Lanthanum-mediated C-H bond activation of propyne and identification of La(C₃H₂) isomers.
Lanthanum-mediated C-H bond activation of propyne and identification of La(C₃H₂) isomers.
复制标题
镧介导的丙炔 C-H 键活化和 La(C₃H2) 异构体的鉴定。
作者：
D. Hewage;M. Roudjane;Ruchira Silva;S. Kumari;Dong
从中性La原子活化丙炔的气相反应混合物中鉴定出La（C_3H_2）的η（2）-丙二烯基镧[La（η（2）-CCCH_2）]和脱丙镧环丁二烯[La（HCCCH）]。这两个异构体的特征在于质量分析阈值电离光谱结合电子结构计算和光谱模拟。La（η（2）-CCCH_2）和La（HCCCH_2）分别由1，3-和3，3-协同脱氢生成。两种异构体都倾向于具有基于La 6s的未配对电子的双重基态，并且La（η（2）-CCCH 2）比La（HCCCH）稍微更稳定。两种异构体的中性双重态电离后，通过去除镧系电子而产生单重态离子，电离后的几何结构变化导致在离子态激发对称的金属-烃伸缩模，而热激发导致在中性态观察到相同的伸缩模.虽然La原子处于+2的形式氧化态，但这些金属-烃自由基的电离能低于中性La原子的电离能。氘化对两种异构体的电离能和La（η（2）-CCCH 2）的金属-烃伸缩模的影响很小，但却显著降低了La（HCCCH 2）的金属-配体伸缩模的频率。
η(2)-Propadienylidenelanthanum [La(η(2)-CCCH2)] and deprotiolanthanacyclobutadiene [La(HCCCH)] of La(C3H2) are identified from the reaction mixture of neutral La atom activation of propyne in the gas phase. The two isomers are characterized with mass-analyzed threshold ionization spectroscopy combined with electronic structure calculations and spectral simulations. La(η(2)-CCCH2) and La(HCCCH) are formed by concerted 1,3- and 3,3-dehydrogenation, respectively. Both isomers prefer a doublet ground state with a La 6s-based unpaired electron, and La(η(2)-CCCH2) is slightly more stable than La(HCCCH). Ionization of the neutral doublet state of either isomer produces a singlet ion state by removing the La-based electron. The geometry change upon ionization results in the excitation of a symmetric metal-hydrocarbon stretching mode in the ionic state, whereas thermal excitation leads to the observation of the same stretching mode in the neutral state. Although the La atom is in a formal oxidation state of +2, the ionization energies of these metal-hydrocarbon radicals are lower than that of the neutral La atom. Deuteration has a very small effect on the ionization energies of the two isomers and the metal-hydrocarbon stretching mode of La(η(2)-CCCH2), but it reduces considerably the metal-ligand stretching frequencies of La(HCCCH).