Lead dithiolates

Tire reaction of the lead dithiolate 18 with elemental sulfur was claimed, without unambiguous structure proof, to give a dithiirane 19 in 75% yield (96ZOR1881). 

Dithiastannacyclopentanes and dithiastannacyclohexanes have been obtained by treating diphenyltin dichloride with the appropriate lead dithiolates (230), e.g.,... 

Cyclic disulfides. Reaction of a dithiol (I) with an aqueous solution oflead acetate gives a lead dithiolate (2) in nearly quantitative yield. These react with sulfur in benzene solution at room temperature to give the cyclic disulfide (3) in high yield. 

These compounds are best prepared from the chlorosilane and sodium thiolate, or thiol and a tertiary amine. Well-dried yellow lead dithiolates Pb(SR)2 proved to be convenient synthetic intermediates3 but the product has to be washed from the resulting white lead chloride as the reaction reverses on heating (equation 1). 

Modification of reaction schemes leading to furans, thiophenes and pyrroles by incorporation of a heteroatom into the substrate provides ready access to imidazoles, thiazoles, oxazoles, dithioles, oxathioles, etc. Incorporation of two heteroatoms into the substrates... 

Thermolysis of the 1,2,3-thiadiazoles (545) in the presence of carbon disulfide leads to the thiocarbonyl carbene (546) adduct, the ring-fused l,3-dithiole-2-thione (547) (76JOC730). 

Few isothiazoles undergo simple cycloaddition reactions. 4-Nitroisothiazoles add to alkynes (see Section 4.17.7.4). With 5-thiones (84) and dimethyl acetylenedicarboxylate, addition to both sulfur atoms leads to 1,3-dithioles (85) (77SST(4)339, 80H(14)785, 81H(16)156, 81H(16)595). Isothiazol-3-one 1-oxide and the corresponding 1,1-dioxide give normal adducts with cyclopentadiene and anthracene (80MI41700), and saccharin forms simple 1 1 or 1 2 adducts with dimethyl acetylenedicarboxylate (72IJC(B)881). 

Another method for slowing oxidation of rubber adhesives is to add a compound which destroys the hydroperoxides formed in step 3, before they can decompose into radicals and start the degradation of new polymer chains. These materials are called hydroperoxide decomposers, preventive antioxidants or secondary antioxidants. Phosphites (phosphite esters, organophosphite chelators, dibasic lead phosphite) and sulphides (i.e. thiopropionate esters, metal dithiolates) are typical secondary antioxidants. Phosphite esters decompose hydroperoxides to yield phosphates and alcohols. Sulphur compounds, however, decompose hydroperoxides catalytically. 

Of greater importance is the reaction of unsaturated compounds with sulfur at 200-250°C, which normally leads to l,2-dithiole-3-thiones (trithiones) but especially with 2-aryIsubstituted 2-butenes and 1- aryl- or 2-aryl-1-butenes, thiophenes are obtained in 15-60% Thus p-methoxy-a-ethylstilbene (50) gives 2-phenyl-3-... 

Many heavy metals react with dithiol to give coloured precipitates, e.g. bismuth, iron(III), copper, nickel, cobalt, silver, mercury, lead, cadmium, arsenic, etc. molybdate and tungstate also react. Of the various interfering elements, only arsenic distils over with the tin when a mixture is distilled from a medium of concentrated sulphuric acid and concentrated hydrobromic acid in a current of carbon dioxide. If arsenic is present in quantities larger than that of the tin it should be removed. 

A hydroxy and an arylthio group can be added to a double bond by treatment with an aryl disulfide and lead tetraacetate in the presence of trifluoroacetic acid." Manganese and copper acetates have been used instead of Pb(OAc)4. ° Addition of the groups OH and RSO has been achieved by treatment of alkenes with O2 and a thiol (RSH)." Two RS groups were added, to give vie- dithiols, by treatment of the alkene with a disulfide RSSR and Bp3-etherate."° This reaction has been carried... 

Answer Various sequences of C-S disconnections would no doubt all lead to good syntheses. Disconnect ion (4a) has the advantage of giving a symmetrical dithiol (5) and available (p T 53) chloroacetyIchloride. 

Alivisatos and coworkers reported on the realization of an electrode structure scaled down to the level of a single Au nanocluster [24]. They combined optical lithography and angle evaporation techniques (see previous discussion of SET-device fabrication) to define a narrow gap of a few nanometers between two Au leads on a Si substrate. The Au leads were functionalized with hexane-1,6-dithiol, which binds linearly to the Au surface. 5.8 nm Au nanoclusters were immobilized from solution between the leads via the free dithiol end, which faces the solution. Slight current steps in the I U) characteristic at 77K were reflected by the resulting device (see Figure 8). By curve fitting to classical Coulomb blockade models, the resistances are 32 MQ and 2 G 2, respectively, and the junction... 

Reaction of the tri- -butylphosphine adduct 180 with compound 157 leads to cycloaddition across the two sulfur atoms to give corresponding 2-tri- -butylphosphoranylidene-l,3-dithiole 181, which can be trapped by in situ Wittig reaction with benzaldehyde to give 182 (Scheme 21) <1994CC2603, 1997T2261>. 

Interestingly, the introduction of two bromomethyl functions in 4- and 5-positions of ethylen-l,3-dithiole-2-thione leads to a packing determined by weak interactions involving also the bromine atoms. One I2 molecule behaves as an acceptor towards S and as donor towards the second I2 molecule, which in turn behaves as donor towards the a c Br orbital (Figure 13). Intermolecu-lar S- -Br, CFF Br and L -I contacts make up a three-dimensional network.480 Reaction of 5,5-dimethyl-2-selenoxoimidazoline-4-one with iodine provided the first structurally characterised compound of the type [RR C Se — I-I].32 The Se-I bond is shorter (269.9 pm) and the I-I contacts are longer (296.2 pm) than in 1 1 adducts of dialkylselenides with iodine (see Chapter 8.2). 

A singlet-triplet behavior is found for those complexes such as [CpNi(oxdt)] [71]or [CpNi(F2pdt)] [72] associated into dyads (Fig. 12), where the strong distortions from planarity of the dithiolate ligands hinder any other interdyad intermolecular contacts. The large Ni S and S S intermolecular distances lead to weak intermolecular interactions with / values of —29 or —8 cnC1 for [CpNi(oxdt)] and [CpNi(F2pdt)] respectively. 

Crosstalk has been discussed fairly extensively, as one of a series of interference phenomena that can lead to a different kind of control of molecular transport than has been discussed in Sect. 7.4. It is also possible to observe intramolecular interference effects. For example, with cross-conjugated molecules [163] or benzene dithiol linked in the 1,3 (or meta) configurations [164-171], both are expected to show substantially reduced transport. 

---