Characterization of Azulenylphosphine Derivatives. Unexpected Debromination and Its Synthetic Utility in the Preparation of 2-Substituted Azulene
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- 作者：A. F. M. Mustafizur Rahman ; Toshihiro Murafuji ; Toshihisa Shibasaki ; Kouichi Suetake ; Kei Kurotobi ; Yoshikazu Sugihara ; Nagao Azuma ; Yuji Mikata
- 刊名：Organometallics
- 出版年：2007
- 出版时间：June 4, 2007
- 年：2007
- 卷：26
- 期：12
- 页码：2971 - 2977
- 全文大小：168K
- 年卷期：v.26,no.12(June 4, 2007)
- ISSN：1520-6041
文摘
(1,3-Dihalo-2-azulenyl)diphenylphosphines 2 [halogen = Cl (a), Br (b)] and homologous bis(1,3-dihalo-2-azulenyl)phenylphosphines 4 have been synthesized, and the effect of the nonalternant azulenylgroup on the reactivity and properties of these phosphines has been studied in comparison with that ofthe group 15 congeners. The electronic structure of the nonalternant conjugation is dramatically affectedby the change in the valency at the phosphorus. Thus, oxidation of 2 and 4 with hydrogen peroxideproceeded with a dramatic color change from green to blue, giving the corresponding phosphine oxides3 and 5, respectively, in high yield. Similar color changes were observed when a solution of each phosphine,2b and 4b, was left standing under ambient conditions, while 2a, 4a, and (2-azulenyl)diphenylphosphine(7) showed no such changes. (1-Bromo-2-azulenyl)diphenylphosphine oxide (9) was isolated from thesolution of 2b. This unexpected reaction was found to occur via electrophilic substitution at the five-membered ring through protonation. The bismuth and antimony congeners of 2b showed no such reactivity,suggesting that the higher nucleophilicity of the phosphorus atom was the deciding factor. Suchdebromination of 2b may be ascribed to the steric congestion around the bromine atom, which is inferredfrom the X-ray crystallographic study. The unexpected reaction was successfully applied to a convenientsynthesis of 2-substituted azulene using triphenylphosphine as a reagent for debromination. The 13C NMRstudy shows the enhanced 
-polarization in the azulenyl group of the phosphine oxides compared to thatof the parent phosphines, but the degree is not as marked as that observed in the bismuth and antimonysystems. Comparison of the crystal structure of 3b with that of 9 with respect to the intermolecularinteraction between the azulenyl groups showed that the slight structural change in the nonalternant azulenylgroup brings about a dramatic change in the packing. Thus, 3b has head-to-tail - stacking, but 9forms a mutual halogen-hydrogen interaction of the bromine atom with a hydrogen atom of its positivelycharged seven-membered ring.
-polarization in the azulenyl group of the phosphine oxides compared to thatof the parent phosphines, but the degree is not as marked as that observed in the bismuth and antimonysystems. Comparison of the crystal structure of 3b with that of 9 with respect to the intermolecularinteraction between the azulenyl groups showed that the slight structural change in the nonalternant azulenylgroup brings about a dramatic change in the packing. Thus, 3b has head-to-tail - stacking, but 9forms a mutual halogen-hydrogen interaction of the bromine atom with a hydrogen atom of its positivelycharged seven-membered ring.