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
H. Stenger et al., 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, Organometallics, 14(9), 1995, pp. 4374-4381
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.