Sulfur oxides insertion reactions

The hrst working lead cell, manufactured in 1859 by a French scientist, Gaston Plante, consisted of two lead plates separated by a strip of cloth, coiled, and inserted into a jar with sulfuric acid. A surface layer of lead dioxide was produced by electrochemical reactions in the first charge cycle. Later developments led to electrodes made by pasting a mass of lead oxides and sulfuric oxide into grids of lead-antimony alloy. 

The S02 molecule has unshared pairs of electrons on both the sulfur and oxygen atoms. As a result, it forms numerous complexes with transitions metals in which it is known to attach in several ways. These include bonding through the sulfur atom, through an oxygen atom, by both oxygen atoms, and various bridging schemes. In most cases, the complexes involve soft metals in low oxidation states. Another important reaction of sulfur dioxide is known as the insertion reaction, in which it is placed... 

To circumvent some of the above-mentioned drawbacks of sulfur-based mercury chemodosimeters, a system based on the alkyne oxymercuration of 58 has been developed (Fig. 22) [146]. 58 shows high selectivity, a limit of detection of ca. 8 ppm, resistance against strong oxidants, and a positive reaction even in the presence of cysteine, which is known to form stable mercury complexes and is used for the extraction of mercury from tissue samples. Another metal that is well-known for its catalytic ability is palladium, catalyzing different reactions depending on its oxidation state. Since this metal is toxic, assessment of the maximum allowable concentration of Pd in consumer products such as pharmaceuticals requires highly sensitive and selective detection schemes. For this purpose, indicator 60 was conceived to undergo allylic oxidative insertion to the fluorescein... 

Pathway III of Fig. 26 has been demonstrated for thiophene and benzo-thiophene with Ir complexes (4) and for all thiophenes, including dibenzo-thiophene, with Rh complexes (94, 95). These oxidative additions appear to be influenced by substituents present on the carbon atoms adjacent to the sulfur atom. Insertion between sulfur and the unsubstituted carbon is highly preferred. For 2-methylthiophene the exclusive product is the 1-5 bond insertion product, whereas for 3-methylthiophene, no preference for insertion was observed (1-2 and 1-5 bond insertion products were equal). In competitive studies, thiophene was found to be about twice as reactive as 2,5-dimethylthiophene. This behavior is similar to that observed for relative reaction rates of substituted thiophenes observed with conventional HDS catalysts. Thus steric limitations can occur, even with monomeric, homogeneous catalysts. 

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). 

Some of the substances that lead to 1,1 insertion reactions into metal-carbon ff bonds are carbon monoxide, CO alkyl- or arylisocyanide, CNR, carbenes CR2 sulfur dioxide, SO2 and nitrogen oxide NO. Most studied are CO, CNR, and SO2 therefore a more detailed account of them is presented. 

Topics of this section include 1,2-insertion reactions of acetylenes (b), olefins (c), allenes (d), oxygen (e), carbon dioxide (f), sulfur dioxide (g), sulfur trioxide (h), and nitric oxide (i). 

Sulfur trioxide is a strong Lewis acid and an oxidant. Insertions into element-carbon bonds to yield alkylsulfonates [reaction (k)] are known for E = Li , AH , Si , Hg °, Sn i and Ge ... 

Insertion into the basal P-P bond is also possible. For example, in the oxidative addition reaction of P4S3 to Vaska s compound, tra/ 5-Ir(CO)CI(PPh3)2 in benzene at 60 °C gives an octahedral Ir complex [Ir(CO)Cl(P4S3)(PPh3)]2 asagreen air-stable solid. Related reactions have been described. Metal centers can also be used to trap reactive arsenic-sulfur species (equation 73). 

The biotin and lipoate synthases catalyze similar reactions, the insertion of sulfur into unactivated C—bonds to generate essential cofactors (Figures 8C and 8D). The substrate in the case of biotin synthase is dethiobiotin, with a single sulfur inserted into two C— FI bonds to generate the tetrahydrothiophene ring of biotin. In the case of lipoate synthase, two atoms of sulfur are inserted, one each into the C—bonds at positions 6 and 8 of octanoic acid to produce dihydrolipoate, which is typically isolated in the oxidized form shown in Figure 8D. (The actual... 

A review has appeared on the synthesis and reactivity of (sUylamino) and (silyl-anilino)phosphines. The S5mthesis, derivatisation and coordination behaviour of the morpholine (69) and piperazine (70) derivatives have been described. They are formed from the appropriate amine with diphenylchlorophosphine, and both react with sulfur or selenium to give the chalcogenide, whilst reaction of (69) with paraformaldehyde leads to insertion of methylene into the P N bond to give the phosphine oxide. The reaction between ethylenediamine and diphenylchlorophosphine can lead to the bis-, tris- and tetrakis(diphenylphosphino)ethylene-diamines, depending upon the stoichiometry. The first two are oxidised in situ whist the latter, (71), is stable. A nickel complex of (71) has been shown to be active as a catalyst for ethylene pol5nnerisation. ... 

The mechanistic nature of these nitrene insertion reactions remains unknown. A number of possible routes can be considered (Fig. 302), including (1) direct insertion, (2) initial formation of a metal-nitrene (imido) complex followed by insertion, (3) initial addition of nitrene fragment to sulfur (i.e., oxidation of sulfur) followed by an isomeric rearrangement. On the basis that copper(II) nitrene complexes are unknown (although they have been implicated in the copper-catalyzed aziridination process) this route is ruled out and literature precedent suggests that route (3) is most likely. 

We have recently found that this reaction is feasible and can be carried out with both the (bpym)PtCl2/H2S04 system as well as with Pd(II) in sulfuric acid [30]. The reaction with Pd(II) is very interesting because, while this system can catalyze the additional oxidative insertion of CO into a CH bond of methane, it... 

Codeposition of silver vapor with perfluoroalkyl iodides at -196 °C provides an alternative route to nonsolvated primary perfluoroalkylsilvers [272] Phosphine complexes of trifluaromethylsilver are formed from the reaction of trimethyl-phosphme, silver acetate, and bis(trifluoromethyl)cadmium glyme [755] The per-fluoroalkylsilver compounds react with halogens [270], carbon dioxide [274], allyl halides [270, 274], mineral acids and water [275], and nitrosyl chloride [276] to give the expected products Oxidation with dioxygen gives ketones [270] or acyl halides [270] Sulfur reacts via insertion of sulfur into the carbon-silver bond [270] (equation 188)... 

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