Initially Pd(OAc)2 and Xantphos were employed in our assay reaction [0.35 mmol 6, 2 eq. KO t Bu, 2.5 mL C6H6, 456 nm LED, 24 h], which, besides affording xylene 9, yielded coupled products 8 and 7 in a ratio of 6.5:1 (Table , entry 1), a notably higher ratio than had been observed under thermal conditions. However, subsequent control reactions showed that KO t Bu in combination with Xantphos or other ligands (entry 2 and S.I), in the absence of palladium, can initiate coupling under irradiation. This additional photoactivated pathway makes KO t Bu unsuitable for photoexcited palladium couplings in our assay reaction. Alternative bases as weak as Cs2CO3, provided coupled products in improved yields (entries 3-5), which is notable as, under thermal conditions, only stronger potassium alkoxide bases such as KO t Bu can promote BHAS coupling (vide infra). However, KOAc is too weak to facilitate the photoreaction (entry 6) and provides similar yields to a reaction in the absence of base (entry 7). Reaction in the absence of base facilitates a ca. 15% conversion of 6 into products, indicating that Cs2CO3 and related bases have a role to play that is different than the role of base in BHAS, and most likely involves regeneration of Pd 0 , as discussed later. Control reactions show that both ligands and Pd(OAc)2 are needed to facilitate coupling (entries 8-9). Reactions were measured to reach 60 °C during irradiation without cooling, but a reaction at 60 °C in the absence of irradiation provided only trace products (entry 10). In a reaction in the absence of haloarene 6, small quantities of biphenyl were still observed (entry 11). Repeating the reaction in benzene-d6 afforded unlabelled biphenyl and confirmed the ligand phenyl groups as the origin of this product (see S.I. Table , entry 15). Exchanging 6 for 2bromo-m-xylene did not significantly hinder the reaction (entry 12), while 2-chloro-m-xylene proved inefficient in this system (entry 13). Recently Maiti reported cross electrophile coupling (XEC) between (hetero)aryl halides enabled by visible light-induced palladium catalysis; 27 however, homocoupling was not observed under our conditions, likely due to the steric hindrance of 6 and its derivatives.