[CrimpJiggler]

I was reading a bit about organolithium compounds and came across methyllithium (CH₃Li) and read that this is actually an ionic compound.  If I'm not mistaken Grignard reagents are covalent compounds and methylsodium doesn't exist. Is what I read about methyllithium true, is the methyl group actually an anion? If so, is this the only compound in which an alkyl group exists as an anion?

[Honclbrif]

The way organolithiums exsist is actually more complex than the cation-anion picture. For instance, n-butyllithium has a melting point of about -78°C, which is pretty darn low for an "ionic" compound. This is because organolithiums actually exist as complicated clusters, the geometry and stoichiometry of which depends on solvent, temperature, and concentration. They're actually pretty cool and if you are interested, you should read up more on them.

http://en.wikipedia.org/wiki/Organolithium_reagent

Isn't a bad place to start