The word "negotiate" itself is a verb, meaning "to discuss something with someone in order to reach an agreement."
If you're looking for related words, you might consider these:
* Re-negotiate: This means to negotiate something again, often after an agreement has been made.
* Pre-negotiate: While not a common word, this could be used to describe the process of preparing for a negotiation.
* Co-negotiate: This implies negotiating jointly with someone else.
Do you have a specific meaning in mind when you ask about prefixes? Maybe you're looking for a word that means "to prevent negotiation" or "to negotiate in a specific way"? Providing more context will help me understand what you're looking for.