N-Heterocyclic-Carbene Complexes Readily Prepared from Di-μ-hydroxopalladacycles Catalyze the Suzuki Arylation of 9-Bromophenanthrene

A Second-Generation Palladacycle Architecture Bearing a N-Heterocyclic Carbene and Its Catalytic Behavior in Buchwald–Hartwig Amination Catalysis

Palladacyclic architectures have been shown as versatile motifs in cross-coupling reactions. NHC-ligated palladacycles possessing unique electronic and steric properties have helped to stabilize the catalytically active species and provide additional control over reaction selectivity. Here, we report on a synthetic protocol leading to palladacycle complexes using a mild base and an environmentally desirable solvent, with a focus on complexes bearing backbone-substituted N-heterocyclic carbene ligands. The readily accessible complexes exhibit high catalytic activity in the Buchwald–Hartwig amination. This is achieved using low catalyst loading and mild reaction conditions in a green solvent.

Lewis-Acid-Catalyzed Selective Friedel-Crafts Reaction or Annulation between Anilines and Glyoxylates

A Lewis-acid-catalyzed selective reaction between anilines and glyoxylates was developed for synthesis of diarylmethanes or oxoimidazolidines. Under the catalysis of AgOTf, a series of anilines-based diarylmethanes, including primary, secondary, and tertiary anilines, were obtained in moderate to good yields. Moreover, stereoselective oxoimidazolidines were performed with the catalysis of Cu(OAc)₂·H₂O.

A comprehensive review of caged phosphines: synthesis, catalytic applications, and future perspectives

Caged phosphines are versatile ligands due to their rigid backbones, exhibiting a range of catalytic activities, as depicted through the given pictorial representation.

Ligand Steric Effects of α-Diimine Nickel(II) and Palladium(II) Complexes in the Suzuki-Miyaura Cross-Coupling Reaction

Nickel catalysts represent a low cost and environmentally friendly alternative to palladium-based catalytic systems for Suzuki-Miyaura cross-coupling (SMC) reactions. However, nickel catalysts have suffered from poor air, moisture, and thermal stabilities, especially at high catalyst loading, requiring controlled reaction conditions. In this report, we examine a family of mono- and dinuclear Ni(II) and Pd(II) complexes with a diverse and versatile α-diimine ligand environment for SMC reactions. To evaluate the ligand steric effects, including the bite angle in the reaction outcomes, the structural variation of the complexes was achieved by incorporating iminopyridine- and acenaphthene-based ligands. Moreover, the impact of substrate bulkiness was investigated by reacting various aryl bromides with phenylboronic acid, 2-naphthylboronic acid, and 9-phenanthracenylboronic acid. Yields were the best with the dinuclear complex, being nearly quantitative (93-99%), followed by the mononuclear complexes, giving yields of 78-98%. Consequently, α-diimine-based ligands have the potential to deliver Ni-based systems as sustainable catalysts in SMC.

Thiazole-based non-symmetric NNC–palladium pincer complexes as catalytic precursors for the Suzuki–Miyaura C–C coupling

New non-symmetric pincer palladacycles, containing [N,N,C] tridentate ligands are synthesized and their catalytic activities in the Suzuki–Miyaura cross coupling reaction are tested using water under aerobic conditions and IR irradiation.

Syntheses and structural aspects of six-membered palladacyclic complexes derived fromN,N′,N′′-triarylguanidines with N- or S-thiocyanate ligands

Linkage isomers8·2/3PhMe and9·MeOH were synthesized, isolated and structurally characterized by SCXRD and the role of solvent of crystallization in the formation of these linkage isomers identified.

Palladacycle-Catalyzed Triple Suzuki Coupling Strategy for the Synthesis of Anthracene-Based OLED Emitters

The development of the site-selective Suzuki-Miyaura cross-coupling of dibromoanthracene as an efficient strategy toward organic light emitting diodes (OLEDs) is disclosed in this article. An unprecedented step-economic palladacycle-promoted triple Suzuki coupling protocol allowed the synthesis of three new OLED emitters and could prove to be a useful general strategy for researchers working in this field. Characterization of the synthesized molecules by UV-vis spectroscopy and thermogravimetric analysis-differential scanning calorimetry followed by density functional theory studies of the different properties strongly confirms the derivatives possess more significant hole mobility character than electron transfer capability.

Density Functional Theoretical Study on the Mechanism of Alcoholysis of Acylpalladium(II) Complexes

The mechanism of alcoholysis of acylpalladium(II) complexes relevant to the alternating copolymerisation of ethene and carbon monoxide has been investigated theoretically in detail. The solvolysis of acylpalladium(II) complexes is an important step in palladium-catalysed reactions. Based on experimental studies, two mechanisms have been proposed for this process, which consist of a concerted reductive elimination and an insertion mechanism (reductive elimination via a Meisenheimer intermediate). Both mechanisms include deprotonating of an acylpalladium(II) complex and according to our calculations, any mechanism involving this step, has an energy barrier higher than that of the rate-determining step. We propose a new mechanism for the insertion in which proton transfer to Pd is simultaneous with an inner-sphere attack of the alkoxide ligand (OCH3) at the carbon atom of the palladium-bound carbonyl group (new Meisenheimer intermediate). Considering solvent effects, the activation energies of the two mechanisms and other contingent mechanisms were calculated and compared with each other and the experimental results.

A new route to π-extended polycyclic aromatic hydrocarbons via cross-dehydrogenative coupling

A rare example of fruitful construction of highly π-extended PAHs expressly via palladium-catalyzed CDC reaction is demonstrated.

N-Methylphthalimide-substituted benzimidazolium salts and PEPPSI Pd-NHC complexes: synthesis, characterization and catalytic activity in carbon-carbon bond-forming reactions

A series of novel benzimidazolium salts (1–4) and their pyridine enhanced precatalyst preparation stabilization and initiation (PEPPSI) themed palladium N-heterocyclic carbene complexes [PdCl₂(NHC)(Py)] (5–8), where NHC = 1-(N-methylphthalimide)-3-alkylbenzimidazolin-2-ylidene and Py = 3-chloropyridine, were synthesized and characterized by means of ¹H and ¹³C{¹H} NMR, UV–vis (for 5–8), ESI-FTICR-MS (for 2, 4, 6–8) and FTIR spectroscopic methods and elemental analysis. The synthesized compounds were tested in Suzuki–Miyaura cross-coupling (for 1–8) and arylation (for 5–8) reactions. As catalysts, they demonstrated a highly efficient route for the formation of asymmetric biaryl compounds even though they were used in very low loading. For example, all compounds displayed good catalytic activity for the C–C bond formation of 4-tert-butylphenylboronic acid with 4-chlorotoluene.

Pincer CNC bis-N-heterocyclic carbenes: robust ligands for palladium-catalysed Suzuki–Miyaura arylation of bromoanthracene and related substrates

Novel pincer-type N-heterocyclic carbene ligands have been synthesised and characterised by FAB-MS and single crystal X-ray analysis. The ligands have proved to be highly active towards palladium-catalysed Suzuki–Miyaura cross-coupling of bromoanthracene and related substrates.