An alternative explanation for the triflate selectivity observed with SIMes is that oxidative addition involves an anionic species [Pd(SIMes)X]−(X = small anionic ligand).20Indeed,DFT calculations predict that an anionic transition structure involving [Pd(SIMes)(OH)]−(TS33a) favors reaction attriflate by 1.5 kcal mol−1(Figure 2B). Formation of apalladium hydroxide species is plausible under the catalytic conditions, which include both water and base (KF). The preference for [Pd(SIMes)OH]− to react at OTf is consistent with previously reported calculations using phosphine ligands.Anionic [Pd(PtBu3)X]−(X = F−or PhB(OH)O−) has been shown computationally to favor oxidative addition at C−OTfover C−Cl. However, interestingly, previous studies suggest that involvement of putative [Pd(PtBu3)X]− is only favored in certain polar solvents like DMF and MeCN.23InTHF or other nonpolar solvents, the active catalyst is [Pd(PtBu3)] and preferential SM cross-coupling at C−Cl is observed. As such, if [Pd(SIMes)X]−is the active catalyst inTHF, it suggests that SIMes is better than PtBu3at stabilizing anionic Pd. Further studies will be needed to distinguish between mechanisms involving [Pd(SIMes)2], [Pd(SIMes)-X]−, or other active catalysts