Feyel Sandra, Schröder Detlef, Schwarz Helmut
Institut für Chemie der Technischen Universität Berlin, Strasse des 17. Juni 135, D-10623 Berlin, Germany.
J Phys Chem A. 2006 Mar 2;110(8):2647-54. doi: 10.1021/jp054799i.
Bare vanadium-oxide and -hydroxide cluster cations (V(m)O(n)H(o)+, m = 2-4, n = 1-10, o = 0, 1) were generated by electrospray ionization in order to examine their intrinsic reactivity toward isomeric butenes and small alkanes using mass spectrometric techniques. Two of the major reactions described here concern the activation of C-H bonds of the alkene/alkane substrates resulting in the transfer of two hydrogen atoms and/or attachment of the dehydrogenated hydrocarbon to the cluster cations; these processes are classified as oxidative dehydrogenation (ODH) and dehydrogenation, respectively. For the dehydrogenation of butene, it evolved as a general trend that high-valent clusters prefer ODH resulting in the addition of two hydrogen atoms to the cluster concomitant with elimination of neutral butadiene, whereas low-valent clusters tend to add the diene with parallel loss of molecular hydrogen. Deuterium labeling experiments suggest the operation of a different reaction mechanism for V2O2(+) and V4O10(+) compared to the other cluster cations investigated, and these two cluster cations also are the only ones of the vanadium-oxide ions examined here that are able to dehydrogenate small alkanes. The kinetic isotope effects observed experimentally imply an electron transfer mechanism for the ion-molecule reactions of the alkanes with V4O10(+).
通过电喷雾电离产生了裸露的钒氧化物和氢氧化物簇阳离子（V(m)O(n)H(o)+，m = 2 - 4，n = 1 - 10，o = 0, 1），以便使用质谱技术研究它们对异构丁烯和小烷烃的固有反应性。这里描述的两个主要反应涉及烯烃/烷烃底物C - H键的活化，导致两个氢原子的转移和/或脱氢烃附着到簇阳离子上；这些过程分别归类为氧化脱氢（ODH）和脱氢。对于丁烯的脱氢反应，一般趋势是高价簇倾向于进行氧化脱氢，导致两个氢原子加到簇上，同时消除中性丁二烯，而低价簇倾向于加成二烯并同时损失分子氢。氘标记实验表明，与所研究的其他簇阳离子相比，V2O2(+)和V4O10(+)的反应机制不同，并且这两个簇阳离子也是这里所研究的钒氧化物离子中仅有的能够使小烷烃脱氢的离子。实验观察到的动力学同位素效应暗示了烷烃与V4O10(+)的离子 - 分子反应的电子转移机制。
