Misochko Eugenii Ya, Akimov Alexander V, Korchagin Denis V, Ganushevich Yulia S, Melnikov Egor A, Miluykov Vasili A
Institute of Problems of Chemical Physics of RAS, Chernogolovka, Moscow Region, Russia.
Phys Chem Chem Phys. 2020 Dec 16;22(47):27626-27631. doi: 10.1039/d0cp05254j.
Triplet phosphinidenes, which have been postulated as important intermediates in numerous organophosphorus reactions, have been previously directly observed only in isolated cases. Recently we have published the first recorded EPR spectrum of triplet phosphinidene-mesitylphosphinidene (A. V. Akimov et al., Angew. Chem., Int. Ed., 2017, 56, 7944). In the present study we considered a series of triplet arylphosphinidenes which have been stabilised and detected for the first time using EPR spectroscopy by photolysis of 1-arylphosphiranes ArPC2H4 (Ar = C6H5, 9-anthracenyl, and 2,4,6-iPr3C6H2) in solid methylcyclohexane. We paid special attention to their magnetic parameters and the conditions of their stabilization during the photolytic cleavage of arylphosphiranes. An unusual influence of o-substituents on the spin-orbit component of the ZFS parameters D is observed. Surprisingly, photolysis of bulky arylphosphirane MesPC2H4 (Mes = 2,4,6-ButC6H2) results in no formation of the stabilized triplet phosphinidene under similar experimental conditions. The performed quantum chemical calculations showed that the highly unstable singlet phosphinidene Mes*P undergoes an almost barrier-free rearrangement affording a stable insertion product, thereby hindering the conversion of the singlet intermediate to a more stable triplet phosphinidene.
三线态磷烯被认为是众多有机磷反应中的重要中间体，但此前仅在个别情况下被直接观测到。最近我们发表了三线态磷烯-均三甲苯基磷烯的首个有记录的电子顺磁共振（EPR）谱（A. V. 阿基莫夫等人，《德国应用化学》，国际版，2017年，第56卷，7944页）。在本研究中，我们考察了一系列三线态芳基磷烯，它们通过在固态甲基环己烷中光解1-芳基磷杂环丙烷ArPC₂H₄（Ar = C₆H₅、9-蒽基和2,4,6-异丙基₃C₆H₂）首次得以稳定并通过EPR光谱检测到。我们特别关注了它们的磁参数以及在芳基磷杂环丙烷光解裂解过程中其稳定化的条件。观察到邻位取代基对零场分裂（ZFS）参数D的自旋-轨道分量有异常影响。令人惊讶的是，在类似实验条件下，位阻较大的芳基磷杂环丙烷MesPC₂H₄（Mes = 2,4,6-叔丁基C₆H₂）的光解并未形成稳定的三线态磷烯。所进行的量子化学计算表明，高度不稳定的单线态磷烯Mes*P经历了几乎无势垒的重排，生成了一种稳定的插入产物，从而阻碍了单线态中间体向更稳定的三线态磷烯的转化。
