Wendell V. F. Brooks

Paramagnetic liquids: the preparation and characterisation of the thermally stable radical ButCNSNS· and its quantitative photochemically symmetry allowed rearrangement to a second stable radical ButCNSSN

The new thermally stable paramagnetic liquid 5-t-butyl-1,3,2,4-dithiadiazolyl has been isolated in the dark and quantitatively photochemically isomerised to the paramagnetic liquid 5-t-butyl-2,3,1,4-dithiadiazolyl (non-systematic numbering for ease of comparison).

Preparation and characterisation of (SeNSNS)n(AsF6)2 containing the ‘electron-rich aromatic’ 6π SeNSNS2+(n= 1) and 7π SeNSNS˙+(n= 2)

Attempted syntheses of SeNSAsF6 from the reactions of SNAsF6 with Se8(AsF6)2(4 : 1) or Se (1 : 1) gave ([graphic omitted])n(AsF6)2(n= 1 and 2), Se4(AsF6)2 and trace amounts of [graphic omitted]e(AsF6)2 and (Se/[graphic omitted]e)2(AsF6)2. The formation of ([graphic omitted])n(AsF6)2(n= 1 and 2) as the major product is consistent with generation of a SeNS+ intermediate which undergoes a concerted symmetry-allowed cycloaddition reaction with SN+ to give [graphic omitted]2+. The crystal structure of [graphic omitted](AsF6)2 consists of disordered [graphic omitted]2+ cations and AsF6– anions, that of ([graphic omitted])2(AsF6)2 consists of AsF6– anions and two independent disordered [graphic omitted]˙+ radical cations weakly linked into a non-centrosymmetric dimer by two long Se ⋯ S bonds [3.12(4), 3.09(2); 3.32(5), 3.16(6)A]. The structure of (Se/[graphic omitted]e)2(AsF6)2 contains a 50:50 mixture of disordered [graphic omitted]e˙+ and [graphic omitted]˙+ radical cations joined by two long Se/S ⋯ Se bonds [3.077(3), 3.138(3)A]. There are significant interionic interactions in all the salts. The 77Se [–60 °C, δ(Me2Se)= 2422.4, ν½, = 10.4 Hz] and 14N NMR [room temperature (r.t.), δ(MeNO2)= 68.9, ν½, = 446 Hz] spectra of [graphic omitted]2+ are consistent with a delocalised 6π ring structure. The [graphic omitted]2+ cation readily reacts with CCl3F to give Cl[graphic omitted]AsF6 the identity of which was confirmed by the determination of its crystal structure. The ESR spectrum of [graphic omitted]˙+ in SO2 solution at r.t. (g= 2.026, broad) and the spectrum of powdered [graphic omitted]˙+ in frozen SO2 at –160 °C were similar to but not identical with those of [graphic omitted]e˙+, [graphic omitted]e˙+ and [graphic omitted]˙+ indicative of a planar 7π system.

Electrophilic behaviour of nitrosyls: the Boedeker reaction, the reactions of sulphite with nitrosyls, and the crystal and molecular structure of cis-bis(2,2′-bipyridine)chloro(nitrosylsulphito)ruthenium

Similar adducts to that, [Fe(CN)5{(NO)(SO3)}]4–, formed in the Boedeker reaction have been obtained by the reaction of SO32– with trans-[RuCl(py)4(NO)]2+(py = pyridine) or cis-[RuX(bipy)2(NO)]2+(X = Cl or Br, bipy = 2,2′-bipyridine). These adducts, [RuCl(py)4{N(O)SO3}] and cis-[RuX(bipy)2{N(O)SO3}], are shown, principally by i.r. spectroscopy, to contain identical [N(O)SO3]– ligands to [Fe(CN)5{N(O)SO3}]4–. The structure of cis-[RuCl(bipy)2{N(O)SO3}] has been determined by X-ray diffraction. It is best regarded as a ruthenium(II) complex containing the hitherto unknown ligand [ONSO3]– which is N-co-ordinated to RuII. The ligand has a long (1.82 A) and weak (force constant 137 N m–1) N–S bond. The reversibility of the adduct formation is demonstrated. Crystal data for cis-[RuCl(bipy)2{N(O)SO3}]: orthorhombic, space group Pbca, a= 14.48(2), b= 19.49(2), c= 14.49(1)A, final R= 0.063 for 290 variables and 1 370 observed reflections. The ruthenium is in a distorted octahedral environment.

Preparation and characterization of 1,3,2-dithiazolidine and 1,4-dithia-7-azabicyclo[2.2.1]heptane cations, and a mechanistic study of the cycloaddition reactions of alkenes with SNS

The cation SNS+(as the AsF6– salt) underwent quantitative concerted symmetry-allowed cycloaddition reactions with alkenes [C2H4, trans- and cis-MeHCCHMe, H2CCMe2, MeHCCH2, Me2CCMe2 and norbornene (bicyclo[2.2.1]hept-2-ene)] to give 1,3,2-dithiazolidine cations 1, which in a second quantitative concerted symmetry-allowed cycloaddition reaction with another alkene molecule gave 1,4-dithia-7-azabicyclo[2.2.1]heptane cations 2(with the exception of Me2CCMe2). The cycloadducts were characterized by elemental analyses and IR and NMR (1H, 13C, 14N) spectroscopies. The vibrational spectra were assigned with the aid of frequencies obtained by ab initio(RHF/6–31G*) calculations. When alkene = C2H4 the calculated geometry of 2 was in good agreement with that obtained from its crystal structure reported previously; that of 1 correlates well with the experimental data (IR, Fourier-transform Raman, NMR). Kinetic studies showed that the rate constants of the first cycloaddition of SNS+ to C2H4 are comparable with those of nitrile and alkyne cycloadditions, indicating that the cycloaddition proceeds via the interaction of the highest occupied molecular orbital of the alkene and the lowest unoccupied one of SNS+ as was previously observed for various nitriles and alkynes. The second cycloaddition leads to stereospecific 2, except for H2CCHMe. Contrary to the prediction of a simple frontier molecular model, the rate of the second cycloaddition was faster than the first for C2H4, cis-MeHCCHMe, and H2CCMe2 and strongly dependent on the steric activity of the alkene. It is proposed that the second cycloaddition likely occurs via a concerted and synchronous pathway.

