Elektronendelokalisation in Ein- und Mehrkernkomplexen des Rutheniums und Platins : Nachweis und Konsequenzen

Das Thema dieser Arbeit ist auf dem Forschungsgebiet der "Molekularen Elektronik" angesiedelt. In diesem Zusammenhang wurde die stufenweise Synthese von Modellen für „Molekulare Drähte“ angestrebt, die auf miteinander verbrückten Rutheniumvinyleinheiten basieren. Ausgehend von einkernigen Rutheniumvinylkomplexen sollten durch die Addition eines mit einer freien Alkinfunktion versehenen, chelatisierenden Brückenliganden und nachfolgende Hydrometallierung mit einem Ru-Hydridkomplex zunächst Zweikernkomplexe des Rutheniums dargestellt werden.Durch erneute Addition des Brückenliganden und anschließender Hydrometallierung sollten dreikernige Systeme und durch weitere Wiederholung dieser Schritte lineare, monodisperse oligonukleare Komplexe des Rutheniums zugänglich sein. Dabei spielte der Brückenligand eine zentrale Rolle. Dieser sollte über eine chelatisierende Donoreinheit stabile Addukte mit Rutheniumvinylkomplexen bilden und durch ein konjugiertes pi-System, welches sich über den gesamten organischen Liganden erstreckt, eine effiziente elektronische Kopplung der verbrückten, redoxaktiven Zentren gewährleisten.Mittels elektrochemischer, IR- sowie UV/Vis/NIR-spektroelektrochemischer und ESR-spektroskopischer Untersuchungen wurden die neuen Verbindungen hinsichtlich ihrer Elektronendelokalisation im einfach oxidierten, gemischtvalenten, im zweifach oxidierten und eventuell in höher oxidierten Zuständen charakterisiert. Dabei stellte sich zunächst heraus, dass 4-Ethinylbenzoat und 2-((4-Ethinylphenylimin)methyl)phenol für den Ausbau eines molekularen Drahtes nicht geeignet sind, da sie in den entsprechenden 4-vinylbenzoat bzw. 2-((4-vinylphenylimin)methyl)phenol-verbrückten Zweikernkomplexen die verbrückten Redoxzentren nicht elektronisch miteinander koppeln.Dies brachten die geringen bzw. nicht beobachteten CO-Bandenverschiebungen sowie das Fehlen von Banden im Vis- bzw. NIR-Bereich bei den spektroelektrochemischen Untersuchungen zum Vorschein. Dagegen konnten für die 2-oxo-5-vinylpyridinverbrückten Zweikernkomplexe eine deutliche Verschiebung der Carbonylbande um 18 cm-1 bzw. 16 cm-1 der jeweils formal nicht oxidierten,sechsfach koordinierten Rutheniumeinheit im Zuge der ersten Oxidation nachgewiesen werden.Zudem wurde dabei das Entstehen von NIR-Banden beobachtet,welchen vor dem Hintergrund quantenchemischer Studien ein gewisser Ladungstransfer von der terminalen zur verbrückenden Vinyleinheit zugesprochen werden kann. Die ESR-Spektroskopie lieferte zusätzliche Indizien für eine weitgehende Delokalisation des HOMOs über die Dirutheniumoxovinylpyridineinheit. Somit liegt in den zweikernigen 5-oxo-2-vinylpyridinverbrückten Systemen eine effiziente elektronische Kommunikation zwischen den redoxaktiven Endgruppen vor.Der Ausbau zu längerkettigen 4-vinylbenzoat, 2-((4-vinylphenylimin)methyl)phenol- und 2-oxo-5-vinylpyridin-verbrückten Systemen ließ sich jedoch nicht realisieren. Für die Darstellung eines 1,4-ethinyl(vinyl)phenylenverbrückten Rutheniumdreikernkomplexes wurde vom iterativen Aufbauprinzip abgewichen. Durch die hohe CO-Bandenverschiebung von 23 cm-1 bzw. 34 cm-1 im Verlauf der zweiten und dritten Oxidation brachte dieser eine starke Elektronendelokalisation über das gesamte dreikernige System zum Vorschein. Dies zeigten auch die intensiven NIR-Banden aller drei oxidierten Spezies in den UV/Vis/NIR-spektroelektrochemischen Untersuchungen. Somit stellt der Komplex ein geeignetes Modell für einen „Molekularen Draht“ mit guten lochleitenden Eigenschaften dar.Ein weiterer Aspekt dieser Arbeit beinhaltet die Darstellung und Charakterisierung neuer Platinphotosensibilisatoren. Bei den dargestellten Verbindungen handelt es sich um zwei Platindiiminbisthiolatkomplexe und einen Platindiiminbisalkoholatkomplex. Als Diiminligand fanden dabei 4,4´-bis-t-Bubipy und als Thiolat- bzw. Alkoholatliganden Cumarine des Typs 4-Methyl-7-thiolatocumarin, 4-Methyl-7-oxocumarin 4-Methyl-6,7-dioxocumarin Verwendung. Die neuen Komplexe zeigten neben mäßig intensiven CT-Absorptionsbanden ((Thiolat/Alkoholat)Pt→Dimin-CT-Übergänge) im sichtbaren Bereich auch intensive Banden im nahen UV. Für letztere ließ sich durch Quantenchemischen Rechnungen ein hoher Anteil eines farbstoffbasierten pi→pi*-Übergangs nachweisen. Lumineszenzmessungen an den Komplexen in gefrorener Lösung zeigten, dass sowohl beim Einstrahlen in die jeweilige CT-Bande als auch bei Anregung bei niedrigeren Wellenlängen im Bereich der intensiven UV-Absorptionsbande und bei noch höherer Energie jeweils die gleichen Emissionsspektren erhalten werden. Somit konnte gezeigt werden, dass kovalent gebundene organische Farbstoffe als „Antennen" für den aktiven MLCT-Zustand genutzt werden können

