Can amides be N-alkylated with alkyl halides? Say I was trying to make N-propyl acetamide. Would iodopropane and acetamide react to form it? Would they react to form N,N-dipropyl acetamide? If so, what catalysts would I need, and if not, why not and how would it be possible?
Sure, there are a number of ways to do this with copper, iridium, or palladium catalysts. This link should hopefully be helpful.
The amide nitrogen is not a good nucleophile to react. But it can become nucleophilic in the form of $\mathrm N^-$ as a conjugate base of a weaker acid. This means that you need a strong enough base to deprotonate the amide. Some standard conditions are NaH in THF or DMF, or n-BuLi, LDA and the like in THF/ether etc.