HETEROCYCLIC-SYSTEMS CONTAINING LEAD(IV) .5. REDISTRIBUTIONS BETWEEN DIARYLLEAD SULFIDES [R2PBS]3 AND [R'2PBS]3(R,R'=PH,O-TOL, M-TOL, AND P-TOL, 2,4-XYL, 2,5-XYL, AND 3,4-XYL, AND P-ANIS) - PI-PI' CHARGE FLOW IN MIXED-SPECIES VIA SIGMA-ASTERISK-LUMOS

Eight lead-sulfur heterocycles of the type [R(2)PbS](3) have been synt hesized. Vibrational data for all compounds and crystal structures for [o-Tol(2)PbS](3) and [p-Tol(2)PbS](3) have been determined. The core of each molecule consists of a six-membered ring in a flexible twisted -boat conformation. Equimolar mixtures of the heterocycles dissolved i n CDCl3 immediately reached the steady state of the dynamic equilibriu m between the starting materials and the redistribution species [(R(2) PbS)(2)(R'2PbS)] and [(R(2)PbS)(R'2PbS)(2)]. Thirteen combinations hav e been followed by Pb-207-NMR spectroscopy (six chemical shifts in an intensity ratio of (1):(1):(1:2):(1:2) and two spin-spin AB systems) a nd by FD mass spectrometry (mixed units with a Pb4S4 core). From these results and the crystal structure data, a possible course of the redi stribution is proposed. Two differently substituted pure heterocycles slowly form a dimer containing two five-coordinated lead atoms. This d imer rearranges by a fast intramolecular nucleophilic attack at these atoms into a ladder structure with a Pb4S4 core and two extraladder gr oups -SPb which are shown to cleave off in the mass spectrum. The slow reversal of the rearrangement leads back to the pure heterocycles or results in the mixed species. The AB systems of the mixed heterocycles result in two-bond couplings (2)J(Pb-207-S-Pb-207). The Pb-207-NMR ch emical shifts are discussed in an order of pi-pi' charge flow between units R(4)Pb(2)/R'Pb-2 via sigma-LUMO's which extend over the entire ring core. 2J decreases along with an increasing charge flow.