Stereochemically Nonrigid Organometallic Compounds. I. π-Cyclopentadienyliron Dicarbonyl σ-Cyclopentadiene<sup>1</sup>

Bennett, M. J.; Cotton, F. Albert; Davison, A.; Faller, J. W.; Lippard, Stephen J.; Morehouse, Sheila M.

doi:10.1021/ja00971a012

Cited by 139 publications

(46 citation statements)

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“…The average C-C bond length in the ring is 1.38 A. This is similar to the average C-C bond length of 1.40.~ in the ncyclopentadienyl ring of (n-CsHs)Fe(a-CsHs)(CO)2 whose crystal structure was determined by Bennett, Cotton, Davidson, Faller, Lippard & Morehouse (1966). The difference between the copper and phosphorus distances to the mean plane through the CsH5 ring is equal to the Cu-P bond length.…”

Section: Resultssupporting

confidence: 66%

The crystal structure of π-cyclopentadienyl(triethylphosphine)copper(I), π-C₅H₅CuP(C₂H₅)₃

Delbaere¹,

McBride²,

Ferguson³

1970

Acta Crystallogr Sect B

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Cyclopentadienyl(triethylphosphine)copper(1), CsHsCuP(C2Hs)3, has the cell dimensions a=8.60+ 0.02, b= 11.04+0.03, c= 7.67 + 0.02 ~ and fl= 115"3+0"05 °. The space group of the crystal is P2j/m and Z= 2. The structure was solved, using the intensities obtained from Weissenberg photographs, by three-dimensional Patterson, Fourier and least-squares methods to a final R index of 0.145 when a set of hydrogen atoms was included at chemically expected positions. The analysis revealed the presence of two enantiomers distributed apparently equally and randomly throughout the crystal. The C5H5 ring is n-bonded to the copper atom with average bond lengths of 2.24 for Cu-C and 1.38 A. for C-C. The Cu-P bond length is 2.14. The presence of a n-bonded C5H5 ring is in accord with the thermal stability of the compound. CsHsCuP(C2Hs)3 is monomeric and obeys the inert gas rule.

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Section: Resultssupporting

confidence: 66%

The crystal structure of π-cyclopentadienyl(triethylphosphine)copper(I), π-C₅H₅CuP(C₂H₅)₃

Delbaere¹,

McBride²,

Ferguson³

1970

Acta Crystallogr Sect B

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“…Such a concept has been proposed by Momii et al 22 for the NMR equivalence of 11 B in B5O6(OH)4 -. Piper et al 23 and Bennett et al 24 also proposed the same concept of rearrangements for the NMR equivalence of 1 H in (C6H5)2Hg and π-cyclopentadienyliron dicarbonyl σ-cyclopentadiene, respectively.…”

Section: B Nmr Study Of Pcba Solutions At Various Phmentioning

confidence: 96%

11B NMR Study of p-Carboxybenzeneboronic Acid Ions for Complex Formation with Some Monosaccharides

2003

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Boron neutron capture therapy (BNCT) is a form of radiation therapy that has two components. The first is the delivery of boron to a tumor. 1 This can be achieved chemically by boronating a tumor-seeking compound, which is stable in vivo and infused intravenously into a subject body. Then, the boronated compound selectively accumulates sufficient amounts in the tumor cells. The second is to irradiate with thermal neutrons. 1 The capture of a thermal neutron by a 10 B nucleus in a tumor causes the nucleus to split, releasing an α ( 4 He)-particle and a lithium ( 7 Li) nucleus in opposite directions. 2A suitable compound for BNCT must have low toxicity, high solubility in water for rapid injection, and a much higher concentration in the tumor cells than in normal cells. 3 A vast array of 10 B-enriched compounds have been synthesized and tested for BNCT. 4 Among a large number of boron compounds, 10 B-enriched p-carboxybenzeneboronic acid (PCBA) was firstly used in clinical trials as a BNCT agent for some brain-tumor patients. 3 According to those trials, PCBA was one of the most promising compounds as a BNCT drug from the standpoint of the tumor/brain boron ratio, but was found to have relatively high toxicity. 5 The solubility of PCBA is so low at physiological pH 7.4 that it is insufficient for medical uses. This compound dissolves in water by a sufficient amount for injection into patients, at pH 9.4. 6 Therefore, an experiment was carried out as Na-salt of PCBA adjusted as this pH. An injection of this alkaline solution resulted in respiratory depression, seizure, and often the death of some patients. 6,7 The authors suggested that if the solubility of PCBA increased at the physiological pH, then the above mentioned toxicity should be decreased.It is well-known that boric acid 8-10 and pboronophenylalanine (p-BPA) react with monosaccharide to form a soluble anionic complex. 11-13 PCBA has a boronic acid group. Therefore, it can be expected that the boronic acid moiety of PCBA may react with a monosaccharide to form an easily soluble anionic PCBA-monosaccharide complex, as indicated in Eq.(1), which should be recommended as an injection to patients for the BNCT of both brain tumor and malignant melanoma.Boronate anion of PCBA + Monosaccharide Complex.According to the above view, our interest has become involved with the characterization of PCBA ions in solution, and with the formation of soluble anionic complexes between the PCBA ion and a neutral polyhydroxy-compound of monosaccharides at the physiological pH. However, to the best of our knowledge, 11 B NMR studies for both the characterization of PCBA ions and for PCBA complexation with monosaccharides have not been reported so far.In this paper, we wish to describe the chemical behaviors of PCBA ions at various pH, the complex formation equilibria of the PCBA ion with several monosaccharides at the physiological pH based on an investigation of the 11 B NMR spectra, and the possible structure of this complex. Experimental ReagentsUnless stated otherwise, all ...

