It is now possible to carry out Heck reactions in the absence of phosphine ligands, but the disadvantage is that the palladium becomes deactivated and gives Pd(O) sediments.  These can be reduced by using certain reaction conditions (NMP solvent, Et3N base, Pd(OAc)2 catalyst).  Precipitation of the “spent” palladium onto a solid support, followed by filtration frees the solution from Pd residues but the recovered palladium has low activity.  Treatment with oxidising agents (a small amount of Br2 or I2 is best) reactivates the catalyst and allows re-use of the catalyst (A H M de Vries, Adv Synth Catalysis, 2002, 344, 996).