hey it's professor Dave let's talk about organolithium reagents
so we've talked a little bit about organometallic reagents such as grignard reagents that's
organometallic because it contains magnesium magnesium being a metal and so
lithium is another metal and so organolithium reagents which as you
might guess are ones that contain lithium are also organometallic reagents
so let's take a look at how we prepare them and what they do so we're gonna
start with some alkyl halide right any 3R is a convenient any kind of alkyl
halide and we're going to react with two lithium atoms so we're gonna use
elemental lithium and we need two lithium atoms for every molecule of the
alkyl halide we're gonna react in some non non polar aprotic solvent like
hexanes and we're going to get our organolithium reagent that's our
organolithium reagent and then the lithium halide by-product so that is the
way that we prepare them and so it's all it is it's some carbon connected
to a lithium atom and so here are some examples of some common organolithium
reagents we can have methyl lithium so that that's a very common one we can
have n butyl lithium where n implies that it's a straight chain butyl so
we've got one two three four lithium and we can also have tert butyl lithium so
here's the lithium and this is essentially a tert-butyl group so these
are three probably the most common organolithium reagents and so what are
the properties of organic organic lynnium reagents we remember when when
we looked at the grignard reagents right this is a bit different because we saw
that the the magnesium atom would insert itself into that carbon halogen bond
whereas here the lithium simply displaces it so we're we don't have that
halogen anymore we just have lithium and as it happens lithium is even less
electronegative than magnesium so whereas with the with the grignard
reagent we saw that we had a partial minus charge on that carbon because it
was a polar bond and carbon was pulling electron density away from the
from magnesium here we see that effect even more so because lithium is less
electronegative than magnesium so this is an extremely polarized covalent bond
this is an extremely this is a very significant partial minus charge on the
carbon so much so that this behaves almost like a carbon ion it is almost as
though this carbon has a formal negative charge and of course we know that that
means that is it is extremely reactive as a species so what are some things
that we can do with these where these are going to lithium reagents one very
common thing is that these are just sources of nucleophilic carbon again
very much like grignard reagents so here's an butyl lithium and remember
that this carbon attached to the lithium is the one that bears that very strong
partial minus charge almost like a formal minus charge so this is clearly
the nucleophilic carbon so that can come up here and attack a carbonyl just like
a grignard reagent and now we've got so this is the bond that was formed right
here right we've got one two three four carbons that's those four carbons and
then these two carbons are right there and we've got that act that oxyanion and
then of course any kind of acidic workup ammonium chloride what-have-you we're
going to be able to protonate and we're gonna get our alcohol so this is
extremely similar to grignard reagents we could also do that with a grignard
reagent and might want to use this instead for various reasons but then one
big difference is that we typically would not use a grignard reagent as a
base but these organolithium reagents are excellent basis because carbon ions
are very very strong bases right we know that alkanes are not acidic whatsoever
they do not want to lose a proton so if by any manner you get a carbon ion it
desperately wants to get that proton back to become an alkane and so we can
use organolithium reagents as basis so one common app one common application we
talked about how we can deprotonate terminal alkynes to get that acetylide
ion to go do some SN2 do some synthetic chemistry that way so we can use an
organolithium reagent to do that right we might use sodamide, NaNH2, but we
also can use an organolithium reagent so we can go
ahead and get that proton on the terminal alkyne which is going to
produce the acetylide ion so then that is going to be able to go and attack an
alkyl halide do some kind of SN2 do some more synthetic chemistry so that is
a little bit about organolithium reagents we talked about how they are
prepared some common examples of organolithium reagents the properties of
organolithium reagents and then two very common applications for organolithium reagents.