Electronic structures and spectra of hexakisphenylisocyanide complexes of Cr(0), Mo(0), W(0), Mn(I), and Mn(II)

Mann, Kent R.; Cimolino, Marc C.; Geoffroy, Gregory L.; Hammond, George S.; Orio, A. A.; Albertin, Gabriele; Gray, Harry B.

doi:10.1016/s0020-1693(00)91697-9

Cited by 95 publications

(99 citation statements)

References 14 publications

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“…This interpretation is compatible with recent computational work on W 0 complexes with monodentate arylisocyanide ligands, which demonstrated that distortion along a normal coordinate involving the CN stretch is important [10]. Furthermore, previous work discussed the coupling of the CN group to the aromatic π-system of arylisocyanides [1,2], and it For the simulations in Figure 2, we summed over ν M values from 0 to 3 and adapted E 0 , S M and h·ω M to match the experimentally observed emission spectra as closely as possible. The outcomes are included in Figure 2 as dotted gray traces, and the fitting parameters are summarized in Table 3 along with those reported previously for the [Ru(dmb) 3 ] 2+ complex [28].…”

Section: Resultssupporting

confidence: 88%

“…Using Equations (1) and (2), this effect can be quantified and the resulting rate constants can be compared to [Ru(dmb) 3 ] 2+ (dmb = 4,4 -dimethyl-2,2 -bipyridine) [28], which is an isoelectronic analogue of our molybdenum complexes ( Table 2). τ −1 = k r + k nr (1) 2+ 3,4 0.83 10.6 1 In toluene. 2 Weighted average of lifetime values (τ) used for the calculation (0.85 × 1110 ns + 0.15 × 2330 ns) [27].…”

Section: Resultsmentioning

confidence: 99%

“…The isocyanides are less π-accepting than CO, yet the ligand field remains very strong (even in the Cr 0 complexes), and all 6 d-electrons are paired in the t 2g -set of d-orbitals, which represent the HOMO in octahedral symmetry. In arylisocyanides, there is some π-conjugation between the C≡N group and the aryl π-system, and consequently antibonding ligand-based orbitals become the LUMO in hexakis(arylisocyanide) complexes of Cr 0 , Mo 0 , and W 0 [1,2]. The resulting electronic structure with a metal-based HOMO and a ligand-centered LUMO is closely related to that encountered for isoelectronic Ru II and Os II polypyridine complexes.…”

Section: Introductionmentioning

confidence: 81%

“…Hexacarbonyl complexes of Cr 0 , Mo 0 , and W 0 are prototypical coordination compounds obeying the 18-electron rule with a low-spin d 6 valence electron configuration. Isocyanides (CNR) are formally isoelectronic with CO, and consequently it is unsurprising that hexakis(isocyanide) complexes of the abovementioned d 6 metals as well as some heteroleptic complexes comprising both CO and CNR ligands have long been known [1][2][3][4][5][6][7]. The isocyanides are less π-accepting than CO, yet the ligand field remains very strong (even in the Cr 0 complexes), and all 6 d-electrons are paired in the t 2g -set of d-orbitals, which represent the HOMO in octahedral symmetry.…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Resultssupporting

confidence: 88%

Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 81%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Herr

Wenger

2020

Inorganics

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“…Of course, conjugation between π*(CN) and aryl π orbitals must be taken into account. 22,23 Localization of excited electron …”

Section: ■ Discussionmentioning

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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