scholarly journals Synthesis, Characterization and Reactivity of Neutral Octahedral Alkyl-Cobalt(III) Complexes Bearing a Dianionic Pentadentate Ligand

2020 ◽  
Author(s):  
Lucie Nurdin ◽  
Warren Piers ◽  
Jian-Bin Lin ◽  
Benjamin S. Gelfand
Keyword(s):  
Strong Acid ◽  
Ambient Atmosphere ◽  
Pyridyl Nitrogen ◽  
Protonation Site ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Radical Trap ◽  
Bond Homolysis ◽  
Pentadentate Ligand

<div>A variety of neutral alkyl-cobalt(III) complexes bearing a dianionic tetrapodal </div><div>pendadentate ligand B2Pz4Py are reported. Compounds 2-R (R = CH3, CH2SiMe3, </div><div>CH2SiMe2Ph, i Bu, CH2(c-C5H9) and (CH2)4CH=CH2) are synthesized in 58-90% yield. These </div><div>diamagnetic, octahedral complexes are thermally stable up to 110˚C and are also </div><div>remarkably stable to ambient atmosphere. They were fully characterized by spectroscopic </div><div>techniques, and in three cases, X-ray crystallography. Evidence for reversible homolytic </div><div>cleavage of the Co-C bonds was found in their reactions with the hydrogen atom donor 1,4-</div><div>cyclohexadiene and the radical trap TEMPO, as well as the observed cyclization of the 5-</div><div>hexenyl group to the methylcyclopentyl derivative over the course of several hours. </div><div>Despite these observations, it can be concluded that the diborate B2Pz4Py ligand provides a </div><div>very stable platform for these Co(III) alkyls. Reduction by one electron to a Co(II) alkyl can </div><div>accelerate bond homolysis, but in this instance, using cobaltocene as the reducing agent, </div><div>leads to ejection of an alkide anion through bond heterolysis, an unusual reaction for </div><div>Co(III) alkyls. Finally, protonation of compound 2-Me with the strong acid HNTf2 leads to </div><div>divergent reactivity in which the major protonation site is the pyridyl nitrogen of the ligand </div><div>as opposed to protonation of the methyl group. The produce of protonation at nitrogen is </div><div>the dimeric species 4 which was prepared via separate synthesis and characterized by Xray crystallography.</div>

scholarly journals Synthesis, Characterization and Reactivity of Neutral Octahedral Alkyl-Cobalt(III) Complexes Bearing a Dianionic Pentadentate Ligand

2020 ◽  
Author(s):  
Lucie Nurdin ◽  
Warren Piers ◽  
Jian-Bin Lin ◽  
Benjamin S. Gelfand
Keyword(s):  
Strong Acid ◽  
Ambient Atmosphere ◽  
Pyridyl Nitrogen ◽  
Protonation Site ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Radical Trap ◽  
Bond Homolysis ◽  
Pentadentate Ligand

<div>A variety of neutral alkyl-cobalt(III) complexes bearing a dianionic tetrapodal </div><div>pendadentate ligand B2Pz4Py are reported. Compounds 2-R (R = CH3, CH2SiMe3, </div><div>CH2SiMe2Ph, i Bu, CH2(c-C5H9) and (CH2)4CH=CH2) are synthesized in 58-90% yield. These </div><div>diamagnetic, octahedral complexes are thermally stable up to 110˚C and are also </div><div>remarkably stable to ambient atmosphere. They were fully characterized by spectroscopic </div><div>techniques, and in three cases, X-ray crystallography. Evidence for reversible homolytic </div><div>cleavage of the Co-C bonds was found in their reactions with the hydrogen atom donor 1,4-</div><div>cyclohexadiene and the radical trap TEMPO, as well as the observed cyclization of the 5-</div><div>hexenyl group to the methylcyclopentyl derivative over the course of several hours. </div><div>Despite these observations, it can be concluded that the diborate B2Pz4Py ligand provides a </div><div>very stable platform for these Co(III) alkyls. Reduction by one electron to a Co(II) alkyl can </div><div>accelerate bond homolysis, but in this instance, using cobaltocene as the reducing agent, </div><div>leads to ejection of an alkide anion through bond heterolysis, an unusual reaction for </div><div>Co(III) alkyls. Finally, protonation of compound 2-Me with the strong acid HNTf2 leads to </div><div>divergent reactivity in which the major protonation site is the pyridyl nitrogen of the ligand </div><div>as opposed to protonation of the methyl group. The produce of protonation at nitrogen is </div><div>the dimeric species 4 which was prepared via separate synthesis and characterized by Xray crystallography.</div>

