101. Mechanism of Acetylene−Vinylidene Rearrangement with Na, Al, and Y Atoms
- Author
-
Glendening, E. D. and Strange, M. L.
- Abstract
Reaction pathways are identified for Na-, Al-, and Y-induced acetylene (HCCH)−vinylidene (CCH
2 ) rearrangements in the gas phase. Density functional and coupled cluster calculations are performed with basis set extrapolations. The rearrangement barriers decrease from 44.0 kcal/mol in the metal-free reaction to 41.3 (Na), 19.1 (Al), and 16.1 (Y) kcal/mol in the metal-induced reactions. This decrease results from the strengthening of the M−C bonds (Na−C < Al−C < Y−C) in the M(HCCH) and M(CCH2 ) complexes. Natural bond orbital analysis reveals the metallacyclopropene and metallaallene character of several of the M(HCCH) and M(CCH2 ) complexes. In addition, analysis of the transition states provides a detailed picture of the redistribution of bonding and nonbonding electrons along the reaction pathway. The metal-free and Na-induced rearrangements proceed via 1,2-hydride shifts, whereas the Al- and Y-induced reactions proceed via 1,2-hydrogen shifts. The latter reactions involve homolytic bond cleavage and formation, with the α and β electron densities undergoing redistribution in opposing directions.- Published
- 2002
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