Zhang Dongju, Liu Chengbu, Bi Siwei, Yuan Shiling
College of Chemistry and Chemical Engineering Shandong University, Jinan, 250100, P. R. China.
Chemistry. 2003 Jan 20;9(2):484-501. doi: 10.1002/chem.200390051.
The reactions of Sc(+)((3)D) with methane, ethane, and propane in the gas phase were studied theoretically by density functional theory. The potential energy surfaces corresponding to Sc, C(n), H(2n+2) (n=1-3) were examined in detail at the B3LYP/6-311++G(3df, 3pd)//B3LYP/6-311+G(d,p) level of theory. The performance of this theoretical method was calibrated with respect to the available thermochemical data. Calculations indicated that the reactions of Sc(+) with alkanes are multichannel processes which involve two general mechanisms: an addition-elimination mechanism, which is in good agreement with the general mechanism proposed from earlier experiments, and a concerted mechanism, which is presented for the first time in this work. The addition-elimination reactions are favorable at low energy, and the concerted reactions could be alternative pathways at high energy. In most cases, the energetic bottleneck in the addition-elimination mechanism is the initial C--C or C--H activation. The loss of CH(4) and/or C(2)H(6) from Sc(+)+C(n)H(2n+2) (n=2, 3) can proceed along both the initial C--C activation branch and the Cbond;H activation branch. The loss of H(2) from Sc(+)+C(n)H(2n+2) (n=2, 3) can proceed not only by 1,2-H(2) and/or 1,3-H(2) elimination, but also by 1,1-H(2) elimination. The reactivity of Sc(+) with alkanes is compared with those reported earlier for the reactions of the late first-row transition-metal ions with alkanes.
采用密度泛函理论对气相中Sc(+)((3)D)与甲烷、乙烷和丙烷的反应进行了理论研究。在B3LYP/6 - 311++G(3df, 3pd)//B3LYP/6 - 311+G(d,p)理论水平下，详细研究了对应于Sc, C(n), H(2n + 2)（n = 1 - 3）的势能面。根据现有的热化学数据对该理论方法的性能进行了校准。计算结果表明，Sc(+)与烷烃的反应是多通道过程，涉及两种一般机制：一种是加成 - 消除机制，这与早期实验提出的一般机制一致；另一种是协同机制，这是本工作首次提出的。加成 - 消除反应在低能量下是有利的，而协同反应可能是高能量下的替代途径。在大多数情况下，加成 - 消除机制中的能量瓶颈是初始的C - C或C - H活化。Sc(+)+C(n)H(2n + 2)（n = 2, 3）中CH(4)和/或C(2)H(6)的损失可以沿着初始的C - C活化分支和C - H活化分支进行。Sc(+)+C(n)H(2n + 2)（n = 2, 3）中H(2)的损失不仅可以通过1,2 - H(2)和/或1,3 - H(2)消除进行，还可以通过1,1 - H(2)消除进行。将Sc(+)与烷烃的反应活性与早期报道的第一排晚期过渡金属离子与烷烃的反应活性进行了比较。
