The reaction mechanism between phosphacyclopropenylidene and methyleneimine has been systematically investigated at the M06–2X/6–311++G(d,p) level of theory in order to better understand the reactivity of unsaturated cyclic phosphorus-bearing carbene. Geometry optimizations and vibrational analyseshave been conducted for the stationary points on the potential energy surface of the system. Calculations show that the spiro bicyclic intermediate could be produced through the cycloaddition process between phosphacyclopropenylidene and methyleneimine initially. The reaction mechanism is illustrated with frontier molecular orbital theory. Introduction of electron-withdrawing group in phosphacyclopropenylidene will better facilitate the addition process. Through subsequent ring-expanding and hydrogen-migrating process, fuse-ring and allene compounds could be produced, respectively. Furthermore, it’s easy for spiro bicyclic intermediate and another methyleneimine to form a spiro tricyclic compound. This study is helpful to understand the reactivity of phosphacyclopropenylidene, the evolution of phosphorus-bearing molecules in space, and to offer an alternative approach to the formation of phosphorus-bearing heterocyclic compound.

中文翻译：

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磷环丙烯基与亚甲基亚胺反应机理的见解：理论研究

在M06–2X / 6–311 ++ G（d，p）的理论水平上，系统地研究了磷环丙烯基与亚甲基亚胺之间的反应机理，以便更好地理解不饱和环状含磷卡宾的反应性。对系统势能表面上的固定点进行了几何优化和振动分析。计算表明，螺环双环中间体最初可通过磷环丙烯基与亚甲基亚胺之间的环加成反应生产。用前沿分子轨道理论阐明了反应机理。在磷环丙烯基中引入吸电子基团将更好地促进加成过程。通过随后的扩环和氢迁移过程，可以分别生产熔环和丙二烯化合物。此外，螺双环中间体和另一亚甲基亚胺很容易形成螺三环化合物。这项研究有助于理解磷环丙烯基的反应性，空间中含磷分子的演化，并为形成含磷杂环化合物提供另一种方法。