scholarly journals Synthesis, Characterization and Reactivity of Neutral Octahedral Alkyl-Cobalt(III) Complexes Bearing a Dianionic Pendadentate Ligand

2020 ◽  
Author(s):  
Lucie Nurdin ◽  
Warren Piers ◽  
Jian-Bin Lin ◽  
Benjamin S. Gelfand
Keyword(s):  
Hydrogen Atom ◽  
Strong Acid ◽  
Ambient Atmosphere ◽  
Pyridyl Nitrogen ◽  
Protonation Site ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Radical Trap ◽  
Bond Homolysis

<div>A variety of neutral alkyl-cobalt(III) complexes bearing a dianionic tetrapodal </div><div>pendadentate ligand B2Pz4Py are reported. Compounds 2-R (R = CH3, CH2SiMe3, </div><div>CH2SiMe2Ph, i Bu, CH2(c-C5H9) and (CH2)4CH=CH2) are synthesized in 58-90% yield. These </div><div>diamagnetic, octahedral complexes are thermally stable up to 110˚C and are also </div><div>remarkably stable to ambient atmosphere. They were fully characterized by spectroscopic </div><div>techniques, and in three cases, X-ray crystallography. Evidence for reversible homolytic </div><div>cleavage of the Co-C bonds was found in their reactions with the hydrogen atom donor 1,4-</div><div>cyclohexadiene and the radical trap TEMPO, as well as the observed cyclization of the 5-</div><div>hexenyl group to the methylcyclopentyl derivative over the course of several hours. </div><div>Despite these observations, it can be concluded that the diborate B2Pz4Py ligand provides a </div><div>very stable platform for these Co(III) alkyls. Reduction by one electron to a Co(II) alkyl can </div><div>accelerate bond homolysis, but in this instance, using cobaltocene as the reducing agent, </div><div>leads to ejection of an alkide anion through bond heterolysis, an unusual reaction for </div><div>Co(III) alkyls. Finally, protonation of compound 2-Me with the strong acid HNTf2 leads to </div><div>divergent reactivity in which the major protonation site is the pyridyl nitrogen of the ligand </div><div>as opposed to protonation of the methyl group. The produce of protonation at nitrogen is </div><div>the dimeric species 4 which was prepared via separate synthesis and characterized by Xray crystallography.</div>

scholarly journals Hydrolysis of Scandium Alkyl Derivatives Supported by a Pentadentate Diborate Ligand: Interconversion of Hydroxo and Oxo Complexes

2019 ◽  
Author(s):  
Daniel W. Beh ◽  
Warren Piers ◽  
Laurent Maron ◽  
Yan Yang ◽  
Benjamin S. Gelfand ◽  
...  
Keyword(s):  
Solid State ◽  
Hydroxo Complex ◽  
Ambient Atmosphere ◽  
X Ray ◽  
X Ray Crystallography ◽  
Hydrolysis Products ◽  
Alkyl Derivatives ◽  
Rapid Formation ◽  
Hydrolysis Of ◽  
Pentadentate Ligand

Uncontrolled reaction of water with scandium alkyls (compounds <b>1-R</b>) supported by a dianionic, pentadentate ligand leads to rapid formation of an oxo-bridged dimer (<b>2</b>). Solid state samples can be exposed to ambient atmosphere to generate samples enriched in the bridging dihydroxo dimer <b>3</b>, which slowly converts to the m-oxo species with elimination of water. DFT computations show that <b>3</b> is actually more thermodynamically stable than <b>2</b>, but the reactivity of <b>3</b> with the water eliminated leads to its decomposition to <b>2</b> and several hydrolysis products. Some of these products were characterized by X-ray crystallography, specifically a hexameric scandium dihydroxo cluster (<b>4</b>) in which the pentadentate ligand has partially demetallated. Attempts to synthesize hydroxo complex <b>3</b> by protonation of <b>2</b> also lead to hydrolysis products.

