The fluoro analogue of Wilkinson's catalyst and unexpected Ph-Cl activation

The fluoro analogue of Wilkinson's catalyst, [(Ph3P)3RhF] (1), was synthesized and fully characterized. Both solution behavior and solid-state geometry parameters of 1 were found to be surprisingly similar to those of Wilkinson's catalyst. Unlike Wilkinson's catalyst however, 1 exhibited most unusual reactivity toward the notoriously inert C-Cl bond of nonactivated chloroarenes. The novel Ph-Cl activation with 1 includes fluorine transfer from the metal to a phosphine ligand and evidently phenyl transfer from the phosphine to Rh to produce an electron-rich sigma-phenylrhodium intermediate.     

Generalized method of stationary phase for the Fourier transform of a rapidly oscillating function

Asymptotic formulas are obtained for a class of integrals that are Fourier transforms of rapidly oscillating functions. These formulas contain special functions and generalize the well-known method of stationary phase.     

Role of the volume and surface breakdown in a formation of microdischarges in a steady-state DBD

The results of an experimental study on a spatial-time behavior of microdischarges (MDs) in steady-state dielectric barrier discharge (DBD) are presented. MDs of DBD have a spatial “memory”, i.e. every subsequent MD appears exactly at the same place that was occupied by the preceding MD. In most cases each MD appears at its fixed place only once by every half-period (HP). Spatial “memory” is derived from slow recombination of plasma in the MDs channels for a period between two neighbor HPs. In steady-state DBD each plasma column was formed only one-time due to local avalanche-streamer breakdown in the very first (initial) gas gap breakdown under inception voltage U^*U^*. After that DBD is sustained under voltage lower than U^*U^*. For the plane-to-plane DBD having the restricted electrode area there is a critical voltage U ₁: DBD is in a steady-state if U > U ₁ but the DBD decays slowly at voltages below U ₁. The decay takes many HPs and occurs due to decreasing the number of MDs inside the gap because of their Brownian motion from central region to the outside of the discharge area. In steady-state DBD there is no correlation between an appearance of alone MD and phase of the applied voltage – each MD has a great scatter in its appearance at the HP. This scatter is attributed to the dispersion in a threshold voltage for local surface breakdowns around the MD base. So, in steady-state DBD the MD volume plasma is responsible for an existence of spatial “memory” (i.e. where the MD appears) but the surface charge distribution around MD is responsible for MD time dispersion (i.e. when the MD appears).     

The Trifluoromethyl Anion

First evidence for the existence of free trifluoromethyl anion CF₃^? has been obtained. The 3D‐caged potassium cation in [K(crypt‐222)]⁺ is inaccessible to CF₃^?, thus rendering it uncoordinated (“naked”). Ionic [K(crypt‐222)]⁺ CF₃^? has been characterized by single‐crystal X‐ray diffraction, solution NMR spectroscopy, DFT calculations, and reactivity toward electrophiles.     

The Influence of Activating Agents on the Controlled Synthesis of Poly(methyl methacrylate) in the Presence of Ruthenacarboranes

The radical polymerization of methyl methacrylate catalyzed by systems based on the carborane complexes of ruthenium(III) is studied in the presence of a number of activating agents: tin 2-ethyl hexanoate, aluminum isopropoxide, isopropylamine, and AIBN. It is shown that in the presence of the systems under consideration, polymerization proceeds in a controlled mode via the ATRP mechanism (AGET or ICAR ATRP) at catalyst concentrations with ppm level relative to that of the monomer. As the degree of monomer conversion grows, the molecular weight of the polymer increases linearly while its polydispersity coefficients decrease linearly. The role of the mentioned agents is to transfer the catalyst to the active form containing a metal atom in the oxidation number +2 and able to interact with halogen-terminated dormant polymer chains. It is first shown that the carborane complexes of ruthenium(II) are applicable for the catalysis of controlled radical polymerization.     

Unexpected H2O-induced Ar-X activation with trifluoromethylpalladium(II) aryls

A series of new complexes [(L-L)Pd(Ar)(CF3)] (L-L = dppe, dppp, tmeda; Ar = Ph, p-Tol, C6D5) have been synthesized and fully characterized in solution and in the solid state. Remarkable Ph-X activation (X = I, Cl) by [(dppe)Pd(Ph)(CF3)] (1) has been found to come about to cleanly produce biphenyl and [(dppe)Pd(Ph)(X)]. This reaction does not take place under rigorously anhydrous conditions but in the presence of traces of water it readily occurs, exhibiting an induction period and being zero order in PhI. As shown by mechanistic studies, the role of water is to promote reduction of small quantities of the Pd(II) complex to Pd(0) which activates the Ph-X bond. Subsequent transmetalation to give diphenyl Pd complexes, followed by Ph-Ph reductive elimination give rise to the observed products. The water-induced reduction to catalytically active Pd(0) has been demonstrated to proceed via both the Pd(II)/P(III) to Pd(0)/P(V) redox mechanism and alpha-F transfer, followed by facile hydrolysis of the difluorocarbene to carbonyl, migratory insertion, and reductive elimination of PhC(X)O (X = F, OH, or OOCPh). In the absence of H2O and ArX, the diphosphine-stabilized trifluoromethyl Pd phenyl complexes undergo slow Ph-CF3 reductive elimination under reinforcing conditions (xylenes, 145 degrees C).