Second Comes First: Switching Elementary Steps in Palladium‐Catalyzed Cross‐Coupling Reactions

: The electron-poor palladium(0) complex L3Pd (L = tris(3,5-bistrifluoromethylphenyl)phosphine) reacts with Grignard reagents RMgX and organolithium compounds RLi via transmetalation to furnish the anionic organopalladates [L2PdR]¯, as shown by negative-ion mode electrospray-ionization mass spectrometry. These palladates undergo oxidative additions of organyl halides R'X (or related SN2-type reactions) followed by further transmetalation. Gas-phase fragmentation of the resulting heteroleptic palladate(II) complexes results in the reductive elimination of the cross-coupling products RR'. This reaction sequence corresponds to a catalytic cycle, in which the order of the elementary steps of transmetalation and oxidative addition is switched relative to that of palladium-catalyzed cross-coupling reactions proceeding via neutral intermediates. An attractive feature of the palladate-based catalytic system is its ability to mediate challenging alkyl-alkyl coupling reactions. However, the poor stability of the phosphine ligand L against decomposition reactions so far prevents its successful use in practical applications.