Modified [(IPr)Pd(R‐acac)Cl] Complexes: Influence of the acac Substitution on the Catalytic Activity in Aryl Amination

Abstract

The synthesis of a series of [(IPr)Pd(R-acac)Cl] precatalysts (acac=acetylacetonato; IPr=1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene), where the acac ligand on palladium has been systematically modified through terminal substitution, is reported. The following substituted acac ligands are employed in this study: dibenzoylmethanato (dbm), benzoylacetonato (bac), tetramethylheptanedionato (tmhd), and hexafluoroacetylacetonato (hfac). Full spectroscopic characterization of the new complexes is provided along with X-ray studies for three of these. Investigation of their catalytic activity in cross-coupling is also presented through a comparative study in an aryl amination reaction. The catalytic results show a strong correlation between the increased steric bulk of the acac substituents and an increased activation rate of the precatalyst, going from the acac to the tmhd ligand. This observation, along with the inertness of the hfac compound, seems to support our previous proposal for the activation mechanism of these complexes under cross-coupling conditions.

Well‐defined NHCPd complex‐mediated intermolecular direct annulations for synthesis of functionalized indoles (NHC = N‐hetero‐cyclic carbene)

“…It has been demonstrated recently [15,16] that, in addition to the dominant NHC ligand, other ancillary ligands surrounding the Pd metal center also play a crucial role in their catalytic performance. As a result, a variety of NHC-Pd complexes stabilized by different anionic ligands, including cinnamyl, 3, [17] and Cp, 4, [18] OAc, 5, [19] acac, 6 [20] and PPh 3 , 7, [21] were also prepared and their catalytic potential evaluated in direct annulation reactions of o-haloanilines and ketones (Scheme 2).…”

Pd-Catalyzed Alkene Diamination Reactions with O-Benzoylhydroxylamine Electrophiles: Evidence Supporting a Pd(II/IV) Catalytic Cycle, the Role of 2,4-Pentanedione Derivatives as Ligands, and Expanded Substrate Scope

“…The use of acac as a “standalone” (no added phosphine) ligand in Pd-catalyzed cross-coupling reactions is extremely rare, and the influence of the acac ligand structure on reactivity in Pd-catalyzed reactions has not thoroughly been explored . In order to determine whether the acac structure has an impact on reactivity or yield, we quickly screened Pd­(acac-F 6 ) 2 as a catalyst for the coupling of 1b with 2a to afford 3b (Table ).…”

Synthesis of Novel Palladium Complexes Containing β‐Diketonate and NHC Ligands and their Catalytic Ability for Addition Polymerizations of the Functional Norbornenes

“…Reagent grade solvents were distilled under nitrogen atmosphere over appropriate drying agents prior to use. Pd(acac) 2 , Pd(tmhd) 2 , Pd(dbm) 2 , (IMes)Pd(acac)Cl, and (IPr)Pd (acac)Cl were prepared by following the literature procedures.…”