Generation of Powerful Tungsten Reductants by Visible Light Excitation

Sattler, Wesley; Ener, Maraia E.; Blakemore, James D.; Rachford, Aaron A.; LaBeaume, Paul; Thackeray, James W.; Cameron, James F.; Winkler, Jay R.

doi:10.1021/ja4047119

Cited by 91 publications

(114 citation statements)

References 56 publications

(59 reference statements)

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“…[9b] From then on, the field of group 6 d 6 isocyanides was dormant until 2013, when new reports on highly emissive W(0) isocyanide complexes appeared. [10] More recently, we found that chelating diisocyanide ligands give access to luminescent Cr(0) and Mo(0) complexes which are analogues of Fe(bpy)3 2+ and Ru(bpy)3 2+ , [11] and we could demonstrate that they are amenable to applications such as triplet-triplet annihilation upconversion or photoredox catalysis.…”

Section: Introductionmentioning

confidence: 91%

Chromium(0), Molybdenum(0), and Tungsten(0) Isocyanide Complexes as Luminophores and Photosensitizers with Long‐Lived Excited States

Büldt

Wenger

2017

Angew Chem Int Ed

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Arylisocyanide complexes based on earth-abundant Group 6 d metals are interesting alternatives to photoactive complexes made from precious metals such as Ru , Re , Os , or Ir . Some of these complexes have long-lived MLCT excited states that exhibit luminescence with good quantum yields as well as nano- to microsecond lifetimes, and they are very strongly reducing. Recent studies have demonstrated that Cr , Mo , and W arylisocyanide complexes have great potential for applications in luminescent devices, photoredox catalysis, and dye-sensitized solar cells.

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Section: Introductionmentioning

confidence: 91%

Chromium(0), Molybdenum(0), and Tungsten(0) Isocyanide Complexes as Luminophores and Photosensitizers with Long‐Lived Excited States

Büldt

Wenger

2017

Angew Chem Int Ed

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“…DFT calculations of all three complexes in THF and pentane solutions yield bonding parameters close to those previously determined crystallographically. 1,2,18 Each complex has a distorted octahedral structure in which the three Aryl−NC−W−CN−Aryl axes are nonequivalent (the three complexes differ in the mutual orientations of the aryl rings of trans-ligands, Figure 1). For W(CNdipp) 6 and W(CNdippPh OMe 2 ) 6 , the trans aryls are nearly coplanar, 3−4°torsion angle, depending on the axis.…”

Section: Inorganic Chemistrymentioning

confidence: 99%

Electronic Excited States of Tungsten(0) Arylisocyanides

Kvapilová

Sattler

et al. 2015

Inorg. Chem.

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W(CNAryl)6 complexes containing 2,6-diisopropylphenyl isocyanide (CNdipp) are powerful photoreductants with strongly emissive long-lived excited states. These properties are enhanced upon appending another aryl ring, e.g., W(CNdippPh(OMe2))6; CNdippPh(OMe2) = 4-(3,5-dimethoxyphenyl)-2,6-diisopropylphenylisocyanide (Sattler et al. J. Am. Chem. Soc. 2015, 137, 1198-1205). Electronic transitions and low-lying excited states of these complexes were investigated by time-dependent density functional theory (TDDFT); the lowest triplet state was characterized by time-resolved infrared spectroscopy (TRIR) supported by density functional theory (DFT). The intense absorption band of W(CNdipp)6 at 460 nm and that of W(CNdippPh(OMe2))6 at 500 nm originate from transitions of mixed ππ*(C≡N-C)/MLCT(W → Aryl) character, whereby W is depopulated by ca. 0.4 e(-) and the electron-density changes are predominantly localized along two equatorial molecular axes. The red shift and intensity rise on going from W(CNdipp)6 to W(CNdippPh(OMe2))6 are attributable to more extensive delocalization of the MLCT component. The complexes also exhibit absorptions in the 300-320 nm region, owing to W → C≡N MLCT transitions. Electronic absorptions in the spectrum of W(CNXy)6 (Xy = 2,6-dimethylphenyl), a complex with orthogonal aryl orientation, have similar characteristics, although shifted to higher energies. The relaxed lowest W(CNAryl)6 triplet state combines ππ* excitation of a trans pair of C≡N-C moieties with MLCT (0.21 e(-)) and ligand-to-ligand charge transfer (LLCT, 0.24-0.27 e(-)) from the other four CNAryl ligands to the axial aryl and, less, to C≡N groups; the spin density is localized along a single Aryl-N≡C-W-C≡N-Aryl axis. Delocalization of excited electron density on outer aryl rings in W(CNdippPh(OMe2))6 likely promotes photoinduced electron-transfer reactions to acceptor molecules. TRIR spectra show an intense broad bleach due to ν(C≡N), a prominent transient upshifted by 60-65 cm(-1), and a weak down-shifted feature due to antisymmetric C≡N stretch along the axis of high spin density. The TRIR spectral pattern remains unchanged on the femtosecond-nanosecond time scale, indicating that intersystem crossing and electron-density localization are ultrafast (<100 fs).

