Other classes of promising air-stable Ni(0) catalysts have subsequently been disclosed by Cornella and Engle, with Ni(0) centers stabilized by either stilbene or quinone p-acids. These catalysts possess the advantage of enabling modular in situ coordination to different ligands, whereas the NHC/p-acid combinations have the advantage of being a single-component system with pre-defined structure and metalligand stoichiometry, as illustrated with electronic-deficient akenes and other olefin classes. We envision that the latter characteristics will offer unique advantages with NHC catalysts in high-throughput arrayed methods where inefficient mixing and imprecise control of metal-ligand stoichiometry are avoided with a single-component, well-defined catalyst source. Prior studies from numerous laboratories have illustrated that judicious choice of alkene ligands can play a key role in tuning the stability and reactivity of numerous families of Ni(0) catalysts, a current gap in the field is the understanding of how Ni(0) complexes stabilized by simple ligands undergo activation to more active forms of the catalyst. A question that remains unanswered for most Ni(0) precatalysts is whether simple ligand dissociation affords active catalyst forms, or if more complex activation steps involving chemical modification of the alkene are required. We have now studied this question in detail with new fumarate catalysts that build on the design features of an NHC ligand paired with a p-acid selected to balance stability and reactivity. In this study, the fate of the stabilizing alkene ligand and mechanism of catalyst activation are elucidated through experimental and computational studies that evaluated different mechanisms for catalyst activation, including displacement as well as covalent sequestration of the stabilizing p-acid.