Study Of Organic Reactions And Polymerizations Based On Elemental Sulfur/Selenium And Alkynes

Sulfur-containing and selenium-containing polymers have attracted attention for their high refractive index,optoelectronic properties,strong affinity to heavy metal ions,rich redox properties,unique dynamic covalent bonds,which are widely applied in materials,medicine,environment,and energy.However,a large number of structurally novel sulfur-containing and selenium-containing polymers have not been reported,especially sulfur-containing and selenium-containing heterocyclic polymers for the lack of efficient and convenient synthetic approaches from easily available monomers.Elemental sulfur and selenium,are readily available,safe,lower toxic,easy-to handle,which may serve as ideal monomers for the synthesis of sulfur-containing and selenium-containing polymers.And alkynes are one of the most desirable synthons in organic synthesis,owing to their versatile reactivity,and could react with sulfur or selenium to afford a series of sulfur-containing or selenium-containing compounds,especially sulfur-containing or selenium-containing heterocyclic compounds.However,the reaction of sulfur or selenium with alkynes often involves high temperatures and harsh reaction conditions,resulting in a large number of active species,reaction intermediates,and reaction products with multiple conversion pathways.The complex reaction systems,multiple by-products,and poor specificity,posing great challenges to the development of new polymerization and the synthesis of new polymer structures.The complex reaction system,multiple by-products,and poor specificity pose great challenges to the development of new polymerizations and construction polymers with new structures.Therefore,our aim is to activate sulfur and selenium by alkali,and react with alkynones or terminal alkynes to afford sulfur-containing or selenium-containing compounds in a mild,efficient and regioselective manner.More importantly,based on the above-mentioned organic reactions,new polymerizations were developed for the synthesis of sulfur and selenium containing polymers with new structures.Firstly,with the target of direct conversion from sulfur to sulfur-containing heterocyclic polymers,the temperature-controlled KOH-promoted organic reactions of sulfur and alkynones were developed for the synthesis of thiophenes and 1,4-dithiins in mild and efficient manner.Then,we have developed one-step conversion from elemental sulfur to polythiophenes and poly（1,4-dithiin）s through KOH-induced regioselective polymerizations at 80 ^oC or room temperature with high molecular weights（M_n up to 21 800 g/mol）in high yield（up to 87%）.The unique structures of polythiophenes and poly（1,4-dithiin）s endowed them better thermal stability,higher char yields,and good solubility.It was the first time to introduce the unique 1,4-dithiin heterocycle into polymer structures.Subsequently,in order to synthesize selenium-containing heterocyclic compounds and polymers,we have succeeded in developing Cs₂CO₃-mediated reactions of Se and alkynones,which can directly and smoothly transform Se into nonaromatic 1,4-diselenins in high efficiency and regioselectivity.The one-pot two-step tandem reaction of selenium and alkynones could also afford selenophenes at room temperature in the presence of Cs₂CO₃.The efficient transition metal-free room temperature polymerizations of Se and alkynones were developed accordingly with Cs₂CO₃ as the base,affording well-defined regioselective poly（1,4-diselenin）s.The one-pot two-step tandem polymerization of Se and alkynone was also realized at room temperature to afford aromatic polyselenophene efficiently.The direct conversion from poly（1,4-diselenin）s to polyselenophenes upon either heating or oxidation was also realized,and the different emission behavior of these polymers enabled the real-time fluorescence monitoring of the room temperature conversion from poly（1,4-diselenin）s to polyselenophenes.Furthermore,the unique structures of poly（1,4-diselenin）s and polyselenophenes have endowed them with excellent solubility,thermal and chemical stability,unique photophysical property,and high refractive indices（up to 1.8487）.The poly（1,4-diselenin）s and polyselenophenes with unique structures were constructed for the first time.These polymerizations generally possessed mild condition,high efficiency,and selectivity.Then,with the target of conversion from selenium to selenium-containing heterochain polymers,the C₂H₅ONa-promoted organic reactions of selenium,terminal alkynes,haloalkane were developed for the synthesis of alkyne selenides in 98%yield at room temperature.With those efforts,the multicomponent polymerization of Se,terminal alkynes and haloalkane was developed for the synthesis of poly（alkynyl selenide）s with high yields（up to 95%）and high molecular weights（M_n up to 18 800 g/mol）.The poly（acetylene selenide）s showed excellent solubility,and thermal stability.Two kinds of organic reactions were also developed.The multicomponent reaction of Se,terminal alkyne and epoxide was developed for the synthesis of alkynyl selenides in the presence of C₂H₅ONa at room temperature.The reaction of elemental selenium with terminal alkynes was also developed for the synthesis of diselenafulvene compounds.We have successfully developed multicomponent reaction and polymerization of selenium,alkyne and haloalkane for the synthesis of a series of alkyne selenide compounds and polymers.This dissertation adopts the strategy of element sulfur and selenium activated by alkali and polymerized with alkynones or terminal alkynes to develop five new polymerization methods in mild conditions and high efficiency.Five different kinds of chalcogen-containing polymers with new structures were prepared,including polythiophenes,poly（1,4-dithiin）s,polyselenophenes,poly（1,4-diselenin）s,and poly（alkynyl selenide）s.It opens new way for the design of organic reactions and the development of polymerizations.