The seminal contributions by Sonogashira, Cassar and Heck in mid 1970s on Pd/Cu- and Pd-catalysed (copper-free) coupling of acetylenes with aryl or vinyl halides have evolved in myriad applications. Despite the enormous success both in academia and in industry, however, critical mechanistic questions of this cross-coupling process remain unresolved. In this study, experimental evidence and computational support is provided for the mechanism of copper-free Sonogashira cross-coupling reaction. In contrast to the consensus monometallic mechanism, the revealed pathway proceeds through a tandem Pd/Pd cycle linked via a multistep transmetallation process. This cycle is virtually identical to the Pd/Cu tandem mechanism of copper co-catalysed Sonogashira cross-couplings, but the role of CuI is played by a set of PdII species. Phosphine dissociation from the square-planar reactants to form transient three-coordinate Pd species initiates transmetallation and represents the rate-determining step of the process.

1-(2-Pyridyl)-, 4-(2-pyridyl)-, 1-(2-picolyl)-, and 4-(2-picolyl)-functionalized 1,3,4-trisubstituted 1,2,3-triazolium salts (1A−D, respectively) were investigated as Nheterocyclic carbene (trzNHC) precursors for bidentate coordination to ruthenium(II) through the C NHC and N pyridyl donors. In addition to the pyridyl and picolyl pendant groups, a variety of para-substituted phenyl rings were attached to the 1,2,3-triazolylidene via carbon or nitrogen atoms. The ruthenation was accomplished by metalation with Ag 2 O to form intermediate silver carbene complexes and subsequent transmetalation with [Ru(η 6 -p-cymene)Cl 2 ] 2 . The cationic ruthenium complexes [Ru(η 6 -p-cymene)(trzNHC)Cl] + (3A−C) were readily obtained with 1-(2-pyridyl)-, 4-(2-pyridyl)-, and 1-(2-picolyl)-1,2,3-triazolium salts (1A−C) but not with the 4-picolyl analogue (1D). The bidentate coordination of the ligand precursors 1 was followed by multinuclear NMR spectroscopy, revealing significant changes in chemical shifts for triazole C-5, pyridine nitrogen atoms, and the neighboring α-proton (H-6 pyridyl ) in 13 C, 15 N, and 1 H NMR spectra. The molecular composition of complexes 3A−C was confirmed by elemental analysis and positive ion electrospray ionization (ESI+) mass spectra, the latter showing ions corresponding to [Ru(η 6 -p-cymene)(trzNHC)Cl] + . The solid-state structures of the three representative complexes were confirmed by single-crystal X-ray analyses; all complexes displayed a typical piano-stool type configuration. Preliminary catalytic activity screening of 3A−C in the oxidation of selected primary and secondary alcohols with tert-butyl hydroperoxide (TBHP) to give carbonyl compounds is also discussed.

Azocarboxamide (azcH) has been combined for the first time with [Ru-Cym] to generate metal complexes with N,N- and N,O-coordination mode, [(Cym)Ru(azc)Cl] and [(Cym)Ru(azcH)Cl](+) [PF6 ](-). Geometric and electronic structures of the complexes are reported along with their in vitro activities against different tumour cell lines and preliminary results on solution chemistry. Compound [(Cym)Ru(azc)Cl] exhibited remarkable cytotoxic properties. It was cell-type specific and had comparable IC50 values towards both cancer cells and their drug-resistant subline. A tenfold increase in the sensitivity towards [(Cym)Ru(azc)Cl] was noted for the tumour cells with depleted intracellular glutathione (GSH) level, suggesting the essential role of GSH in cell response to this compound.

Catalytic Mitsunobu reactions have been substantially improved based on strict optimization, mechanistic studies and discovery of a new catalyst.

A novel bis(pyridyl-functionalized 1,2,3-triazol-5-ylidene)-palladium(II) complex [Pd(Py-tzNHC)2](2+) catalyses the copper-, amine-, phosphine-, and additive-free aerobic Sonogashira alkynylation of (hetero)aryl bromides in water as the only reaction solvent. The catalysis proceeds along two connected Pd-cycles with homogeneous bis-carbene Pd(0) and Pd(II) species, as demonstrated by electrospray ionization mass spectrometry.

An investigation of the recently reported "fully catalytic Mitsunobu reaction" using catalytic amounts of a phosphine reagent and an azo reagent has shown that although benzyl 4-nitrobenzoate is formed under the fully catalytic conditions, the same result is obtained if the hydrazine catalyst is omitted, indicating that this is not a Mitsunobu reaction. In addition, when the reaction between (-)-ethyl lactate and 4-nitrobenzoic acid was carried out using the "fully catalytic" method, the corresponding ester was formed but in very low yield and with predominant retention of configuration. Unfortunately, the system catalytic in phosphine reagent is incompatible with that in the azo reagent.

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N‐Sulfonylformamidines were produced from sulfonamides or N‐acylated sulfonamides using Vilsmeier reagent obtained in situ from N,N‐disubstituted formamides and oxalyl chloride. Optically active substrates did not racemize during the process. The efficient and mild cleavage of N‐sulfonylformamidines can be achieved with hydrazine hydrate in ethanol. The entire procedure constitutes a simple method for protecting, and deprotecting, the sulfonamide moiety.