Metal–Micelle Cooperativity: Phosphine Ligand-Free Ultrasmall Palladium(II) Nanoparticles for Oxidative Mizoroki–Heck-type Couplings in Water at Room Temperature

Abstract

The amphiphile PS-750-M generates stable, phosphine ligand-free, and catalytically active ultrasmall Pd(II) nanoparticles (NPs) from Pd(OAc) 2 , preventing their precipitation, polymerization, and oxidation state changes. PS-750-M directly interacts with Pd(II) NP surfaces, as confirmed by high-resolution mass spectrometry and IR spectroscopy, resulting in their high stability. The Pd cations in NPs are most likely held together by hydroxides and acetate ions. The NPs were characterized by HRTEM, revealing their morphology and particle size distribution, and by HRMS and IR, providing evidence for NP–amphiphile interaction. The NP catalytic activity was examined in the context of oxidative Mizoroki–Heck-type couplings in water at room temperature. Hot filtration, hot extraction, and three-phase tests indicate heterogeneous catalysis occurring at the micellar interface rather than homogeneous catalysis occurring in the solution. NMR studies indicate that the catalytic activity stems from metal cation−π interactions of the styrene along with transmetalation by the arylboronic acid, followed by insertion and β-H elimination to furnish the coupled product along with the reoxidation of Pd by benzoquinone to complete the catalytic cycle. This method is very mild and sustainable, both in terms of NP synthesis and subsequent catalysis, and shows broad substrate scope while circumventing the need for organic solvents for this important class of couplings.

Palladium-Catalyzed γ,γ′-Diarylation of Free Alkenyl Amines

“…87 While we envision that a Pd 0 nanoparticle is formed, Pd II nanoparticles have also been used for Mizoroki-Heck reactions. 88 Free amine can also react with the Pd II salt to give I', although this is not expected to be a productive pathway. Conveniently, the insertion pathway is open to both the cis and trans.…”

External Catalyst‐Free Oxidation of Benzyl Halides to Benzoic Acids Using NaOH/TBHP in Water

“…Although a variety of catalytic methods based on transition metals [3] and main group based metal‐free catalysts [4] have been developed for oxidation reactions of alcohols, most of these methods suffer from drawbacks, such as the requirement of precious metals, expensive ligands, high temperature, volatile and environmentally unfriendly organic solvents, as well as expensive and toxic additives. Recently, both in industry and academia, there are many reactions being reported of organic synthesis where traditional organic solvents are being replaced by water as a green, inexpensive and safe solvent [5a–h] . However, the development of suitable methods that can help to efficiently isolate the desired compound from the reaction mixture is also an essential part of green chemistry [5i–l] .…”

Shielding Effect of Nanomicelles: Stable and Catalytically Active Oxidizable Pd(0) Nanoparticle Catalyst Compatible for Cross-Couplings of Water-Sensitive Acid Chlorides in Water

“… 45 − 47 Our group recently leveraged this amphiphile’s ability to stabilize Pd(II) NPs and employed it in efficient oxidative Mizoroki–Heck type couplings. 48 Stabilization of Pd(II) NPs and their accommodation in the micellar interface enabled oxidative cross-couplings under mild conditions. Herein, we report a phosphine ligand-free synthesis of ultrasmall Pd(0) NPs from Pd(II) salt in an aqueous micellar solution and their applications in cross-couplings of water-sensitive acid chlorides ( Figure 1 ).…”