Further mechanistic analysis, supported by stoichiometric Pd chemistry. With only limited information to base our mechanistic predictions about the catalytic cycle(s) operative in this complicated chemistry, we recognized that our HTE/data analysis would be complemented by traditional stoichiometric studies involving appropriate Pd precursor compounds. Previously proposed catalytic cycles reported by Porée et al. were based primarily on DFT calculations using PH3 as a model for the PPh3 ligand (along with an N-methyl substrate variant of 1a). Such a model makes a Pd II /Pd IV catalytic cycle possible, in principle (Scheme 2). While higher oxidation state Pd IV intermediates are experimentally feasible, 10 evidence for the stabilization of Pd IV species by phosphines is relatively limited, exceptions being PPh3 34 and transphos. Indeed, the scientific community at large have often doubted Pd catalytic cycles involved phosphine-stabilized Pd IV intermediates. While dppe could be related to these ligands, we conducted stoichiometric 31 P NMR and MS experiments to better understand dppe interactions at Pd. (3) taken after 45 minutes heating at 80 °C; (4) taken after 16 hours heating at 80 °C. We have assigned species to the five phosphorus species, cross-referenced with the ESI-MS analysis. The species at δ 57.35 is a trace product, derived from the formation of Pd 0 (dba)(dppe) / Pd 0 (dppe)2, which is distinct to the species at δ 56.77 ppm, formed at higher temperature, assigned to PdBr2(dppe) VIII.