Infrared Spectra of HCC-MH and M−η2-(C2H2) from Reactions of Laser-Ablated Group- 4 Transition-Metal Atoms with Acetylene
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- 作者：Han-Gook Cho ; Gary P. Kushto ; Lester Andrews ; Charles W. Bauschlicher Jr.
- 刊名：Journal of Physical Chemistry A
- 出版年：2008
- 出版时间：July 17, 2008
- 年：2008
- 卷：112
- 期：28
- 页码：6295 - 6304
- 全文大小：609K
- 年卷期：v.112,no.28(July 17, 2008)
- ISSN：1520-5215
文摘
Reactions of laser-ablated group 4 transition-metal atoms with acetylene have been carried out. The ethynyl metal hydrides (HC
C-MH) and corresponding π complexes (M−η2-(C2H2)) are identified in the matrix infrared spectra. The observed M−H and C−M stretching absorptions show that oxidative C−H insertion readily occurs during codeposition and photolysis afterward. The absorptions from the π complex, on the other hand, are relatively weak in the original deposition spectrum but increase dramatically in the process of annealing. The vinylidene complex, another plausible product, is not identified in this study. The observed spectra and DFT calculations both show that the back-donations from the group 4 metals to the antibonding π* orbital of C2H2 are extensive such that the group 4 metals form unusually strong π complexes. Thus, it is the formation of two Ti−C bonds in the group 4 systems than leads to the stronger bonding than that in the group 8 systems. While bonds form, the Ti atom is weakly bound to C2H2, and we still refer to it as a π complex. Evidence of relativistic effects is also observed in frequency trends for the Ti, Zr, and Hf products.
C-MH) and corresponding π complexes (M−η2-(C2H2)) are identified in the matrix infrared spectra. The observed M−H and C−M stretching absorptions show that oxidative C−H insertion readily occurs during codeposition and photolysis afterward. The absorptions from the π complex, on the other hand, are relatively weak in the original deposition spectrum but increase dramatically in the process of annealing. The vinylidene complex, another plausible product, is not identified in this study. The observed spectra and DFT calculations both show that the back-donations from the group 4 metals to the antibonding π* orbital of C2H2 are extensive such that the group 4 metals form unusually strong π complexes. Thus, it is the formation of two Ti−C bonds in the group 4 systems than leads to the stronger bonding than that in the group 8 systems. While bonds form, the Ti atom is weakly bound to C2H2, and we still refer to it as a π complex. Evidence of relativistic effects is also observed in frequency trends for the Ti, Zr, and Hf products.