Lanthanum-mediated dehydrogenation of 1- and 2-butynes: Spectroscopy and formation of La(C4H4) isomers.
Lanthanum-mediated dehydrogenation of 1- and 2-butynes: Spectroscopy and formation of La(C4H4) isomers.
复制标题
镧介导的 1- 和 2- 丁炔脱氢：La(C4H4) 异构体的光谱和形成。
作者：
W. Cao;D. Hewage;Dong
在激光汽化分子束源中，进行了镧原子与1-丁炔和2-丁炔的反应。这两种反应从丁炔的脱氢和碳-碳键断裂和偶联产生相同的La-烃产物。采用质量分析阈值电离（MATI）光谱和量子化学计算对脱氢物种La（C4 H4）进行了表征。两个反应产生的La（C_4H_4）的MATI谱显示出两个相同的跃迁，每个跃迁都由一个强的本征带和几个振动间隔组成。这两个跃迁归因于两种异构体的电离：La（η4-CH 2CCCH 2）（Iso A）和La（η4-CH 2CHCCH）（Iso B）。Iso A的基电子态为2A 1（C2 v），Iso B的基电子态为2A（C1）。每种异构体的双重态的电离去除了基于La 6s的电子，并产生Iso A的1A 1离子和Iso B的1A离子。由2-丁炔形成Iso A和由1-丁炔形成Iso B涉及La加成到C = C三键，两个C（sp3）-H键的活化，以及H2分子的协同消除。由1-丁炔形成Iso A和由2-丁炔形成Iso B除了协同的H2消除之外还涉及两种丁炔异构化为1，2-丁二烯。
La atom reactions with 1-butyne and 2-butyne are carried out in a laser-vaporization molecular beam source. Both reactions yield the same La-hydrocarbon products from the dehydrogenation and carbon-carbon bond cleavage and coupling of the butynes. The dehydrogenated species La(C4H4) is characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of La(C4H4) produced from the two reactions exhibit two identical transitions, each consisting of a strong origin band and several vibrational intervals. The two transitions are assigned to the ionization of two isomers: La(η4-CH2CCCH2) (Iso A) and La(η4-CH2CHCCH) (Iso B). The ground electronic states are 2A1 (C2v) for Iso A and 2A (C1) for Iso B. The ionization of the doublet state of each isomer removes a La 6s-based electron and results in a 1A1 ion of Iso A and a 1A ion of Iso B. The formation of Iso A from 2-butyne and Iso B from 1-butyne involves the addition of La to the C≡C triple bond, the activation of two C(sp3)-H bonds, and concerted elimination of a H2 molecule. The formation of Iso A from 1-butyne and Iso B from 2-butyne involves the isomerization of the two butynes to 1,2-butadiene in addition to the concerted H2 elimination.