Energetics and mechanism of ammonia synthesis through the Chatt Cycle: conditions for a catalytic mode and comparison with the Schrock Cycle.
Energetics and mechanism of ammonia synthesis through the Chatt Cycle: conditions for a catalytic mode and comparison with the Schrock Cycle.
复制标题
通过查特循环合成氨的能量学和机制：催化模式的条件以及与施罗克循环的比较。
作者：
Gerald C Stephan;C. Sivasankar;F. Studt;F. Tuczek
通过一系列的密度泛函计算，得到了CHATT循环的能量分布。这是我们早期对施罗克旋回(Angew.化学。2005,117,5783；Angew。化学。内部艾德2005，44,5639)，应用相同的量子化学方法和近似。在施洛克循环中，十甲基铬起到了还原剂的作用。质子化反应被认为是由HBF4/二乙醚或lutidine催化的。对于所有质子化和还原步骤，计算了相应的自由反应热变。得到的能量分布和相应的反应机理与Schrock循环有很大的相似之处。特别是，最耗能的反应是N_2络合物的第一次质子化，最耗能的反应是N-N键的断裂。如果使用Lutidina作为酸，使用CP2*Cr作为还原剂，则反应过程涉及不允许加热的步骤。然而，对于HBF4/二乙醚作为酸，CP2*Cr作为还原剂，由热允许反应组成的催化循环基本上是可行的。这个循环包括一个钼碘氟络合物作为氮素中间体。结果表明，在该体系中，MoO-双(氮气)络合物的再生是不可能的。此外，钼碘氟氮络合物不稳定地发生歧化反应。讨论了这些结果对实现以钼和钨膦络合物为基础的催化体系的意义。
Through a series of DFT calculations the energy profile of the Chatt cycle is evaluated. This is the counterpiece of our earlier investigations of the Schrock cycle (Angew. Chem. 2005, 117, 5783; Angew. Chem. Int. Ed. 2005, 44, 5639), applying the same quantumchemical methodology and approximations. As for the Schrock cycle, decamethylchromocene acts as reductant. The protonation reactions are considered to be mediated by HBF4/diethyl ether or lutidinium. For all protonation and reduction steps the corresponding free reaction enthalpy changes are calculated. The derived energy profile and corresponding reaction mechanism bear strong similarities to the Schrock cycle. In particular, the most endergonic reaction is the first protonation of the N2 complex and the most exergonic reaction is the cleavage of the N--N bond. If lutidinium is employed as acid and Cp2*Cr as reductant, the reaction course involves steps that are not thermally allowed. For HBF4/diethyl ether as the acid and Cp2*Cr as reducant, however, a catalytic cycle consisting of thermally allowed reactions is principally feasible. This cycle involves a Mo I-fluoro complex as dinitrogen intermediate. It is shown that regeneration to the Mo 0-bis(dinitrogen) complex is thermally not accessible in this system. Moreover, the Mo I fluoro-dinitrogen complex is labile towards disproportionation. The implications of these results with respect to the realization of a catalytic system on the basis of Mo and W phosphine complexes are discussed.
影响因子：
4.6
作者：
D. Yandulov;R. Schrock
通讯作者：
D. Yandulov;R. Schrock