Lead, xanthate structures

There are two types of objects in supramolecular chemistry supermolecules (i.e., well-defined discrete oligomolecular species that result from the inter-molecular association of a few components), and supramolecular arrays (i.e., polymolecular entities that result from the spontaneous association of a large, undefined number of components) (4, 5). Both are observed in some metal-xanthate structures to be described herein. The most frequent intermolecular forces leading to self-assembly in metal xanthates are so-called secondary bonds . The secondary bond concept has been introduced by Nathaniel W. Alcock to describe interactions between molecules that result in interatomic distances longer than covalent bonds and shorter than the sum of van der Waals radii (6). Secondary bonds [sometimes called soft-soft interactions (7)] are typical for heavier p-block elements and play an important role as bonding motifs in supramolecular organometallic chemistry (8). Other types of intermolecular forces (e.g., Ji- -ji stacking) are also observed in the crystal structures of metal xanthates. 

The addition of silyl radicals to thiocarbonyl derivatives is a facile process leading to a-silylthio adducts (Reaction 5.37). This elementary reaction is the initial step of the radical chain deoxygenation of alcohols or Barton McCombie reaction (see Section 4.3.3 for more details). However, rate constants for the formation of these adducts are limited to the value for the reaction of (TMS)3Si radical with the xanthate c-C6HuOC(S)SMe (Table 5.3), a reaction that is also found to be reversible [15]. Structural information on the a-silylthio adducts as well as some kinetic data for the decay reactions of these species have been obtained by EPR spectroscopy [9,72]. 

The Pb- -S mediated chains observed in the structure of polymeric Pb(S2COEt)2 are disrupted upon the addition of base. The immediate coordination geometry about the lead atom in the adduct Pb(S2CO—i-Pr)2(py) (231) is shown in Fig. 145(a). The lead atom is coordinated by the pyridine nitrogen atom and two xanthate ligands, one that forms asymmetric Pb—SI and Pb—S2 distances of 2.72(2) and 3.06(2) A, and one that forms symmetric bonds of... 

Briggs et al. proposed a new strategy for the synthesis of tricyclic structures using acyl xanthates as precursor for acyl radicals [121]. Irradiation with visible light of a solution of acyl xanthate in presence of 1,6-diene 126 afforded czs-fused bicyclic compound 127 in a good yield (Scheme 38). Radical reduction of xanthate and subsequent aldol condensation leads to the formation of [5.5.5]-fused ring systems similar to those of the triquinane terpene family. 

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