Stephen R. Foley

The metallocyclic ring in mononuclear iminoisoindoline-based palladacycle [(κ²-iminoisoidoline)PdCl(PCy₃)] (3) can be ring opened by coordination of phosphine to form the trans bis(phosphine) iminoisoindoline-based palladium(II) complex [(η¹-iminoisoidoline)PdCl(PCy₃)₂] (4) where the η¹-iminoisoindoline is coordinated only by an Ar–Pd bond. The ring-opened analogue showed significantly higher coupling activity in Suzuki-Miyaura reactions with aryl chlorides than any iminoisoindoline-based palladacycle studied to date. These results are compared to existing mononuclear palladacycles and reported acyclic analogues.

This mini-review provides coverage of chitosan-based adsorbents and their modified forms as sustainable solid-phase extraction (SPE) materials for precious metal ions, such as gold species, and their complexes in aqueous media. Modified forms of chitosan-based adsorbents range from surface-functionalized systems to biomaterial composites that contain inorganic or other nanomaterial components. An overview of the SPE conditions such as pH, temperature, contact time, and adsorbent dosage was carried out to outline how these factors affect the efficiency of the sorption process, with an emphasis on gold species. This review provides insight into the structure-property relationships for chitinaceous adsorbents and their metal-ion removal mechanism in aqueous media. Cross-linked chitosan sorbents showed a maximum for Au(III) uptake capacity (600 mg/g), while S-containing cross-linked chitosan display favourable selectivity and uptake capacity with Au(III) species. Compared to industrial adsorbents such as activated carbon, modified chitosan sorbents display favourable uptake of Au(III) species, especially in aqueous media at low pH. In turn, this contribution is intended to catalyze further research directed at the rational design of tailored SPE materials that employ biopolymer scaffolds to yield improved uptake properties of precious metal species in aqueous systems. The controlled removal of gold and precious metal species from aqueous media is highly relevant to sustainable industrial processes and environmental remediation.

Air and moisture stable homoleptic bis(diimidazolylidine)nickel(II) complexes, ([(diNHC)₂Ni]²⁺) 3a,b and their corresponding silver(I) 4a,b and palladium(II) 5a,b complexes were synthesized and characterized by NMR and single crystal X-ray analysis. The catalytic potential of complex 3a was assessed in Mizoroki–Heck and Suzuki–Miyaura coupling reactions. In the Suzuki–Miyaura coupling reaction, nickel precatalyst 3a was active for the coupling of aryl chlorides as well as aryl fluorides. The analogously synthesized Pd(II) complexes resulted in formation of (diNHC)PdCl₂ species which were not active for the coupling of aryl fluorides. For the Mizoroki–Heck reaction, it was found that aryl iodides could be activated in the absence of nickel or palladium precatalysts when using Na₂CO₃ or NEt₃ as base while aryl iodides and aryl bromides could be activated in the Suzuki–Miyaura reaction sans precatalyst when K₃PO₄ was used as base.

A series of air- and moisture-stable iminoisoindoline-based palladacycles have been prepared in two operationally simple steps from commercially available reagents. para-Substituted N,N′-diphenyliminoisoindoline ligands are easily synthesized from phthalaldehyde and para-substituted anilines and further reaction of the iminoisoindoline ligands with Pd(OAc)₂ in dichloromethane at room temperature results in formation of six-membered [C,N] dinuclear cyclopalladated complexes with the general formula [(iminoisoindoline)Pd(μ-OAc)]₂. The resulting palladacyclic complexes were tested as precatalysts in Heck and Suzuki coupling reactions.

The title compound, C₁₃H₁₉NO, exhibits a non-planar structure in which the 2,6-diisopropylphenyl ring is tilted at a dihedral angle of 77.4 (1)° with respect to the formamide group. This is the largest dihedral angle known among structurally characterized formamides. The molecules are linked via N—H...O hydrogen bonds, forming infinite chains which run along the b-axis directions.

In the title compound, (C(20)H(17)N(2))(2)[Pd(2)Cl(6)]·2C(6)H(6), the dichloride-bridged [Pd(2)Cl(6)](2-) anion lies across an inversion center with each Pd(II) ion in a slightly distorted square-planar environment. In the crystal structure, two cations and an anion are connected via N-H⋯Cl hydrogen bonds between the NH groups of the iminioisoindoline cations and terminal Cl atoms of a hexa-chloridodipalladate(II) anion. The Pd-Cl distance of the terminal chloride engaged in hydrogen bonding is slightly longer than the Pd-Cl distance of the adjacent terminal chloride which is not involved in hydrogen bonding.