Novel and facile synthesis of fluorinated enamino ketones and amino alcohols

Selected imines and one bis-imine react via their enamine tautomers with terminal perfluorinated epoxides, e.g. hexafluoropropene oxide to produce fluorinated enamino ketones or imino ketones. In contrast, internal perfluorinated linear epoxides and one cyclic epoxide yield intermediate imino alcohols, which in one case added hexafluoroacetone, furnishing a new imino diol investigated by X-ray diffraction.     

Fluorothiazynes, 50 years old and still exciting: electrophilic attack at the thiazyl nitrogen of NSF2NS(O)F2

One of the most interesting compounds in sulfur nitrogen fluorine chemistry is NSF₂NS(O)F₂ (3) (reported by Glemser and Höfer 30 years ago): in the NS backbone a triple and a double bond are connected by a single bond. Electrophiles (metal cations, fluoro Lewis acids, “CH₃⁺”) attack this multifunctional system exclusively at the thiazyl nitrogen of the triple bond. [M(NSF₂NS(O)F₂)₄][AsF₆]₂ (M = Ni (4b), Cu (4c)), [Re(CO)₅(NSF₂NS(O)F₂)][AsF₆]⁻ (5), F₅A·NSF₂NS(O)F₂ (A = As (6), Sb (7)), F₃B·NSF₂NS(O)F₂ (8) and [H₃CNSF₂NS(O)F₂]⁺[AsF₆]⁻ (9) were isolated. The X-ray structures of 4c, 6, 8 and 9 are reported, bonding in these complexes is compared with the recently reported related NSAr₂NS(X)Ar₂ (X = O, NH) species.     

The first N-alkyl-N′-polyfluorohetaryl sulfur diimide

The first AlkNSNHet_F sulfur diimide 6 (Alk=adamant-1-yl, Het_F=2,3,5,6-tetrafluoropyrid-4-yl) was prepared by trapping of the corresponding alkylthiazylamide [AlkNSN]⁻3 with pentafluoropyridine, followed by X-ray structural characterization. For 6, the Z,E configuration was found. From the reaction of 3 with octafluoronaphthalene, hexafluorinated naphthothiadiazole 7 was isolated along with the parent AlkNH₂.     

1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazolidyl: a long-lived radical anion and its stable salts

[1,2,5]Thiadiazolo[3,4-c][1,2,5]thiadiazole (1) is synthesized in 62% yield by fluoride ion-induced condensation of 3,4-difluoro-1,2,5-thiadiazole with (Me(3)SiN=)(2)S. The reversible electrochemical reduction of 1 leads to the long-lived [1,2,5]thiadiazolo[3,4-c][1,2,5]thiadiazolidyl radical anion (2) and further to the dianion (3). The radical anion 2 is also obtained by the chemical reduction of the precursor 1 with t-BuOK in MeCN. The radical anion 2 is characterized by ESR spectroscopy in solution and in the crystalline state. The stable salts [K(18-crown-6)][2] and [K(18-crown-6)][2].MeCN (8 and 9, respectively) are isolated from the spontaneous decomposition of the [K(18-crown-6)][PhXNSN] (6, X = S; 7, X = Se) salts in MeCN solution followed by XRD characterization. The radical anion 2 acts as a bridging ligand in 8 and as chelating ligand in 9. The structural changes observed by XRD in going from 1 to 2 are explained by means of DFT/(U)B3LYP/6-311+G calculations.     

Anionic triazine systems

The synthesis of TAS+ C3N3F4- (1) (TAS+ = (Me2N)3S+) and the reactions of 1 with Me3SiOSiMe3 and Me3SiCF3 to give TAS+ C3N3F2O- (2) and TAS+[(NCF)(NCCF3)(NC(CF3)(2)]- (4) are reported. An isomer of 4, TAS+[(NCCF3)2(NCFCF3)]-, compound 6, was obtained by fluoride ion addition to (CF3CN)3. From the reactions with Me3SiNMe2 neutral fluoroamino triazines C3N3Fn(NMe2)(n-1) (n = 1, 2) were isolated. Possible reaction pathways are discussed, the X-ray structures of 1, 2, 4 and 6 were determined.     

Structural Report for 2,5-Bis(trifluoroacetyl)cyclohexane-1,4-dione and <Emphasis Type="Italic">o</Emphasis>,<Emphasis Type="Italic">o</Emphasis>′-bis(trifluoroacetyl)-<Emphasis Type="Italic">p</Emphasis>-cresol

Abstract  

The crystal structures of 2,5-bis(trifluoroacetyl)cyclohexane-1,4-dione (1) and o,o′-bis(trifluoroacetyl)-p-cresol (2) is reported. The first compound crystallizes in monoclinic space group P2₁/n with a = 6.5040(10), b = 10.1610(10), c = 8.2420(10) ?, β = 91.690(10)° and V = 0.54445(12) nm³. Double enolization (U-structure) with a considerable electron density delocalization in the enolone backbone was established in this case. Phenol 2 crystallizes in triclinic space group P-1 with a = 7.0690(10), b = 9.4890(10), c = 9.8190(10) ?, α = 103.720(10), β = 110.760(10), γ = 102.150(10)° and V = 0.56598(12) nm³. In contrast to CDCl₃ solution, a “bifurcate” structure of 2 with jumping OH proton is quenched: only one of both trifluoroacetyl moieties is bonded by intramolecular hydrogen bond.     

Structural investigations of silicon nanostructures grown by self-organized island formation for photovoltaic applications

The self-organized growth of crystalline silicon nanodots and their structural characteristics are investigated. For the nanodot synthesis, thin amorphous silicon (a-Si) layers with different thicknesses have been deposited onto the ultrathin (2 nm) oxidized (111) surface of Si wafers by electron beam evaporation under ultrahigh vacuum conditions. The solid phase crystallization of the initial layer is induced by a subsequent in situ annealing step at 700 °C, which leads to the dewetting of the initial a-Si layer. This process results in the self-organized formation of highly crystalline Si nanodot islands. Scanning electron microscopy confirms that size, shape, and planar distribution of the nanodots depend on the thickness of the initial a-Si layer. Cross-sectional investigations reveal a single-crystalline structure of the nanodots. This characteristic is observed as long as the thickness of the initial a-Si layer remains under a certain threshold triggering coalescence. The underlying ultra-thin oxide is not structurally affected by the dewetting process. Furthermore, a method for the fabrication of close-packed stacks of nanodots is presented, in which each nanodot is covered by a 2 nm thick SiO₂ shell. The chemical composition of these ensembles exhibits an abrupt Si/SiO₂ interface with a low amount of suboxides. A minority charge carrier lifetime of 18 µs inside of the nanodots is determined.