The good thing is that a lot of US flights won't have transit security when you arrive in DOH. 1h45m is definitely plenty even if you have transit security (bus gate for example), but doesn't leave time to really enjoy the lounges, etc. But despite it being a huge airport it's very efficient for connections. You'll easily make your connecting flight if you leave BOS on time and chances are going eastbound you'll end up in DOH a bit early.