Why doesn't my iPhone 5s connect to my iMac (2011) via bluetooth?

I have a 2011 iMac running El Capitan and I've never been able to connect my iPhone 5s to it using bluetooth. I get all the way to the part where the computer sends the pairing code. When I accept the code on the phone, the computer says it connects for a split second then says it was unsuccessful. Any ideas?