Paramagnetic moment measurements by nmr. A micro technique

Löliger, J.; Scheffold, Rolf

doi:10.1021/ed049p646

Cited by 158 publications

(99 citation statements)

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“…The spin state of 2 (in CH 3 CN) was determined using the 1 H NMR Evans method, 45–47 and gave a magnetic moment of 3.3 µ B at 15 °C which indicates that 2 is a low-spin ( S = 1) Fe IV =O species.…”

Section: Results and Analysesmentioning

confidence: 99%

[Fe^IV═O(TBC)(CH₃CN)]²⁺: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation

et al. 2012

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[FeIV=O(TBC)(CH3CN)]2+ (TBC = 1,4,8,11-tetrabenzyl-1,4,8,11-tetraazacyclotetradecane) is characterized and its reactivity differences relative to [FeIV=O(TMC)(CH3CN)]2+ (TMC = 1,4,8,11-tetramethyl-1,4,8,11-tetraazacyclotetradecane) are evaluated in hydrogen atom (H-atom) abstraction and oxo-transfer reactions. Structural differences are defined using X-ray absorption spectroscopy (XAS) and correlated to reactivities using density functional theory (DFT). The S = 1 ground states are highly similar and result in large activation barriers (~25 kcal/mol) due to steric interactions between the cyclam chelate and the substrate (e.g., ethylbenzene) associated with the equatorial π-attack required by this spin state. Conversely, H-atom abstraction reactivity on an S = 2 surface allows for a σ-attack with an axial substrate approach. This results in decreased steric interactions with the cyclam and a lower barrier (~9 kcal/mol). For [FeIV=O(TBC)(CH3CN)]2+, the S = 2 excited state in the reactant is lower in energy and therefore more accessible at the transition state due to a weaker ligand field associated with the steric interactions of the benzyl substituents with the trans-axial ligand. This study is further extended to the oxo-transfer reaction, which is a two-electron process requiring both σ and π electron transfer and thus a non-linear transition state. In oxo-transfer, the S = 2 has a lower barrier due to sequential vs. concerted (S = 1) two electron transfer which gives a high-spin ferric intermediate at the transition state. The [FeIV=O(TBC)(CH3CN)]2+ complex is more distorted at the transition state, with the iron farther out of the equatorial plane due to the steric interaction of the benzyl groups with the trans-axial ligand. This allows for better orbital overlap with the substrate, a lower barrier, and an increased rate of oxo-transfer.

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Section: Results and Analysesmentioning

confidence: 99%

[Fe^IV═O(TBC)(CH₃CN)]²⁺: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation

et al. 2012

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“…Infrared spectra were obtained on a JASCO FT-IR 6300 spectrometer via ATR on a ZnSe crystal. Magnetic susceptibility data was measured using the Evans Method at 293 K using a Varian 300 MHz NMR with ferrocene as the indicator [58]. Cyclic voltammograms were recorded in 0.1 M n-Bu 4 NPF 6 and 1.0 mM diruthenium species solution (THF or DMF, N 2 degassed) by a CHI620A voltammetric analyzer with a glassy carbon working electrode (diameter ¼ 2 mm), Pt-wire counter electrode, and a Ag/AgCl reference electrode with ferrocene used as an internal reference (E 1/2 ¼ 0.57 V, THF; 0.54 DMF) (Figs.…”

Section: General Proceduresmentioning

confidence: 99%

Diruthenium σ-iminophenylacetylide complexes from on-complex Schiff base condensation

Cummings

Geanes

Fanwick

et al. 2011

Journal of Organometallic Chemistry

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“…Im Hinblick auf eine moglichst effektive Fixierung einer chiralen Konformation des Ligand-Systems wurde vorerst das stark raumbeanspruchende 3,4,5, (4) (3,91), 670 (3.35). IR (KBr): 29708, 2930m, 2870(sh), 1600s, 1520vs, 1495vs, 1475vs, 1445m, 1395m, 1380m, 1370m, 1355w, 1300s, 1265m, 1250.…”

Section: Schema Iunclassified

Synthese chiraler Kobalt‐Komplexe mit planoid‐tetradentatem Ligand‐System

Härter

Wegmuth

Scheffold

et al. 1993

Helvetica Chimica Acta

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Synthesis of Cbiral Cobalt Complexes with Planoid-Tetradentate Ligand SystemThe synthesis of a series of Cbl-related, achiral Co"' complexes 9a-c as well as enantiomerically pure, C2-symmetric Co"' complexes 15 and 18, is reported (Schemes 3,5, and 7). The crystal structures of 9c and 15 were determined. Complex I8 acts as an enantioselective catalyst in the isornerization of I ,Qepiperoxides to hydroxycycloalkenones.Einleitung. - Es besteht daher ein Bedarf an synthetischen, B,,-ahnlichen Metallkomplex-Kataly-

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Paramagnetic moment measurements by nmr. A micro technique

Abstract: The technique described was elaborated for studying the kinetics of ligand rearrangements of transition metal complexes (porphin and eorrin type metal complexes) (1).

Cited by 158 publications

References 1 publication

[Fe^IV═O(TBC)(CH₃CN)]²⁺: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation

[Fe^IV═O(TBC)(CH₃CN)]²⁺: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation

Diruthenium σ-iminophenylacetylide complexes from on-complex Schiff base condensation

Synthese chiraler Kobalt‐Komplexe mit planoid‐tetradentatem Ligand‐System

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Paramagnetic moment measurements by nmr. A micro technique

Abstract: The technique described was elaborated for studying the kinetics of ligand rearrangements of transition metal complexes (porphin and eorrin type metal complexes) (1).

Cited by 158 publications

References 1 publication

[FeIV═O(TBC)(CH3CN)]2+: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation

[FeIV═O(TBC)(CH3CN)]2+: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation

Diruthenium σ-iminophenylacetylide complexes from on-complex Schiff base condensation

Synthese chiraler Kobalt‐Komplexe mit planoid‐tetradentatem Ligand‐System

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[Fe^IV═O(TBC)(CH₃CN)]²⁺: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation

[Fe^IV═O(TBC)(CH₃CN)]²⁺: Comparative Reactivity of Iron(IV)-Oxo Species with Constrained Equatorial Cyclam Ligation