The Nuclear Magnetic Resonance of Some Paramagnetic Transition Metal Acetylacetonates

Eaton, D. R.

doi:10.1021/ja01092a015

Cited by 175 publications

(51 citation statements)

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“…We also conclude that contact effects are more important than dipolar effects in determining changes in the isottopic shifts caused by ligand substitution. This is consistent with an earlier suggestion (16) regarding isotropic shifts in first row transition metal complexes but in no way disagrees with the results of Horrocks and Hall (12) showing that there is a substantial dipolar contribution to the absolute shifts in these Co(l1) compounds. …”

Section: Cornpoundtsupporting

confidence: 89%

Isotropic Nuclear Magnetic Resonance Shifts of Co(II) Complexes with Mixed Ligands

Eaton¹,

Chua²

1973

Can. J. Chem.

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Isotropic n.m.r. shifts of several Co(I1) complexes involving P-diketonate ligands are reported. A change of substituent on one P-diketonate ligand significantly affects the shifts of protons or fluorine atoms on the other P-diketonate ligand of the same compound. An argument is presented to suggest that these substituent shifts arise predominantly from contact rather than dipolar effects. The pattern of shifts is compared with that previously observed for P-diketone complexes of V(II1) and a similar interpretation is proposed.Les dtplacements chimiques isotropes (en r.m.n.) de plusieurs complexes du Co(I1) contenant des coordinats du type P-dicetonate ont t t t ttudits. Le changement d'un substituant sur un des coordinats P-dicktonate a modifi6 de manitre significative les dtplacements chimiques des protons ou des fluors sur I'autre coordinat P-dicttonate du m&me compost. On prCsente alors une hypothtse selon laquelle les deplacements chimiques des substituants proviennent principalement des effets de contact plut6t que des effets dipolaires. Le patron des dtplacements chimiques est compare a celui observe antCrieurement pour des complexes de V(II1) contenant des coordinats P-dicetone; une interprttation similaire est avancte.

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Section: Cornpoundtsupporting

confidence: 89%

Isotropic Nuclear Magnetic Resonance Shifts of Co(II) Complexes with Mixed Ligands

Eaton¹,

Chua²

1973

Can. J. Chem.

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“…A corollary of this assumption is that the observed shifts are proportional to the spin transferred according to the well known McConnell (7) model. In making this assumption we are following the conclusions of several groups (2)(3)(4) who have studied isotropic shifts of vanadium complexes. It should be realized though, that even if metal-to-ligand n* spin transfer is the dominant effect there may be smaller contributions from other mechanisms which could disrupt quantitative analysis.…”

Section: Analysis Of the Data Examination Of The Experimental Resultsmentioning

confidence: 99%

“…The ligand protons of this compound show large isotropic n.m.r. shifts relative to the free ligand or a diamagnetic complex which have been attributed (2)(3)(4) to contact interactions resulting from partial delocalization of the unpaired electrons from the metal d orbitals to the lowest unoccupied ligand K* orbitals. The basic experiment consists of measuring the change in isotropic shift of a given proton which occurs when there is a change of substituent on one of the other ligands.…”

Section: Introductionmentioning

confidence: 99%

Charge Density Distribution in Vanadium Complexes

Eaton¹,

Chua²

1973

Can. J. Chem.

