Electrochemical versus optical insight in frontier orbitals of Ti(IV), Zr(IV), and Hf(IV) bent metallocenes

Loukova, G. V.; Strelets, V. V.

doi:10.1016/s0022-328x(00)00361-2

Cited by 34 publications

(16 citation statements)

References 27 publications

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“…Accordingly, the slow decomposition of photoexcited Cp 2 TiCl 2 and Cp 2 TiBr 2 occurs via loss of neutral C 5 H 5 and not by loss of Cl or Br . The titanocenes exhibit an intense, long‐lived charge‐transfer phosphorescence at 77 K from the lowest ligand‐to‐metal charge‐transfer (LMCT) in the solid state (Cp 2 TiCl 2 : circa 800 μs) . At 25 °C, the lifetimes are decreased even in the solid state.…”

Section: Methodsmentioning

confidence: 99%

Titanocenes as Photoredox Catalysts Using Green‐Light Irradiation

et al. 2020

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Section: Methodsmentioning

confidence: 99%

Titanocenes as Photoredox Catalysts Using Green‐Light Irradiation

et al. 2020

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“…Correlations between electrochemical gap (difference between oxidation and reduction potentials) and ligand-to-metal charge transference (LMCT) energy were reported to [Cp 2 MCl 2 ] (M D Ti, Zr or Hf). 12 The catalytic species resulting from the interaction between [Me 2 Si(Cp) 2 MAO or trimethylaluminum (TMA) were also investigated by cyclic voltammetry. 13 Loukova et al 12,14,15 investigated [Cp 2 MCl 2 ] (M D Ti, Zr or Hf) systems, determining their reduction potentials, and correlated the electrochemical gap with the LMCT energy.…”

Section: Introductionmentioning

confidence: 99%

“…12 The catalytic species resulting from the interaction between [Me 2 Si(Cp) 2 MAO or trimethylaluminum (TMA) were also investigated by cyclic voltammetry. 13 Loukova et al 12,14,15 investigated [Cp 2 MCl 2 ] (M D Ti, Zr or Hf) systems, determining their reduction potentials, and correlated the electrochemical gap with the LMCT energy. Langmaier et al 16 studied some metallocene catalysts and estimated the relationship between the number of ligands in the Cp ring and their influence on the reduction potential.…”

Section: Introductionmentioning

confidence: 99%

Structural and electronic effects in metallocene catalysts studied by x‐ray techniques

et al. 2008

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A series of metallocenes, namely, [Cp 2 ZrCl 2 ], [(MeCp) 2 ZrCl 2 ], [(nBuCp) 2 ZrCl 2 ], [(iBuCp) 2 ZrCl 2 ], [(tBuCp) 2 ZrCl 2 ], [Et(Ind) 2 ZrCl 2 ], [Et(IndH 4 ) 2 ZrCl 2 ], and [MeSi 2 (Ind) 2 ZrCl 2 )] were analyzed by extended x-ray absorption fine structure (EXAFS) and x-ray photoelectron spectroscopy (XPS). Complementary techniques, UV-vis spectroscopy and cyclic and differential pulse voltammetry, were employed to characterize the organometallic complexes. The catalysts were evaluated in ethylene polymerization, having methylaluminoxane (MAO) as the cocatalyst, and the resulting polymers were characterized by gel permeation chromatography. The structural and electronic effects caused by the coordination sphere around the metal center and their effects on the catalytic activity and polymer characteristics are discussed.

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“…One of the most promising approaches to an understanding of the nature and properties of frontier orbitals of organometallic π complexes of Group IVB metalsmajor components of catalysts of a large number of organic syntheses-involves generation and study of electronically excited and ground redox states of molecules [1][2][3][4][5][6]. However, fundamental processes, such as energy and electron transfer, and properties of electronically excited states of organometallic compounds have been little studied partly due to the complexity of their synthesis and of manipulations with solutions of these compounds (especially with catalytic concentrations), which are extremely sensitive to moisture and oxygen traces and to minor impurities [7].…”

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Photophysical Properties and Coordination Interaction of d 0 Metallocenes with Unsaturated Hydrocarbons

2005

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One of the most promising approaches to an understanding of the nature and properties of frontier orbitals of organometallic π complexes of Group IVB metalsmajor components of catalysts of a large number of organic syntheses-involves generation and study of electronically excited and ground redox states of molecules [1-6]. However, fundamental processes, such as energy and electron transfer, and properties of electronically excited states of organometallic compounds have been little studied partly due to the complexity of their synthesis and of manipulations with solutions of these compounds (especially with catalytic concentrations), which are extremely sensitive to moisture and oxygen traces and to minor impurities [7].In this paper, we report on direct photophysical experiments that demonstrate for the first time the triplet nature of long-lived ligand-to-metal charge transfer (LMCT) excited states based on Group IVB metallocenes. A strong specific interaction and competitive coordination of substrates of Ziegler-Natta catalystsunsaturated hydrocarbons (UHCs)-with metallocene precursors of active centers have been observed. Our approach is based on the method of radiationless T − T energy transfer from organometallic complexes of d 0 metals to UHCs and on the shift of optical spectra.It should be noted that solutions of metallocenes Cp 2 M ( IV ) Cl 2 (M = Zr, Hf; C = 10 -5 -10 -4 mol L -1 ) in unsaturated and saturated hydrocarbons were prepared and the hydrocarbons used additionally purified from trace impurities and moisture immediately prior to photophysical experiments. Energy transfer between UHC molecules and aromatic or organometallic donors at low concentrations of the donor ( c D ≤ 10 -4 M) and acceptor ( c Ä ~ 0.1-0.5 M) and cooperative effects were studied in glassy solutions of individual UHCs and in binary glassy solutions (UHC acceptor-MCH (methylcyclohexane), 1 : 1 vol/vol) at 77 K.Group IVB metal ions in most compounds have a closed electronic configuration d 0 and act as rather hard acids. However, as follows from the photoproperties of the representative triad of π complexes Cp 2 M ( IV ) Cl 2 , their radiative lifetimes decrease manyfold in the series Ti 4+ → Zr 4+ → Hf 4+ (table). It is worth noting that this is a consequence of a considerable increase in spinorbit coupling typical for transition metal ions with open electronic subshells, i.e., for soft acids.Previously [2,4,5], we assumed that these longlived states (their experimental lifetimes are among the largest known for metal-containing molecules) are triplet. In this case, we should observe their luminescence quenching in the presence of a triplet quencher of UHCs with large S -T splitting energies. Note that the properties of excited, especially triplet, states of UHCs have not hitherto been systematically studied; therefore, they represent a fundamental independent problem [8,9]. Under the conditions of the series (in MCH glasses), the lowest triplet level of UHCs with one or several unconjugated C=C bonds (3,3-dimethyl-1-butene...

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Electrochemical versus optical insight in frontier orbitals of Ti(IV), Zr(IV), and Hf(IV) bent metallocenes

Cited by 34 publications

References 27 publications

Titanocenes as Photoredox Catalysts Using Green‐Light Irradiation

Titanocenes as Photoredox Catalysts Using Green‐Light Irradiation

Structural and electronic effects in metallocene catalysts studied by x‐ray techniques

Photophysical Properties and Coordination Interaction of d 0 Metallocenes with Unsaturated Hydrocarbons

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