Electronic Structure and Reactivity of a Well-Defined Mononuclear Complex of Ti(II)

Wijeratne, Gayan B.; Zolnhofer, Eva M.; Fortier, Skye; Grant, Lauren N.; Carroll, Patrick J.; Chen, Chun-Hsing; Meyer, Karsten; Krzystek, J.; Ozarowski, Andrew; Jackson, Timothy A.; Mindiola, Daniel J.; Telser, Joshua

doi:10.1021/acs.inorgchem.5b01796

Cited by 36 publications

(47 citation statements)

References 175 publications

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“…Due to instrument limitations, the MCD data were unable to be collected below 9500 cm −1 . The notches in the MCD spectra at ∼10 000 and ∼12 500 cm −1 are artifacts of the instrument detector and have been observed in other samples 85.…”

supporting

confidence: 57%

Spectroscopic and Computational Investigations of a Mononuclear Manganese(IV)-Oxo Complex Reveal Electronic Structure Contributions to Reactivity

et al. 2016

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The mononuclear Mn(IV)-oxo complex [Mn(O)(N4py)], where N4py is the pentadentate ligand N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine, has been proposed to attack C-H bonds by an excited-state reactivity pattern [ Cho, K.-B.; Shaik, S.; Nam, W. J. Phys. Chem. Lett. 2012 , 3 , 2851 - 2856 (DOI: 10.1021/jz301241z )]. In this model, a E excited state is utilized to provide a lower-energy barrier for hydrogen-atom transfer. This proposal is intriguing, as it offers both a rationale for the relatively high hydrogen-atom-transfer reactivity of [Mn(O)(N4py)] and a guideline for creating more reactive complexes through ligand modification. Here we employ a combination of electronic absorption and variable-temperature magnetic circular dichroism (MCD) spectroscopy to experimentally evaluate this excited-state reactivity model. Using these spectroscopic methods, in conjunction with time-dependent density functional theory (TD-DFT) and complete-active space self-consistent-field calculations (CASSCF), we define the ligand-field and charge-transfer excited states of [Mn(O)(N4py)]. Through a graphical analysis of the signs of the experimental C-term MCD signals, we unambiguously assign a low-energy MCD feature of [Mn(O)(N4py)] as the E excited state predicted to be involved in hydrogen-atom-transfer reactivity. The CASSCF calculations predict enhanced Mn-oxyl character on the excited-state E surface, consistent with previous DFT calculations. Potential-energy surfaces, developed using the CASSCF methods, are used to determine how the energies and wave functions of the ground and excited states evolved as a function of Mn═O distance. The unique insights into ground- and excited-state electronic structure offered by these spectroscopic and computational studies are harmonized with a thermodynamic model of hydrogen-atom-transfer reactivity, which predicts a correlation between transition-state barriers and driving force.

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confidence: 57%

Spectroscopic and Computational Investigations of a Mononuclear Manganese(IV)-Oxo Complex Reveal Electronic Structure Contributions to Reactivity

et al. 2016

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“…Bulky aromatic heterocycles derived from phosphaalkynes, which are much poorer donors than Cp-based ligands, can also stabilize Sc II complexes 56 . An improved synthesis and full electronic characterization of py 4 TiCl 2 ( 5 ) 57 , a rare example of a Ti II coordination complex, have recently been reported, building upon earlier studies by several groups 58,59 . The chemistry of low-valent early transition metal isocyanide 60–62 and arene complexes 63,64 has also continued to expand, including the recent synthesis of the formally Ta 0 complex 6 (REF 60 ).…”

Section: Generation Of Low-valent Complexesmentioning

confidence: 90%

Modern applications of low-valent early transition metals in synthesis and catalysis

et al. 2018

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Low-valent early transition metals are often intrinsically highly reactive as a result of their strong propensity toward oxidation to more stable high-valent states. Harnessing these highly reducing complexes for productive reactivity is potentially powerful for C-C bond construction, organic reductions, small-molecule activation and many other reactions that offer orthogonal chemoselectivity and/or regioselectivity patterns to processes promoted by late transition metals. Recent years have seen many exciting new applications of low-valent metals through building new catalytic and/or multicomponent reaction manifolds out of classical reactivity patterns. In this Review, we survey new methods that employ early transition metals and invoke low-valent precursors or intermediates in order to identify common themes and strategies in synthesis and catalysis.

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“…Divalent group 4 metal ions are potential candidates for spin-flip emissive d 2 complexes [37,38]. However, stable complexes of, e.g., Ti II are quite rare and their investigation so far focused on electrochemical properties and reactivity [133][134][135][136][137][138][139]. Thus, no spin-flip luminescence with Ti II complexes has been reported to date, while examples for luminescent solid-state materials containing Ti 2+ , such as MgCl 2 :Ti 2+ and NaCl:Ti 2+ , exist [37,38].…”

Section: Spin-flip Emitters Based On Other Transition Metals and Elec...mentioning

confidence: 99%

Spin-flip luminescence

Kitzmann

Moll

Heinze

2022

Photochem Photobiol Sci

149

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In molecular photochemistry, charge-transfer emission is well understood and widely exploited. In contrast, luminescent metal-centered transitions only came into focus in recent years. This gave rise to strongly phosphorescent CrIII complexes with a d3 electronic configuration featuring luminescent metal-centered excited states which are characterized by the flip of a single spin. These so-called spin-flip emitters possess unique properties and require different design strategies than traditional charge-transfer phosphors. In this review, we give a brief introduction to ligand field theory as a framework to understand this phenomenon and outline prerequisites for efficient spin-flip emission including ligand field strength, symmetry, intersystem crossing and common deactivation pathways using CrIII complexes as instructive examples. The recent progress and associated challenges of tuning the energies of emissive excited states and of emerging applications of the unique photophysical properties of spin-flip emitters are discussed. Finally, we summarize the current state-of-the-art and challenges of spin-flip emitters beyond CrIII with d2, d3, d4 and d8 electronic configuration, where we mainly cover pseudooctahedral molecular complexes of V, Mo, W, Mn, Re and Ni, and highlight possible future research opportunities. Graphical abstract

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Electronic Structure and Reactivity of a Well-Defined Mononuclear Complex of Ti(II)

Cited by 36 publications

References 175 publications

Spectroscopic and Computational Investigations of a Mononuclear Manganese(IV)-Oxo Complex Reveal Electronic Structure Contributions to Reactivity

Spectroscopic and Computational Investigations of a Mononuclear Manganese(IV)-Oxo Complex Reveal Electronic Structure Contributions to Reactivity

Modern applications of low-valent early transition metals in synthesis and catalysis

Spin-flip luminescence

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