N-Phosphanyl-N-heterocyclic carbenes (NHCPs) featuring a saturated imidazolin-2-ylidene or tetrahydropyrimid-2-ylidene ring have been synthesized and characterized. The free carbenes exhibit good stability and can be stored in the solid state for months at ambient temperature without decomposition. Contrary to imidazoline-based NHCPs, which decompose by ring opening, N-phosphanyltetrahydropyrimid-2-ylidenes isomerize to 2-phosphanyl tetrahydropyrimidines upon heating. The free carbenes are capable of acting as chelating ligands toward palladium(II), forming very stable mononuclear complexes that have been structurally characterized. The catalytic potential of the complexes has been preliminarily assessed in cross-coupling reactions, most notably in the Suzuki coupling of aryl chlorides, where these complexes display promising activity, and in the copper-and amine-free Sonogashira coupling of aryl bromides.

Three original approaches to the synthesis of N‐alkyl‐N′‐phosphanylbenzimidazolium salts, which are precursors of the corresponding carbenes, were developed. New stable N‐alkyl‐N′‐phosphanylbenzimidazol‐2‐ylidenes were prepared in good yields. X‐ray analysis of a carbene was made and the chemical properties of the carbenes were studied. The reactions with O‐, N‐, and C‐nucleophiles were found to proceed with or without cleavage of the P–N bond. Thermal rearrangement of the carbenes afforded 2‐phosphorylated benzimidazoles.

The catalytic potential of palladium(II) complexes with chelating N -phosphanyl- N -heterocyclic carbenes featuring a saturated imidazolin-2-ylidene or tetrahydropyrimid-2-ylidene ring has been investigated in intermolecular alkyne hydroamination reactions. The complexes were found to be among the most active Pd-based catalysts for these processes and to enable the use of low reaction temperatures (40 °C) and of solventless conditions. The Pd complexes require activation by 2 equiv of a silver salt to remove chlorido ligands from the metal coordination sphere; they can however also be presynthesized in active form, which allows their use under silver-free conditions. The hydroamination reaction was found to efficiently proceed with terminal alkynes and different ring-substituted, primary arylamine substrates.

A small library of dinuclear gold(I) complexes with the title ligands has been prepared, encompassing, neutral, mono- and dicationic complexes. The luminescence properties of the complexes in the solid state...

No abstract

No abstract

A novel two‐step method for formylation of fluoropyridines with silylformamidine 1 under catalyst‐free conditions was developed. A series of possible 18 fluoropyridines featuring one to four fluorine atoms were subjected to the reaction with 1 existing in equilibrium with its carbenic form 1′.12 Fluoropyridines were shown to react via C‐H insertion. The reaction proceeded either at β‐ or γ‐positions affording the corresponding aminals. The more fluorine atoms in pyridines, the easier the reaction proceeded. We also hypothesized that the pyridines in which the fluorine was substituted by other halogens would react in a similar manner. To test the hypothesis, a set of 3,5‐disubstituted pyridines with various combination of halogen atoms was prepared. 3,5‐Difluoropyridine was taken as a compound for comparison. All the pyridines in the series also reacted likewise. In most cases, hydrolysis of the aminals afforded the corresponding aldehydes. As DFT calculations indicate, the reaction mechanism includes deprotonation of pyridine by 1′ as a strong base and the following rearrangement of the formed tight ionic pair to the final product. An alternative reaction pathway involving addition of 1′ to the pyridine carbon with the following hydrogen transfer via a three‐membered transition state structure required much higher activation energy.

We found that 1-phosphanyl-1,2,3,4-tetrahydroquinazolines undergo ring enlargement. Their treatment with trifluoroacetic or hydrochloric acid afforded diazaphosphepinium salts. Deprotonation of these salts gave the corresponding neutral diazaphosphepines. The reaction of 1-phosphanyl-1,2,3,4-tetrahydroquinazolines with diazomethane or phenylazide afforded triazaphosphocine derivatives via insertion of P–N moiety. At the same time, an analogous hexahydropyrimidine derivative reacted with phenylazide in a normal manner at the phosphorus atom to afford the P­(V) derivative.