Cyclic Palladium Formamidinate: Synthesis, Structure, Reactivity, and Application to Suzuki–Miyaura Cross-Coupling

Abstract

The deprotonation of acyclic palladium amidine chloride (1) with potassium tert-butoxide in tetrahydrofuran results in palladium bis(formamidinate) (2). 2 undergoes a nucleophilic addition reaction with acetonitrile in the presence of PdCl 2 or Pd(OAc) 2 (OAc = acetate) to give dinuclear cyclic six-membered (triazapentadiene)palladium complexes (4a and 4b). These compounds are also prepared from cyclic six-membered (tap)PdCl 2 (5; tap = triazapentadiene) or formamidinium salts (6a−6c) with Pd(OAc) 2 /NaOAc in acetonitrile, whereas the direct reaction of 2 with acetonitrile or acrylonitrile resulted in palladium black or an acyclic C−N-coupled product (3). A comparison of structure 4 from 2 suggests a possible intermediate dinuclear palladium complex whose structure was identified through theoretical calculations. Further, Suzuki−Miyaura cross-coupling reactions were carried out under different solvents notably in an ethanol/water medium at room temperature.

N‐Heterocyclic Carbene‐Palladium Polymers Network: Recyclable Pre‐catalyst for Effective Suzuki–Miyaura Coupling Reaction in Water

“…The transition‐metal‐catalyzed cross‐coupling reaction is one of the most valuable and straightforward methods for the formation of carbon‐nitrogen or carbon‐carbon bonds in modern organic synthesis, [1–4] especially in chemical and pharmaceutical [5,6] . Among them, the palladium‐catalyzed Suzuki–Miyaura cross‐coupling reaction between organic halides and boronic acids is one of the most convenient and efficient methods for the synthesis of biaryls [7–10] . Sustainable efforts have been devoted to developing the palladium complex catalytic systems with interesting structures, properties as well as uniform solubility at the molecular level in the reaction medium, therefore, exhibiting high catalytic activity [11–14] .…”

“…[5,6] Among them, the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction between organic halides and boronic acids is one of the most convenient and efficient methods for the synthesis of biaryls. [7][8][9][10] Sustainable efforts have been devoted to developing the palladium complex catalytic systems with interesting structures, properties as well as uniform solubility at the molecular level in the reaction medium, therefore, exhibiting high catalytic activity. [11][12][13][14] However, molecular homogeneous catalysts suffer from difficult separation from the reaction mixture, leaching of expensive palladium metal, products contamination with trace metals, catalyst deactivation through the agglomeration, and difficulty in recycling, which limit their wide application in industry.…”