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首页> 外文期刊>The journal of physical chemistry, A. Molecules, spectroscopy, kinetics, environment, & general theory >Gas-phase reactions of [VO_2(OH)_2]~- and [V_2O_5(OH)]~- with methanol: Experiment and theory
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Gas-phase reactions of [VO_2(OH)_2]~- and [V_2O_5(OH)]~- with methanol: Experiment and theory

机译：[VO_2（OH）_2]〜-和[V_2O_5（OH）]〜-与甲醇的气相反应：实验和理论

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摘要

The gas-phase reactivity of the vanadium hydroxides [VO_2(OH)_2]~- and [V_2O_5(OH)]~- toward methanol was examined using a combination of ion-molecule reactions (IMRs) and collision-induced dissociation (CID) in a quadrupole ion trap mass spectrometer. Isotope-labeling experiments with CD_3OH, ~(13)CH_3OH, and CH_3 ~(18)OH were used to confirm the stoichiometry of ions and the observed sequence of reactions. The experimental data were interpreted with the aid of density functional theory calculations, carried out at the B3LYP/SDD6-311++G* level of theory. While [VO_2(OH)_2]~- is unreactive, [V_2O_5(OH)]~- undergoes a metathesis reaction to yield [V_2O_5(OCH_3)]~-. The DFT calculations reveal that the metathesis reaction of methanol with [VO _2(OH)_2]~- suffers from a barrier of +0.52 eV (relative to separated reactants) but that the reaction of [V_2O_5(OH)]~- with methanol readily proceeds via addition/elimination reactions with both transition states being below the energy of the separated reactants. CID of [V_2O_5(OCH_3)]~- (m/z 213) yields three ions arising from activation of the methoxo ligand: [V_2, O_6, C, H]~- (m/z 211); [V_2, O_5, H]~- (m/z 183); and [V_2, O_4, H]~- (m/z 167). Additional experiments and DFT calculations suggest that these ions arise from losses of H2, formaldehyde and the sequential losses of H_2 and CO_2, respectively. The use of an ~(18)O-labeled methoxo ligand in [V_2O_5(~(18)OCH_3)]~- (m/z 215) showed the competing losses of H_2C~(16)O and H_2C~(18)O and [H2 and C~(16)O ~(18)O] and [H_2 and C~(16)O_2], highlighting that ~(16)O/~(18)O exchange between the methoxo ligand and the vanadium oxide occurs prior to the subsequent fragmentation of the ligand. DFT calculations reveal that a key step involves hydrogen atom transfer from the methoxo ligand to the oxo ligand of the same vanadium center, producing the intermediate [V_2O_4(OH)(OCH_2)]~- containing a ketyl radical ligand and a hydroxo ligand. This intermediate can either undergo CH_2O loss, or the ketyl radical can couple with an oxo ligand of the adjacent vanadium center, producing [V_2O_3(μ_2-O_2CH_2)]~-, which is a key intermediate in the ~(16)O/~(18)O scrambling and in the H_2 loss channel.
机译：使用离子分子反应（IMR）和碰撞诱导解离（CID）的组合检查了氢氧化钒[VO_2（OH）_2]〜-和[V_2O_5（OH）]〜-对甲醇的气相反应性在四极离子阱质谱仪中用CD_3OH，〜（13）CH_3OH和CH_3〜（18）OH进行同位素标记实验可确定离子的化学计量和观察到的反应顺序。实验数据借助密度泛函理论计算进行解释，该计算在B3LYP / SDD6-311 ++ G *理论水平上进行。当[VO_2（OH）_2]-没有反应性时，[V_2O_5（OH）]-发生易位反应，产生[V_2O_5（OCH_3）]-。 DFT计算表明，甲醇与[VO _2（OH）_2]〜-的复分解反应具有+0.52 eV的势垒（相对于分离的反应物），但是[V_2O_5（OH）]〜-与甲醇的反应容易通过加/消除反应进行，两个过渡态均低于分离出的反应物的能量。 [V_2O_5（OCH_3）]〜-（m / z 213）的CID产生了三个因甲氧配体的活化而产生的离子：[V_2，O_6，C，H]〜-（m / z 211）; [V_2，O_5，H]〜-（m / z 183）;和[V_2，O_4，H]〜-（m / z 167）。额外的实验和DFT计算表明，这些离子分别来自H2，甲醛的损失以及H_2和CO_2的顺序损失。在[V_2O_5（〜（18）OCH_3）]〜-（m / z 215）中使用〜（18）O标记的甲氧基配体显示了H_2C〜（16）O和H_2C〜（18）O的竞争损失和[H2和C〜（16）O〜（18）O]和[H_2和C〜（16）O_2]，突出表明〜（16）O /〜（18）O在甲氧羰基配位体和氧化钒之间交换发生在配体随后的断裂之前。 DFT计算表明，关键步骤涉及氢原子从甲基氧配体转移到同一钒中心的氧代配体，从而产生含有酮基自由基配体和羟基配体的中间体[V_2O_4（OH）（OCH_2）]-。该中间体可能会发生CH_2O损失，或者酮基可以与相邻钒中心的羰基配体偶联，生成[V_2O_3（μ_2-O_2CH_2）]〜-，这是〜（16）O /〜中的关键中间体（18）O加扰并处于H_2丢失通道中。

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