Mechanisms of 1,1-Reductive Elimination from Palladium

Article abstract of DOI:10.1021/ja00535a018

The 1,1-reductive elimination of ethane from three cis-bis(phosphine)dimethylpalladium complexes, L2Pd(CH3)2 (L = PPh3, PPh2CH3; L2 = Ph2PCH2CH2PPh2), and three trans analoques phenantrene (TRANSPHOS)> was carried out.The three cis complexes underwent reductive elimination in the presence of coordinating solvents (Me2SO, DMF, THF).The trans complexes which could isomerize to cis (L = PPh3, PPh2CH3) did so in polar solvents and then underwent reductive elimination. (TRANSPHOS)dimethylpalladium would not undergo reductive elimination of ethane, even at 100 deg C in Me2SO.The eliminations from the cis isomers were intramolecular as determined by the lack of crossover with the pentadeuteriomethylpalladium analogue and displayed first-order kinetics (k = 1.04 * 10_-3 s_-1, L = PPh3, 60 deg C; K = (6.5-9.5) * 10_-5 s_-1, L = PPh2CH3, 60 deg C; k = 4.78 * 10_-7 s_-1, L2 = Ph2PCH2CH2PPh2, 80 deg C).The presence of diphenylacetylene in the reaction mixture traps the palladium(0) product as the bis(diphenylmethylphosphine)(diphenylacetylene)palladium complex.Although (TRANSPHOS)dimethylpalladium would not undergo a 1,1-reductive elimination of ethane, the addition of CD3I to a Me2SO soliution of this complex at 25 deg C rapidly produced CD3-CH3, implicating a transient palladium(IV) intermediate.