Tris(bipyridine)ruthenium(II) chloride: Difference between revisions

| verifiedrevid = 416297568

| IUPACName =

| ImageFile = Tris(bipyridine)ruthenium(II) chloride.png

| ImageFile1 = Tris(bipyridine)ruthenium(II)-chloride-powder.jpg

| OtherNames = Ru-bipy<br />Ruthenium-tris(2,2’-bipyridyl) dichloride

| CASNo = 14323-06-9

| CASNo_Comment = (anhydrous)

| CASNo1 = 50525-27-4

| CASNo1_Comment = (hexahydrate)

| RTECS = VM2730000

| Formula = C₃₀H₂₄N₆Cl₂Ru&middot;6H₂O

}}

| Section2 = {{Chembox Properties

| MolarMass = 640.53 g/mol (anhydrous)<br />748.62 g/mol (hexahydrate)

| Appearance = red solid

| Density = solid

| Solubility = Soluble

| MeltingPt = >300 °C

| MolShape = [[Octahedral molecular geometry|Octahedral]]

| Dipole = 0 [[Debye|D]]

| MainHazards = mildly toxic

| RPhrases = none

| SPhrases = {{S22}} {{S24/25}}

| OtherCpds = [[Ruthenium trichloride]]}}

'''Tris(bipyridine)ruthenium(II) dichloride''' is the [[coordination compound]] with the formula [Ru(bipy)₃]Cl₂. This red crystalline salt is obtained as the [[water of crystallization|hexahydrate]], although all of the properties of interest are in the [[cation]] [Ru(bipy)₃]²⁺, which has received much attention because of its distinctive optical properties. The chlorides can be replaced with other [[anion]]s, such as [[hexafluorophosphate|PF₆⁻]].

[[Image:Delta-ruthenium-tris(bipyridine)-cation-3D-balls.png|thumb|left|100px|Structure of [Ru(bipy)₃]²⁺]]

This salt is prepared by treating an aqueous solution of [[ruthenium trichloride]] with [[2,2'-bipyridine]]. In this conversion, Ru(III) is reduced to Ru(II), and [[hypophosphorous acid]] is typically added as a reducing agent.<ref>Broomhead, J. A.; Young, C. G. “Tris(2,2’-bipyridine)Ruthenium(II) Dichloride Hexahydrate” Inorganic Syntheses, 1990, volume 28, pp. 338-340. {{DOI|10.1002/9780470132593.ch86}}</ref>. [Ru(bipy)₃]²⁺ is an octahedral [[coordination complex]]. The complex is chiral, with D₃ [[symmetry group|symmetry]]. It has been resolved into its [[enantiomer]]s, which are kinetically stable.

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==Photochemistry of [Ru(bipy)₃]²⁺==

[Ru(bipy)₃]²⁺ absorbs [[UV light]] and visible light. An aqueous solution absorbs at 452 (+/-3&nbsp;nm) with an extinction coefficient of 11,500 M⁻¹cm⁻¹. Solutions of the resulting [[excited state]] have a comparatively long lifetime of 890 [[nanosecond]]s in acetonitrile<ref>{{cite book|last=Montalti|first=Marco|title=Handbook of Photochemistry 3rd edition|year=2006|publisher=CRC press Taylor & Francis Group|location=6000 Broken Sound Prkway NW, Suite 200 Boca Raton, FL|isbn=0-8247-2377-5|pages=379-404|coauthors=Alberto Cedi, Luca Prodi, M. Teresa Gandolfi}}</ref> and 650 ns in water<ref>{{cite book|last=Montalti|first=Marco|title=Handbook of Photochemistry 3rd edition|year=2006|publisher=CRC press Taylor & Francis Group|location=6000 Broken Sound Prkway NW, Suite 200 Boca Raton, FL|isbn=0-8247-2377-5|pages=379-404|coauthors=Alberto Cedi, Luca Prodi, M. Teresa Gandolfi}}</ref> . The excited state relaxes to the [[ground state]] by emission of a [[photon]] at the [[wavelength]] of 600&nbsp;nm. The long lifetime of the excited state is attributed to the fact that it is [[spin triplet|triplet]], whereas the ground state is a [[Diradical|singlet state]] and in part due to the fact that the structure of the molecule allows for charge separation. Singlet-triplet transitions are forbidden and therefore often slow.

