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

Abstract

The haptotropic rearrangement of diiron carbonyl species on the conjugate π-ligand in (µ 2 ,η 3 :η 5 -acenaphthylene)Fe 2 (CO) 5 (1) and its analogue (µ 2 ,η 3 :η 5 -aceanthrylene)Fe 2 (CO) 5 ( 2) is investigated in both solution and solid states. The diiron complexes 1 and 2 have two isomers, and each isomer is isolated and characterized. Isomers 1-A and 2-A are thermodynamically more stable than 1-B and 2-B, respectively (∆G°2 96 ) 2.3 kcal/mol for 1; ∆G°2 96 > 2.3 kcal/mol for 2). The thermodynamically less stable isomers can be prepared photochemically. Interconversions between 1-A and 1-B and between 2-A and 2-B occur both thermally and photochemically. Kinetic studies on the thermal isomerizations in solution provide ∆G q 298 ) 23 ( 1 kcal/mol, ∆H q 298 ) 23 ( 1 kcal/mol, and ∆S q 298 ) 1 ( 4 cal/mol‚deg for the reaction of 1-B to 1-A, and ∆G q 298 ) 26 ( 1 kcal/mol, ∆H q 298 ) 26 ( 1 kcal/mol, and ∆S q 298 ) 0 ( 2 cal/mol‚deg for the reaction of 2-B to 2-A. Photochemical interconversion at λ ) 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 shorter wavelength tends to give lower ratios of the thermodynamically less stable isomers. The quantum yields of the isomerization reactions are found to be Φ 1-Af1-B ) 0.30(3), Φ 1-Bf1-A ) 0.09(1), Φ 2-Af2-B ) 0.013(2), and Φ 2-Bf2-A ) 0.009(1). From these experimental data the reaction mechanisms of the thermal and photochemical haptotropic rearrangements are discussed with the aid of EHMO calculations. A single crystal of 1-B converts to a single crystal 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 reversible interconversion between 1-A and 1-B in the solid state, which can be monitored by the IR absorption at ν ) 1825 cm -1 . The cycle is repeatable for over 10 times without change in the signal intensity. These results are the first to indicate a possible organometallic photochromism in the solid state detectable by the IR light.

Photochromism of an Organorhodium Dithionite Complex in the Crystalline-State: Molecular Motion of Pentamethylcyclopentadienyl Ligands Coupled to Atom Rearrangement in a Dithionite Ligand

“…Crystalline-state photochromism usually proceeds with interconversion ratios of less than 30% because light penetration into the bulk crystal is prohibited by the absorption of the photogenerated isomer (inner-filter effects), even if special techniques, such as two-photon excitation or linearly polarized irradiation, are used to overcome inner-filter effects. , Surprisingly, the crystalline-state photochromic system involving 1 and 2 proceeds with an interconversion ratio of ∼100%, as described in the following discussion.…”

“…Organic photochromic molecules, especially diarylethene derivatives, have been used to build photochromic crystals . On the other hand, in the field of coordination chemistry, there are no promising molecular crystals utilizing the characteristic features of the metal complexes, and there is a lack of synthetic strategies . Hence, it is still a challenge to find new photochromic crystals of metal complexes that can easily be modified chemically and to determine their photochromic reaction mechanism and dynamics.…”

Intramolecular Haptotropic Rearrangements of the Tricarbonylchromium Complex in Small Polycyclic Aromatic Hydrocarbons

“…In most of the cases, experimental results in this area are obtained for chromium tricarbonyl complexes; however, intramolecular IRHRs have also been described for Fe, − Mo, Ir, Ru, − Mn, and Ni, and so far in organolanthanoid chemistry for Yb among others. First examples of intramolecular IRHRs of the Cr(CO) 3 complex established the possibility to control the position of the metal tripod on a specific ring of the arene by varying the temperature conditions (usually within 70−120 °C) and the substituents. − Usually, the most stable isomer is obtained when the metal complex is attached to the least-substituted ring, which is normally the most aromatic one .…”

19 Organometallic chemistry of bi- and polymetallic complexes

“…The cycles are repeatable for over 10 times, and can be induced in both solution and solid (KBr) states. 45 Catalytic reactivity of the ruthenium analogues in the silane-induced polymerisation of vinyl ethers has also been reported. 46 Transition metal complexes and clusters are beginning to attract attention as potential molecular building blocks for use in the construction of molecular devices because of their various electrochemical, chemical and structural properties.…”