How to elucidate and control the redox sequence in vinylbenzoate and vinylpyridine bridged diruthenium complexes

Vinylbenzoate-bridged diruthenium complexes (RHC[double bond, length as m-dash]CH)(CO)(PiPr3)2Ru(μ-4-OOCC6H4–CH[double bond, length as m-dash]CH)RuCl(CO)(PiPr3)2 (R = Ph, 3a or CF3, 3b) and vinylpyridine-bridged (η6-p-cymene)Cl2Ru(μ-NC5H4-4-CH[double bond, length as m-dash]CH)RuCl(CO)(PiPr3)2 (3c) have been prepared from their monoruthenium precursors and investigated with respect to the sequence of the individual redox steps and electron delocalization in their partially and fully oxidized states. Identification of the primary redox sites rests on the trends in redox potentials and the EPR, IR and Vis/NIR signatures of the oxidized radical cations and is correctly reproduced by quantum chemical investigations. Our results indicate that the trifluoropropenyl complex 3b has an inverse FMO level ordering (Ru1-bridge-Ru2 > terminal vinyl-Ru1 site) when compared to its styryl substituted counterpart 3a such that the primary oxidation site in these systems can be tuned by the choice of the terminal alkenyl ligand. It is further shown that the vinylbenzoate bridge is inferior to the vinylpyridine one with regard to charge and spin delocalization at the radical cation level. According to quantum chemical calculations, the doubly oxidized forms of these complexes have triplet diradical ground states and feature two interconnected oxidized vinyl ruthenium subunits

Fully delocalized (ethynyl)(vinyl)phenylene-bridged diruthenium radical complexes.

