Chalcogen insertion

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. 

Sulfur and selenium heterocycles have also been prepared by reaction of zirconium-benzyne complexes with the elemental chalcogens. In these reactions, chalcogens insert into both of the zirconium-carbon bonds (Scheme 7).53-55 Interestingly, neither para-bromo norpara-dimethylamino substituents in 65 interfere with their conversion to 66 (60-80% yields).54 Complexes 66 react further with mono- and bifunctionalized electrophiles (Scheme 7) to yield ort/io-dichalcogenated benzenic compounds 67-69. 

If four molar equivalents of LDA are used in the metallation [48], all four protons of TTF can be replaced (19). Numerous products can be prepared from this intermediate [48—52] (Scheme 6). This is the preferred route for preparing tetrahalotetrathiafulvalenes pathways involving electrophilic aromatic substitution are not practical in general. Chalcogen insertion (Se, Te) offers a good pathway to mixed chalcogen donors. For... 

In contrast, until recently, the only reported reaction for starma- and plumbacy-clobutanes [(7)Pb]2 (Eq. (9)) was their oxidation by elementary chalcogen to afford chalcogenate species resulting from the chalcogen insertion into the C-M bond [113]. 

The chalcogen atoms readily insert into Li-C or Mg-C bonds and this method is widely used to prepare in situ these reagents for further reactions. 

Insertion of Chalcogens to Single Bonds of Group 14 Elements... 

Dibismuthines are very sensitive to oxidation. Thus tetramethyldibismuthine fumes in air, and tetraphenyldibismuthine in toluene solution rapidly absorbs oxygen. Under controlled conditions, dibismuthines react with chalcogens resulting in cleavage of the bismuth—bismuth bond and insertion of a... 

The reaction of tetrachlorodisilane with chalcogenation reagents is one of the synthetic methods to bis-nor-adamantane or double-decker type compounds. When a solution of di-terf-butyltetrachlorodisilane 66 in THF is refluxed together with one equivalent of lithium sulfide or stirred with lithium selenide at room temperature, the tetra(ferf-butylsilicon)pentachalcogenides 67 and 68, respectively, are formed (Scheme 18)6. Each pentachalcogenide exhibits one resonance of a ferf-butyl group in the H and 13C NMR spectra. Most likely, the bis-nor-adamantane derivatives 69 and 70 are initially formed. Insertion of a sulfur or selenium atom into one of the two strained Si—Si bonds would then lead to the observed products. 

The stable silylenes react, however, with water and alcohols, by straightforward insertion into O—H bonds. Silylenes 59, 61 and 62 all react with methyl iodide, inserting into the C—I bond. Examples of these reactions are shown for 59 in Scheme 18. Compounds 59 and 61 also react with elemental chalcogens. For 61 with Ss, Ses or Te 37°, and for 59 with... 

Aryl iodides, in Grignard reagent preparation, 9, 35 Aryl isocyanides, chalcogen—chalcogen additions, 10, 752 Aryl isonitriles, in insertion reactions, 1, 106-107 Aryl ketones, via intramolecular G—H functionalizations,... 

Hexaphosphapentaprismane 11a exhibits a specific reactivity at the central P-P bond. Chalcogene atoms insert into the bond to form cages 53 (Scheme 15) <2001AGE3474>. 

Heating diary) ditellurium compounds in pyridine with selenium dioxide or diselenium dichloride led to the insertion of a selenium atom into the Te — Te bond and the oxidation of one or more of the chalcogen atoms in the bis[aryltelluro] selenides7. 

Further reactions of P-hydridocyclotriphosphazenes (See Section IV,E) have been described. They undergo insertion reactions with aldehydes, ketones, isothiocyanates and electrophilic olefins. Addition of sulfur or oxidation with KMn04 gives thioxo-or oxo-cyclotriphos-phazene derivatives which are methylated at the chalcogen to afford methylthio- and methoxy- cyclotriphosphazenes (36). Hydridocyclo-phosphazenes can also be oxidized to give symmetric and unsymmetric bis(cyclotriphosphazenyl) oxides (35). 

Electrophilic attack at carbyne complexes may ultimately place the electrophile on either the metal or the (former) carbyne carbon, the two possibilities being related in principle by a-elimination/migratory insertion processes (Figure 5.39). The reactions of the osmium carbyne complex are suggestive of an analogy with alkynes. Each of these reactions (hydro-halogenation, chlorination, chalcogen addition, metal complexation see below) have parallels in the chemistry of alkynes. 

Metal-containing groups can be inserted into the chalcogen-chalcogen bond of [Fe2(CO)2(E2)] under facile conditions. The insertion of metal-containing groups can occur such that mixed-metal complexes of the structure shown in Fig. 64 are formed (Table IV). 

Insertion of coordinatively unsaturated species into the chalcogen-chalcogen bonds can also be accompanied by formation of new metal-metal bonds, giving rise to square-pyramidal cluster cores (Fig. 65). These can be of two types, one in which the hetero-metal atom occupies an apical site (A) and another in which the hetero-metal atom is located on the basal site (B). 

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