Reactions of diaryl thioketones with diazomethane at room temperature afford 4,4,5,5‐tetraaryl‐1,3‐dithiolanes; the scope of this surprising 2:1 interaction has been studied for decades (Schönberg Reaction). The clue to the mechanism was our observation that the stoichiometry is 1:1 at −78 °C, and 2,5‐dihydro‐2,2‐diaryl‐1,3,4‐thiadiazoles are formed as primary [2+3] cycloadducts. They lose N2 at −45 °C in first‐order reactions generating diaryl thioketone S‐methylides which can be intercepted by thioketones (→1,3‐dithiolanes), multiple CC bonds, or acids HX. In the absence of trapping reagents, the elusive intermediates either dimerize furnishing 2,2,3,3‐tetraaryl‐1,4‐dithianes or give rise to 2,2‐diarylthiiranes by electrocyclization. Beyond thiobenzophenone and diazomethane, our main model reaction, the studies involve fluorene‐9‐thione, 4,4‐dimethoxy‐ and 4,4‐dichlorothiobenzophenone. The ring of 2,5‐dihydro‐2,2‐diphenyl‐1,3,4‐thiadiazole (8) is opened by LDA at −78 °C and derivatives of anion 12 are obtained. − In summa: The Schönberg reaction consists of two 1,3‐dipolar cycloadditions, linked by a 1,3‐dipolar cycloreversion.

Keywords: Iron / Cluster compounds / S ligands / Hydrogenases / Density functional calculationsThe reactions of 1,2,4-trithiolane (1a), 3,3,5,5-tetramethyl-1,2,4-trithiolane (1b), 3,3,5,5-tetraethyl-1,2,4-trithiolane (1c), 3,3,5,5-bis(pentamethylene)-1,2,4-trithiolane (1d) and dispiro{tricyclo[3.3.1.1]decane-2,3ЈЈ-(1,2,4)-trithiolane-5Ј,2Ј-tricyclo[3.3.1.1]decane} (1e) with nonacarbonyldiiron (2) have been investigated. The sulfurdithiolatodiiron complexes 3a-e, which can be considered as novel model complexes of the active site of the [Fe-only] hydrogenase, were isolated as the main products of these reactions. X-ray structure analyses were performed on compounds 3b-e. The carbon dithiolato (SCR 2 S)-bridged diiron side-products 4a-e and the tetranu-

Analogues of the [2Fe-2S] subcluster of hydrogenase enzymes in which the central group of the three-atom chain linker between the sulfur atoms is replaced by GeR and SnR groups are studied. The six-membered FeSCECS rings in these complexes (E=Ge or Sn) adopt an unusual conformation with nearly co-planar SCECS atoms perpendicular to the Fe-Fe core. Computational modelling traces this result to the steric interaction of the Me groups with the axial carbonyls of the Fe (CO) cluster and low torsional strain for GeMe and SnMe moieties owing to the long C-Ge and C-Sn bonds. Gas-phase photoelectron spectroscopy of these complexes shows a shift of ionization potentials to lower energies with substantial sulfur orbital character and, as supported by the computations, an increase in sulfur character in the predominantly metal-metal bonding HOMO. Cyclic voltammetry reveals that the complexes follow an ECE-type reduction mechanism (E=electron transfer and C=chemical process) in the absence of acid and catalysis of proton reduction in the presence of acid. Two cyclic tetranuclear complexes featuring the sulfur atoms of two Fe S (CO) cores bridged by CH SnR CH , R=Me, Ph, linkers were also obtained and characterized.

Extremely rare: A CS triple bond can be assigned to HCSOH, a new molecule prepared from H2CSO by a photochemical [1,3]H‐shift. But does this formal description agree with analyses on the basis of IR vibrations, bond lengths, bond orders, molecular orbitals, and compliance constants? Molecules like this challenge and refine our current understanding of chemical bonding.

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2,2,4,4-Tetramethyl-3-thioxocyclobutanone (8b) easily reacts with gaseous chlorine to yield the stable alpha-chloro sulfenyl chloride 10. The same product was obtained when 8b was treated either with phosphorus pentachloride (PCl(5)) or sulfuryl chloride (SO(2)Cl(2)) in CCl(4) solution. Sulfur dichloride (SCl(2)) reacts with 8b to give the alpha-chloro thiosulfenyl chloride 12 along with an almost equimolar amount of the trisulfide 13b. The less reactive disulfur dichloride (S(2)Cl(2)) was shown to react slowly with 8b and the symmetrical tetrasulfide 15 was found as the exclusive product. The pure thiosulfenyl chloride 12 added to adamantanethione (8c) yielded the unsymmetrical trisulfide 13c. When 12 was treated with thioacetic acid, the acetylated trisulfide 17 was formed in high yield. "Unzipping" reactions with the acetylated disulfide 16 and trisulfide 17 with morpholine in THF at -40 degrees C led to the formation of mixtures of two sulfur-rich heterocycles identified as the pentathiepane 6b and the hexathiepane 7b. A mixture of analogous products was obtained when alpha-chloro sulfenyl chloride 10 was treated with sodium sulfide in anhydrous THF at -40 degrees C. The formation of 6b and 7b is believed to occur via the intermediate dithiirane 1b and/or the isomeric thiosulfine 2b. In the case of 17 the reaction starts probably with the formation of a nonisolable tetrathiane 18b as presented in Scheme 5.

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