Recent Developments in the Synthesis and Characterization of the Neutral Diradical Bis(1,3,2,4-dithiadiazolyl)

Abstract It has been shown1 that SNS+ undergoes cycloaddition with various nitriles to give 6π 1,3,2,4-dithiadiazolium salts that give 7π 1,3,2,4- dithiadiazolyl radicals on reduction. SNSAsF6 reacts with cyanogen (NC-CN) to produce which on reduction forms the neutral species (1). The X-ray single crystal structures of the related and show the two rings of each dication to be coplanar. To date, we do not have a crystal structure of the title compound, but spectroscopic and computational evidence indicates that the two rings of the neutral are also coplanar.

The energetics of formation and X-ray crystal structure of SNSNS(AsF6)2, containing the lattice-stabilized aromatic 6π 1,3,4,2,5-trithiadiazolium(2+) cation formed by the crystal-lattice-energy-driven, symmetry-allowed cycloaddition of SN+ and SNS+

We report the preparation, vibrational spectra and X-ray crystal structure of [graphic omitted](AsF6)2, containing the 6π 1,3,4,2,5-trithiadiazolium(2+) cation, which dissociates in solution to SN+ and SNS+, consistent with ab initio 6–31G* calculations (estimated gas-phase dissociation enthalpy: –400 kJ mol–1); the [graphic omitted]2+ ring represents a local energy minimum, and the cycloaddition of SN+ and SNS+ is driven in the solid state by the high lattice energy of the 1 : 2 salt.

The kinetics and thermodynamics of some halogen facilitated oxidation reactions of AsF5; and the preparation and energetics of formation and x-ray Crystal structure of S3N2(AsF6)2 containing the lattice stabalized S3N22+

Abstract An excess of AsF5 oxidises sulphur only as far as S8(ASF6)2 even under forcing conditions, whereas in the presence of a trace of halogen X2(XBrClI) crystalline S4(AsF6)2 is quantitatively formed according to eq. (1) in SO2 within minutes The thermodyamics and kinetics of this reaction and related reactions leading to SNSAsF6 and SNAsF6 will be presented (S3N2)2(AsF6)2 is quantitatively oxidised by AsF5 in the presence of traces of bromine to give SNAsF6 and SNSAsF6 in SO2. Single crystals of S3N2(AsF6)2 are obtained at O°C effecting the concerted symmetry allowed cycloaddition of SN+ and SNS+. The crystal structure of S3N2(AsF6)2 is isomorphous with all SexS3−xN2(AsF6)2 (x = 1,2,3) salts, and contains planar SNSNS 2+ rings with a geometry very similar to that calculated. Although it is a 6π system and often cited in sulphur-nitrogen chemistry, it very readily abstracts F−, accepts an electron to form the stable radical cation S3N2+· and also dissociates completely in SO2 at r.t. This latter result is reflected in the results of 6-31G* calculations, which predict that S3N22+ is unstable with respect to SN+ and SNS+ by 400 kJ/mol in the gas phase with a small activation energy barrier. However, we estimate that S3N2(AsF6)2(s) is about 80 kJ/mol more stable than SNAsF6(s) and SNSAsF6(s), and owes its existence to the high lattice energy of the 2:1 salt. The identity of S3N2(AsF6)2 is also supported by vibrational spectroscopy and a normal coordinates analysis

The reaction of S2NAsF6 with halogens: preparation and X-ray crystal structure of bis(difluorothio)nitronium hexafluoroarsenate(V), (SF2)2NAsF6; preparation of (SBr)2NAsF6, and vibrational spectrum and normal-co-ordinate analysis of the (SX)2N+(X = Cl or Br) cations

Solutions of S2NAsF6 in liquid SO2 react with elemental chlorine and bromine yielding (SX)2NAsF6(X = Cl or Br), essentially quantitatively. No reaction was detected with iodine. The vibrational spectrum of (SBr)2N+ was similar to that of (SCl)2N+ of known structure, implying a similar structure for the bromine derivative. This conclusion was supported by a normal-co-ordinate analysis of (SX)2N+. The analysis was consistent with some positive interaction between the halogen atoms in (SX)2N+, possibly accounting for the cis planar geometry of these cations. Attempts to prepare (SF)2NAsF6 were unsuccessful. However, (SF2)2NAsF6 was synthesised by the reaction of S2NAsF6 and XeF2 in liquid SO2F2, essentially quantitatively. The structure of (SF2)2NAsF6 was determined by X-ray diffraction. The crystals are orthorhombic with a= 14.909(1), b= 9.843(4), c= 12.113(1)A, and Z= 8. The structure was refined in space group Pbca to a conventional R factor of 0.076 for 902 independent reflections with I 2σ(I). It consists of discrete (SF2)2N+ and AsF6– with some cation–anion interactions. The (SF2)2N+ cation has approximate C2v. symmetry with essentially eclipsed fluorine–sulphur bonds as viewed along the sulphur–sulphur axis. The average S–N and S–F distances are 1.551(10) and 1.523(8)A, and the average FSF and FSN bond angles are 94.0(5) and 100.2(6)°. The SNS bond angle is 121.1(6)°. The vibrational spectrum of (SF2)2NAsF6 is reported.