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“…Thus, in analogy to this well-known class of precious metal-based complexes, arylisocyanide complexes of Cr 0 , Mo 0 , and W 0 have energetically low-lying metal-to-ligand charge transfer (MLCT) absorptions. An early investigation already reported luminescence from a 3 MLCT state in W 0 arylisocyanide complexes [2], and more recent work demonstrated that high luminescence quantum yields and long excited-state lifetimes are achievable by optimizing the ligand design [8][9][10]. Moreover, these W 0 lifetimes are achievable by optimizing the ligand design [8][9][10].…”

Section: Introductionmentioning

confidence: 99%

“…An early investigation already reported luminescence from a 3 MLCT state in W 0 arylisocyanide complexes [2], and more recent work demonstrated that high luminescence quantum yields and long excited-state lifetimes are achievable by optimizing the ligand design [8][9][10]. Moreover, these W 0 lifetimes are achievable by optimizing the ligand design [8][9][10]. Moreover, these W 0 complexes with monodentate arylisocyanide ligands are very strong photoreductants, capable, for example, of reducing anthracene to its radical anion form.…”

Section: Introductionmentioning

confidence: 99%

Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands

Herr

Wenger

2020

Inorganics

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Diisocyanide ligands with a m-terphenyl backbone provide access to Mo 0 complexes exhibiting the same type of metal-to-ligand charge transfer (MLCT) luminescence as the well-known class of isoelectronic Ru II polypyridines. The luminescence quantum yields and lifetimes of the homoleptic tris(diisocyanide) Mo 0 complexes depend strongly on whether methyl-or tert-butyl substituents are placed in α-position to the isocyanide groups. The bulkier tert-butyl substituents lead to a molecular structure in which the three individual diisocyanides ligated to one Mo 0 center are interlocked more strongly into one another than the ligands with the sterically less demanding methyl substituents. This rigidification limits the distortion of the complex in the emissive excited-state, causing a decrease of the nonradiative relaxation rate by one order of magnitude. Compared to Ru II polypyridines, the molecular distortions in the luminescent 3 MLCT state relative to the electronic ground state seem to be smaller in the Mo 0 complexes, presumably due to delocalization of the MLCT-excited electron over greater portions of the ligands. Temperature-dependent studies indicate that thermally activated nonradiative relaxation via metal-centered excited states is more significant in these homoleptic Mo 0 tris(diisocyanide) complexes than in [Ru(2,2 -bipyridine) 3 ] 2+ . complexes with monodentate arylisocyanide ligands are very strong photoreductants, capable, for example, of reducing anthracene to its radical anion form. Many different kinds of metal complexes with isocyanide ligands have been explored over the past few decades [11][12][13][14][15], but metals with the d 6 or d 10 electron configurations are unique in their ability to show luminescence from a 3 MLCT excited state.Whilst structurally more flexible, multidentate isocyanide chelate ligands had been known for some time [16], we found that chelating diisocyanide ligands based on a m-terphenyl backbone permit the synthesis of homoleptic tris(diisocyanide) complexes of Cr 0 and Mo 0 that luminesce from 3 MLCT excited states (Figure 1) [17]. The molecular and the electronic structures of these compounds are reminiscent of Fe II and Ru II polypyridine complexes, which have been investigated extensively in the past. Until now, no convincing case of steady-state MLCT luminescence from a Fe II complex has been reported despite significant advances in extending their 3 MLCT lifetimes in recent years [18][19][20][21][22][23]; hence, our Cr 0 complex currently seems to be the only example of a first-row d 6 -metal complex showing MLCT luminescence in solution at room temperature under steady-state photo-irradiation [24]. The Mo 0 diisocyanide complexes are not only emissive, but they can furthermore be employed in photoredox catalysis of thermodynamically challenging reductions, which cannot be performed with more widely known photoreductants such as fac-[Ir(ppy) 3 ] (ppy = 2-phenylpyridine) [25]. Thus, the Mo 0 diisocyanide complexes represent Earth-abundant alternatives to precious-...

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Generation of Powerful Tungsten Reductants by Visible Light Excitation

Cited by 91 publications

References 56 publications

Chromium(0), Molybdenum(0), and Tungsten(0) Isocyanide Complexes as Luminophores and Photosensitizers with Long‐Lived Excited States

Chromium(0), Molybdenum(0), and Tungsten(0) Isocyanide Complexes as Luminophores and Photosensitizers with Long‐Lived Excited States

Electronic Excited States of Tungsten(0) Arylisocyanides

Excited-State Relaxation in Luminescent Molybdenum(0) Complexes with Isocyanide Chelate Ligands

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