International audienceDiruthenium complexes [(X)(dppe)2Ru-C≡C-1,4-C6H4-CH:CH-RuCl(CO)(PiPr3)2] (1a,b, X = = Cl, C≡CPh) contg. an unsym. (ethynyl)(vinyl)phenylene bridging ligand were prepd. by alkyne insertion into Ru-H-bond and compared to their sym. 1,4-bis(ethynyl)phenylene- and 1,4-divinylphenylene-bridged congeners and their mononuclear alkynyl precursors. Electrochem. and UV/vis/NIR, IR, and EPR spectroscopic studies on the neutral complexes and their various oxidized forms indicate bridging ligand-centered oxidn. processes and uniform charge and spin delocalization over both dislike organoruthenium moieties despite differences in their intrinsic redox potentials. Comparison between the chloro and the phenylacetylide-terminated derivs. 1a,b suggests further that the conjugated organometallic π-system extends over the entire unsatd. backbone including the terminal ligand at the alkynyl ruthenium site. This paves the way to even more extended π-conjugated organoruthenium arrays for long-range electronic interactions. [on SciFinder(R)

Doubly N-Functionalized Pentafulvenes and Redox-Responsive [N,N]- and [N,C,N]-Pincer Bis(imidoyl)pentamethylruthenocene Metalloligands

New doubly functionalized pentafulvenes are easily obtained by a regioselective one-pot reaction of sodium cyclopentadienide with imidoyl chlorides of different electrophilicity. Under thermodynamic control, benzimidoyl chlorides as electrophiles afford hydrogen-bridged 6-arylamino-2-benzimidoylfulvenes, whereas under kinetic control trifluoroacetimidoyl chlorides afford non-hydrogen-bridged 6-arylamino-3-imidoylfulvenes. Structurally, these [N,N]H fulvenes exist either as pairs of rapidly interconverting tautomers (fulvenes with intramolecular hydrogen bridges) or as regular fulvenes (fulvenes without intramolecular but with intermolecular hydrogen bridges) in solution and in the solid state, as shown by NMR studies and single-crystal X-ray diffraction. Both types of fulvenes represent interesting ambidentate [N,N]H ligands per se as well as precursors to novel doubly functionalized bis(imidoyl)metallocenes. Synthetically, after deprotonation of these acceptor-substituted [N,N]H-fulvenes, 1,2- or 1,3-bis(imidoyl)pentamethylruthenocenes are easily accessible by reaction with [Cp*Ru(CH3CN)3]PF6 as a source of the electron-rich Cp*Ru+-synthon. Structurally, these new [N,N]-pentamethylruthenocene metalloligands are related to diazabutadienes or bis(imino)-[N,C,N]H pincer ligand systems, respectively. Electrochemical investigations show that the bis(imidoyl)(pentamethyl)ruthenocenes are novel redox-active metalloligands and reveal the strongly electron-withdrawing effect of the appended imine moieties. All new compounds were fully characterized by spectroscopic methods and by a total of 11 single-crystal X-ray analyses

Fully delocalized (ethynyl)(vinyl)phenylene bridged triruthenium complexes in up to five different oxidation states

