Generation, Characterization, and Reactivity of the Transition Metal-o-Benzyne Analog of Pyrazine (Fe+-2,3-Didehydropyrazine) in the Gas Phase: An Experimental and Theoretical Study
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- 作者：Huiping Chen ; Denley B. Jacobson ; and Ben S. Freiser
- 刊名：Organometallics
- 出版年：1999
- 出版时间：April 26, 1999
- 年：1999
- 卷：18
- 期：9
- 页码：1774 - 1785
- 全文大小：344K
- 年卷期：v.18,no.9(April 26, 1999)
- ISSN：1520-6041
文摘
Fe+-2,3-didehydropyrazine (2) has been generated and its reactivity with simple olefinsand alkynes studied by using Fourier transform ion cyclotron resonance (FTICR) massspectrometry. 2, which is prepared by dehalogenation of chloropyrazine by Fe+, undergoesa simple adduct formation (no ligand coupling) with ethene and ethene-d4. Ethyne also yieldsadduct formation; however, ligand coupling has clearly occurred in this reaction. Interestingly, reactions with propene and isobutene yield the same products with similar productdistributions. Again, ligand coupling is involved and a metal-centered mechanism featuringactivation of the allylic carbon-hydrogen bonds is proposed. Propyne, allene, 1-butene, andcis-2-butene yield a variety of products with 2. However, 2 yields exclusive dehydrogenationwith 1,3-butadiene to generate FeC8H6N2+. CID results suggest that this FeC8H6N2+ ionconsists of quinoxaline bound to Fe+. Ligand displacement reactions yield a bond dissociationenergy of 47 ± 5 kcal/mol for D
(Fe+-quinoxaline). FeC4H2N2+ ion (2) has also beeninvestigated theoretically. Density functional calculations predicted that the ground stateof 2,3-didehydropyrazine is the triplet state, with the singlet state being 9.9 kcal/mol higherthan the triplet state. 2 has C2v symmetry with the metal center coplanar with the 2,3-didehydropyrazine ring. 2 has a sextet ground state with doublet and quartet states 4.9and 6.8 kcal/mol higher, respectively. The bond dissociation energy D(Fe+-C4H2N2) for thesextet ground state is computed to be 87 ± 10 kcal/mol.
(Fe+-quinoxaline). FeC4H2N2+ ion (2) has also beeninvestigated theoretically. Density functional calculations predicted that the ground stateof 2,3-didehydropyrazine is the triplet state, with the singlet state being 9.9 kcal/mol higherthan the triplet state. 2 has C2v symmetry with the metal center coplanar with the 2,3-didehydropyrazine ring. 2 has a sextet ground state with doublet and quartet states 4.9and 6.8 kcal/mol higher, respectively. The bond dissociation energy D(Fe+-C4H2N2) for thesextet ground state is computed to be 87 ± 10 kcal/mol.