Synthesis of novel palladium allyl complexes bearing heteroditopic NHC–S ligands. Kinetic study on the carbene exchange between bis-carbene palladium allyl complexes

Ligand Rearrangement Leads to Tetrahydrothiophene-Functionalized N,S-Heterocyclic Carbene Palladium(II) Complexes

Tetrahydrothiophene-functionalized N,S-heterocyclic carbene palladium(II) complexes are synthesized through an unexpected rearrangement that proceeds with palladium(II) trifluoroacetate and not with palladium(II) acetate, palladium(II) bromide, or palladium(II) chloride. A series of these complexes were isolated and characterized by X-ray crystallography. The mechanism of formation of these [3.2.1]-palladabicycles was explored, and the catalytic capabilities of these complexes were demonstrated in representative C-C coupling reactions.

Palladium(II)-η3 -Allyl Complexes Bearing N-Trifluoromethyl N-Heterocyclic Carbenes: A New Generation of Anticancer Agents that Restrain the Growth of High-Grade Serous Ovarian Cancer Tumoroids

The first palladium organometallic compounds bearing N-trifluoromethyl N-heterocyclic carbenes have been synthesized. These η³ -allyl complexes are potent antiproliferative agents against different cancer lines (for the most part, IC₅₀ values fall in the range 0.02-0.5 μm). By choosing 1,3,5-triaza-7-phosphaadamantane (PTA) as co-ligand, we can improve the selectivity toward tumor cells, whereas the introduction of 2-methyl substituents generally reduces the antitumor activity slightly. A series of biochemical assays, aimed at defining the cellular targets of these palladium complexes, has shown that mitochondria are damaged before DNA, thus revealing a behavior substantially different from that of cisplatin and its derivatives. We assume that the specific mechanism of action of these organometallic compounds involves nucleophilic attack on the η³ -allyl fragment. The effectiveness of a representative complex, 4 c, was verified on ovarian cancer tumoroids derived from patients. The results are promising: unlike carboplatin, our compound turned out to be very active and showed a low toxicity toward normal liver organoids.

Synthesis, characterization, catalytic and biological application of half-sandwich ruthenium complexes bearing hemilabile (κ2-C,S)-thioether-functionalised NHC ligands

A series of cationic Ru(ii)(η⁶-p-cymene) complexes with thioether-functionalised N-heterocyclic carbene ligands have been prepared and fully characterized. Steric and electronic influence of the R thioether substituent on the coordination of the sulfur atom was investigated. The molecular structure of three of them has been determined by means of X-ray diffractrometry and confirmed the bidentate (κ²-C,S) coordination mode of the ligand. Interestingly, only a single diastereomer, as an enantiomeric couple, was observed in the solid state for complexes 1c, 1i and 1j. DFT calculations established a low energy inversion barrier between the two diastereomers through a sulfur pyramidal inversion pathway with R donating group while a dissociative/associative mechanism is more likely with R substituents that contain electron withdrawing group, thus suggesting that the only species observed by the ¹H-NMR correspond to an average resonance position of a fluxional mixtures of isomers. All these complexes were found to catalyse the oxydant-free double dehydrogenation of primary amine into nitrile. Ru complex bearing NHC-functionalised S-tBu group was further investigated in a wide range of amines and was found more selective for alkyl amine substrates than for benzylamine derivatives. Finally, preliminary results of the biological effects on various human cancer cells of four selected Ru complexes are reported.

Synthesis of new allyl palladium complexes bearing purine-based NHC ligands with antiproliferative and proapoptotic activities on human ovarian cancer cell lines

A series of new palladium allyl complexes bearing purine-based carbenes derived from caffeine, theophylline and theobromine have been prepared and characterized by NMR spectroscopy, and elemental analysis and in two cases by single crystal X-ray diffraction. The cytotoxic and proapoptotic activities of compounds have been determined in vitro on human ovarian cancer A2780 and SKOV-3 cell lines. These experiments have shown that the palladium-allyl fragment induces a general cytotoxicity, but the choice of the supporting ligands is of paramount importance for achieving the best results. In particular complexes 4c, 4d and 5d exhibit a higher antiproliferative effect (IC50: 0.09, 0.81 and 0.85 μM respectively) than cisplatin (IC50: 1.5 μM) on A2780 cells, and 4d (IC50: 1.7 μM vs. 5.94 μM) on SKOV-3 cell line. Moreover in many cases it has been proved that the cytotoxicity of our complexes is associated with the induction of apoptosis.

Expedient Mechanosynthesis of N,N-Dialkyl Imidazoliums and Silver(I)-Carbene Complexes in a Ball-Mill

The absence of solvent, associated with intensive mechanical agitation, allowed the first mechanosynthesis of high-value silver(I)-carbene complexes and the corresponding N,N-dialkylimidazolium precursors. This procedure gave outstanding results in terms of yield and reaction time, when compared to solution-based conditions previously described in literature, and was generalized to unprecedented compounds. Silver(I)-carbene complexes could either be obtained from N,N-dialkylimidazolium salts or directly from imidazole and alkyl halides in a one-pot two-step procedure without isolating the imidazolium intermediate. Additionally, an efficient one-pot three-step sequence, including imidazole alkylation, silver metalation, and transmetalation is reported.

Pincer versus pseudopincer: isomerism in palladium(ii) complexes bearing κ3C,S,C ligands

In NHC pincer complexes incorporating a hemilabile donor site, there exists an equilibrium between the true pincer form and a pseudopincer coordination isomer.