Beyond Samarium Diiodide: Vistas in Reductive Chemistry Mediated by Lanthanides(II)

Szostak, Michal; Procter, David J.

doi:10.1002/anie.201201065

Cited by 157 publications

(100 citation statements)

References 284 publications

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“…In addition to divalent Eu, Yb, and Sm solid-state complexes, other isolable divalent lanthanide complexes comprising Tm, Dy, and Nd have previously been confirmed by X-ray crystallography. 28,29 These divalent complexes are strong reducing agents due to the much lower reduction potentials of these Ln as compared with Eu, Yb, and Sm. 24,30 Consistent with this notion, the Nd(L) 2 2+ , Dy(L) 2…”

Section: +mentioning

confidence: 99%

Dissociation of Diglycolamide Complexes of Ln³⁺ (Ln = La–Lu) and An³⁺ (An = Pu, Am, Cm): Redox Chemistry of 4f and 5f Elements in the Gas Phase Parallels Solution Behavior

et al. 2014

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Tripositive lanthanide and actinide ions, Ln(3+) (Ln = La-Lu) and An(3+) (An = Pu, Am, Cm), were transferred from solution to gas by electrospray ionization as Ln(L)3(3+) and An(L)3(3+) complexes, where L = tetramethyl-3-oxa-glutaramide (TMOGA). The fragmentation chemistry of the complexes was examined by collision-induced and electron transfer dissociation (CID and ETD). Protonated TMOGA, HL(+), and Ln(L)(L-H)(2+) are the major products upon CID of La(L)3(3+), Ce(L)3(3+), and Pr(L)3(3+), while Ln(L)2(3+) is increasingly pronounced beyond Pr. A C-Oether bond cleavage product appears upon CID of all Ln(L)3(3+); only for Eu(L)3(3+) is the divalent complex, Eu(L)2(2+), dominant. The CID patterns of Pu(L)3(3+), Am(L)3(3+), and Cm(L)3(3+) are similar to those of the Ln(L)3(3+) for the late Ln. A striking exception is the appearance of Pu(IV) products upon CID of Pu(L)3(3+), in accord with the relatively low Pu(IV)/Pu(III) reduction potential in solution. Minor divalent Ln(L)2(2+) and An(L)2(2+) were produced for all Ln and An; with the exception of Eu(L)2(2+) these complexes form adducts with O2, presumably producing superoxides in which the trivalent oxidation state is recovered. ETD of Ln(L)3(3+) and An(L)3(3+) reveals behavior which parallels that of the Ln(3+) and An(3+) ions in solution. A C-Oether bond cleavage product, in which the trivalent oxidation state is preserved, appeared for all complexes; charge reduction products, Ln(L)2(2+) and Ln(L)3(2+), appear only for Sm, Eu, and Yb, which have stable divalent oxidation states. Both CID and ETD reveal chemistry that reflects the condensed-phase redox behavior of the 4f and 5f elements.

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Section: +mentioning

confidence: 99%

Dissociation of Diglycolamide Complexes of Ln³⁺ (Ln = La–Lu) and An³⁺ (An = Pu, Am, Cm): Redox Chemistry of 4f and 5f Elements in the Gas Phase Parallels Solution Behavior

et al. 2014

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“…Brown crystals formed over 3 days, which were separated by filtration and dried under reduced pressure to yied 170 mg (88%) of X-rayquality crystals of 3. 1 Synthesis of 4. To a brown solution of 3 in toluene (50 mg, 0.074 mmol) was added 1 equiv of bipyrdine (12 mg, 0.077 mmol), and the resulting solution was warmed to 70°C over a period of 3 days, after which the solution turned dark green.…”

