Thietane and Selenetane Complexes by Thermal Cycloaddition of Vinyl Ethers to Transition‐Metal‐Coordinated Thio‐ and Selenoaldehydes – Crystal Structure of Pentacarbonyl(7‐phenyl‐2‐oxa‐8‐thiabicyclo[4.2.0]octane‐S)tungsten(0)

Abstract

Pentacarbonyl(thiobenza1dehyde)tungsten und pentacarbonyl(selenobenza1dehyde)tungsten ( l a and l b ) undergo a thermal [2 + 21 cycloaddition with several vinyl ethers to give highly substituted transition metal-coordinated thietanes and selenetanes. The addition is highly regio-and stereospecific. The products undergo acid-catalyzed rearrangements, which lead to thermodynamically more stable diastereomers of the Thio-and selenoaldehydes not stabilized by either bulky substituents or by conjugation with heteroatoms like nitrogen or sulfur are unstable and immediately oligomerize['"pt~. The high reactivity considerably restricts the use of thio-and selenoaldehydes as building blocks in organic synthesis. Until now, only inter-[2a-e] or intramolecular [3aa,b] [4 + 21 cycloadditions with conjugated dienes and ene reactions are known. In these reactions the heteroaldehydes are generated in situ. One way to circumvent the problems connected with the high reactivity of thio-and selenocarbonyl compounds is to use their transition metal complexes [4]. In the past decade, we successfully employed pentacarbonyl(thiobenza1dehyde)tungsten complexes [5] in cycloaddition reactions with electron-rich alkynes[""-"] and die n e~[~~-~] and observed a similar reactivity pattern for the analogous selenobenzaldehyde Recently, cationic thiobcnzaldehyde complexes of ruthenium, [(q5-C5H5)(P-P)Ru{S=C(C6H4R)H}]+ (P-P = dppe, dppm, dmpe; R = H, CI, OMe), were also used as starting compounds in cycloaddition reactions with cyclopentadiene and 2,3-dimethylb~tadiene[~~.~I.We now report on (a) the reactions of thiobenzaldehyde and selenobenzaldehyde complexes with vinyl ethers, (b) a study of the isomerization of the kinetically controlled reaction product containing a fimr-membered heterocycle to its more stable isomer and (c) an X-ray structural analysis of a thietane tungsten complex. A preliminary account of part of this work as well as a kinetical investigation of the cycloaddition reaction have appeared['".' l]. Results and DiscussionWhen a solution of pentacarbonyl(thiobenza1dehydc)-tungsten (la)"' in dichloromethane was treated with an exthietanes and selenetanes. The stereochemistry of both addition and rearrangement was established by reaction of deuterium-labeled vinyl ethers and by reaction of the cis and trans isomers of ethyl propenyl ether. The crystal structure of the bicyclic addition product of l a and 3,4-dihydro-2H-pyran is reported.cess of ethyl vinyl ether, the dark violet solution turned redbrown within several hours. Since l a slowly decomposes in solution at ambient temperature, the reaction had to be carried out at -30°C. Column chromatography of the reaction products on silica gel afforded the thietane complex 3a (Scheme 1) as a yellow oil. The structure of 3a was established by spectroscopic means. According to the IR spectrum of the yellow oil the pentacarbonyl tungsten fragment is still present in the isolated compound. The elemental analysis and the mass spectrum both indicated a 1 : 1 adduct of l a and the v...

Tris[(alkylthio)methyl]silanes: Syntheses and Structures of Chromium, Molybdenum, and Tungsten Complexes with a Tripodal Thioether Ligand

“…We also note that, assuming a covalent radius of 1.04 Å for sulfur24a and using the values proposed by Cotton for the radii of octahedral Cr(0) and Mo(0),24b the estimated lengths for Cr−S and Mo−S single bonds are 2.52 and 2.66 Å, respectively. In the case of the tungsten compound, the W−S bond lengths (average 2.562 Å) are within the range of reported W(0)−SR 2 distances (2.51−2.59 Å) . Furthermore, the observed W−S bond lengths are also slightly shorter than the corresponding values found in the Mo analogue, a phenomenom that is not uncommon and is considered to be an effect of the lanthanide contraction .…”