A Review on Molecular Electrochemistry of Metallocene Dichloride and Dimethyl Complexes of Group 4 Metals: Redox Properties and Relation with Optical Ligand-to-Metal Charge Transfer Transitions

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

doi:10.1135/cccc20010185

Cited by 28 publications

(25 citation statements)

References 116 publications

(135 reference statements)

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“…However, solvent effects and transitions involving the SHOMO and SLUMO (and potentially other MOs), as well as changes in relative orbital energies and electron configurations, can significantly complicate the situation to the extent that one can generally only get meaningful information by comparing closely related compounds [25,26]. Although group 4 half-sandwich complexes have been investigated by cyclic voltammetry and UV/visible spectroscopy [26][27][28][29], the processes and orbitals involved are quite different from those observed in diindenyl ferrocene systems: Firstly, oxidation of the group 4 complexes occurs from ligand-based orbitals rather than metal-based d orbitals [26,29,30], and, secondly, although the UV/visible spectroscopy provides information on the HOMO-LUMO gap in both systems, it is an LMCT process from the indenyl to a d 0 metal centre in the group 4 complexes [26,27,29] rather than a d-d transition of the d 6 Fe atom [19,31]. One must be careful, therefore, when making comparisons between these systems.…”

Section: Resultsmentioning

confidence: 99%

Electrochemistry and UV/visible spectroscopy of phosphino-substituted bis(η5-indenyl)iron(II) complexes

Curnow

Fern

Jenkins

2006

Journal of Organometallic Chemistry

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Six phosphino-functionalized diindenyl ferrocenes have been characterized by UV/visible spectroscopy and cyclic voltammetry in dichloromethane. The complexes contain the following ligands: 1-diphenylphosphino-(1), 1-diphenylphosphino-2-methyl-(2), 1-diphenylphosphino-3-methyl-(3), 1-diphenylphosphino-3-trimethylsilyl-(4), 1-diphenylphosphino-2,3-dimethyl-(5), and 1-diphenylphosphino-4,7-dimethyl-indenide (6). The cyclic voltammetry shows an approximately additive relationship between oxidation potential and the type of substituent and its ring position, but with increasing substitution leading to lower than otherwise expected oxidation potentials. The UV/visible spectra show two absorptions with the low energy band moving to lower energy with increasing substitution on the C 5 ring.

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Section: Resultsmentioning

confidence: 99%

Electrochemistry and UV/visible spectroscopy of phosphino-substituted bis(η5-indenyl)iron(II) complexes

Curnow

Fern

Jenkins

2006

Journal of Organometallic Chemistry

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“…Earlier, it was demonstrated that the same MOs are involved in both optical and redox electron transfer in these metallocenes [2,[5][6][7].…”

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“…Experimental study of the properties of organometallic compounds of early transition metals [2,3] and their shortlived intermediates (catalysis [4], redox processes [5], including free radical ones, etc.) is a difficult task.…”

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Photoisomerization and the nature of bond cleavage in π-complexes of early transition metals in photo and redox processes

2005

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Determination of the energy and other characteristics of the frontier orbitals in complex molecules is a fundamental problem in photochemistry [1], coordination chemistry, and metal-complex catalysis. Experimental study of the properties of organometallic compounds of early transition metals [2,3] and their shortlived intermediates (catalysis [4], redox processes [5], including free radical ones, etc.) is a difficult task. In this work, the reversible isomerization of bridged metallocene was investigated for the first time; we also proposed an approach to comparative estimation of the factors that cause breaking of the structural integrity of d 0 -metal ion complexes upon single-photon excitation such as charge transfer from ligand to metal (LMCT), electrochemical transfer of an electron ( e -) to the lowest unoccupied MO (LUMO) (reduction), and generation of a vacancy ( h + ) on the highest occupied MO (HOMO) (oxidation). Earlier, it was demonstrated that the same MOs are involved in both optical and redox electron transfer in these metallocenes [2,[5][6][7].In the photolysis of Group IVB metallocenes with visible light in the absence of active additives, various photochemical reactions such as dissociation, isomerization, etc. can occur [2,5,8,9]. In this study, we discovered reversible photoisomerization of the ansa -metallocene complex C 6 H 10 ( IndH 4 ) 2 ZrCl 2 (Ind is indenyl) in media with different solvation abilities, particularly, in cyclopentadiene (most likely, the photoisomerization follows the dissociative mechanism through a biradical excited state). The complex C 6 H 10 ( IndH 4 ) 2 ZrCl 2 exists as rac-and meso -isomers. Its dissolved forms were examined by optical spectroscopy: single crystals of the rac -isomer (electron transfer between the frontier orbitals; λ LMCT = 366 nm) and a racemic mixture of rac-(55%) and meso -isomers (45%). The structure of the rac -isomer was confirmed by X-ray diffraction analysis; the composition of the racemic mixture was determined from NMR data (our unpublished data).The absorption and luminescence spectra of the racisomer are slightly shifted toward shorter wavelengths ( ∆ E 0-0 = 150, ∆ E Ï ‡ı ≈ 500 cm -1 ) as compared to the spectra of the racemic mixture containing the meso -isomer (the rac -isomer mainly absorbs at 300 nm, while the meso -isomer absorbs at 360 nm). The radiation lifetimes of the rac -isomer and the racemic mixture are the same within the instrumental error (i.e., τ rac ≥ τ meso ). When exposed to UV light with λ ≈ 310 nm, the dissolved rac -isomer transforms to the racemic mixture (more intense absorption peak at 360 nm), while exposure of the racemic mixture to UV light with λ = 366 nm makes it pass into the rac -isomer (more intense absorption peak at 300 nm). Such transitions occur repeatedly; however, prolonged irradiation of the complex results in its decomposition.Our calculations performed with the Latimer diagram [10] for Cp 2 MCl 2 (where Cp is cyclopentadienyl and M = Ti, Zr, and Hf) showed that π -complexes of early transitio...

