TY - JOUR
T1 - On the Nature of the Intermediates and the Role of Chloride Ions in Pd-Catalyzed Allylic Alkylations: Added Insight from Density Functional Theory
AU - Fristrup, Peter
AU - Ahlquist, Mårten Sten Gösta
AU - Tanner, David Ackland
AU - Norrby, Per-Ola
PY - 2008
Y1 - 2008
N2 - The reactivity of intermediates in palladium-catalyzed allylic alkylation was investigated using DFT (B3LYP) calculations including a PB-SCRF solvation model. In the presence of both phosphine and chloride ligands, the allyl intermediate is in equilibrium between a cationic eta(3)-allylPd complex with two phosphine ligands, the corresponding neutral complex with one phosphine and one chloride ligand, and a neutral eta(1)-allylPd complex with one chloride and two phosphine ligands. The eta(1)-complex is unreactive toward nucleophiles. The cationic eta(3)-complex is the intermediate most frequently invoked in the title reaction, but in the presence of halides, the neutral, unsymmetrically substituted eta(3)-CoMplex will be formed rapidly from anionic Pd(0) complexes in solution. Since the latter will prefer both leaving group ionization and reaction with nucleophiles in the position trans to phosphorus, it can rationalize the observed "memory effect" (a regioretention) in the title reaction, even in the absence of chiral ligands.
AB - The reactivity of intermediates in palladium-catalyzed allylic alkylation was investigated using DFT (B3LYP) calculations including a PB-SCRF solvation model. In the presence of both phosphine and chloride ligands, the allyl intermediate is in equilibrium between a cationic eta(3)-allylPd complex with two phosphine ligands, the corresponding neutral complex with one phosphine and one chloride ligand, and a neutral eta(1)-allylPd complex with one chloride and two phosphine ligands. The eta(1)-complex is unreactive toward nucleophiles. The cationic eta(3)-complex is the intermediate most frequently invoked in the title reaction, but in the presence of halides, the neutral, unsymmetrically substituted eta(3)-CoMplex will be formed rapidly from anionic Pd(0) complexes in solution. Since the latter will prefer both leaving group ionization and reaction with nucleophiles in the position trans to phosphorus, it can rationalize the observed "memory effect" (a regioretention) in the title reaction, even in the absence of chiral ligands.
U2 - 10.1021/jp801759z
DO - 10.1021/jp801759z
M3 - Journal article
C2 - 18630868
SN - 1089-5639
VL - 112
SP - 12862
EP - 12867
JO - Journal of Physical Chemistry A
JF - Journal of Physical Chemistry A
IS - 50
ER -