By flanking a carbene carbon with two substituents, it is possible to synthesize persistent triplet carbenes and isolable singlet carbenes. Isolable singlet carbenes are among the most powerful tools in chemistry, and they have even found medicinal and materials science applications. Between the rich chemistry of disubstituted carbenes and the transient parent carbene are the monosubstituted carbenes that, so far, have only been observed in matrices at very low temperatures of just a few K. Herein, we describe the synthesis of a crystalline monosubstituted carbene. The key for isolating such a species was to design the correct substituent, namely a benzo[c]pyrrolidino heterocycle, which can single-handedly tame the intrinsic tendency of carbenes towards dimerization. The π-donor ability of the nitrogen atom, coupled with the steric bulk of chemically inert substituents at the two adjacent quaternary carbons, make these scaffolds very attractive for the isolation of a variety of other hitherto elusive electron-deficient species.

通过将具有两个取代基的卡宾碳侧接，可以合成持久性三重态卡宾和可分离的单重态卡宾。可分离的单线态卡宾是化学领域中最强大的工具之一，甚至在医学和材料科学领域也得到了应用。迄今为止，仅在基质中只有几K的非常低的温度下才观察到单取代的碳烯，这是在双取代的碳烯和瞬态母体卡宾的丰富化学之间。在这里，我们描述了结晶的单取代的卡宾的合成。分离此类物质的关键是设计正确的取代基，即苯并[ c]] pyrrolidino杂环，可以单调驯化羧甲酸酯向二聚化的内在趋势。氮原子的π供体能力，再加上两个相邻的季碳上的化学惰性取代基的空间体积，使这些支架对于分离其他迄今难以捉摸的电子缺陷物种非常有吸引力。