Halide‐Free Diarylcalcium Complexes—Syntheses,Structures, and Stability

A general procedure was developed for the synthesis of diarylcalcium complexes by addition of KOtBu to arylcalcium iodides in THF. Intermediate arylcalcium tert‐butanolate dismutates immediately leading to insoluble tert‐butanolate precipitates of calcium. Depending on the steric demand and denticity of additional neutral aliphatic azabases, mononuclear or dinuclear complexes trans‐[Ca(α‐Naph)₂(thf)₄] ( 1 ), [Ca(β‐Naph)₂(thf)₄] ( 2 ), [Ca(Tol)₂(tmeda)]₂ ( 3 ), [Ca(Ph)₂(tmeda)]₂ ( 4 ), [Ca(Ph)₂(pmdta)(thf)] ( 5 ), [Ca(hmteta)(Ph)₂] ( 6 ), and [Ca([18]C‐6)(Ph)₂] ( 7 ) were isolated (Naph=naphthyl; meda=N,N,N′,N′‐tetramethylethylenediamine; pmdta= N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine; hmteta=N,N,N′,N′′,N′′′,N′′′‐hexamethyltriethylenetetramine). The Ca?C bond lengths vary between 250.8 and 263.5 pm, the ipso‐carbon atoms show low‐field‐shifted resonances in the ¹³C NMR spectra.     

Syntheses and Structures of F6XeNCCH3 and F6Xe(NCCH3)2

Acetonitrile and the potent oxidative fluorinating agent XeF₆ react at ?40 °C in Freon‐114 to form the highly energetic, shock‐sensitive compounds F₆XeNCCH₃ ( 1 ) and F₆Xe(NCCH₃)₂?CH₃CN ( 2 ?CH₃CN). Their low‐temperature single‐crystal X‐ray structures show that the adducted XeF₆ molecules of these compounds are the most isolated XeF₆ moieties thus far encountered in the solid state and also provide the first examples of Xe^VI? N bonds. The geometry of the XeF₆ moiety in 1 is nearly identical to the calculated distorted octahedral (C_3v) geometry of gas‐phase XeF₆. The C_2v geometry of the XeF₆ moiety in 2 resembles the transition state proposed to account for the fluxionality of gas‐phase XeF₆. The energy‐minimized gas‐phase geometries and vibrational frequencies were calculated for 1 and 2 , and their respective binding energies with CH₃CN were determined. The Raman spectra of 1 and 2 ?CH₃CN were assigned by comparison with their calculated vibrational frequencies and intensities.     

Synthesis of 6aλ4-thia-1,6-diselena-3,4-diazapentalenes, 1,6,6aλ4-triselena-3,4-diazapentalenes, 6aλ4-thia-1,3,4,6-tetraazapentalenes,and 6aλ4-Selena-1,3,4,6-tetraazapentalenes from cyclic thioureas and selenoureas

Imidazolidine-2-thione (7a) and the corresponding 2-selone (7b), hexahydropyrimidine-2-thione (7c) and 2-selone (7d), and hexahydro-1H-1,3-diazepine-2-thione (7e) and 2-selone (7f) reacted with 2,4-dinitrobenzyl chloride to give the 2-(2,4-dinitrobenzylthio) and 2-(2,4-dinitrobenzylseleno) derivatives (8a)-(8f) of 4,5-dihydroimidazolium chloride, 1,4,5,6-tetrahydropyr-imidinium chloride, and 4,5,6,7-tetrahydro-1H-1,3-diazepinium chloride. Deprotonation of the chlorides (8a)-(8f) gave, respectively, 2-(2,4-dinitrobenzylthio)-and 2-(2,4-dinitrobenzylseleno)-4,5-dihydroimidazole (9a) and (9b), 2-(2,4-dinitrobenzylthio)- and 2-(2,4-dinitrobenzylseleno)-1,4,5,6-tetrahydropyrimidine (9c) and (9d), and 2-(2,4-dinitrobenzylthio)- and 2-(2,4-dinitrobenzylseleno)-4,5,6,7-tetrahydro-1H-1,3-diazepine (9e) and (9f). The bases (9a)-(9f) reacted with isoselenocyanates with elimination of 2,4-dinitrotoluene and concomitant addition of two molecules of the isoselenocyanate to give 1,6,6aλ⁴-triheterapentalenes of two structural types, depending on the size of the heteroring in the bases (9a)-(9f). The imidazoles (9a) and (9b) gave 6aλ⁴-thia-1,6-diselena-3,4-diazapentalenes (10a)-(10j) and 1,6,6aλ⁴-triselena-3,4-diazapentalenes (11a)-(11h), respectively. The sulfur-containing bases (9c) and (9e) gave 6aλ⁴-thia-1,3,4,6-tetraazapentalenes (12a)-(12j) and (14a)-(14d), respectively, and the selenium-containing bases (9d) and (9f) gave 6aλ⁴-selena-1,3,4,6-tetraazapentalenes (13a)-(13j) and (15a)-(15d). Heteroatom-heteroatom covalent bond energies have been estimated for representative members of the series (10)-(14) by using the Huggins equation and experimentally determined bond lengths. © 1997 John Wiley & Sons, Inc.