Deoxygenation of chalcogen oxides EO2 (E = S, Se) with phospha-Wittig reagents

In here we present the deoxygenation of the chalcogen oxides EO₂ (E = S, Se) with R-P(PMe₃), so-called phospha-Wittig reagents. The reaction of DABSO (DABCO·2SO₂) with R-P(PMe₃) (R = Mes*, 2,4,6-tBu₃-C₆H₂; ^MesTer, 2,6-(2,4,6-Me₃-C₆H₂)₂-C₆H₃) resulted in the formation of thiadiphosphiranes (RP)₂S (1:R), while selenadiphosphiranes (RP)₂Se (2:R) were afforded with SeO₂, both accompanied by the formation of OPMe₃. Utilizing the sterically more encumbered ^DipTer-P(PMe₃) (^DipTer = 2,6-(2,6-iPr₂-C₆H₃)₂-C₆H₃) a different selectivity was observed and (^DipTerP)₂Se (2:DipTer) along with [Se(μ-P^DipTer)]₂ (3:DipTer) were isolated as the Se-containing species in the reaction with SeO₂. Interestingly, the reaction with DABSO (or with equimolar ratios of SeO₂ at elevated temperatures) gave rise to the formation of the OPMe₃-stabilized dioxophosphorane (phosphinidene dioxide) ^DipTerP(O)₂-OPMe₃ (4:DipTer) as the main product. This contrasting reactivity can be rationalized by two potential pathways in the reaction with EO₂: (i) a Wittig-type pathway and (ii) a pathway involving oxygenation of the phospha-Wittig reagents and release of SO. Thus, phospha-Wittig reagents are shown to be useful synthetic tools for the metal-free deoxygenation of EO₂ (E = S, Se).

Schematic Design of Metal-Free NHC-Mediated Sequestering and Complete Conversion of SO2 to Thiocarbonyl S-Oxide Derivatives at Room Temperature

The sequestering and complete conversion of SO₂ to valuable chemicals in a metal-free pathway is highly demanded. The recent success of SO₂ fixation by N-heterocyclic carbenes instigated further studies in this regard. Previous reports were confined within the carbene-SO₂ reaction mechanism and the stability of oxathiirane S-oxide derivatives. The complete conversion of captured SO₂ to precious chemicals was not studied. The present inquisition has accomplished the scarcity of the earlier studies. It is observed that in the presence of an excess amount of carbene, the registered SO₂ is converted to the ketone derivative and thiocarbonyl S-oxide derivative. An electronic level investigation of these reactions is carried out. From the change of the molecular orbitals along the reaction path, it is concluded that the reaction between the oxathiirane S-oxide derivative and carbene follows a frog's hunting mechanism.

Bis(amidinato)- and bis(guanidinato)silylenes and silylenes with one sterically demanding amidinato or guanidinato ligand: synthesis and reactivity

Silylenes 1–4 have great synthetic potential for the synthesis of higher coordinate silicon(ii) and silicon(iv) complexes with unprecedented structural motifs.

Cationic Five-Coordinate Bis(guanidinato)silicon(IV) Complexes with SiN4 El Skeletons (El=S, Se): "Heterolytic Activation" of S-S and Se-Se Bonds

The donor-stabilized silylene [iPrNC(NiPr2 )NiPr]2 Si (2) reacts with PhEl-ElPh (El=S, Se) to form the respective cationic five-coordinate bis(guanidinato)silicon(IV) complexes {[iPrNC(NiPr2 )NiPr]2 SiSPh}(+) PhS(-) (4) and {[iPrNC (NiPr2 )NiPr]2 SiSePh}(+) PhSe(-) (5). Compounds 4 and 5 were characterized by crystal structure analyses and NMR spectroscopic studies in the solid state.

Activation of SO2 by [Zn(Cp*)2] and [(Cp*)ZnI–ZnI(Cp*)]

The reactions of SO₂ with [Zn(Cp*)₂] and [(Cp*)Zn^I–Zn^I(Cp*)] proceeded with insertion of SO₂ into the Zn–C bonds, and oxidation of the Zn^I–Zn^I bond in the reaction with [(Cp*)Zn^I–Zn^I(Cp*)].

Synthesis, structure and reactivity of a donor-stabilised silylene with a bulky bidentate benzamidinato ligand

A novel donor-stabilised silicon(ii) complex with an SiN₃ skeleton was synthesised and its reactivity profile was characterised (reactions with N₂O, S₈, Se, Te, Me₃SiN₃, PhSCH₂N₃ and [Fe(CO)₅]).