In the official rules of Monopoly, can you offer immunity to other players in deals?
The official rules are here. I can see nothing in the rules that would explicitly prevent one player offering immunity to another player. You only have to pay rent if the owner of the property asks you for it:


  The owner may not collect the rent if he/she fails to ask for it before the second player following throws the dice.


However, you could argue that offering immunity violates the spirit of the no lending rule:


  No player may borrow from or lend money to another player.