1271-03-0Relevant articles and documents
Synthesis, electronic structure, and reactivity of palladium(I) dimers with bridging allyl, cyclopentadienyl, and indenyl ligands
Chalkley, Matthew J.,Guard, Louise M.,Hazari, Nilay,Hofmann, Peter,Hruszkewycz, Damian P.,Schmeier, Timothy J.,Takase, Michael K.
, p. 4223 - 4238 (2013)
The synthesis of three new Pd(I) dimers, (μ-All)(μ-Cp){Pd(PEt 3)}2 (All = C3H5, Cp = C 5H5), (μ-All)(μ-Ind){Pd(PEt3)} 2 (Ind = C7H9), and (μ-Cp)(μ-Ind) {Pd(PEt3)}2, which contain a combination of bridging allyl, Cp, or indenyl ligands and are all supported by triethylphosphine as the ancillary ligand, is reported. The solid-state geometries, electronic structures, and reactivity of these new compounds have been compared with those of the dimers (μ-All)2{Pd(PEt3)}2 and (μ-Cp)2{Pd(PEt3)}2, which have previously been reported. This work establishes that there are many similarities in the solid-state and electronic structures of complexes containing bridging allyl, Cp, or indenyl ligands. For example, in all cases the bridging ligands bind through three carbon atoms to the two Pd atoms, with only the central carbon atom of the bridging group bound to both metal centers. However, there are also important differences based on the identity of the bridging ligand. As a result of different overlap between the metal centers and the π orbitals of the bridging allyl, Cp, or indenyl ligand, Cp ligands are more likely to result in an anti relationship between the two bridging ligands, while allyl and indenyl ligands are more likely to give a syn relationship. The solid-state structures indicate that bridging allyl ligands bind the most tightly to the metal center and bridging Cp ligands bind the least tightly. DFT calculations reveal that the nature of the bridging ligand alters the HOMO of the Pd(I) dimers. As a result, in some cases it is possible to selectively protonate one of the bridging ligands using the electrophile 2,6-lutidinium chloride.
Knoevenagel Adducts as Trimethylenemethane Dipole Surrogates
Vertesaljai, Peter,Navaratne, Primali V.,Grenning, Alexander J.
, p. 317 - 320 (2016)
Knoevenagel adducts derived from readily available acetoxyacetone and malonic acid derivatives served as trimethylenemethane surrogates for formal 1,3-difunctionalization through a sequence of selective γ-deprotonation/α-alkylation and palladium(0)-catalyzed allylic alkylation. Herein, we report the discovery and development of a three-component 1,3-difunctionalization of Knoevenagel adducts as well as a unique palladium(0)-catalyzed branch-selective allylic alkylation.
Mechanism of the reaction of an NHC-coordinated palladium(II)-hydride with O2 in acetonitrile
Knapp, Spring M. M.,Konnick, Michael M.,Stahl, Shannon S.
, (2020/03/25)
PdII-hydride species are important intermediates in many Pd-catalyzed aerobic oxidation reactions, and their reaction with molecular oxygen has been the subject of considerable previous study. This investigation probes the reactivity of trans-[(IMes)2Pd(H)(OBz)] (IMes = 1,3-dimesitylimidazol-2-ylidene) with O2 in acetonitrile, a polar coordinating solvent that leads to substantial changes in the kinetic behavior of the reaction relative the previously reported reaction in benzene and other non-coordinating solvents. In acetonitrile, the benzoate ligand dissociates to form the solvent-coordinated complex trans-[(IMes)2Pd(H)(NCMe)][OBz]. Upon exposure to O2, this cationic PdII–H complex reacts to form the corresponding PdII-hydroperoxide complex trans-[(IMes)2Pd(OOH)(NCCD3)][OBz]. Kinetic studies of this reaction revealed a complex rate law, rate = k1k2[3][OBz]/(k?1[CD3CN] + k2[OBz]) + k3[3][OBz], which is rationalized by a mechanism involving two parallel pathways for rate-limiting deprotonation of the PdII–H species to generate the Pd0 complex, Pd(IMes)2. The latter complex undergoes rapid (kinetically invisible) reaction with O2 and BzOH to afford the PdII-hydroperoxide product. The results of this study are compared to observations from the previously reported reaction in benzene and discussed in the context of catalytic reactivity.
Pd(0)-catalyzed alkene oxy- and aminoalkynylation with aliphatic bromoacetylenes
Nicolai, Stefano,Sedigh-Zadeh, Raha,Waser, Jeroime
, p. 3783 - 3801 (2013/06/26)
Tetrahydrofurans and pyrrolidines are among the most important heterocycles found in bioactive compounds. Cyclization-functionalization domino reactions of alcohols or amines onto olefins constitute one of the most efficient methods to access them. In this context, oxy- and aminoalkynylation are especially important reactions, because of the numerous transformations possible with the triple bond of acetylenes, yet these methods have been limited to the use of silyl protected acetylenes. Herein, we report the first palladium-catalyzed oxy- and aminoalkynylation using aliphatic bromoalkynes, which proceeded with high diastereoselectivity and functional group tolerance. A one-pot hydrogenation of the triple bond gave then access to alkyl-substituted tetrahydrofurans and pyrroldines. Finally, a detailed study of the side products formed during the reaction gave a first insight into the reaction mechanism.
