Thermally Reversible Photochemical Haptotropic Rearrangement of Diiron Carbonyl Complexes Bearing a Bridging Acenaphthylene or Aceanthrylene Ligand

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• 作者：Shota Niibayashi ; Kouki Matsubara ; Masa-aki Haga ; and Hideo Nagashima
• 刊名：Organometallics
• 出版年：2004
• 出版时间：February 16, 2004
• 年：2004
• 卷：23
• 期：4
• 页码：635 - 646
• 全文大小：243K
• 年卷期：v.23,no.4(February 16, 2004)
• ISSN：1520-6041

文摘

The haptotropic rearrangement of diiron carbonyl species on the conjugate -ligand in(₂,³:⁵-acenaphthylene)Fe₂(CO)₅ (1) and its analogue (₂,³:⁵-aceanthrylene)Fe₂(CO)₅ (2)is investigated in both solution and solid states. The diiron complexes 1 and 2 have twoisomers, and each isomer is isolated and characterized. Isomers 1-A and 2-A are thermodynamically more stable than 1-B and 2-B, respectively (G₂₉₆ = 2.3 kcal/mol for 1; G₂₉₆> 2.3 kcal/mol for 2). The thermodynamically less stable isomers can be preparedphotochemically. Interconversions between 1-A and 1-B and between 2-A and 2-B occurboth thermally and photochemically. Kinetic studies on the thermal isomerizations in solutionprovide G₂₉₈ = 23 ± 1 kcal/mol, H₂₉₈ = 23 ± 1 kcal/mol, and S₂₉₈ = 1 ± 4 cal/mol·degfor the reaction of 1-B to 1-A, and G₂₉₈ = 26 ± 1 kcal/mol, H₂₉₈ = 26 ± 1 kcal/mol, andS₂₉₈ = 0 ± 2 cal/mol·deg for the reaction of 2-B to 2-A. Photochemical interconversion at = 600 nm provides the isomer ratio of 1-A:1-B = 9:91 at the photostatic state, and 2-A:2-B = 66:34. In both of the isomerization reactions, irradiation with light of shorterwavelength tends to give lower ratios of the thermodynamically less stable isomers. Thequantum yields of the isomerization reactions are found to be _1-A1-B = 0.30(3), _1-B1-A= 0.09(1), _2-A2-B = 0.013(2), and _2-B2-A = 0.009(1). From these experimental data thereaction mechanisms of the thermal and photochemical haptotropic rearrangements arediscussed with the aid of EHMO calculations. A single crystal of 1-B converts to a singlecrystal of 1-A upon heating. A photolysis (5 min by a 500 W xenon lamp)/thermal treatment(10 min at 100 C) cycle of a KBr pellet containing 1-A or 1-B results in reversibleinterconversion between 1-A and 1-B in the solid state, which can be monitored by the IRabsorption at = 1825 cm^-1. The cycle is repeatable for over 10 times without change in thesignal intensity. These results are the first to indicate a possible organometallic photochromism in the solid state detectable by the IR light.