So you have an existing domain? That's B2C? That's served you well? And you're going to redirect them to another domain? And that new domain is expanding (?) to cover B2C + B2B? And then you're going to manage those two target markets on that one site?

I would say that unless you can make a strong case to combine them, don't do it. If you intend to grow the B2B audience then give it the focus and attention it deserves. (Which also means the site / market that isn't broken keeps printing money).

If B2B gets enough traction and in the future merging the two makes sense, well that's a good problem to have.