International audienceTriruthenium [(dppe)(2)Ru{-C≡C-1,4-C(6)H(2)-2,5-R(2)-CH═CH-RuCl(CO)(P(i)Pr(3))(2)}(2)](n+) (4a, R = H; 4b, R = OMe) containing unsymmetrical (ethynyl)(vinyl)phenylene bridging ligands and displaying five well-separated redox states (n = 0-4) are compared to their bis(alkynyl)ruthenium precursors (dppe)(2)Ru{-C≡C-1,4-C(6)H(2)-2,5-R(2)-C≡CR'} (2a,b: R' = TMS; 3a,b: R' = H) and their symmetrically substituted bimetallic congeners, complexes {Cl(dppe)(2)Ru}(2){μ-C≡C-1,4-C(6)H(2)-2,5-R(2)-C≡C} (A(a), R = H; A(b), R = OMe) and {RuCl(CO)(P(i)Pr(3))(2)}(2){μ-CH═CH-1,4-C(6)H(2)-2,5-R(2)-CH═CH} (V(a), R = H; V(b), R = OMe) as well as the mixed (ethynyl)(vinyl)phenylene bridged [Cl(dppe)(2)Ru-C≡C-1,4-C(6)H(4)-CH═CH-RuCl(CO)(P(i)Pr(3))(2)] (M(a)). Successive one-electron transfer steps were studied by means of cyclic voltammetry, EPR and UV-vis-NIR-IR spectroelectrochemistry. These studies show that the first oxidation mainly involves the central bis(alkynyl) ruthenium moiety with only limited effects on the appended vinyl ruthenium moieties. The second to fourth oxidations (n = 2, 3, 4) involve the entire carbon-rich conjugated path of the molecule with an increased charge uniformly distributed between the two arms of the molecules, including the terminal vinyl ruthenium sites. In order to assess the charge distribution, we judiciously use (13)CO labeled analogues to distinguish stretching vibrations due to the acetylide triple bonds and the intense and charge-sensitive Ru(CO) IR probe in different oxidation states. The comparison between complex pairs 4a,b(n+) (n = 0-3), A(a,b)(n+) and V(a,b)(n+) (n = 0-2) serves to elucidate the effect of the methoxy donor substituents on the redox and spectroscopic properties of these systems in their various oxidation states and on the metal/ligand contributions to their frontier orbitals

Fully Delocalized (Ethynyl)(vinyl)phenylene Bridged Triruthenium Complexes in up to Five Different Oxidation States

Triruthenium [(dppe)₂Ru­{−CC–1,4-C₆H₂–2,5-R₂–CHCH–RuCl­(CO)­(P^<i>i</i>Pr₃)₂}₂]^<i>n</i>+ (<b>4a</b>, R = H; <b>4b</b>, R = OMe) containing unsymmetrical (ethynyl)­(vinyl)­phenylene bridging ligands and displaying five well-separated redox states (<i>n</i> = 0–4) are compared to their bis­(alkynyl)ruthenium precursors (dppe)₂Ru­{−CC–1,4-C₆H₂–2,5-R₂–CCR′} (<b>2a</b>,<b>b</b>: R′ = TMS; <b>3a</b>,<b>b</b>: R′ = H) and their symmetrically substituted bimetallic congeners, complexes {Cl­(dppe)₂Ru}₂{μ-CC–1,4-C₆H₂–2,5-R₂–CC} (<b>A</b>_<b>a</b>, R = H; <b>A</b>_<b>b</b>, R = OMe) and {RuCl­(CO)­(P^<i>i</i>Pr₃)₂}₂{μ-CHCH–1,4-C₆H₂–2,5-R₂–CHCH} (<b>V</b>_<b>a</b>, R = H; <b>V</b>_<b>b</b>, R = OMe) as well as the mixed (ethynyl)­(vinyl)­phenylene bridged [Cl­(dppe)₂Ru–CC–1,4-C₆H₄–CHCH–RuCl­(CO)­(P^<i>i</i>Pr₃)₂] (<b>M</b>_<b>a</b>). Successive one-electron transfer steps were studied by means of cyclic voltammetry, EPR and UV–vis–NIR–IR spectroelectrochemistry. These studies show that the first oxidation mainly involves the central bis­(alkynyl) ruthenium moiety with only limited effects on the appended vinyl ruthenium moieties. The second to fourth oxidations (<i>n</i> = 2, 3, 4) involve the entire carbon-rich conjugated path of the molecule with an increased charge uniformly distributed between the two arms of the molecules, including the terminal vinyl ruthenium sites. In order to assess the charge distribution, we judiciously use ¹³CO labeled analogues to distinguish stretching vibrations due to the acetylide triple bonds and the intense and charge-sensitive Ru­(CO) IR probe in different oxidation states. The comparison between complex pairs <b>4a,b</b>^{<b><i>n</i>+</b>} (<i>n</i> = 0–3), <b>A</b>_<b>a,b</b>^{<b><i>n</i>+</b>} and <b>V</b>_<b>a,b</b>^{<b><i>n</i>+</b>} (<i>n</i> = 0–2) serves to elucidate the effect of the methoxy donor substituents on the redox and spectroscopic properties of these systems in their various oxidation states and on the metal/ligand contributions to their frontier orbitals