Section: ■ Experimental Sectionmentioning

confidence: 99%

Multiple One-Electron Transfers in Bipyridine Complexes of Bis(phospholyl) Thulium

et al. 2014

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The synthesis of original neutral bis-(phospholyl) thulium complexes, Dtp 2 Tm(L), where L is tetramethylbiphosphinine (tmbp) and bipyridine (bipy), is reported. The electronic structures of these complexes have been investigated and it appears that, in both cases, an electron transfer occurs from the divalent metal to the ligand, a consequence of the strong reduction potential of the bis(phospholyl) thulium fragment, Dtp 2 Tm. When 1 equiv of bipyridine is added to the Dtp 2 Tm(tmbp) complex, another electron transfer occurs to form the Dtp 2 Tm(bipy) complex along with free tmbp ligand. Astonishingly, despite the apparent trivalent nature of the thulium center, the Dtp 2 Tm(bipy) complex is still reactive toward neutral bipyridine to form a new complex in which one phospholyl ligand is replaced by a bipyridine radical anion. An experimental kinetic analysis is reported to rationalize this unprecedented redox reaction with thulium and reveals an associative type of mechanism. ■ INTRODUCTIONThe use of divalent lanthanide halides as reductive sources of single electrons is a current topic of interest in organic chemistry. 1 While the use of SmI 2 has been known for more than 30 years, the reason for new recent developments lies in the discovery of easy access to nonclassical divalent lanthanides such as TmI 2 , DyI 2 , and NdI 2 , 2−7 as opposed to the classical SmI 2 and YbI 2 . 8 The first report of a Tm(II) organometallic complex in 2002 9 opened a new area of synthetic organometallic chemistry 10 and electron transfer reactivity, among them the reports of small-molecule activationincluding N 2  pyridine reductive coupling, and strong bond cleavage. 11−14 A strategy to prevent reductive side reactions in the synthesis of divalent thulium complexes is to suit the reactive metal ion with bulky ligands, and cyclopentadienyl or phospholyl ligands bearing bulky tert-butyl or trismethylsilyl groups proved to be efficient. 9,15,16 The fact that the steric hindrance around the reactive metal center plays a direct role in the eventuality of an electron transfer to occur or not is not in doubt 17−21 and makes chemical sense. However, in contradiction to this, in organolanthanides, the same increased bulk around a trivalent metal center−that is supposed to be inert to redox chemistryis known to induce a reductive chemistry similar to that observed with divalent lanthanide complexes. 22 This type of reactivity discovered and substantiated over the past decade by Evans and his group is named "sterically induced reduction" and remains an attractive research area. 23,24 In these reactions the electron is provided from a bulky ligand that inclines to reduce a substrate, although in the absence of the lanthanide metal center no redox reaction would occur and therefore these singular reactions prompt the question of the way organolanthanides manipulate electrons within the overall edificemetal, ligand, and substrate.Additionally, it constitutes another topic of broad interest, since there are reports of lanthanide complexes...

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“…Redox behaviour of trivalent lanthanide ions is expected to be quite interesting, especially of Eu, Yb and Sm, having electronic configuration approaching or attending half filled or full filled 4f orbitals. [19][20][21][22][23][24][25][26][27][28][29] In fact, limited studies have been carried out on the ET processes involving divalent lanthanide ions as the electron donors. [15][16][17][18] The one electron reduction potential of Eu(III) is most favourable in the Table 1 Electronic configurations of trivalent lanthanide ions along with their one-electron reduction potentials [15][16][17][18] series due to the formation of a half-filled f-subshell in Eu(II) stabilizing the product state.…”

Section: Introductionmentioning

confidence: 99%

“…One-electron reduction potentials of trivalent lanthanide ions E Ln(III)/Ln(II) are listed in Table 1. [23][24][25][26][27][28][29] For, trivalent lanthanide ions, even though their reduction potentials are not very favorable, yet they can participate in a photoinduced electron transfer (PET) reaction, as the excitation energy adds favourably towards the energetics of the ET process. Similarly the one electron reduction potential of Yb(III) is favourable due to the formation of a completely filled f-subshell in Yb(II).…”

Section: Introductionmentioning

confidence: 99%

Intriguing multichannel photoinduced electron transfer in lanthanide(iii)–diphenylamine systems

Verma

Sawant

Pal

2015

Phys. Chem. Chem. Phys.

