you may need to use a more powerful phospine ligand to force oxidative addition. try something like Cy3P or nBu3P. There must be examples of these in the literature, have you given it a thorough search? dppf doesnt seem unreasonable, it does have a large bite angle so it will help create some free coordination site on your metal center as well as encourage reductive elimination, but i dont think those are the issues you are facing, its more likely oxidative addition. let us know how it goes!