Synthesis and characterisation of ruthenium complexes containing a pendent catechol ring

Abstract

This submission was created using the RSC Article Template (DO NOT DELETE THIS TEXT) (LINE INCLUDED FOR SPACING ONLY -DO NOT DELETE THIS TEXT)A series of [Ru(bipy) 2 L] + and [Ru(phen) 2 L] + complexes where L is 2-[5-(3,4-dimethoxyphenyl)-4H-1,2,4-triazol-3-yl]pyridine (HL1) and 4-(5-pyridin-2-yl-4H-1,2,4-triazol-3-yl)benzene-1,2-diol (HL2) are reported. The compounds obtained have been characterised using x-ray crystallography, NMR, UV/Vis and emission spectroscopies. Partial deuteriation is used to determine the nature of the emitting state and to simplify the NMR spectra. The acid-base properties of the compounds are also investigated. The electronic structure of the HL1 complex is examined using ZINDO. Electro and spectroelectrochemical studies on [Ru(bipy) 2 (L2)] + suggest that proton transfer between the catechol and triazole moieties on L2 takes place upon oxidation of the L2 ligand. IntroductionThe hydroquinone/quinone redox couple plays an essential role as electron mediator in the charge separation processes in photosynthesis. 1 As a result there has been extensive interest in the redox properties of quinone containing metal complexes and in their potential to act as electron acceptors or donors. 2 In these studies catechol based ligands are coordinated to a wide range of metals. 3 Much less attention has been paid to the interaction between metal centres and pendent hydroquinone/quinone groupings, although such materials may participate in light induced electron transfer reactions. 4 We are presently involved in a systematic study of the electrochemical and photophysical properties of ruthenium complexes containing pendent hydroquinone/quinones. 5,6 In an earlier study on ruthenium polypyridyl complexes incorporating pyridyltriazole ligands with free hydroquinone groupings, electrochemically induced intramolecular protonation of the ruthenium centre was observed upon oxidation of the hydroquinone moiety. 6 In this contribution the synthesis and deprotection of the methoxy complexes [Ru(bipy) 2 (L1)]PF 6 .5H 2 O and [Ru(phen) 2 (L1)]PF 6 .2H 2 O (where HL1 is 2-[5-(3,4-dimethoxyphenyl)-4H-1,2,4-triazol-3-yl]pyridine) to produce the catechol type complexes with the ligand HL2 4-(5-Pyridin-2-yl-4H-1,2,4-triazol-3-yl)benzene-1,2-diol are described (for ligand structures see Figure 1). The partially deuteriated analogues [Ru(d 8 -bipy) 2 (L1)] + and [Ru(d 8 -phen) 2 (L1)] + are also described. The materials obtained have been characterised by X-ray crystallography and 1 H-NMR spectroscopy. The absorption, emission, photophysical and electrochemical properties of the complexes are also examined. To aid interpretation of the results obtained, semi-empirical calculations using ZINDO were carried out on [Ru(bipy) 2 (HL1)] 2+ and [Ru(bipy) 2 (L1)] + , where the triazole moieties are in the protonated and deprotonated states respectively. ExperimentalAll synthetic reagents were of commercial grade and used without further purification. The solvents used in spectroscopic measurements were HPLC grade. Perdeute...

Regioselective Functionalization of Tetrabromophenanthroline−Ruthenium Complexes

“…This finding correlates well with the data obtained for the oxidation potential of Ru II / III , which clearly shows that the four bromine substituents significantly decrease the electron density at the metal center (difference of 137 mV). Introduction of the methoxy groups increases the electron density, as expected 9. The introduction of two methoxy groups has a pronounced influence on the photophysical properties, and this is in agreement with an electron‐donating substituent.…”

Inspired by nature: light driven organometallic catalysis by heterooligonuclear Ru(ii) complexes

“…7 In the following step the bridging ligand can be coordinated at this centre to form Ru-B and subsequent purification using HPLC methods results in the pure complex. 8 The introduction of the catalytic metal centre (by the "complex as ligand approach") may require more effort. In a recent example introduction of allyl-palladium units was possible using LiBu in dry deoxygenated solvents resulting in the formation of a heterotetranuclear Ru 2 Pd 2 -complex.…”

Synthesis, Characterization, Solid-State Structures, and Spectroscopic Properties of Two Catechol-Based Luminescent Chemosensors for Biologically Relevant Oxometalates

“…The quantitative demethylation of both complexes was achieved with BBr 3 and confirmed by TLC, mass spectrometry, NMR spectroscopy, and X-ray crystallography. In the proton NMR spectra of both compounds, the completeness of the deprotection was verified by the absence of the two characteristic methyl resonances.…”

“…Catechol units that are linked to luminescent signaling units have previously been shown to function as sensors, − redox switches, and photo- and electrocatalysts . [Ru(bpy) 3 ] 2+ -type luminophores are the most commonly studied; however, [ReX(CO) 3 (bpy)]-type luminophores (with bpy = 2,2‘-bipyridine and X = Br, Cl) are beginning to appear more frequently in the field. − In addition, complexes with functionalized 1,10-phenanthroline ligands are being developed. − These often have significantly higher emission quantum yields and lifetimes than corresponding bipyridine-based systems …”

“…Catechol units that are linked to luminescent signaling units have previously been shown to function as sensors, [15][16][17] redox switches, 18 and photo- 19 and electrocatalysts. 20 [Ru-(bpy) 3 ] 2+ -type luminophores are the most commonly studied; however, [ReX(CO) 3 (bpy)]-type luminophores (with bpy ) 2,2′-bipyridine and X ) Br, Cl) are beginning to appear more frequently in the field.…”