Exceptionally efficient catalytic hydrodechlorination of persistent organic pollutants: application of new sterically shielded palladium carbene complexes.

A new sterically shielded carbene with branched aromatic substituents (9a) and two palladium halogenide complexes (11a,b) have been prepared. The single crystal X-ray structures of free carbene 9a and palladium carbene complexes 10b and 11a were determined. Very high catalytic efficiencies were evident for the sterically shielded palladium carbene complexes 10b and 11a,b when the latter complexes were employed as catalysts for hydrodechlorination of the chloroarenes p-dichlorobenzene and hexachlorobenzene. When optimized, the foregoing approach is significantly more effective than those of currently known transition metal carbene complexes. The most active catalysts were found to be the monocarbene complexes of palladium chloride and iodide, both of which feature highly branched aromatic substituents (11a,b).

Syntheses of sterically shielded stable carbenes of the 1,2,4-triazole series and their corresponding palladium complexes: efficient catalysts for chloroarene hydrodechlorination.

The new sterically shielded 1,3,4-trisubstituted 1,2,4-triazol-5-ylidenes 8b­d were synthesized by a three step method starting from 2-phenyl-1,3,4-oxadiazole. The syntheses of palladium complexes 9a­d and 10a­d (including the sterically shielded derivatives 9c,d and 10a­d) were carried out via the reactions of the stable carbenes 8a­d with palladium halogenide salts in THF or toluene solution. Complexes 9c,d and 10a­d were found to be excellent catalysts for the reductive dechlorination (hydrodechlorination) of p-dichlorobenzene. The structures of 8c, 9a,b, and 10a were determined by single-crystal X-ray diffraction.

Bis(dialkylamide)hydrogen dibromobromate precursors of hypobromite ion in reactions with nerve and blister agent simulants.

Hypobromite ion, BrO(-), is an effective alpha-nucleophile that reacts rapidly with activated phosphorus(V) and sulfonate esters. The parent acid rapidly oxidizes organic sulfides and aryloxide ions. At pH 10-11 BrO(-) and HOBr coexist in water and are potentially useful as decontaminants of chlorosulfide blister agents and the phosphonyl nerve agents. Bis(dialkylamide)hydrogen dibromobromates are well characterized, stable, solids which rapidly form HOBr-BrO(-) in mildly alkaline water. Reactions of 4-nitrophenyl diethyl phosphate and phosphonate, which are simulants of the phosphonofluoridate nerve agents, and of 4-nitrophenyl tosylate, with BrO(-) are rapid (t(1/2) = 60-700 s) with 0.1 M BrO(-), under conditions in which oxidations of organic sulfides are too fast to be followed by conventional methods.

Evaluation of the parameters of 1:1 charge transfer complexes from spectrophotometric data by non-linear numerical method.

The non-linear numerical method for evaluation of equilibrium constants and molar extinction coefficients of molecular complexes from a spectrophotometric experiment is described, which in contrast to linear models has no limitations with respect to concentrations of the components. The proposed procedure is applied to donor-acceptor interaction in solution between N-ethyl carbazole (EtCz) and 7,7,8,8-tetracyanoquinodimethane (TCNQ) or n-hexyl 2,5,7-trinitro-9-dicyanomethylenefluorene-4-carboxylate (HexDTFC) to evaluate the method and to obtain the parameters of charge transfer complexes (CTCs) formation. Association constants (K) and molar extinction coefficients (epsilon) of CTCs derived from non-linear approach (EtCz-TCNQ: K = 2.49+0.19 M(-1); epsilon = 2950 +/- 160 M(-1) cm(-1). EtCz-HexDTFC: K = 12.1 +/- 0.3 M(-1); epsilon = 1335 +/- 24 M(-1) cm(-1)) are close to that from linear models but show lower standard errors in parameter estimations.