I'm the current tech lead and team lead of our development team. We usually function like clockwork (with the intern somewhat behind), but today I encountered a problem that I wasn't able to solve.

We have a relatively big project on our hands. This project is a bit different from the others that we usually do, centering itself not on money, human resources or financial transactions—our usual thing—but instead focuses on a lot of predictive analytics. This is usually the type of project I absolutely love to do, so I got extremely hyped about it.

With the idea of a big, tasty and juicy project coming our way, I was ordered by my boss to pick two developers of the team to work on it while the rest of the team would stay on the usual maintenance/upgrade cycle of our other systems.

Since this project needs a math background that our developers currently don't have, we would pay for them to take relevant courses in the area. It's a bit outside their normal task scope as developers because it's a fairly specific skill.

So, I called the two oldest and most experienced developers I have on my team and presented the project to them. While one of them seemed really interested in it, the other one was... less than amused, to say the least.

"I'm not paid enough to do something like this."

"I'm sorry, what?"

"This is work that needs a lot of really difficult research on math stuff. I'm paid to develop software, not to do this sort of research. If you want me to work on this, you'll have to give me a raise for the extra responsibilities as a researcher I'll have."

And then ... I got stuck.

While it is true that he is a software developer and his job doesn't include academic-level research projects, I'm not sure if he has the right to argue about a raise for those reasons. Since this is basically software R&D, I think it falls inside our current responsibilities as developers. Yes, he will need to learn a few new skills, but this learning would be done on company time, using company resources.

Can someone ask for a raise when they are presented with a problem that is "too hard" for their current position or that demands "extra responsibilities"? How should I address this?

Please note that the training will be done on company time and will be paid using company money. If the employee needs 4 hours on a day for a given class, those hours will count toward the worked hours on that day. This is our usual policy for training, so it's nothing new for the employees.