Helmut Poleschner

Trip2C6H3SeF: The First Isolated Selenenyl Fluoride

Joining the stable: The first examples of the highly instable selenenyl fluorides RSeF are prepared from the reaction on the tin selenide RSeSnMe(3) with XeF(2). Through the use of extremely large protecting groups (m-terphenyl ligands) which stabilizes the RSeF units against disproportionation, the compounds could be isolated and characterized by NMR spectroscopy and single-crystal structure analysis (see structure).

XeF2/Fluoride Acceptors as Versatile One-Electron Oxidants†

No phlogiston but xenon is released when XeF2 /F(-) acceptors act as new one-electron oxidants. F(-) acceptors are Lewis acids BF3 , B(C6 F5 )3 , and Al{OC(CF3 )3 }3 , and silyl derivatives TfOSiMe3 , Tf2 NSiMe3 , Me3 Si(+) u2009B(C6 F5 )4 (-) , and Me3 Si(+) u2009CHB11 Cl11 (-) . The anions BF4 (-) , TfO(-) , Tf2 N(-) , FB(C6 F5 )3 (-) , FAl{OC(CF3 )3 }3 (-) , B(C6 F5 )4 (-) , or CHB11 Cl11 (-) can be introduced into oxidation products of R2 E2 (E=S, Se, Te), [FeCp2 ], [(FeCpS)4 ], tetrathiafulvalene, thianthrene, and (2,4-Br2 C6 H3 )3 N.

13C, 19F and 77Se NMR study of vicinal (E)‐fluoro(organylseleno)olefins and [(E)‐fluoroalkenyl]diorganylselenonium salts

13C, 19F and 77Se NMR spectra of the (E)‐fluoro(organylseleno)olefins R1(F)Cαuf8feCβR2(SeR3) and the [(E)‐fluoroalkenyl]diorganylselenonium salts R1(F)Cαuf8feCβR2(Se+R3R4) X− were measured and assigned. The 13C, 19F and 77Se NMR chemical shifts, the 1JF,C and 2JF,C−β couplings, the vicinal 3JSe,F couplings, some selected 13C, 13C and 77Se, 13C couplings and the 19F, 13C couplings to the groups R1– R4 are discussed in relation to the structure of the compounds investigated. 1JF,C increases with deshielding of the 13C‐α atoms of the fluoro(organylseleno)olefins and the fluoroalkenyldiorganylselenonium salts, i.e. both quantities are influenced by the same electronic effects. Linear Hammett correlations of para‐substituted phenylseleno derivatives (R=MeO, Me, Ph, H, Cl, COOH, COOEt, CN; R1=R2=Et) between δ(13C‐α), δ(13C‐β), δ(19F), δ(77Se) and 3JSe,F, respectively, and σp values, and linear correlations between the experimental quantities δ(77Se)/δ(19F), δ(77Se)/3JSe,F and δ(19F)/3JSe,F (each with a positive slope) show that close relations exist (i) between the NMR chemical shifts within the FCuf8feCSe moiety and (ii) between the NMR chemical shifts (77Se, 19F) and the couplings 3JSe,F by alteration of the electron density in this structural element. The vicinal 3JSe,F coupling constant across the Cuf8feC double bond (trans‐coupling) is sensitive to structural alterations (<1 to 68.5u2009Hz). In the case of 1,1‐difluorovinylphenyl selenide, F2Cuf8feCHSePh, the 3JSe,F coupling constants obey the relation 3Jtrans > 3Jcis (40.8, 3.2u2009Hz). Copyright

A Practical Synthesis of Thiopyrylium Tetrafluoroborate from Ethyl Vinyl Sulfide

A new, efficient synthesis of thiopyrylium tetrafluoroborate (C5H5S+xa0BF4−) is described. It is based on the three-step sequence ethyl vinyl sulfide propargyl vinyl sulfide 2H-thiopyran C5H5S+xa0BF4− in an overall yield of 54%. Preparations of C5H5S+xa0BPh4−, C5H5S+xa0I−, and C5H5S+xa0CF3SO3− (TfO−) are also described. The latter is the subject of the first X-ray single crystal structure determination of the thiopyrylium ion.

