Base-catalyzed insertion of dioxygen into rhodium-hydrogen bonds: kinetics and mechanism.
Base-catalyzed insertion of dioxygen into rhodium-hydrogen bonds: kinetics and mechanism.
复制标题
碱催化将双氧插入铑-氢键：动力学和机制。
作者：
Ewa Szajna;A. Bakac
在碱性水溶液中，氧分子与铑（L =（NH（3））（4），trans-L（1），cis-L（1），其中L（1）= cyclam）反应，迅速生成相应的过氧化氢配合物。在pH 8 < pH < 12的范围内，动力学对[OH（-）]呈一级依赖关系。对[O（2）]的依赖性小于一阶，并且在所使用的最高浓度下接近饱和。这些数据表明，在25 ℃时，OH（-）对trans-L（1）（OH）RhH（+）的氢化物进行攻击，k =（1.45 +/- 0.25）x 10（3）M（-1）s（-1），导致Rh-H键的异裂断裂并形成反应性Rh（I）中间体。O（2）和H（2）O对Rh（I）的竞争是观察到的O（2）依赖性的来源。在此基础上，发现反应的初始阶段存在明显的动力学同位素效应：L（1）（OH（D））RhH（D）（+）+ OH（D）（-）k（1）/k（-1）L（1）（OH（D））Rh（I）+ H（D）（2）O，k（1H）/k（1D）= 1.7，k（-1H）/k（-1D）= 3.0。反式-L（1）（OH）RhH（+）的k（1）活化参数为Δ H（++）= 64.6 +/-1.3 kJ mol（-1）和Δ S（++）= 40 +/-4 J mol（-1）K（-1）。
The reaction between molecular oxygen and rhodium hydrides L(OH)RhH(+) (L = (NH(3))(4), trans-L(1), and cis-L(1), where L(1) = cyclam) in basic aqueous solutions rapidly produces the corresponding hydroperoxo complexes. Over the pH range 8 < pH < 12, the kinetics exhibit a first order dependence on [OH(-)]. The dependence on [O(2)] is less than first order and approaches saturation at the highest concentrations used. These data suggest an attack by OH(-) at the hydride with k = (1.45 +/- 0.25) x 10(3) M(-1) s(-1) for trans-L(1)(OH)RhH(+) at 25 degrees C, resulting in heterolytic cleavage of the Rh-H bond and formation of a reactive Rh(I) intermediate. A competition between O(2) and H(2)O for Rh(I) is the source of the observed dependence on O(2). In support of this mechanism, there is a significant kinetic isotope effect for the initial step, L(1)(OH(D))RhH(D)(+) + OH(D)(-) k(1)/k(-1) L(1)(OH(D))Rh(I) + H(D)(2)O, k(1H)/k(1D) = 1.7, and k(-1H)/k(-1D) = 3.0. The activation parameters for k(1) for trans-L(1)(OH)RhH(+) are DeltaH(++) = 64.6 +/- 1.3 kJ mol(-1) and DeltaS(++) = 40 +/-4 J mol(-1) K(-1).