Thermal and photo substitution reactivity and crystal structures of tridentate Schiff base–ruthenium(II) complexes containing phosphorus or sulfur donor atoms

doi:10.1016/S0020-1693(01)00628-4

Inorganica Chimica Acta

Volume 325, Issues 1–2, 3 December 2001, Pages 36-44

https://doi.org/10.1016/S0020-1693(01)00628-4 Get rights and content

Abstract

Tridentate Schiff base–ruthenium(II) complexes containing soft phosphorus or sulfur donor atoms were prepared, and their bidirectional thermal and photo substitution reactions were investigated. In acetonitrile, the chloro ligands of trans(Cl,Cl)[RuCl₂(ppb-etol)(PPh₃)] (1, ppb-etol=2-(Ph₂P)C₆H₄CHN(CH₂)₂OH) were substituted by acetonitrile molecules stepwise to yield [RuCl(CH₃CN)(ppb-etol)(PPh₃)]Cl (2) (first step) and [Ru(CH₃CN)₂(ppb-etol)(PPh₃)]Cl₂ (3) (second step). Complexes 2 and 3 reverted to complex 1 in acetonitrile upon irradiation with UV–Vis light. Similar thermal and photo substitution reactions were also observed for trans(Cl,Cl)[RuCl₂(btb-etol)(PPh₃)] (4, btb-etol=2-(^tBuS)C₆H₄CHN(CH₂)₂OH). The substitution rates were measured for the first-step reactions of complexes 1 and 4 over the temperature range of 19.5–29.5 °C in acetonitrile. Kinetic parameters were determined to be k_obsd=(1.13±0.04)×10⁻⁴ s⁻¹ (25.0 °C), ΔH^‡=83.1±1.7 kJ mol⁻¹, and ΔS^‡=−41.9±5.6 kJ mol⁻¹ for complex 1, and k_obsd=(1.57±0.06)×10⁻³ s⁻¹ (25.0 °C), ΔH^‡=88.8±1.9 kJ mol⁻¹, and ΔS^‡=−0.9±6.5 kJ mol⁻¹ for complex 4. Accordingly, the substitution reaction of complex 4 proceeded faster than that of complex 1. The structures of [RuCl₂{ppb-(1R,2S)-ephe}(PPh₃)] (5, ppb-(1R,2S)-ephe=2-(Ph₂P)C₆H₄CHNCH(Me)CH(Ph)OH), complex 2, and [Ru(CH₃CN)₂{ppb-(R)-btol}(PPh₃)](BF₄)₂ (6, ppb-(R)-btol=2-(Ph₂P)C₆H₄CHNCH(Et)CH₂OH) were determined by X-ray analyses. In each complex, the geometry around the ruthenium atom is distorted octahedral, and the tridentate Schiff base and triphenylphosphine ligands occupy the equatorial positions.

Tridentate Schiff base–ruthenium(II) complexes containing soft phosphorus or sulfur donor atoms were prepared, and their bidirectional thermal and photo substitution reactions were investigated. The structures of the complexes were characterized by X-ray analyses, and the kinetic parameters for the first step thermal substitution reaction were determined.

Introduction

The photochemistry of complexes containing the cis-bis(bipyridine)ruthenium(II) moiety and its analogue has been the subject of study for many years [1], [1](a), [1](b), [1](c), [1](d), [1](e), and the photochemical and electrochemical properties have been extensively explored in connection with approaches to photochemical molecular devices and the conversion of light to chemical and electrical energy [2], [2](a), [2](b), [2](c), [2](d). However, photochemical studies for complexes with trans geometry with respect to two axial ligands are limited to just a few examples, except for porphyrins and phthalocyanines [3], [3](a), [3](b), [3](c). It is expected that the photochemical properties of ruthenium complexes can be widely changed by introducing various kinds of new ligands with a different coordination mode. It should be an attractive approach to constructing new photoresponsive complexes. Previously, we prepared tetradentate Schiff base–ruthenium(II) complexes containing phosphorus or sulfur donor atoms, and reported their structures and photo substitution reactivities [4]. The complexes, [RuCl₂(L¹)] (L¹; tetradentate Schiff base ligand), had trans geometry with respect to the two chloro ligands, and underwent photosubstitution of a chloro ligand in acetonitrile under room light to yield [RuCl(CH₃CN)(L¹)]Cl. The second chloro ligand was not substituted, and the cationic complex reverted to [RuCl₂(L¹)] in dichloromethane upon photo irradiation. The substitution reactions did not proceed in the dark. Recently, we also briefly reported the photochromic reversible substitution reaction of tridentate Schiff base–ruthenium(II) complexes, [RuCl₂(L²)(PPh₃)], as a short communication [5].

In this paper, we describe the preparation, structures, spectroscopic and electrochemical properties, and thermal and photo substitution reactivity of several tridentate Schiff base–ruthenium(II) complexes containing phosphorus or sulfur donor atoms (Fig. 1).

Section snippets

General

[RuCl₂(PPh₃)₃] was prepared according to the literature procedure [6]. All syntheses of the complexes were carried out using standard Schlenk tube and vacuum line techniques under an argon atmosphere. ¹H NMR spectra were measured at 400 MHz on a JEOL JNM LA-400 spectrometer with TMS as an internal reference. UV–Vis spectra were obtained on a Shimadzu UV-2500PC spectrophotometer. Electrochemical data were obtained by cyclic voltammetry using a BAS 100B/W electrochemical workstation in

Preparation and structural characterization of complexes 1, 4, and 5

The tridentate Schiff base ligands (ppb-etol, btb-etol, and ppb-(1R,2S)-ephe) were prepared in situ and used for complex preparation without isolation. Complex 1 was synthesized by treating [RuCl₂(PPh₃)₃] with an equimolar amount of the ppb-etol ligand in dichloromethane, and complexes 4 and 5 were obtained in a similar procedure. A single crystal suitable for X-ray analysis was obtained for complex 5. Fig. 2 shows a perspective view of complex 5, and selected bond distances and angles are

Supplementary material

Tables of non-hydrogen atom coordinates and anisotropic thermal parameters, coordinates of the hydrogen atoms, and bond lengths and angles have been deposited with the Cambridge Crystallographic Data Centre, CCDC Nos. 168604–168606 for complexes 2, 5, and 6. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44–1223–336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).

Acknowledgements

The present work was supported by a Grant-in-Aid for Scientific Research No. 13640557 from the Ministry of Education, Science, and Culture. We express our thanks to the Institute for Molecular Science, Okazaki, for allowing the use of facilities for X-ray diffraction measurements.

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Thermal and photo substitution reactivity and crystal structures of tridentate Schiff base–ruthenium(II) complexes containing phosphorus or sulfur donor atoms

Abstract

Introduction

Section snippets

General

Preparation and structural characterization of complexes 1, 4, and 5

Supplementary material

Acknowledgements

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Inorg. Chem.

Inorg. Chem.

Inorg. Chem.

Inorg. Chim. Acta

Chem. Lett.

Acc. Chem. Res.

J. Am. Chem. Soc.

Inorg. Chem.

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Inorg. Chem.

Inorg. Chem.

Inorg. Chim. Acta