Flash vacuum pyrolysis studies. 9. Photoelectron spectra and molecular properties. 101. Synthesis and thermal decomposition of 1,3-dithietane and its S-oxides

Dipolar 1,3-cycloaddition of thioformaldehyde S-methylide (CH2 SCH2 ) to ethylene and acetylene. A comparison with (valence) isoelectronic O3 , SO2 , CH2 OO and CH2 SO

Methods rooted in the density functional theory and in the coupled cluster ansatz were employed to investigate the cycloaddition reactions to ethylene and acetylene of 1,3-dipolar species including ozone and the derivatives issued from replacement of the central oxygen atom by the valence-isoelectronic sulfur atom, and/or of one or both terminal oxygen atoms by the isoelectronic CH₂ group. This gives rise to five different 1,3-dipolar compounds, namely ozone itself (O₃ ), sulfur dioxide (SO₂ ), the simplest Criegee intermediate (CH₂ OO), sulfine (CH₂ SO), and thioformaldehyde S-methylide (CH₂ SCH₂ , TSM). The experimental and accurate theoretical data available for some of those molecules were employed to assess the accuracy of two last-generation composite methods employing conventional or explicitly correlated post-Hartree-Fock contributions (jun-Cheap and SVECV-f12, respectively), which were then applied to investigate the reactivity of TSM. The energy barriers provided by both composite methods are very close (the average values for the two composite methods are 7.1 and 8.3 kcal mol^-1 for the addition to ethylene and acetylene, respectively) and comparable to those ruling the corresponding additions of ozone (4.0 and 7.7 kcal mol^-1 , respectively). These and other evidences strongly suggest that, at least in the case of cycloadditions, the reactivity of TSM is similar to that of O₃ and very different from that of SO₂ .

Synthesis, Structure, and Chemistry of New, Mixed Group 14 and 16 Heterocycles: Nucleophile-Induced Ring Contraction of Mesocyclic Dications

More than 40 new 4- to 12-membered ring heterocycles containing various combinations of Group 14 and 16 elements Si, Sn, S, Se, and Te have been synthesized and fully characterized. Synthesis of these small-ring as well as medium-ring (mesocyclic) heterocycles from alpha,omega-dihalides is facilitated by the presence of gem-dialkylsilyl and gem-dialkylstannyl groups in the precursors. Conformations of several of the new ring systems in the solid state have been determined by X-ray crystal structure analysis. Oxidation of mixed S(Se, Te)/Si eight-membered ring mesocycles with NOPF6 or Br2 gives dications or a bicyclic dibromide, respectively, which can be characterized by NMR methods. On treatment with nucleophiles, mesocyclic dications, or the corresponding radical cations undergo ring contraction, giving five- or six-membered ring heterocycles. Photolysis of a S/Se four-membered ring heterocycle gives selenoformaldehyde, trapped in 80% yield with 2,3-dimethyl-1,3-butadiene.

New 10-membered inorganic heterocyclic diphosphanes, PhN(PX)(2)[(-OC(6)H(2)((T)Bu)(2))(mu-S)(((t)Bu)(2)C(6)H(2)O-)] (x = cl, f). Synthesis and transition metal complexes (molybdenum(0), ruthenium(II), palladium(II), and platinum(II)) of heterocyclic diphosphanes. crystal and molecular structures of the chloro derivative, PhN(PCl)(2)[(-OC(6)H(2)((t)Bu)(2))(mu-S)(((t)Bu)(2)C(6)H(2)O-)], and of a molybdenum(0) complex of the fluoro derivative, [Mo(CO)(3)[eta(3)-PhN(PF)(2)[(-OC(6)H(2)((t)Bu)(2))(mu-S)(((t)Bu)(2)C(6)H(2)O-)]-kappa P,kappa P,kappa S]]

Bis(dichlorophosphino)aniline, PhN(PCl(2))(2), reacts with stoichiometric amounts of 2,2'-thiobis(4,6-di-tert-butylphenol) to afford a 10-membered heterocycle, PhN(PCl)(2)[(-OC(6)H(2)((t)Bu)(2))(mu-S)(((t))Bu)(2)C(6)H(2)O-)] (1), in high yield. The structure of the heterocycle has been determined by a single-crystal X-ray analysis. The 10-membered heterocycle 1 reacts with SbF(3) to afford the corresponding fluoro derivative 2 in good yield. The compounds 1 and 2 act as tridentate ligands with molybdenum carbonyl derivatives, forming complexes of the type [Mo(CO)(3)[eta(3)-PhN(PX)(2)[(-OC(6)H(2)((t)Bu)(2))(mu-S)(((t)Bu)(2)C(6)H(2)O-)]-kappa P,kappa P,kappa S]] (3 X = Cl, 4 X = F). A crystal structure of the fluoro derivative 4 showed the facial tricarbonyl complex comprising a relatively strain-free tetracyclic structure with molybdenum in an octahedral environment; the two phosphorus and the sulfur centers were the donor atoms. Compound 2 readily reacts with Ru(II), Pd(II), and Pt(II) derivatives to form chelate complexes, demonstrating the eta(2) mode of coordination.

Synthesis and Physical Properties of Sterically Congested Cycloalkenes, 1,2-Di-tert-butyl-3,3,5,5-tetramethylcyclopentene and 1,2-Di-tert-butyl-3,3,6,6-tetramethylcyclohexene

Two sterically congested cycloalkenes (9 and 10), congeners of tetra-tert-butylethylene, were synthesized and characterized. Oxidation of the bicyclic 1,3-dithietane 8 with dimethyldioxirane (DMD) gave the endo,endo-disulfoxide 13, thermal isomerization of which to the endo,exo-disulfoxide 15 followed by oxidation with DMD gave the trioxide 18. Heating 18 in refluxing 1,3-dimethyl-2-imidazolidinone furnished 1,2-di-tert-butyl-3,3,5,5-tetramethylcyclopentene (9) in 69% yield by a 2-fold extrusion process. The reaction of the 1,6-diketone dihydrazone 23 with Se(2)Cl(2) gave the selenadiazoline 34 and the 1,3-diselenetane 35. Heating 34 at 115-130 degrees C gave 1,2-di-tert-butyl-3,3,6,6-tetramethylcyclohexene (10), a "didehydro" derivative of tetra-tert-butylethylene, in 43% yield. The C=C bond in 10 is strained in degree comparable to those of most strained alkenes reported so far.

Reduction of permanganate by thioanisole: lewis acid catalysis

The oxidation of sulfides and sulfoxides by permanganate in anhydrous acetone solutions is catalyzed by Lewis acids such as iron(III) chloride, zinc chloride, and mercury(II) chloride. The reaction kinetics unequivocally confirm that the function of these catalysts is to activate the oxidant by forming permanganate/Lewis acid complexes analogous to the protonation of Mn by Bronsted acids. A Hammett analysis of the rate constants for the oxidation of a series of substituted thioanisoles gives a negative rho value (-1. 11) indicative of an electron deficient transition state. No secondary kinetic isotope effect is observed when the hydrogens of the methyl group are replaced by deuterium. Despite previous observations that sulfoxides are preferentially oxidized in competitive experiments, sulfides are oxidized more rapidly when individual rates are measured. All of these observations are most consistent with a mechanism in which the reductant reacts with the oxidant via initial ligation.