Nucleophilic Attack on (π‐Allyl)palladium Complexes: Direction of the Attack to the Central or Terminal Carbon Atom by Ligand Control

Abstract

Strongly stabilized carbon nucleophiles such as dialkyl malonates can also attack the central carbon of (π‐allyl)palladium complexes. The regiochemistry of the reaction (attack at the terminal or C2 carbon atom; see picture) is controlled by the choice of the ligands L in the palladium complex. E = CO2Et, L = PPh3, PtBu3, P(OPh)3, etc.

Reaction Mechanism, Origins of Enantioselectivity, and Reactivity Trends in Asymmetric Allylic Alkylation: A Comprehensive Quantum Mechanics Investigation of a C(sp3)–C(sp3) Cross-Coupling

“…In addition to reactivity at the π-allyl carbon termini, nucleophilic attack at the central carbon of the allyl fragment to afford palladacyclobutane species is known . Previous experimental and computational studies find the mode of reactivity to be highly dependent on the σ-donating/π-accepting nature of the ancillary ligand and the basicity of the nucleophile .…”

“…In addition to reactivity at the π-allyl carbon termini, nucleophilic attack at the central carbon of the allyl fragment to afford palladacyclobutane species is known . Previous experimental and computational studies find the mode of reactivity to be highly dependent on the σ-donating/π-accepting nature of the ancillary ligand and the basicity of the nucleophile . Palladacyclobutane complexes have been proposed as mechanistic intermediates in palladium-mediated cyclopropanation reactions, as well as isolated and characterized by X-ray crystallography …”

Advances in Palladium‐Catalyzed Decarboxylative Cycloadditions of Cyclic Carbonates, Carbamates and Lactones

“…In contrast, electron‐deficient ligands tended to produce the spirocyclic 2‐pyrrolidinone 164 f . These results could be attributed to that because the two empty n (non‐bonding) and π * (antibonding) orbitals of π ‐allyl palladium moiety are very close in energy level, [61b–d] electron‐deficient ligand would facilitate lowering the energy level of the π *‐derived empty orbital. Thus the π * orbitals overlapped well with the HOMO of the incoming nucleophile to produce the preferential formation of palladacyclobutane 4.1B (Scheme 78), delivering the spirocyclic 2‐pyrrolidinone 164 f after reductive elimination of the palladacyclobutane.…”

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

“…Hoffmann confirmed the attack of nucleophile on the central carbon of allyl ligand of π-allylpalladium complex by isolation of the reaction intermediate formed by the nucleophilic attack on a π-allylpalladium complex . 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 .…”

“…7 Backvall 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 carbonattacked product was given when nitrogen ligand was used. 8 Musco and Santi reported a catalytic version of the cyclo-propanation reaction using 1,1′-bis(diphenylphosphino)ferrocene (DPPF) as ligand to produce allylation/cyclopropanation products in a ratio of 1.5−6.5:1. 9 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.…”