The [[triplet state|triplet excited state]] has both oxidizing and reducing properties. This unusual situation arises because the excited state can be described as an Ru³⁺ complex containing a bipy^- ligand. Thus, the photochemical properties of [Ru(bipy)₃]²⁺ are reminiscent of the [[photosynthesis|photosynthetic assembly]], which also involves separation of an [[electron]] and a [[Electron hole|hole]].<ref>{{cite journal | author = A. J. Bard and M. A. Fox | title = Artificial Photosynthesis: Solar Splitting of Water to Hydrogen and Oxygen | year = 1995 | journal = [[Acc. Chem. Res.]] | volume = 28 | issue = 3 | pages = 141–145 | doi=10.1021/ar00051a007}}</ref>

[Ru(bipy)₃]²⁺ has been examined as a [[photosensitiser]] for both the oxidation and reduction of water. Upon absorbing a photon, [Ru(bipy)₃]²⁺ converts to the aforementioned triplet state, denoted [Ru(bipy)₃]²⁺*. This species transfers an electron, located on one bipy ligand, to a sacrificial oxidant such as [[persulfate]] (S₂O₈^2-). The resulting [Ru(bipy)₃]³⁺ is a powerful oxidant and oxidizes water into O₂ and protons via a metal oxide [[catalyst]].<ref>{{cite journal | author = M. Hara, C. C. Waraksa, J. T. Lean, B. A. Lewis and T. E. Mallouk | title = Photocatalytic Water Oxidation in a Buffered Tris(2,2'-bipyridyl)ruthenium Complex-Colloidal IrO2 System | year = 2000 | journal = [[J. Phys. Chem. A]] | volume = 104 | issue = 22 | pages = 5275–5280 | doi=10.1021/jp000321x}}</ref> Alternatively, the reducing power of [Ru(bipy)₃]²⁺* can be harnessed to reduce [[viologen|methylviologen]], a recyclable carrier of electrons, which in turn reduces protons at a [[platinum]] catalyst. For this process to be catalytic, a sacrificial reductant, such as [[EDTA]]^4- or [[triethanolamine]] is provided to return the Ru(III) back to Ru(II).

Derivatives of [Ru(bipy)₃]²⁺ are numerous.<ref>{{cite journal | author = A. Juris, V. Balzani, F. Barigelletti, S. Campagna, P. Belser and A von Zelewsky | title = Ru(II) polypyridine complexes - photophysics, photochemistry, electrochemistry, and chemiluminescence | year = 1988 | journal = Coord. Chem. Rev. | volume = 84 | issue = | pages = 85–277 | doi=10.1016/0010-8545(88)80032-8}}</ref><ref>{{cite journal | author = S. Campagna, F. Puntoriero, F. Nastasi, G. Bergamini and V. Balzani | title = Photochemistry and photophysics of coordination compounds: ruthenium | year = 2007 | journal = Top. Curr. Chem. | volume = 280 | issue = | pages = 117–214 | doi=10.1007/128_2007_133}}</ref> Such complexes are widely discussed for applications in biodiagnostics, [[Dye-sensitized solar cells|photovoltaics]] and [[organic light-emitting diode]], but no derivative has been commercialized.

