Ubiquitous Role of Phosphine-Based Water-Soluble Ligand in Promoting Catalytic Reactions in Water

Catalysis has been at the forefront of the developments that has revolutionised synthesis and provided the impetus in the discovery of platform technologies for efficient C-C or C-X bond formation. Current environmental situation however, demands a change in strategy with catalysis being promoted more in solvents that are benign (Water) and for that the development of hydrophilic ligands (especially phosphines) is a necessity which could promote catalytic reactions in water, allow recyclability of the catalytic solutions and make it possible to isolate products using column-free techniques that involve lesser usage of hazardous organic solvents. In this review, we therefore critically analyse such catalytic processes providing examples that do follow the above-mentioned parameter.

Functionalization of Framboidal Phenylboronic Acid-Containing Nanoparticles via Aqueous Suzuki-Miyaura Coupling Reactions

Polymeric nanoparticles with reactive functional groups are an attractive platform for drug carriers that can be conjugated with drugs through a cleavable covalent linkage. Since the required functional groups vary depending on the drug molecule, there is a need for development of a novel post-modification method to introduce different functional groups to polymeric nanoparticles. We recently reported phenylboronic acid (PBA)-containing nanoparticles (BNP) with a unique framboidal morphology created via one-step aqueous dispersion polymerization. Since BNPs have high surface area due to their framboidal morphology and contain a high density of PBA groups, these particles can be used as nanocarriers for drugs that can bind to PBA groups such as curcumin and a catechol-bearing carbon monoxide donor. To further explore the potential of BNPs, in this article we report a novel strategy to introduce different functional groups to BNPs via the palladium-catalyzed Suzuki-Miyaura cross-coupling reaction between the PBA groups and iodo- and bromo-coupling partners. We developed a new catalytic system that efficiently catalyzes Suzuki-Miyaura reactions in water without the need for an organic solvent, as confirmed by NMR. Using this catalyst system, we show that BNPs can be functionalized with carboxylic acids, aldehyde, and hydrazide groups while keeping their original framboidal morphology as confirmed via IR, alizarin red assay, and TEM. Furthermore, the potential of the functionalized BNP in drug delivery applications was demonstrated by conjugating the hydrogen sulfide (H₂S)-releasing compound anethole dithiolone to carboxylic acid-functionalized BNPs and show their H₂S-releasing capability in cell lysate.

Pd/β-cyclodextrin-catalyzed C–H functionalization in water: a greener approach to regioselective arylation of (NH)-indoles with aryl bromides

A greener and more practical approach to the regioselective C3/C2-arylation of (NH)-indoles with (hetero)aryl bromides in water is developed via the Na2PdCl4-catalyzed and β-cyclodextrin ligand-mediated cross-coupling reactions.

Water-soluble SNS cationic palladium(II) complexes and their Suzuki-Miyaura cross-coupling reactions in aqueous medium

Unlike their SCS analogues, SNS pincer complexes are poorly studied for their use in coupling reactions. Accordingly, a series of water soluble cationic Pd(II) SNS pincer complexes have been successfully synthesised and investigated in detail for their catalytic activity in Suzuki-Miyaura coupling reactions. By using only 0.5 mol % loading of the complexes, the coupling of inactivated aryl bromides and activated aryl chlorides with various boronic acids in water was achieved in excellent yields and the catalysts were found to be reusable for three cycles without a significant loss of activity. The investigation of the mechanism of the reaction revealed that a Pd(II) to Pd(IV) route is the more likely pathway which was further supported by computational studies.

Facile one-pot nanocatalysts encapsulation of palladium–NHC complexes for aqueous Suzuki–Miyaura couplings

Pd–NHC loaded nanocatalysts (NCs) were readily constructed by a facile one-pot self-assembly approach. These nanoparticles exhibited excellent catalytic activity in aqueous Suzuki–Miyaura couplings.

One-step highly selective borylation/Suzuki cross-coupling of two distinct aryl bromides in pure water

A one-step borylation/Suzuki cross-coupling of two distinct aryl bromides by Na₂PdCl₄ catalysis mediated by B₂(OH)₄ was developed in pure water, allowing the synthesis of various biaryls and heterobiaryls.

Chemoselective hydrogen peroxide oxidation of primary alcohols to aldehydes by a water-soluble and reusable iron(iii) catalyst in pure water at room temperature

A novel, water-soluble and reusable FeCl₃ catalyst showed high catalytic activity and chemoselectivity in the H₂O₂-oxidation of primary alcohols into aldehydes.

A phase-reversible Pd containing sphere-to-bridge-shaped peptide nanostructure for cross-coupling reactions

A sphere-to-bridge-shaped peptide/Pd(ii) nanostructure was constructed and used as a recyclable Pd nano-catalyst for cross-coupling reactions.

Synthesis of zwitterionic palladium complexes and their application as catalysts in cross-coupling reactions of aryl, heteroaryl and benzyl bromides with organoboron reagents in neat water

Imidazolium substituted quinoxaline based zwitterionic Pd(ii) complexes were synthesized and found to be excellent catalysts for carrying out Suzuki–Miyaura cross-coupling reactions in neat water.