PhSeOTf–Et3N·3HF and PhSeSbF6–Et3N·3HF as new PhSe–F equivalents in the fluoroselenenylation of acetylenes

The novel reagents PhSeOTf–Et3N·3HF and PhSeSbF6–Et3N·3HF act as PhSe–F equivalents in the fluoroselenenylation of alkynes. Oct-4-yne, cycloundecyne and cyclododecyne, as well as the unsymmetrical alkynes Ph–CC–Me and Bu–CC–R (R = Me, Et, iPr and tBu) give the corresponding (E)-fluoro(phenylseleno)alkenes in preparative yields. The reagent PhSeOTf–Et3N·3HF gives a similar product composition of regioisomers to Ph2Se2–XeF2 in addition reactions to Bu–CC–R. This is indicative of a similar reaction mechanism of the reagents. Probably a selenirenium ion acts as an intermediate. X-Ray single crystal structure analysis of (E)-1-fluoro-2-phenylselenocycloundecene confirms the trans-addition of [PhSe–F] to cycloundecyne.

The First Structure of a Vicinal (E)-Fluoroselenoolefin: (E)-(5-Fluoro- 4-octen-4-yl)dimethylselenonium Picrate

The structure of the title compound, C10H20FSe+.C6H2 N307-, synthesized from (E)-4-methylseleno-5-fluoro-4octene with trimethyloxonium tetrafluoroborate, followed by anion exchange with sodium picrate, proves the trans addition of RSeF equivalents in the fluoroselenenylation of acetylenes with XeF2-R2Se2 and XeF2-PhSeSiR3 reagents [dihedral angle Se--C4C5--F -178.7 (1)°].

Calculated structures of thiopyrylium-S-fluoride and S-trifluoride and attempts of their preparation

Abstract Structures and energies of cyclo-C 5 H 5 SF and cyclo-C 5 H 5 SF 3 have been calculated. In both cases the 2- and 4-CF-isomers are more stable than the SF and SF 3 isomers. The fluxional behavior of the sulfur bonded fluorides has been calculated also. In cyclo-C 5 H 5 SF an ellipsoidal rotation of the sulfur bonded fluorine atom is observed with a barrier of a few kcalxa0mol −1 . In sulfur bonded cyclo-C 5 H 5 SF 3 the (Turnstile) rotation is predicted to occur without noticeable barrier, in agreement with previous work. Attempts to isolate the sulfur bonded isomers failed entirely: always 2 or 4-carbon-fluorides were obtained for cyclo-C 5 H 5 SF. The acyclic SF 5 − carrying precursors for the synthesis of cyclo-C 5 H 5 SF 3 failed in crucial steps of the reactions.

Reactions of RSe–EMe3 (E = Si, Ge, Sn, Pb) with XeF2 — RSe–F Equivalents in the Fluoroselenenylation of Acetylenes[1]

Selenides of the type R1Se–EMe3 (E = Si, Ge, Sn, Pb) react with xenon difluoride by cleavage of the Se–E bond to yield the R1Se–F intermediate and the fluorides Me3E–F, whereas the Se–C bond in PhSe–tBu (E = C) is stable against XeF2. The presence of R1Se–F intermediates is confirmed by addition to acetylenes (4-octyne, 3-hexyne). Thus, the fluoroselenenylation of acetylenes gives fluoro(organylseleno)olefins in preparative yields. In the cases of E = Si, Ge, Sn, and Pb, aryl and n-alkyl groups are suitable as the substituent R1. The X-ray crystal structural analysis of (E)-3-(p-carboxyphenylseleno)-4-fluorohex-3-ene – the first example of an uncharged fluoroselenoolefin synthesized from p-EtO2C–C6H4–Se–SnMe3, XeF2, and 3-hexyne followed by an ester hydrolysis – shows that the addition of the selenenylfluoride intermediate to the acetylene proceeds via a trans-addition, as is known for the R2Se2–XeF2 reagents.

Seleniranium and Telluriranium Salts

Seleniranium salts [Ad2 SeR]+ X- (2-8), which are moderately stable at room temperature, were synthesized by addition of RSe+ X- equivalents to the bulky olefin bis(adamantylidene) Ad=Ad (1), where R is aryl or alkyl and X- is Tf2 N- , B(C6 F5 )4 - , or SbCl6 - . Unstable telluriranium salts [Ad2 TeR]+ X- (9-12) were obtained by addition of RTe+ X- equivalents to 1 (R=Ph, Et; X- =Tf2 N- , BF4 - ). The compounds were characterized by NMR spectroscopy and quantum chemical calculations, and the Se compounds also by ESI mass spectrometry. Crystal structures were determined for seleniranium salts 2 and 7 and telluriranium salt 9.