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Rhenium allenylidenes and their reactivity toward phosphines: A theoretical study

机译：all烯基亚烷基及其对膦的反应性：理论研究

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摘要

Density functional and local MP2 calculations have been performed to study the electronic structure of the rhenium(I) allenylidene [(triphos)(CO) _2Re(=C=C=CRR')]~+ species [triphos = MeC(CH _2PPh_2)_3; R, R' = aryl group] and its reactivity toward tertiary phosphines. The calculated electronic structure shows a relatively electron-rich nature of the [(triphos)(CO)_2Re]~+ synthon in agreement with the experimental behavior of the corresponding allenylidene complex [(triphos)(CO)_2Re(=C=C=CPh_2)] ~+ (R = R' = Ph). Both the kinetics and the thermodynamics of the nucleophilic addition of tertiary phosphines PMe_(3-x)Ph_x (x = 0, 1, 2, and 3) have been considered. The results indicate lower activation energies for the phosphine attack to C_γ, which leads, however, to products higher in energy than those of the attack to C_α. The computed behavior agrees with the experimental evidence showing that the products of the attack to C_γ are kinetically favored, while the products of the attack to C_α are thermodynamically favored. Finally, we addressed the mechanism of phosphine migration from C _γ to C_α, finding a low-energy path corresponding to an incomplete detachment of the phosphine moiety that then shifts from the C_γ to the C_α atoms while remaining weakly bound to the allenylidene unit.
机译：已进行密度泛函和局部MP2计算，以研究（（I）亚烯基[（triphos）（CO）_2Re（= C = C = CRR'）]〜+物种[triphos = MeC（CH _2PPh_2） _3; [R，R'＝芳基]及其对叔膦的反应性。计算出的电子结构表明[（triphos）（CO）_2Re]〜+合成子具有相对富电子的性质，与相应的亚烯基配合物[（triphos）（CO）_2Re（= C = C = CPh_2）]〜+（R = R'= Ph）。已经考虑了叔膦PMe_（3-x）Ph_x（x = 0、1、2和3）亲核加成的动力学和热力学。结果表明，磷化氢攻击C_γ的活化能较低，但是，所生成的产物的能量却比攻击C_α的产物高。计算结果与实验证据吻合，实验证据表明，对C_γ的进攻产物在动力学上是有利的，而对C_α的进攻产物在热力学上是有利的。最后，我们研究了膦从C_γ迁移到C_α的机理，发现了一条与磷化氢部分不完全分离相对应的低能量路径，然后该部分从C_γ转移至C_α原子，同时仍与烯基亚烯键保持弱结合。

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