Preparation of Stable Triplet Carbenes and Its Application to Stable High-Spin Molecules

本研究旨在稳定和分离一种三重态碳，并将其作为稳定的高自旋有机分子的自旋单元。位阻保护是稳定三联体卡宾的理想方法，因为在卡宾中心附近引入保护基团不仅可以阻止卡宾中心与外部试剂的接触，而且可以通过增加中心键角来实现热力学稳定。然而，由于碳烯对电子的贪欲，当烷基作为保护基团时，这种策略受到限制。在这种情况下，开发一种新的保护基团是至关重要的，它是立体拥挤的，但对三联体碳没有反应。我们发现，理论上体积庞大但供氢能力差的烷基，如双环[2.2.2]辛基和三基，以及杂原子取代基，如溴和三氟甲基，是三联体卡宾的有效动力学保护剂，并能产生三联体二苯基卡宾，在室温下在溶液中存活1小时以上。我们还偶然发现，这些稳定的三联体碳的前体重氮甲烷也相当稳定，可以用作制备聚重氮化合物的基石。例如，我们能够在空间拥挤的二苯基重氮甲烷的对位上引入乙基，并通过随后的1,3,6 -三（碘）苯偶联反应制备三和六（重氮）甲烷。由这些聚重氮化合物生成的聚碳化合物具有高自旋态。

This research was undertaken to stabilize and isolate a triplet carbene and to use it as a spin unit for stablehigh-spin organic molecules.Steric protection is an ideal method of stabilizing the triplet carbene since a protecting group when introduced near carbene center not only blocks the carbene center from external reagents but also results in thermodynamic stabilization by increasing the central bond angle. However, clue to a voracious appetite of carbenes for electrons, this strategy encounters limitation when alkyl groups are employed as protecting group. In this light, it is crucial to develop a new protecting group which is sterically congesting but unreactive toward triplet carbenes. We found the oretically bulky yet poor H donating alkyl groups such as bicyclo[2.2.2]octyl and triptycyl groups and heteroatomsubstituents such as bromine and trifluoromethyl groups are effective kinetic protectors toward triplet carbenes and were able to generate triplet diphenylcarbene surviving more than one hour in solution at room temperature.We also found serendiptously that the precursor diazomethanes for those stable triplet carbenes are also fairly stable and can be used as a building block for preparing poly(diazo) compounds. For instance, we were able to introduce ethynyl group at the para position of sterically congested diphenyldiazomethanes and to prepare tris- and hexakis(diazo)-methanes by subsequent coupling reaction using l, 3,6-tri(iodo)benzene. Polycarbenes generated from those poly(diazo) compounds were shown to have high spin states.