Tungsten complexes sulfur

The first examples of a chalcogen insertion into a transition metal-carbene bond were reported in 1981. Stirring solutions of the pentacarbonyl-(diarylcarbene)tungsten complexes 39 in pentane in the presence of solid sulfur afforded the thioketone complexes 40 [Eq. (8)].171 The reaction rate increased considerably when pentane was replaced by CS2 as the solvent due to the higher solubility of elemental sulfur in CS2. 

Figure 2 provides a record of the infrared intensity at 1350 cm l of sulfur dioxide with increasing temperature for Indiana coal with and without a diluent. A low flow rate of oxygen was necessary to avoid direct combustion (flashing) of the undiluted coal sample. This sample shows intense sulfur dioxide evolution over a rather short range (exotherm) followed by rather weak evolution at higher temperatures. In contrast, coal samples diluted with tungsten trioxide or other diluents to reduce the exothermic behavior show a more complex sulfur dioxide evolution curve. 

Addition of l,3-thiazolium-4-olates to (l-alkynyl)carbene tungsten complexes lb,n affords thiophene and/or pyridone complexes, 64 and 65, by extrusion of sulfur and isocyanate, respectively, from the [3+2] adduct formed initially (Scheme 21).97 [3+2] cycloaddition reactions of azomethine... 

First, the sulfur atom from a thiirane is added to one of the carbon atoms of the thiirane ligand of the complex, with formation of a zwitterionic intermediate. The zwitterionic intermediate undergoes elimination of ethylene to yield a reactive alkene disulfide tungsten complex. The dithietane ligands from two or more molecules, then combine to form the cyclic polysulfides. If the macrocyclization of thiirane catalyzed by W(CO)s(SC2H4) is performed in the presence of DMAD, small quantities of polythioether macrocycles 156 and 157 are formed <1997OM1430>. 

Organylisothiocyanates (R = Me, Et, Ph) and -selenocyanates (R = Ph) also act as nucleophilic S and Se atom donors and react with carbene complexes 259 (M = Cr or W, R = H, Me, Br, OMe, CFj, or NMc2), to yield i/ -arylphenylthioketone and -selenoketone pentacarbonyl chromium and tungsten complexes (260) (170,171). Kinetic results suggest an associative stepwise mechanism with a nucleophilic attack of the sulfur at the carbene carbon in the first reaction step (172). It is also possible to isolate thio- and selenobenzaldehyde complexes 262 (M = Cr or W, E = S or Se,... 

Many molybdenum and tungsten complexes have been synthesized to date, mimicking oxygen, sulfur and selenium transfer reactions. Studying their kinetic characteristics can be undertaken via several alternative routes and procedures. These methodologies and their respective results are presented in the following parts of this chapter. 

Fig. 1. Analysis certificate of the "expected" chorocarbene tungsten complex "(C0)5W=C(C1)C6H5", which compound turned out to be the first "carbyne complex (CO)4aWsC(C6H5). The analysis was correct, as always for a new compound in E. 0/s laboratory The Fischer institute has run an excellent microanalysis laboratory, directed by Manfred Barth since the year of 1965. At present, approximately 2000 C,HJ analyses plus numerous oxygen, halogen, sulfur, and metd analyses are performed there every year.

ITie tungsten complex (19) and its derivatives (20) and (21) formed by treatment with sulfur and diazomethane, respectively, are all fluxional. Rotation about the W = As bond of (19) is associated with AG227K of 11.1 kcal mol" compared with a value of 10.9 kcal mol" for the Mo analogue. Rotations of the 17 ligands of (20) and (21) are also fast enough... 

In the tungsten complex [W(SC6F5)3(CO)(> -Cp)] exchange between the two isomers (17a) and (17b) can occur by rotation about the W—S bonds or by inversion at the pyramidal sulfurs. F NMR studies could not distinguish between the two processes. In the square planar... 

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