theyre not independent from eachother
what are the hydrogens of dihydride
theyre independent of eachother
from dihydrogen complexes to dihydride complexes,, is it a spectrum or just 2 extremes
its a spectrum meaning complexes can be anywhere between them
when u have a dihydrogen complex,, what happens to the oxidation state of the metal when sufficient backbonding occurs and causes dihydride complex to form
u get an n+2 complex
aka u need to increase the metals oxidation state by 2.
bc 2e- came from the dihydrogen bond and 2e- came from the metal via backbonding.
so theres 2e- in each M-H- bond in dihydride complexes.
whats the reaction called when u go from a dihydrogen complex to a dihydride complex,, increasing the oxidation state of the metal
its called an oxidative addition reaction
in an oxidative addition reaction what doesnt change
the total amount of e- doesnt change
how do u form hydrids: 4 diff ways
- oxidative addition of H2
( dihydrogen complex oxidatively adds to form dihydride) - protonation of metal centre ( [Mn(CO)5]- + H+ –> [H-Mn(CO)5]
- substitution with H- [BrMn(CO)5] + H- —> [H-Mn(CO)5] + Br-
- hydride elimination reactions
remember that hydride is M-H,, so when trying to form them,, just try think of diff ways u can add a H to a metal:
- the oxidative addition
- protonation of the metal
- substitution with H-
youve got this girl 💗