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An empirical method for investigating the effect of substituents on the charge distribution of transition metal complexes is presented. This method is based on the measurement of n.m.r. chemical shifts of paramagnetic compounds and is applied to a series of V(II1) complexes. Measurements are reported on the sixteen isomers which result from the systematic replacement of CH3 groups by CF3 groups in V(II1) trisacetylacetonate. Ninety-nine of the possible 100 ' H and I9F chemical shifts have been measured. Substituent shifts of several thousand Hz are observed and have been interpreted using a model invoking charge redistribution in both a a n d norbitals. Similar experiments involving phenyl substituents are also reported. The model adopted enables the data to be fitted with a precision of around 2%. The substituent parameters derived from this model are discussed in terms of changes in electron density and the results compared with substituent effects in aromatic compounds. The important differences arise from the three dimensional nature of metal complexes which leads to interactions between the a and .rr electrons of a type not found in simple aromatic compounds. The significance of these results to the rationalization of ligand effects on ligand exchange and catalytic reactions is discussed.Afin d'Ctudier I'effet des substituants sur la distribution des charges dans des complexes de rnCtaux de transition, on a &labor& une methode empirique. Cette mCthode est basee sur la mesure des diplacements chimiques en r.m.n. de composes paramagnetiques et est appliquCe a une sCrie de complexes du V(II1). Des mesures furent effectuees sur les seize isomeres obtenus lors de la substitution systkrnatique des groupes CH3 par des groupes CF3 dans le tris V(1II)acCtylacCtonate. On a mesure 99 des 100 deplacements chimiques possibles du ' H et du I9F. Des deplacements induits par les substituants de plusieurs milliers de Hz ont CtC observes et ont 6tC interprCtCs en utilisant un modele impliquant des redistributions des charges dans les orbitales v e t n. On a rapport6 aussi des experiences similaires impliquant des substituants phenyles. Le modele adopte a permis d'obtenir des donnees avec une precision d'environ 2%. Les parametres des substituants obtenus de ce modele sont discutCs en fonction des changements dans la densite Clectronique et les resultats sont comparCs avec les effets de substituants dans les composCs aromatiques. Les diffkrences importantes proviennent de la nature tridimensionelle des complexes metalIiques qui implique des interactions entre les Clectrons a et nqui ne se retrouvent pas chez les composCs aromatiques simples. On discute de l'importance de ces resultats en ce qui a trait a la rationalisation des effets des coordinats sur I'tchange des coordinats ainsi que sur les rCactions catalytiques.[Traduit par le journal]Can. J . Chern., 51, 2260Chern., 51, (1973 Introduction We have previously reported (I) n.m.r. studies of complexes of V(II1) with mixed ligands and have suggested that experiments of th...

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“…In the praseodymium complex spectrum, aromatic ring protons of biphenolic ring are shifted to up field, whereas hetero-aromatic quinonolic ring protons and hydroxyl protons are oppositely shifted to lower field as compared with the diamagnetic lanthanum complex. Praseodymium generally induces up field shifts and, therefore, the resonances of complex have small isotropic shift in the proton spectrum [20,21,40,41]. The proton resonances of quinonolic aromatic ring displayed least downfield shift.…”

Section: Thermal Analysismentioning

confidence: 99%

“…From the literature reports [41], electron delocalization in lanthanide complexes may be obtained from NMR studies of paramagnetic species, provided nuclear relaxation times are short enough to allow well-resolved spectra to be obtained. A large number of reports are available in literature [20][21][22][23][24][25][26]41] about the paramagnetic shift (dipolar or pseudo-contact) in paramagnetic trivalent lanthanide complexes. The dipolar shift may arise from two sources, contact or pseudo-contact interactions when the paramagnetic centre is a rare earth ion; the pseudo-contact shift (dipolar) is expected to be substantial contributions, particularly in the absence of extensive conjugation.…”

Section: Thermal Analysismentioning

confidence: 99%

¹H NMR, spectroscopic and molecular modeling studies on paramagnetic lanthanide(III)-quercetin complexes

Ansari

2008

Main Group Chemistry

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The Nuclear Magnetic Resonance of Some Paramagnetic Transition Metal Acetylacetonates

Cited by 175 publications

References 3 publications

Isotropic Nuclear Magnetic Resonance Shifts of Co(II) Complexes with Mixed Ligands

Isotropic Nuclear Magnetic Resonance Shifts of Co(II) Complexes with Mixed Ligands

Charge Density Distribution in Vanadium Complexes

¹H NMR, spectroscopic and molecular modeling studies on paramagnetic lanthanide(III)-quercetin complexes

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The Nuclear Magnetic Resonance of Some Paramagnetic Transition Metal Acetylacetonates

Cited by 175 publications

References 3 publications

Isotropic Nuclear Magnetic Resonance Shifts of Co(II) Complexes with Mixed Ligands

Isotropic Nuclear Magnetic Resonance Shifts of Co(II) Complexes with Mixed Ligands

Charge Density Distribution in Vanadium Complexes

1H NMR, spectroscopic and molecular modeling studies on paramagnetic lanthanide(III)-quercetin complexes

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¹H NMR, spectroscopic and molecular modeling studies on paramagnetic lanthanide(III)-quercetin complexes