Ambivalence of nucleophilic attack on central and terminal allyl carbon atoms of [(η3-allyl)ML2]+ (M  Pd or Pt) complexes

Pd-Catalyzed Asymmetric Cyclopropanation Reaction of Acyclic Amides with Allyl and Polyenyl Carbonates. Experimental and Computational Studies for the Origin of Cyclopropane Formation

“…Bäckvall showed that a nucleophile was favored to attack the terminal carbon of π-allylpalladium complex using a Pd-catalyst with phosphine as ligand, whereas a central carbon-attacked product was given when nitrogen ligand was used . Musco and Santi reported a catalytic version of the cyclopropanation reaction using 1,1′-bis­(diphenylphosphino)­ferrocene (DPPF) as ligand to produce allylation/cyclopropanation products in a ratio of 1.5–6.5:1 . Satake realized cyclopropanation using a neutral Pd-catalyst, asymmetric catalytic version of the reaction was also provided though the allylation/cyclopropanation ratio as well as the ee values were rather lower .…”

Pyridine-NHC: Effective Ligand in Pd-Catalyzed Cyclopropanation of Esters with Substituted Allyl Carbonates

“…From the reaction mechanism, the valence state of Pd for allylic substitution is Pd(0) to Pd(II) to Pd(0), whereas that for cyclopropanation should be Pd(0) to Pd(II) to Pd(II) to Pd(0) (Figure ). Good yields of cyclopropanation products were afforded by the Hegedus and Hoffmann groups when they used HMPA/Et 3 N and TMEDA as ligand, but lower ratios of cyclopropanes were obtained when Musco and co-workers used a diphosphine ligand, though both N and P are coordination atoms with strong σ-donor character. − Bäckvall and colleagues had a similar observation that nucleophile favored terminal attack of π-allylpalladium with phosphine ligands while central carbon-attacked product was given if a nitrogen ligand was used in the Pd-catalyzed reaction of an allyl substrate and nucleophile . These results indicate that the nitrogen ligands TMEDA and Et 3 N, the tertiary amine, should be beneficial for the cyclopropane formation.…”

“…Hegedus et al were the first to observe the formation of cyclopropane via the attack of a nucleophile to the central carbon of the π-allylpalladium complex in 1980 . Since then, some procedures appeared for the preparation of cyclopropanes by Pd-mediated/catalyzed reaction of allyl reagents with nucleophiles. − Hoffmann and co-workers reported the cyclopropanation reaction of a Pd-ally complex with nucleophiles in the presence of tetramethyl ethylenediamine (TMEDA) in a stoichiometric manner . Musco and co-workers developed a catalytic version of the reaction with DPPF as ligand to afford allylation and cyclopropanation products in a ratio of 1.5–6.5/1 .…”

“…Since then, some procedures appeared for the preparation of cyclopropanes by Pd-mediated/catalyzed reaction of allyl reagents with nucleophiles. − Hoffmann and co-workers reported the cyclopropanation reaction of a Pd-ally complex with nucleophiles in the presence of tetramethyl ethylenediamine (TMEDA) in a stoichiometric manner . Musco and co-workers developed a catalytic version of the reaction with DPPF as ligand to afford allylation and cyclopropanation products in a ratio of 1.5–6.5/1 . The Satake group made a substantial improvement using a catalytic amount of neutral Pd-pyridinylpyrazole catalyst in the reaction of esters and allyl reagents, providing cyclopropanes in high yields with three examples .…”

Mechanisms of the Nucleophilic Substitution of the Allyl Carbons of (π-Allyl)platinum and (π-Allyl)palladium Complexes

“…In the allylic alkylation reactions, a nucleophile attacks the allyl moiety, either at the terminal carbon or at the central carbon. The nucleophilic attack at the central carbon of a π-allyl ligand attached to transition metals has attracted much attention. − For instance, the nucleophilic attack to the central carbon of an allyl moiety in (π-allyl)platinum complexes has been reported for the reactions of oxatrimethylenemethane, azatrimethylenemethane, 2-chloro-2-propenyl ethyl carbonate, 2-chloro-2-propenyl- N,N -diethylcarbamate, and 2-chloro-2-propenyl acetate with platinum complexes. − Unlike the usual cases in which a nucleophile attacks a terminal carbon of an allyl moiety to give alkene complexes, this process converts (π-allyl)metal complexes into various metallacyclobutanes. − In some cases, it leads to the formation of cyclopropane derivatives through reductive elimination from metallacyclobutanes. − On the other hand, nucleophilic attacks at the terminal carbon have been reported for (π-allyl)palladium complexes. These reactions afford the allylated products, except for the cases that have been carried out by using complexes with some amine ligands 11,13,14 (eq 1).…”