Fully Delocalized (Ethynyl)(vinyl)phenylene Bridged Triruthenium Complexes in up to Five Different Oxidation States

Triruthenium [(dppe)₂Ru­{−CC–1,4-C₆H₂–2,5-R₂–CHCH–RuCl­(CO)­(P^<i>i</i>Pr₃)₂}₂]^<i>n</i>+ (<b>4a</b>, R = H; <b>4b</b>, R = OMe) containing unsymmetrical (ethynyl)­(vinyl)­phenylene bridging ligands and displaying five well-separated redox states (<i>n</i> = 0–4) are compared to their bis­(alkynyl)ruthenium precursors (dppe)₂Ru­{−CC–1,4-C₆H₂–2,5-R₂–CCR′} (<b>2a</b>,<b>b</b>: R′ = TMS; <b>3a</b>,<b>b</b>: R′ = H) and their symmetrically substituted bimetallic congeners, complexes {Cl­(dppe)₂Ru}₂{μ-CC–1,4-C₆H₂–2,5-R₂–CC} (<b>A</b>_<b>a</b>, R = H; <b>A</b>_<b>b</b>, R = OMe) and {RuCl­(CO)­(P^<i>i</i>Pr₃)₂}₂{μ-CHCH–1,4-C₆H₂–2,5-R₂–CHCH} (<b>V</b>_<b>a</b>, R = H; <b>V</b>_<b>b</b>, R = OMe) as well as the mixed (ethynyl)­(vinyl)­phenylene bridged [Cl­(dppe)₂Ru–CC–1,4-C₆H₄–CHCH–RuCl­(CO)­(P^<i>i</i>Pr₃)₂] (<b>M</b>_<b>a</b>). Successive one-electron transfer steps were studied by means of cyclic voltammetry, EPR and UV–vis–NIR–IR spectroelectrochemistry. These studies show that the first oxidation mainly involves the central bis­(alkynyl) ruthenium moiety with only limited effects on the appended vinyl ruthenium moieties. The second to fourth oxidations (<i>n</i> = 2, 3, 4) involve the entire carbon-rich conjugated path of the molecule with an increased charge uniformly distributed between the two arms of the molecules, including the terminal vinyl ruthenium sites. In order to assess the charge distribution, we judiciously use ¹³CO labeled analogues to distinguish stretching vibrations due to the acetylide triple bonds and the intense and charge-sensitive Ru­(CO) IR probe in different oxidation states. The comparison between complex pairs <b>4a,b</b>^{<b><i>n</i>+</b>} (<i>n</i> = 0–3), <b>A</b>_<b>a,b</b>^{<b><i>n</i>+</b>} and <b>V</b>_<b>a,b</b>^{<b><i>n</i>+</b>} (<i>n</i> = 0–2) serves to elucidate the effect of the methoxy donor substituents on the redox and spectroscopic properties of these systems in their various oxidation states and on the metal/ligand contributions to their frontier orbitals

Improvement of (bipy)Pt(XR)₂ (X = O; S) type photosensitiezers by covalent dye attachment

Irradiation into the dye-based absorption band of complexes (tBu₂bipy)Pt(SR)₂ and (tBu₂bipy)Pt(OR)₂ where R denotes a coumarine-based thiolate and alkoxolate substituent populates the same excited triplet state as is obtained by excitation into the much weaker (RX)₂Pt-tBu₂bipy (X = O, S) charge-transfer band. This paves the way toward more efficient photosensitizers