== [Ru(bipy)₃]²⁺ and photoredox catalysis ==

Photoredox catalysis using combination of [Ru(bipy)₃]²⁺ catalyst and visible light has been considered as a tool for preparative organic chemistry since the 1970s.<ref>{{cite journal | author = F. Teply | title = Photoredox catalysis by [Ru(bpy)3]2+ to trigger transformations of organic molecules. Organic synthesis using visible-light photocatalysis and its 20th century roots | year = 2011 | journal = [[Collect. Czech. Chem. Commun.]] | publisher=Free access article | volume = 76 | issue = 7 | pages = 859-917 | doi=10.1135/cccc2011078}}</ref> However, only a few research groups dealt with this topic until the beginning of the 21^st century. Since 2008, development of this bond-forming strategy for organic synthesis has gained considerable momentum due to the seminal studies by MacMillan,<ref>{{cite journal | author = D. A. Nicewicz, D. W. C. MacMillan | title = Merging photoredox catalysis with organocatalysis: The direct asymmetric alkylation of aldehydes | year = 2008 | journal = [[Science]] | volume = 322 | pages = 77-80 | doi=10.1126/science.1161976}}</ref> Yoon,<ref>{{cite journal | author = M. A. Ischay, M. E. Anzovino, J. Du, T. P. Yoon | title = Efficient visible light photocatalysis of [2+2] enone cycloadditions | year = 2008 | journal = [[J. Am. Chem. Soc.]] | volume = 130 | pages = 12886-12887 | doi=10.1021/ja805387f }}</ref> and Stephenson<ref>{{cite journal | author = J. M. R. Narayanam, J. W. Tucker, C. R. J. Stephenson | title = Electron-transfer photoredox catalysis: Development of a tin-free reductive dehalogenation reaction | year = 2009 | journal = [[J. Am. Chem. Soc.]] | volume = 131 | pages = 8756-8757 | doi=10.1021/ja9033582}}</ref> groups. Depending on the choice of suitable reductive or oxidative quencher, the [Ru(bipy)₃]²⁺ catalyst can be used to trigger photoreduction or photooxidation, respectively. Current status of this field has been recently summarized in several review articles.<ref>{{cite journal | author = F. Teply | title = Photoredox catalysis by [Ru(bpy)3]2+ to trigger transformations of organic molecules. Organic synthesis using visible-light photocatalysis and its 20th century roots | year = 2011 | journal = [[Collect. Czech. Chem. Commun.]] | publisher=Free access article | volume = 76 | issue = 7 | pages = 859-917 | doi=10.1135/cccc2011078}}</ref><ref>{{cite journal | author = J. M. R. Narayanam, C. R. J. Stephenson | title = Visible light photoredox catalysis: applications in organic synthesis | year = 2011 | journal = [[Chem. Soc. Rev.]] | volume = 40 | pages = 102-113 | doi=10.1039/b913880n}}</ref><ref>{{cite journal | author = T. P. Yoon, M. A. Ischay, J. Du | title = Visible light photocatalysis as a greener approach to photochemical synthesis | year = 2010 | journal = [[Nat. Chem.]] | volume = 2 | pages = 527-532 | doi=10.1038/nchem.687}}</ref><ref>{{cite journal | author = K. Zeitler | title = Photoredox catalysis with visible light | year = 2009 | journal = [[Angew. Chem. Int. Ed.]] | volume = 48 | pages = 9785-9789 | doi=10.1002/anie.200904056}}</ref> It can be anticipated that photoredox reactivity of complexes based on metals other than Ru (e.g. Ir, Re, and bimetallic photocatalysts) will also be intensively explored. Additionally, transformations triggered by purely organic photoredox catalysts start to attract attention as highlighted in the recent report by Zeitler group.<ref>{{cite journal | author = M. Neumann, S. Füldner, B. König, K. Zeitler | title = Metal-free, cooperative asymmetric organophotoredox catalysis with visible light | year = 2011 | journal = [[Angew. Chem. Int. Ed.]] | volume = 50 | pages = 951-954 | doi=10.1002/anie.201002992}}</ref>

Metal bipyridine as well as related [[phenanthroline]] complexes are generally bioactive, as they can act as intercalating agents.

{{reflist}}

[[Category:Ruthenium compounds]]

[[Category:Coordination compounds]]