Chalcogen-lead bonds

The growing availability of numerous reactive plumbylenes opens routes to new lead(IV) compounds with halogen-lead81-82 (39) or chalcogen-lead bonds (40).83 However, there are also new data for mesityllead bromides (41,42)84 and trimeric diaryllead sulfides (Ar2PbS)3 (43),85 prepared in the usual ways. 

This interpretation of the experimental results was corroborated by ab initio calculations on the relative stabilities of a series of double bond compounds, [H2Pb=X] and their plumbylene type isomers, [frans-H-Pb-X-H] and [ciT-H-Pb-X-H] (X = O, S, Se, and Te) (vide supra) 6 The results of the theoretical calculations and experiments for lead-chalcogen double bond species are in sharp contrast to those of the other Group 14 element analogues which do not isomerize to the divalent compounds.14b... 

Among the silicon-chalcogen double-bond compounds, the silicon-sulfur doubly-bonded compounds (silanethiones) are considered to be easier to synthesize, since it has been predicted by the theoretical calculations that a silicon-sulfur double bond is thermodynamically and kinetically more stable than a silicon-oxygen double bond (silanone)13,14. According to the calculations, the lower polarization of Si=S compared to Si=0 should lead to a lower reactivity of Si=S. In addition, H2Si=S (1) is calculated to be by 8.9 kcal mol-1 more stable than its divalent isomer, H(HS)Si , whereas H2Si=0 (2) is by 2.4 kcal mol-1 less stable than H(HO)Si . 

In some reactions intramolecular chalcogen nitrogen interactions may lead to stereochemical control. For example, selenenyl bromides react with C=C double bonds, providing a convenient method of introducing various functional groups. The reaction proceeds readily, but affords a racemic mixture. The modified reagent 15.22 contains a chiral amine in close interaction with the selenium atom. It reacts with olefins affording up to 97% ee of isomer A (Scheme 15.2). ... 

The presence of a fragment corresponding to the loss of selenium in mass spectroscopy under electronic impact of germaneselone 179 points to a thermal instability of the Ge = Se bond.132 Heating a solution of 179 in benzene at 80°C in the presence of sulfur leads to a chalcogen exchange, likely via the divalent species (ArO)2Ge 141 [Eq. (38)]. 

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. 

Terminal chalcogenido zirconium complexes (23) are conveniently synthesized by the reactions of dicarbonylzir-conocene with either N2O or the elemental chalcogens (S, Se, Te) see Chalcogens) in the presence of pyridine. The Zr=E bond in these complexes is highly reactive and leads to a variety of 1,2-addition and cycloaddition reactions (Scheme 8). ... 

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