Roles of π-Alkyne, Hydride–Alkynyl, and Vinylidene Metal Species in the Conversion of Alkynes into Vinylidene: New Theoretical Insights
✍ Scribed by Enrique Peréz-Carreño; Paola Paoli; Andrea Ienco; Carlo Mealli
- Publisher
- John Wiley and Sons
- Year
- 1999
- Tongue
- English
- Weight
- 329 KB
- Volume
- 1999
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
The transformation of acetylene into vinylidene, as promoted acetylide intermediate to vinylidene (20.6 kcal/mol) is easier to surmount compared to that for reversion to the reactants by the metal fragment [(pp 3 )Co] + [pp 3 = P(CH 2 CH 2 PPh 2 ) 3 ], is unimolecular and features the hydride-acetylide species as (28.6 kcal/mol). The situation is reversed for the analogous Rh I system, with the initial π-acetylene adduct being slightly an intermediate. The paper describes a detailed ab initio study of the reaction, in particular with regard to the step more stable. Although higher in energy, the hydrideacetylide species is the experimentally detected product of involving 1,3-H shift. The best computational results are obtained by mimicking the pp 3 ligand with actual ethylenic the reaction of acetylene with the fragment [(pp 3 )Rh] + . The salient chemical aspects of the 1,3-H shift are discussed in chains rather than with single PH 3 molecules. The keypoints along the two-step reaction path (π-acetylene, hydride-terms of perturbation theory arguments. Parallel EHMO calculations, which have provided a relatively good acetylide, and vinylidene complexes, as well as intermediate transition states) have been optimized for Co I and Rh I consistency with the ab initio results, allow the proposal of an orbital rationale for the mode of migration of the hydride derivatives at the MP2 level. For the fragment [(pp 3 )Co] + , the barrier associated with transformation of the hydride-ligand along the substantially linear Co-C α -C β grouping.
[CpMn(CO) 2 ]. [3] More recent ab initio calculations were II [a] Istituto per lo Studio della Stereochimica ed Energetica dei