With this working hypothesis in hand, we began our investigation using an equimolar ratio of 4-bromo-2-methoxypyridine (11) and 4-iodo-1-methyl-1H-pyrazole (12) as starting materials (Fig. ). We first sought to identify suitable ancillary ligand for successful realization of this synergistic monometallic catalysis approach in the presence of Pd(OAc)2 as catalyst, Cs2CO3 as base, CH3CN as solvent, and 456 nm blue LEDs as the visible light source. After systematic experimentation with various ligands (see supporting information for details), it was determined that only phosphinebased ligands were able to produce the desired cross-coupled product, albeit in low to moderate yields. Simple trialkylphosphines were found to have deleterious effect in this catalytic paradigm, which might be due to the lack of additional stabilizing interaction, leading to the instability of the Pd(0) active catalyst supported by this class of ligands. The electron rich biaryl monophosphines were identified as the relatively good ligands for the formation of cross-coupled product 13 in moderate yield with reasonable selectivity (Fig. ). The better performance of electron rich ligand might arise from the stability of LnPd(0) active catalyst as well as improved reactivity towards oxidative addition with 11. As ancillary ligands have been found to have a huge impact on this dual palladium based catalytic cycle, we next set out to design ligands for the further improvement in yield of 13. The following factors were taken into consideration for designing the ligands: a) presence of non-covalent interactions which are shown to have influential effects on transition metal catalysts, b) modulation of steric and electronic properties to influence elementary steps . Accordingly, we have developed a new class of bench-stable phosphine ligands, namely SudipPhos (L79), to access highly selective formation of desired cross-coupled product 13 in excellent yield (86%). The inclusion of NMe2 groups at 2,4-position of the bottom ring of this biphenyl phosphine modulate its stereoelectronic properties in such a way that it can serve dual function of stabilizing the active Pd(0) complex via a π-interaction and increasing the electron density at Pd in the active catalyst resulting in facile oxidative addition (Fig. ). Furthermore, the NMe2 group at 2-position maintains an optimum steric bulk along the biaryl axis of the ligand which might simultaneously decrease the energy barrier of the direct reductive elimination from transitory Pd(III) intermediate 8. The choice of base and solvent was also crucial for successful realization of this protocol. While the use of alternative potassium containing phosphate, carbonate, acetate bases resulted in a significantly decreased yield, sodium and lithium containing bases did not produce the desired cross-coupled product (13) at all. However, organic bases such as DIPEA and 1,2,2,6,6pentamethylpiperidine (PMP) were moderately effective for this transformation (Fig. ). Other polar and non-polar solvents, such as DMF, THF, Et2O, hexane, and acetone resulted in poor yield of 13 (see Supplementary Table ). Several control reactions confirmed the necessity of metal catalyst systems, base, solvent and light source (see Supplementary Table ). To ensure that the observed cross-selectivity was the result of synergy between the two proposed catalysis mode of palladium, we performed two sets of reactions. First we examined the comparative reactivity of iodo and bromo coupling partners for a SET event in the presence of excited state palladium catalyst. An equimolar mixture of 11 and 12 was reacted with 4-tert-butylstyrene under standard conditions, affording only the pyrazole coupled product in 95% yield, but bromo starting material remained as such (Fig. ). This result validates our proposed hypothesis of reactivity differentiation based on bond dissociation enthalpy. Secondly, the reaction with stoichiometric amount of independently synthesized oxidative addition complex of 12 afforded the cross-coupled product only in 10% yield, which demonstrate that the single catalytic cycle is poorly effective (Fig. ). These findings are consistent with the formation of selective cross-product from our proposed mechanistic hypothesis.