Reactivity and Stability of Dinuclear Pd(I) Complexes: Studies on the Active Catalytic Species, Insights into Precatalyst Activation and Deactivation, and Application in Highly Selective Cross-Coupling Reactions

Abstract

The catalysis derived from the dinuclear Pd(I)-Pd(I) complex, {[PtBu(3)]PdBr}(2), has been studied with experimental, computational, and spectroscopic techniques. Experimental selectivity studies were performed, and the reactivity was subsequently investigated with density functional theory (B3LYP-D and M06L) to deduce information on the likely active catalytic species. The reactivity with aryl chlorides and bromides was found to be inconsistent with direct catalytic involvement of the Pd(I) dimer but consistent with mononuclear Pd(0) catalysis. Computational studies suggest that precatalyst transformation to the active catalytic species does not proceed via a direct disproportionation mechanism; a reductive pathway is the most likely scenario instead. Through (31)P NMR investigations it was identified that the combination of ArB(OH)(2), KF, and water triggers the conversion of the precatalyst to Pd(PtBu(3))(2) and, most likely, Pd-black as a competing side process, explaining the incomplete conversions of aryl chlorides in Suzuki cross-coupling reactions under Pd(I) dimer conditions. New applications in highly regio- and chemoselective transformations in short reaction times at room temperature are also demonstrated.

Air-Stable Dinuclear Iodine-Bridged Pd(I) Complex - Catalyst, Precursor, or Parasite? The Additive Decides. Systematic Nucleophile-Activity Study and Application as Precatalyst in Cross-Coupling

“…9 The alternative disproportionation to Pd (0) (PtBu 3 ) 2 and Pd (II) Br 2 was also highly disfavored (ΔG rxn = 65.4 kcal/mol). No direct conversion of the Pd (I) dimer to the active species will, therefore, take place, and external stimuli, i.e., in the form of other reagents, are necessary for activation.…”

Computational Studies of Synthetically Relevant Homogeneous Organometallic Catalysis Involving Ni, Pd, Ir, and Rh: An Overview of Commonly Employed DFT Methods and Mechanistic Insights

“…One way to overcome this issue is through the use of precatalysts. 182 In this context, Hazari and Balcells studied a class of (μ-allyl)(μ-Cl)Pd 2 (NHC) 2 dimers as the source for highly active monoligated Pd(0). 183 (iPrOH) M06L/6-31G(d) (SDD) level of theory in combination with experimental studies uncovered a mechanism for the activation of these Pd(I) dimers by various nucleophiles (i.e., Nu = isopropanol or olefins) to release Nu−Pd(0)−NHC and Pd(II).…”

Palladium (0) catalyzed Suzuki cross-coupling reactions of 2,4-dibromothiophene: selectivity, characterization and biological applications

“…The compound 2b has already been reported by different methodologies. [17,19,21] In the present study, various compounds (2a-f) were synthesized using the Suzuki-coupling reactions in the presence of two different bases, namely, K 3 PO 4 and K 2 CO 3 . Since both water and base were found to be necessary to activate boronic acid reactions, [22] the correct combination of solvent and base was extremely important.…”

“…The authors found that in the case of brominated thiophenes, the cross-coupling preferably occurs at the C-2-position. [17] Due to this regioselectivity of coupling at the C-2 position, there is paucity of work for conducting a second coupling at the remaining C4 position. Bey et al [18] presented in their work that bis(hydroxyphenyl) thiophenes exhibited a high selectivity to 17β-hydroxysteroid dehydrogenase type 2 (17β-HSD2).…”