Many people keep lions in reef tanks because they are technically reef safe, but the will eat small shrip and other inverts. I have also read they don't like a high flow rate, which is generally required to keep a successful reef tank. Plus they eat a lot so produce a lot of waste.

However, a dwarf may do just fine. I would wait until you're into the 46 gal before you decide to pick one up. They are cool fish that's for sure.