Oxygen/Sulfur Scrambling During the Copolymerization of Cyclopentene Oxide and Carbon Disulfide: Selectivity for Copolymer vs Cyclic [Thio]carbonates

The catalytic coupling of cyclopentene oxide with carbon disulfide has been investigated utilizing (salen)­CrCl in the presence of added onium salts. Both polymeric and cyclic materials were produced, with oxygen/sulfur atom scrambling observed in both instances. This atom redistribution process was found to require (salen)­CrCl and excess epoxide, though an increase in the rate of atom scrambling was noted upon the addition of the onium salt. Cyclopentene sulfide was observed as a side product of the coupling reaction and was found to be unreactive toward both CS2 and CO2, instead undergoing desulfurization to cyclopentene under the conditions of the reaction. Of the 12 cyclic cyclopentene [thio]­carbonates possibly produced by this coupling reaction, eight were observed, and the crystal structure of trans-cyclopentene trithiocarbonate is reported herein. Computational studies reveal that the cis- cyclic materials are more stable than their trans-counterparts by >5 kcal/mol of enthalpy, and there is a 10–25 kcal/mol preference for the formation of a CO vs CS double bond. When trans-cyclohexene trithiocarbonate was exposed to the catalyst system in the presence of excess cyclopentene oxide, mixed-species scrambling was observed, whereby cyclic [thio]­carbonate compounds displaying both cyclopentyl and cyclohexyl backbones were produced. A proposed mechanistic pathway for atom scrambling involves nucleophilic alkoxide attack at a [thio]­carbonyl center to induce oxygen/sulfur atom exchange.

本研究针对环氧环戊烷（cyclopentene oxide）与二硫化碳（carbon disulfide）的催化偶联反应展开探究，以(salen)氯化铬（(salen)CrCl）为催化剂，并添加鎓盐（onium salts）作为助剂。反应同时生成聚合物与环状产物，两类产物中均观测到氧/硫原子重排现象。研究发现，该原子重排过程需要(salen)氯化铬与过量环氧化物参与，而添加鎓盐可加快原子重排的反应速率。偶联反应的副产物为环戊烯硫醚，该副产物无法与二硫化碳或二氧化碳发生反应，反而在反应条件下发生脱硫反应生成环戊烯。在该偶联反应可能生成的12种环状环戊烯（硫代）碳酸酯中，本研究共观测到8种，同时报道了反式环戊烯三硫代碳酸酯（trans-cyclopentene trithiocarbonate）的晶体结构。计算化学研究表明，顺式环状产物的焓比其反式异构体高出超过5 kcal/mol，且相较于碳硫双键，形成碳氧双键的焓变优势为10~25 kcal/mol。当将反式环己烯三硫代碳酸酯（trans-cyclohexene trithiocarbonate）置于过量环氧环戊烷存在的催化剂体系中时，观测到混合物种原子重排现象，即生成同时带有环戊基与环己基骨架的环状（硫代）碳酸酯类化合物。本文提出的原子重排反应机理路径为：亲核性烷氧基团进攻（硫代）羰基中心，从而诱导氧/硫原子发生交换。