Synthesis Of Tetrathiafulvalene And Its Silyl-Substituted Derivatives

For more than three decades,much attention has been focused on the studies of tetrathiafulvalene(TTF) and its derivatives as organic molecular conductors on account of their good electron-donor properties.Recently,the studies on TTF derivatives have progressively been extended to the fields such as molecular electronic devices,Langmuir-Blodgett films,nonlinear optical materials,and macrocyclic and supramolecular chemistry.As a result,large varieties of new TTF derivatives have been synthesized.Varies of TTF derivatives can be conveniently obtained by the metallation of TTF.However, very few reports on studies of the synthetic routes to TTF skeleton are found up till now. Furthermore,commercial TTF is very expensive.So the first part of this dissertation is focused on the synthetic route to TTF.During the studies on the literature route using piperidine and CS₂ as starting materials,we encountered difficulty in obtaining scalable TTF as reported.This is mainly because of the limited capacity of the reaction vessels and large quantity of solvent required in some steps,which make it fairly hard to get larger scale.We have,therefore,developed another reliable and high yield route by modifications of reported literature procedures.The route starts from the reaction of dimethyl acetylenedicarboxylate(DMAD) with ethylene trithiocarbonate. Hydrolysis and decarboxylation of the diester are efficiently carried out to afford 1,3-dithiole-2-thione.Treatment of the thione with Hg(OAc)₂ followed by the coupling in triethyl phosphite affords TTF in relatively high yield(44%).A practical advantage of our route is that we have notably shortened the time required in the synthesis of TTF.In addition,high yield and almost no limit by solvent make it more appropriate for large-scale preparation.Also,an interesting side-reaction was discovered in the reaction of DMAD with ethylene trithiocarbonate.The by-product thiopyran-4-spiro-2'-(1,3-dithiolane)-2,3,5,6-tetracarboxylate is the first thiopyran-4-spiro-2'-(1,3-dithiolane) heterocyclic compound.This by-product could be isolated and purified by recrystallization with about 4%yield.Single crystal structure of the new spiro compound revealed that the thiopyran ring and 1,3-dithiolane moiety were perpendicular to each other.We also proposed the possible formation mechanism of the spiro compound:at first a[2 + 2]cycloaddition between ethylene trithiocarbonate and DMAD takes place to produce a spirocyclic intermediate. Then another intermediate is formed,which undergoes a ring-opening process.Subsequent[4 + 2] cycloaddition of the intermediate with DMAD furnishes the thiopyran-4-spiro-2'-(1,3-dithiolane) heterocyclic compound.Among the variety of TTF derivatives,silyl-substituted TTF derivatives are seldom reported. However,the interaction between silyl group andÏ€-conjugation can increase the delocalization of the electons.From this viewpoint,the introduction of silyl group to TTF is of much significance. So in the second part of our work,we designed and synthesized several new silyl-substituted TTF derivatives,including three macrocyclic TTF derivatives.[Zn(DMlT)₂]was used as a starting material.Four new silyl-substituted l,3-dithiole-2-thiones were synthesized and characterized. Conversion of the thiones was easily achieved by treatment with Hg(OAc)₂.Coupling was achieved in triethyl phosphite to afford the four corresponding TTF detivatives: 2,3,6,7-tetra(trimethylsilylmethylthio)-1,4,5,8-tetrathiafulvalene,2,3;6,7-bis{oxybis[(dimethylsilyl) -methylthio]}-1,4,5,8-tetrathiafulvalene,2,3;6,7-bis[(1',1',3',3'-tetramethyldisilazan-1',3'-dimethyl) -dithio]-1,4.5,8-tetrathiafulvalene and 2,3;6,7-bis{[benzene-1,4-bis(oxydimethylsilylmethyl)] -dithio}-1,4,5,8-tetrathiafulvalene.UV spectra of these TTF derivatives showed remarkable shifts in maximum absorbance wavelength compared to BEDT-TTF.The results indicated that the introduction of silyl group at p-position of the peripheral sulfur atom may probably change the electrochemical property of the molecules due to the variation of the molecular energy states.In conclusion,a new high yield and time-saving synthetic route to TTF has been developed in this dissertation,which may probably be used in large-scale peraparation of TTF.A new spiro compound is discovered and characterized.Four new silyl-substituted TTF compouds,including three macrocyclic TTF derivatives,have been synthesized and characterized.