Optimal conditions developed for formation of 3a were applied to the coupling of aryl bromides 1a-1m with aryl iodides 2a-2q (Table ). An initial set of experiments, the structure of aryl bromide 1a was held constant and different aryl iodides 2a-2n were explored. It was found that coupling can occur in the presence of electron rich bromides (3b), and the reaction is tolerant of Lewis basic nitrogen heterocycles (3e), phenols (3g, 3h) and primary alcohols (3i), as well as triflates (3j), pinacol boronates (3k), anilines (3l, 3m) and unprotected indoles (3n). In a similar set of experiments, the structure of iodide 2a was held constant and different aryl bromides 1b-1h were explored. Beyond adducts derived from 2-substituted pyridines (3o, 3q) and quinolines (3p), it was found that other electron-deficient aryl bromides are tolerated, including 4bromobenzenesulfonamide (3r), 2-bromothiazole (3s), as well as methyl 5-bromo-and 4-bromothiophene-2-carboxylate methyl esters (3t, 3u). At this stage, more diverse couplings of activated bromides and electron rich iodides were surveyed, and similarly high levels of functional group compatibility were observed. Notably, pinacol boronates (3k, 3mm) and anilines (3l, 3m, 3cc, 3jj) are tolerated, demonstrating orthogonality with respect to Suzuki and Buchwald-Hartwig coupling processes. It also bears mentioning that 2bromopyridines and related 2-bromoheterocycles are especially effective participants, as corresponding 2-heteroaryl boronates are problematic coupling partners due to facile protodeboronation. In cases where lower yields are obtained, for example, 3ff, homo-coupling of the bromide or iodide accounted for the majority of the mass balance, likely due to disparate rates of oxidative addition (vide infra). Indeed, under standard conditions, homo-coupling of bromides or iodides is an efficient process (Figure ). Notably, aryl halide transfer hydrogenolysis was seldom observed, although palladiumcatalyzed processes of this type are well-established. 16 Although the present processes appear to involve dimeric palladium species (vide supra), we were keen to assess the feasibility of generating diaryl Pd(II) species from monometallic aryl palladium complexes via palladium-to-palladium transmetalation. Hence, the synthesis and stoichiometric reaction of the arylpalladium oxidative addition complexes derived from 2-bromo-6-methylpyridine 1a and 4-iodoanisole 2a were explored (Scheme 1). As the P t Bu3-modified complexes Pd(X)(P t Bu3)(Ar) (X = Br, I) could not be isolated in pure form, the more tractable XPhos-modified complexes Pd-1a and Pd-2a were prepared. Heating equimolar quantities of Pd-1a and Pd-2a in dioxane:H2O (9:1, 0.02 M) at 100 ⁰C for 1 hour resulted in formation of the cross-coupled product 3a in 42% yield. The formation of dimer-1a accounted for the remaining mass balance of Pd-1a. Mass spectrometric analysis of the reaction mixture also revealed the presence of the indicated arylated XPhos derivative XPhos-2a, which arises from a known Heck-type side reaction. Although intramolecular transfer of the 4-methoxyphenyl moiety of Pd-2a to XPhos limits the yield of 3a, the conversion of Pd-1a and Pd-2a to 3a and dimer-1a corroborates palladium-to-palladium transmetalation, albeit in a monometallic system. Notably, Pd-1a and 4-iodoanisole 2a do not react under these conditions to form 3a, suggesting aryl halide oxidative addition to form diaryl Pd(IV) intermediates 25 or mechanisms involving C-X reductive elimination are not operative.