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Photoinduced electron transfer (PET) and charge transfer (CT) interactions of trivalent lanthanide ions (Ln(3+)) with a fluorogenic diphenylamine (DPA) donor in aqueous solution have been investigated. Present donor-acceptor systems have a relevance to the leaching out and mitigation of lanthanide ions in the geoenvironment where DPA finds its presence as industrial and agricultural waste. The formation of weak ground state CT complexes in the present systems is confirmed from ground state absorption studies. There is no emissive exciplex formation as evidenced from steady-state (SS) fluorescence measurements. SS fluorescence quenching results, however, indicate substantial static quenching, attributed to ground state complex formation. Time-resolved (TR) fluorescence quenching results show a quite efficient dynamic quenching process. It is established that the TR fluorescence quenching of DPA by lanthanide ions is not due to energy transfer but due to PET from excited DPA to Ln(3+). Direct evidence for the PET mechanism is obtained from laser flash photolysis measurements where a transient absorption band at around 670 nm for the DPA cation is clearly evident. The time constant for DPA cation growth confirms that PET occurs from the excited S1 state of DPA to lanthanide ions. No correlation is, however, observed for the estimated quenching constants with the free energy changes of the PET reactions, due to the participation of multiple PET channels involving vacant electronic states of lanthanide ions. As realized, lanthanide ions are complex electron acceptors in the PET reactions and many extensive follow up studies are expected to understand the details of the multichannel PET in these geologically important redox systems.

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Beyond Samarium Diiodide: Vistas in Reductive Chemistry Mediated by Lanthanides(II)

Cited by 157 publications

References 284 publications

Dissociation of Diglycolamide Complexes of Ln³⁺ (Ln = La–Lu) and An³⁺ (An = Pu, Am, Cm): Redox Chemistry of 4f and 5f Elements in the Gas Phase Parallels Solution Behavior

Dissociation of Diglycolamide Complexes of Ln³⁺ (Ln = La–Lu) and An³⁺ (An = Pu, Am, Cm): Redox Chemistry of 4f and 5f Elements in the Gas Phase Parallels Solution Behavior

Multiple One-Electron Transfers in Bipyridine Complexes of Bis(phospholyl) Thulium

Intriguing multichannel photoinduced electron transfer in lanthanide(iii)–diphenylamine systems

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Beyond Samarium Diiodide: Vistas in Reductive Chemistry Mediated by Lanthanides(II)

Cited by 157 publications

References 284 publications

Dissociation of Diglycolamide Complexes of Ln3+ (Ln = La–Lu) and An3+ (An = Pu, Am, Cm): Redox Chemistry of 4f and 5f Elements in the Gas Phase Parallels Solution Behavior

Dissociation of Diglycolamide Complexes of Ln3+ (Ln = La–Lu) and An3+ (An = Pu, Am, Cm): Redox Chemistry of 4f and 5f Elements in the Gas Phase Parallels Solution Behavior

Multiple One-Electron Transfers in Bipyridine Complexes of Bis(phospholyl) Thulium

Intriguing multichannel photoinduced electron transfer in lanthanide(iii)–diphenylamine systems

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Dissociation of Diglycolamide Complexes of Ln³⁺ (Ln = La–Lu) and An³⁺ (An = Pu, Am, Cm): Redox Chemistry of 4f and 5f Elements in the Gas Phase Parallels Solution Behavior

Dissociation of Diglycolamide Complexes of Ln³⁺ (Ln = La–Lu) and An³⁺ (An = Pu, Am, Cm): Redox Chemistry of 4f and 5f Elements in the Gas Phase Parallels Solution Behavior