A further survey of ligands was then carried out using Pd(OAc)2, as the range of ligands routinely employed in visible light-promoted palladium reactions is relatively small compared to that of the ground-state. DPEPhos, a structural relative of Xantphos, also facilitated radical coupling, albeit in lower yields (Table , entry 2). A range of ferrocene-based ligands and BINAP (entries 3-6), all of which initiated BHAS under ground-state conditions with KO t Bu, as well as bulky XPhos (entry 7), also produced ratios of 8:7 that were consistent with radical processes. It is notable that dippf, which bears no phenyl groups on the phosphine, also provides a high 8:7 ratio of 4.8. Interestingly, when ligands that under thermal conditions promoted non-radical coupling were employed (Dppe, PPh3 and PCy3, entries 8-10), ratios were now observed that supported a radical mechanism, highlighting an entirely different reactivity under irradiation. Tertiary alkyl phosphine P t Bu3 was not very effective in the reaction (entry 11). Alternative palladium sources were explored (Table ). As expected in the absence of phosphine ligands, Pd2dba3 or PdCl2 did not facilitate the reaction (entries 1-2). When either Xantphos or BINAP was added to either of these Pd sources (entries 3-5), effective couplings were seen, similar to those obtained in Table using Pd(OAc)2, indicating a similar Pd active catalyst. Employing Pd(PPh3)4 in the reaction (entry 6) provided results comparable to using Pd(OAc)2/4PPh3 (table 2, entry 9), while (PPh3)2PdCl2 alone was quite ineffective (entry 7). Addition of Xantphos to either of these Pd sources (entries 8-9) as a mixed-ligand system (i.e. combination of bidentate and monodentate phosphines) led to significantly higher yields, but slightly lower 8:7 ratios. Kinetic isotope effects Scheme 2. Kinetic isotope effects for attack of xylyl radical on benzene, or HAT by xylyl radical.