Ultrafast Ligand Exchange: Detection of a Pentacoordinate Ru(II) Intermediate and Product Formation

Liu, Yao; Turner, David B.; Singh, Tanya N.; Angeles‐Boza, Alfredo M.; Chouai, Abdellatif; Dunbar, Kim R.; Turró, Claudia

doi:10.1021/ja806860w

Cited by 95 publications

(147 citation statements)

References 12 publications

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“…The differences in photoinduced ligand exchange among 1−3 are illustrated in Figure S12 (Supporting Information), which shows that the substitution of the two CH 3 CN ligands in 2 and 3 is complete in 5−60 min. In contrast, the photosubsitution of one CH 3 CN ligand for CD 3 41 It is evident in Figure 3 that irradiation of complex 1 in H 2 O for 20 min (λ irr ≥ 550 nm) results in a well-defined absorption peak with a maximum at 518 nm, attributed to the monoaqua intermediate 4, with negligible spectral changes with continued irradiation with this wavelength. However, when 4 is further irradiated with higher energy light (λ irr ≥ 420 nm), the bis-aqua species, 5, is formed after 3 h ( Figure S14 In contrast to the results described with respect to 1, irradiation of 2 (λ irr ≥ 455 nm, Figure 4a) and 3 (λ irr ≥ 610 nm, Figure 4b) results in complete conversion to the corresponding bis-aqua species.…”

Section: ■ Results and Discussionmentioning

confidence: 96%

“…40,41 It was shown that ligand exchange occurred in a stepwise manner and that the quantum yield for the exchange of the second CH 3 CN ligand is ∼2-fold lower than that of the first CH 3 CN ligand. 40,41 Moreover, in [Ru(bpy)(CH 3 CN) 4 ] 2+ , which possesses four potential sites for exchange, only the axial CH 3 CN ligands undergo stepwise substitution with water upon irradiation. 40 This reactivity provides an important synthetic tool for the preparation of new trans Tris−heteroleptic Ru(II) complexes, as well as PCT agents with photolablile ligands that can function in hypoxic environments without the need for oxygen.…”

Section: ■ Introductionmentioning

confidence: 99%

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Selective Photoinduced Ligand Exchange in a New Tris–Heteroleptic Ru(II) Complex

2013

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The complex cis-[Ru(biq)(phen)(CH3CN)2](2+) (1, biq = 2,2'-biquinoline, phen = 1,10-phenathroline) displays selective photosubstitution of only one CH3CN ligand with a solvent molecule upon irradiation with low energy light (λ(irr) ≥ 550 nm), whereas both ligands exchange with λ(irr) ≥ 420 nm. In contrast, [Ru(phen)2(CH3CN)2](2+) (2) and [Ru(biq)2(CH3CN)2](2+) (3) exchange both CH3CN ligands with similar rates upon irradiation with a broad range of wavelengths. The photolysis of 1 in the presence of pyridine (py) results in the formation of the intermediate cis-[Ru(biq)(phen)(py)(MeCN)](2+), which was isolated and characterized by X-ray crystallography, revealing that the CH3CN positioned trans to the phen ligand is more photolabile than that positioned trans to the biq ligand when irradiated with low energy light. These results are explained using the calculated stabilities of the two possible products, together with the molecular orbitals involved in the lowest energy excited state.

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Section: ■ Results and Discussionmentioning

confidence: 96%

Section: ■ Introductionmentioning

confidence: 99%

Selective Photoinduced Ligand Exchange in a New Tris–Heteroleptic Ru(II) Complex

2013

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“…The 1 MLCT absorption maxima of 3 and 4 are red-shifted compared to the analogous CH 3 CN complexes, as is well-known for other cis -Ru(II) complexes coordinated by two CH 3 CN and py ligands. 37,90 The quinoline moiety in 4 leads to a further red shift as compared to 3 . Again, the intensities of these transitions are in good agreement with those of [Ru(TPA)(py) 2 ] 2+ 57.…”

Section: Resultsmentioning

confidence: 99%

Unusual Role of Excited State Mixing in the Enhancement of Photoinduced Ligand Exchange in Ru(II) Complexes