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“…The greater reliability of G ‡ determined from the most accurate rate obtained at a given temperature suggests that one should focus on comparisons of G ‡ values. The errors and problems in evaluating rates has been reviewed elsewhere, 34-37 but a convenient and accurate evaluation of the rate can be obtained as the resonances begin to broaden above the limiting low-temperature spectrum by using equation (3). k = πW (3) In this expression, k is the first-order rate constant for leaving one site and W is the broadening in excess of the natural line-width (in Hz).…”

Section: Measurement Of Barriers To Interconversionmentioning

confidence: 99%

“…The errors and problems in evaluating rates has been reviewed elsewhere, 34-37 but a convenient and accurate evaluation of the rate can be obtained as the resonances begin to broaden above the limiting low-temperature spectrum by using equation (3). k = πW (3) In this expression, k is the first-order rate constant for leaving one site and W is the broadening in excess of the natural line-width (in Hz). Thus, if one assumes that the lowtemperature limit is reached when the excess broadening is ≈1 Hz, one can make a fairly accurate estimate of G ‡ from this temperature (see Table 1).…”

Section: Measurement Of Barriers To Interconversionmentioning

confidence: 99%

“…There are, however, alternative paths that differ in the details by which nuclei are permuted among the sites. It was well known in 1966 that the variations in line-width in the NMR spectra allowed the determination of rates of rearrangement, but using NMR to distinguish possible mechanisms was first used 3 with the classic example of a fluxional organometallic, Cp 2 Fe(CO) 2 (2). Although this molecule had been formulated as (η 5 -Cp)Fe(CO) 2 (η 1 -Cp), only singlets were originally observed for the cyclopentadienyl ligands in the 1 H NMR spectrum.…”

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confidence: 99%

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Stereochemical Nonrigidity of Organometallic Complexes

Faller¹

2005

Encyclopedia of Inorganic Chemistry

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Compounds that undergo intramolecular rearrangements at rates that affect the NMR line shapes in generally accessible temperature ranges are described as stereochemically nonrigid. Analysis of 1D and 2D NMR spectra as a function of temperature often allow the rates, as well as the mechanisms of interconversion of conformers or isomers, to be determined. Examples were selected to illustrate the importance of stereochemical nonrigidity in reactivity and the potential for affecting stereochemistry in the products of reactions.

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Stereochemically Nonrigid Organometallic Compounds. I. π-Cyclopentadienyliron Dicarbonyl σ-Cyclopentadiene¹

Cited by 139 publications

References 1 publication

The crystal structure of π-cyclopentadienyl(triethylphosphine)copper(I), π-C₅H₅CuP(C₂H₅)₃

The crystal structure of π-cyclopentadienyl(triethylphosphine)copper(I), π-C₅H₅CuP(C₂H₅)₃

11B NMR Study of p-Carboxybenzeneboronic Acid Ions for Complex Formation with Some Monosaccharides

Stereochemical Nonrigidity of Organometallic Complexes

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Stereochemically Nonrigid Organometallic Compounds. I. π-Cyclopentadienyliron Dicarbonyl σ-Cyclopentadiene1

Cited by 139 publications

References 1 publication

The crystal structure of π-cyclopentadienyl(triethylphosphine)copper(I), π-C5H5CuP(C2H5)3

The crystal structure of π-cyclopentadienyl(triethylphosphine)copper(I), π-C5H5CuP(C2H5)3

11B NMR Study of p-Carboxybenzeneboronic Acid Ions for Complex Formation with Some Monosaccharides

Stereochemical Nonrigidity of Organometallic Complexes

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Stereochemically Nonrigid Organometallic Compounds. I. π-Cyclopentadienyliron Dicarbonyl σ-Cyclopentadiene¹

The crystal structure of π-cyclopentadienyl(triethylphosphine)copper(I), π-C₅H₅CuP(C₂H₅)₃

The crystal structure of π-cyclopentadienyl(triethylphosphine)copper(I), π-C₅H₅CuP(C₂H₅)₃