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“…The long lived excited state of complex 1 is formed due to the ligand to metal charge transfer, which is rarely observed in the photophysics of organometallic compounds. [10][11][12] Solutions of single crystals were studied. All solvents used were multiply purified from traces of impurities, oxy gen, and moisture and subjected to freezing-thawing out cycles using known procedures.…”

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Intense luminescence of the group IVB metal π-complex in solutions at room temperature

2007

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Studies of luminescence, in particular, phosphore scence, are significant in development of the theory of triplet state. 1-3 An important role in photophysics and photochemistry belongs to the solvent, which can also be a reactant and specific quencher of luminescence: the majority of molecules do not luminesce in the liquid phase. Compounds of Group IVB metals 4,5 gained special sig nificance as catalysts of many organic reactions, includ ing olefin polymerization 6-8 and activation of small inert molecules (N 2 , CO, CO 2 , etc.). 9 However, no systematic studies on the interaction of organometallic complexes of early transition metals (in particular, Group IVB metals) with the medium were carried out.The previous study of the Cp 2 M IV Cl 2 complexes (Cp = η 5 C 5 H 5 , M = Ti, Zr, Hf) has revealed 10 their lumines cence in solid solutions at low temperature and in poly crystals at low and elevated temperatures. In the present work, we studied for the first time the d 0 metallocene complex based on the Group IVB metal, namely, racemate of trans 1,2 [(bis(η 5 tetrahydroindenyl)cyclohexane]zir conium(IV) dichloride, rac C 6 H 10 (IndH 4 ) 2 ZrCl 2 (1), which intensely luminesces in liquid solutions. The long lived excited state of complex 1 is formed due to the ligand to metal charge transfer, which is rarely observed in the photophysics of organometallic compounds. 10-12Solutions of single crystals were studied. All solvents used were multiply purified from traces of impurities, oxy gen, and moisture and subjected to freezing-thawing out cycles using known procedures. 10-12 The concentration of the complex in solutions was 10 -5 -10 -4 mol L -1 . Spec tral measurements were conducted by an earlier described procedure. 13 Complex 1 luminesces in the liquid phase at room temperature (the luminescence lifetime in hydrocarbon media is ∼2 ms at 77 K). The absorption and lumine scence spectra of complex 1 at 20 °C in acetonitrile and methylcyclohexane are shown in Fig. 1. It can be seen that an increase in the polarity of the solvent results in the red shift of the absorption spectra and (to a greater extent) luminescence spectra: up to 1000 cm -1 and more. The quantum yields (Φ) of luminescence of solutions pre sented in Fig. 2 (to Φ ∼30% in dichloromethane) are Fig.

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A Review on Molecular Electrochemistry of Metallocene Dichloride and Dimethyl Complexes of Group 4 Metals: Redox Properties and Relation with Optical Ligand-to-Metal Charge Transfer Transitions

Cited by 28 publications

References 116 publications

Electrochemistry and UV/visible spectroscopy of phosphino-substituted bis(η5-indenyl)iron(II) complexes

Electrochemistry and UV/visible spectroscopy of phosphino-substituted bis(η5-indenyl)iron(II) complexes

Photoisomerization and the nature of bond cleavage in π-complexes of early transition metals in photo and redox processes

Intense luminescence of the group IVB metal π-complex in solutions at room temperature

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