Loftus

Fillman

et al. 2017

J. Am. Chem. Soc.

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Four Ru(II) complexes were prepared bearing two new tetradentate ligands, cyTPA and 1-isocyTPQA, which feature a piperidine ring that provides a structurally rigid backbone and facilitates the installation of other donors as the fourth chelating arm, while avoiding the formation of stereoisomers. The photophysical properties and photochemistry of [Ru(cyTPA)(CH3CN)2]2+ (1), [Ru(1-isocyTPQA)(CH3CN)2]2+ (2), [Ru(cyTPA)(py)2]2+ (3), and [Ru(1-isocyTPQA)-(py)2]2+ (4) were compared. The quantum yield for the CH3CN/H2O ligand exchange of 2 was measured to be Φ400 = 0.033(3), 5-fold greater than that of 1, Φ400 = 0.0066(3). The quantum yields for the py/H2O ligand exchange of 3 and 4 were lower, 0.0012(1) and 0.0013(1), respectively. DFT and related calculations show the presence of a highly mixed 3MLCT/3ππ* excited state as the lowest triplet state in 2, whereas the lowest energy triplet states in 1, 3, and 4 were calculated to be 3LF in nature. The mixed 3MLCT/3ππ* excited state places significant spin density on the quinoline moiety of the 1-isocyTPQA ligand positioned trans to the photolabile CH3CN ligand in 2, suggesting the presence of a trans-type influence in the excited state that enhances ligand exchange. Ultrafast spectroscopy was used to probe the excited states of 1–4, which confirmed that the mixed 3MLCT/3ππ* excited state in 2 promotes ligand dissociation, representing a new manner to effect photoinduced ligand exchange. The findings from this work can be used to design improved complexes for applications that require efficient ligand dissociation, as well as for those that require minimal deactivation of the 3MLCT state through low-lying metal-centered states.

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“…In contrast, with the exception of [Ru(bpy) 3 ] 2+ , [39][40][41] a fundamental understanding of the ultrafast excited state processes of transition metal complexes is still lacking.…”

Section: Introductionmentioning

confidence: 99%

Femtosecond spectroscopy of the dithiolate Cu(ii) and Ni(ii) complexes

et al. 2014

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Femtosecond spectroscopy was applied to study the ultrafast dynamics for the excited states of dithiolate Cu(ii) and Ni(ii) complexes. The detailed information on the initial steps after the absorption of a photon by the metal complexes is of fundamental importance to understand the mechanism of photochemical reactions. The fast processes for the dithiolate complexes have hardly been studied. In this review the spectra of transients and their lifetimes will be presented. For example, the xanthogenate Ni(S2COEt)2 complex in acetonitrile and CCl4 after the pulse of the second harmonic (100 fs, 400 nm) of a Ti:S laser moves to the excited (1)LMCT state which decays in 0.76 ps to the excited (3)LF state. In 6.8 ps the (3)LF state undergoes vibrational cooling and then it slowly decays in 550 ps to the ground state. However, for many dithiolate complexes the kinetic curves can be well treated in a two-exponential approximation. A short time (less than 1 ps) may include several processes (relaxation of the Franck-Condon state, redistribution of vibrational energy (IVR), internal conversion (IC) and intersystem crossing (ISC)). A long time (a few picoseconds) usually reflects the vibrational cooling of the ground state. The quantum yields of the dithiolate and dithiolene complex disappearance in halogen containing solvents have a strong dependence on the wavelength of irradiation. It is very likely that electron transfer to the acceptor becomes effective when the electron in the excited complex moves to antibonding ligand orbitals localized at the periphery of the complex close to the acceptor molecule (halogenated solvent).

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Ultrafast Ligand Exchange: Detection of a Pentacoordinate Ru(II) Intermediate and Product Formation

Cited by 95 publications

References 12 publications

Selective Photoinduced Ligand Exchange in a New Tris–Heteroleptic Ru(II) Complex

Selective Photoinduced Ligand Exchange in a New Tris–Heteroleptic Ru(II) Complex

Unusual Role of Excited State Mixing in the Enhancement of Photoinduced Ligand Exchange in Ru(II) Complexes

Femtosecond spectroscopy of the dithiolate Cu(ii) and Ni(ii) complexes

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