I believe the first on screen death of a Transformer we ever saw was Optimus Prime. The scene is called "The Death of Optimus Prime" along with an accompany music score of the same name. So we know that Primegave his life in a final showdown with Megatron. He gave away the Matrix and then lost all life support functions. When he did this he appeared for the first time to turn lifeless and gray. The only other time we see this occur is right before Starscream is turned into ash. He also becomes lifeless and gray. Having said that Wheeljack and Windcharger who we do not see become gray even though they appear lifeless do not qualify as dead given the above definition. Ironhide we can assume become lifeless and gray though it was not shown on film. Prowl we can sort of see go lifeless due to the eye flicker just not his gray body being shown. Ratchet received the same amount of damage as Ironhide give or take a shot but was not blasted by Megatron. His gray body was never shown either.