Pincer Complex-Catalyzed Allylation of Aldehyde and Imine Substrates via Nucleophilic η¹-Allyl Palladium Intermediates

Abstract

Electrophilic allylic substitution of allylstannanes with aldehyde and imine substrates could be achieved by employment of palladium pincer complex catalysts. It was found that the catalytic activity of the pincer complexes is highly dependent on the ligand effects. The best results were obtained by employment of PCP pincer complexes with weakly coordinating counterions. In contrast to previous applications for electrophilic allylic substitutions via bisallylpalladium complexes, the presented reactions involve monoallylpalladium intermediates. Thus, employment of pincer complex catalysts extends the synthetic scope of the palladium-catalyzed allylic substitution reactions. Moreover, use of these catalysts eliminates the side reactions occurring in transformations via bisallylpalladium intermediates. The key intermediate of the electrophilic substitution reaction was observed by (1)H NMR spectroscopy. This intermediate was characterized as an eta(1)-allyl-coordinated pincer complex. Density functional theory (DFT) modeling shows that the electrophilic attack can be accomplished with a low activation barrier at the gamma-position of the eta(1)-allyl moiety. According to the DFT calculations, this reaction takes place via a six-membered cyclic transition-state (TS) structure, in which the tridentate coordination state of the pincer ligand is preserved. The stereoselectivity of the reaction could be explained on the basis of the six-membered cyclic TS model.

Palladium Pincer Complex Catalyzed Cross‐Coupling of Vinyl Epoxides and Aziridines with Organoboronic Acids

“…Furthermore, palladium(0) complexes readily undergo oxidative addition to aromatic carbonÀhalogen bonds, which might be undesired limiting the synthetic scope of the corresponding reaction. [1][2][3][4] We have recently found [13][14][15][16][17][18] that palladium pincer complexes, [5,6,[19][20][21][22] such as 1 a-d [23][24][25] (Scheme 1), are particularly useful species to catalyze redox free synthesis and transformation of organo stannanes and silanes. Thus, we have shown that allylic and propargylic substrates undergo substitution reactions with dimetallic reagents (such as distannane and silylstannane reagents) to give allyl and propargyl stannanes and silanes.…”

Novel silica immobilized NCN-pincer palladium(II) and platinum(II) complexes: Application as Lewis acid catalysts

“…Current efforts focus on the use of organometallic pincersiloxane reagents for surface modification and on the use of pincer-metal silica hybrid materials for other catalytic conversions (e.g., C-C and C-X bond formation) [45,[64][65][66][67][68][69]. The integrity and stability of the silica support will be another important aspect of these studies.…”

Pd-Catalyzed Telomerization of 1,3-Dienes with Multifunctional Renewable Substrates: Versatile Routes for the Valorization of Biomass-Derived Platform Molecules

“…This can be explained by the interaction and coupling of the C8 chains of two distinct palladium intermediates, i.e. the Z The nucleophilic nature of Z 1 -allyl palladium groups, such as the s-allyl group in B, is well documented [68]. Indeed, Kiji et al demonstrated the nucleophilic nature of B itself in the telomerization of butadiene with electrophilic reagents, such as benzaldehyde, to give pyran products [57].…”