when we say we have a M=CR2 ,, what do we mean and how many are there
Fischer alkylidene
Schrock Alkylidene
what’s a fischer alkylidene
singlet alkylidene
C donates to the M
forms a sigma and a pi bond
describe a schrock alkylidene
triplet alkylidene
2 covalent bonds polarised towards the C
u have e- in both the metal and the C however none of them are paired up. they’re all single.
two match up to give a sigma bond, two match up to give a pi bond
what are carbenes in terms of ligands
carbenes are neutral 2 e- donors
how do we make a metal carbene complex (schrock explanation)
Ta (5)Cl5 (add Me2Zn) to give Me3Ta(5)Cl2 (add 2TiCp) (u lose a TiCl)
u get a complex with Ta(5) as the metal,, 3CH3 and 2Cp
this is an 18e- complex
we then add a Y with ph on each end and a + C in the middle,, and we also add CH3CPh3
we get a Ta(5) CH3, 2Cp, CH2–H
this is a 16e- complex and the Ta is so e- deficient it wants the electrons in the CH2—H sigma bond.
we then react this with a base to give Ta(3) 2Cp, CH3, CH2 which is 18e-
if a metal is electron poor and there’s a CH3 ligand next to it what can it do
the sigma bonded CH electron pair can be used to stabilise the reactive intermediate
this is called an agostic interaction
on Ta(3) what is CH2 equal to
it’s equal to a triplet carbon
on Ta(5) what is CH2
it’s equal to the triplet carbon if there were e- pairs not singular electrons
it’s CH2 with two lone pairs and a charge of -2
when is catalyst activation needed
it’s needed for early,, aka high oxidation state,, transition elements
if we have WCl6 and Sn(ch3)4 what happens
u get WCl4,, CH3(2)
this then loses a CH3 to give
W=CH2, 4Cl
what is ROMP
ring opening metathesis polymerisation
what is ROMP used for
it’s used in the synthesis of complex organic molecules (drugs etc)
what are the troubles in trying to make linear polybutadiene synthesis
butadiene is difficult to polymerise and often forms branched products
we obvs don’t want this
how can linear polybutadiene be made from cyclic structures
a cyclic butadiene equivalent may be used to be polymerised into a-linear polybutadiene
how do we use a cyclic butadiene equivalent to form a linear polybutadiene
butadiene is formed into a dimer or a trimmer
ROMP then occurs with a grubbs catalyst
this forms linear polybutadiene with a carbene ligand from the grubbs catalyst being terminal.
aka at the end u have a benzene
when we form a linear polybutadiene from a cyclic butadiene equivalent what is the thermodynamic driving force
the thermodynamic driving force would be the release of ring strain
this is due to the ring becoming a linear polymer
aka release of ring strain in cyclic olefin monomers
the thermodynamic driving force for ROMP is what,, and what does this mean
it’s the release of ring strain when a equivalent ring structure turns into a linear polymer
this means that triangle rings ring open faster than 6 membered rings as their ring strain is larger
what’s tricky about cycloalkanes
it’s hard to polymerise them in a controlled manner by other means
whats ROMP good at
ROMP is very effective at yielding high quality materials
metathesis in catalysis: poly acetylene: what is polyacetylene
u have (CH=CH)n
what is polyacetylene important in
it’s important in electronics industry bc it’s a conducting polymer
what was the original polyacetylene synthesis
via a heterogeneous ZN process
