Somebody have had this problem while is uploading the bootloader??
Error while sending: missing configuration parameter 'upload.tool'
You're using an incomplete board definition that omits the upload.tool parameter, or you're using a board definition from pre-1.6 days with a modern version of the IDE.
For most common use cases, there's a modern board package available, usually through board manager - if you tell us what you're bootloading, we can point you to the right one. Unfortunately a lot of pre-1.6 tutorials that tell people to modify boards.txt (which nowadays you should never be doing) are still being used, when the correct solution is to use an existing board package.