Aging and Ball-Milling as Low-Energy and Environmentally Friendly Methods for the Synthesis of Pd(II) Photosensitizers

Mechanochemistry for the synthesis of non-classical N-metalated palladium(II) pincer complexes

The peculiarities of cyclopalladation of a series of non-classical pincer-type ligands based on monothiooxalyl amides bearing ancillary N- or S-donor groups in the amide units have been scrutinized both under conditions of conventional solution-based synthesis and in the absence of a solvent according to a solid-phase methodology including mechanochemical activation. Grinding the functionalized monothiooxamides with PdCl₂(NCPh)₂ in a mortar or vibration ball mill is shown to serve as an efficient and green alternative to the synthesis of these complex metal-organic systems in solution that can offer such advantages as the absence of any auxiliary and significant rate and yield enhancement, especially for the challenging ligands. The realization of S,N,N- or S,N,S-monoanionic tridentate coordination in the resulting pincer complexes has been confirmed by multinuclear NMR (including 2D NMR) and IR spectroscopy and, in some cases, X-ray diffraction. The course and outcome of the solid-phase reactions have been studied by a combination of different spectroscopic methods as well as SEM/EDS analysis. The preliminary evaluation of cytotoxic activity against several human cancer cell lines has revealed the high potency of some of the cyclopalladated derivatives obtained, rendering further development of solvent-free synthetic routes to this type of complexes very urgent.

Hydrogen-bonded 3D network of d10-metal halide coordination polymer containing N-(3-pyridinyl) nicotinamide: influence of ligand conformation, halide anions and solvent

The crystal structures of four new d¹⁰-metal halide coordination polymers are determined as one-dimensional (1D) zigzag chains which are in contact with each other by C/N–H⋯X (X = Cl, Br, I) hydrogen bonds.

Poly(ethylene glycol)s as grinding additives in the mechanochemical preparation of highly functionalized 3,5-disubstituted hydantoins

The mechanochemical preparation of highly functionalized 3,5-disubstituted hydantoins was investigated in the presence of various poly(ethylene) glycols (PEGs), as safe grinding assisting agents (liquid-assisted grinding, LAG). A comparative study under dry-grinding conditions was also performed. The results showed that the cyclization reaction was influenced by the amount of the PEG grinding agents. In general, cleaner reaction profiles were observed in the presence of PEGs, compared to dry-grinding procedures.

Mechanochemistry for facilitated access to N,N-diaryl NHC metal complexes

A solvent-free synthesis of NHC–silver, gold, copper and palladium complexes in a ball-mill was achieved.

A novel route towards water-soluble luminescent iridium(iii) complexes via a hydroxy-bridged dinuclear precursor

The synthesis and photophysical characterization of a new family of luminescent water-soluble ionic iridium(iii) complexes of the general formula [(ppy)₂Ir(bpy)]X are reported. The Ir(iii) complexes incorporate a cyclometalated 2-phenylpyridine (ppy), the ancillary ligand 2,2'-bipyridyl (bpy) and different counterions (X^- = EtO^-, OH^-, EtOCH₂CO₂^-, MeOCH₂CO₂^-). These complexes were obtained starting from the cyclometalated Ir(iii) chloro-bridged dimer [(ppy)₂Ir(μ-Cl)]₂, for the first time synthesized through a new microwave assisted synthetic procedure, and subsequently converted into the corresponding hydroxy-bridged dimer [(ppy)₂Ir(μ-OH)]₂. The latter was eventually used as a sole reagent for the synthesis of all the reported complexes by simply varying the nature of the reaction solvent from water to alcohols and glycol ethers. This study demonstrates the versatility of the [(ppy)₂Ir(μ-OH)]₂ complex as a precursor to water soluble ionic Ir(iii) complexes. Indeed, [(ppy)₂Ir(μ-OH)]₂ has shown its peculiar chemical reactivity due to both a strong base character and an unexpected oxidative ability towards the alcoholic function of glycol ethers. All the synthesized complexes exhibit, in water solution, an orange emission centred at 606 nm. Moreover, all complexes display the ability to give rise to gel phases in water upon increasing their concentration, and the photophysical study evidenced the various interactions governing the gelification process. The water-solubility of these new luminescent Ir(iii) complexes makes them potentially useful in bio-related systems.

Vapour-induced solid-state C–H bond activation for the clean synthesis of an organopalladium biothiol sensor

Room-temperature accelerated aging in the solid state has been applied for quantitative azobenzene C–H bond activation by Pd(OAc)₂. Water-soluble dicyclopalladated methyl orange is a selective chromogenic biothiol sensor at physiologically-relevant micromolar concentrations in aqueous media.

Mechanochemical C-H bond activation: rapid and regioselective double cyclopalladation monitored by in situ Raman spectroscopy

The first direct mechanochemical transition-metal-mediated activation of strong phenyl C-H bonds is reported. The mechanochemical procedure, resulting in cyclopalladated complexes, is quantitative and significantly faster than solution synthesis and allows highly regioselective activation of two C-H bonds by palladium(II) acetate in asymmetrically substituted azobenzene. Milling is monitored by in situ solid-state Raman spectroscopy which in combination with quantum-chemical calculations enabled characterization of involved reaction species, direct insight into the dynamics and reaction pathways, as well as the optimization of a milling process.

Insight into luminescent bisazoaromatic CNN pincer palladacycle: synthesis, structure, electrochemistry and some catalytic applications in C–C coupling

The 2-(phenylazo)azobenzene furnished novel palladacycles in excellent yield, which showed luminescence at rt and catalytic activity. The optoelectronic and electrochemical responses were substantiated with DFT and TDDFT.