scholarly journals Hydrolysis of Scandium Alkyl Derivatives Supported by a Pentadentate Diborate Ligand: Interconversion of Hydroxo and Oxo Complexes

2019 ◽  
Author(s):  
Daniel W. Beh ◽  
Warren Piers ◽  
Laurent Maron ◽  
Yan Yang ◽  
Benjamin S. Gelfand ◽  
...  
Keyword(s):  
Solid State ◽  
Hydroxo Complex ◽  
Ambient Atmosphere ◽  
X Ray ◽  
X Ray Crystallography ◽  
Hydrolysis Products ◽  
Alkyl Derivatives ◽  
Rapid Formation ◽  
Hydrolysis Of ◽  
Pentadentate Ligand

Uncontrolled reaction of water with scandium alkyls (compounds <b>1-R</b>) supported by a dianionic, pentadentate ligand leads to rapid formation of an oxo-bridged dimer (<b>2</b>). Solid state samples can be exposed to ambient atmosphere to generate samples enriched in the bridging dihydroxo dimer <b>3</b>, which slowly converts to the m-oxo species with elimination of water. DFT computations show that <b>3</b> is actually more thermodynamically stable than <b>2</b>, but the reactivity of <b>3</b> with the water eliminated leads to its decomposition to <b>2</b> and several hydrolysis products. Some of these products were characterized by X-ray crystallography, specifically a hexameric scandium dihydroxo cluster (<b>4</b>) in which the pentadentate ligand has partially demetallated. Attempts to synthesize hydroxo complex <b>3</b> by protonation of <b>2</b> also lead to hydrolysis products.

The Pyrolytic Rearrangement of 1-Alkynoyl-3-methylpyrazoles: Synthesis of Pyrazolo[1,5-a]pyridin-5-ols and Related Compounds

1994 ◽  
Vol 47 (6) ◽  
pp. 991 ◽  
Author(s):  
RFC Brown ◽  
FW Eastwood ◽  
GD Fallon ◽  
SC Lee ◽  
RP Mcgeary
Keyword(s):  
Carbon Chain ◽  
Ring Structure ◽  
High Yield ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Fused Ring ◽  
Related Compounds

Flash vacuum pyrolysis of 1-(alkyn-2′-oyl)-3-methylpyrazoles at 650°/0.03 mm forms pyrazolo[1,5-a]pyridin-5-ols, often in high yield, which may bear substituents at C2, C3 or C7. In the absence of a 3-methyl group in the precursor, N-ethynylpyrazoles are formed in low yield. The formation of both types of product is interpreted as involving 3-(N-pyrazolyl)propadienones formed by N1 → N2 migration of the N-alkynoyl group with inversion of the three-carbon chain. The fused-ring structure of 2-methylpyrazolo[1,5-a]pyridin-5-ol (25) was established by X-ray crystallography of the O-benzoyl derivative (27).

Halogenated Terpenoids. XXIX The 1-Bromo 1-Bromomethyl Cyclohexyl System

1997 ◽  
Vol 50 (7) ◽  
pp. 689 ◽  
Author(s):  
Douglas J. Brecknell ◽  
Raymond M. Carman ◽  
Ross A. Edwards ◽  
Karl A. Hansford ◽  
Tomislav Karoli ◽  
...  
Keyword(s):  
Free Energy ◽  
Bromine Atom ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Bromo Derivative ◽  
A Value ◽  
Derivative Free ◽  
Methylene Groups

Bromination of methylene groups exocyclic to cyclohexyl systems normally affords two isomeric products; the axial 1-bromo equatorial 1-bromomethyl compound and the axial 1-bromomethyl equatorial 1-bromo derivative. Free energy differences between these two isomers, and the conformations adopted by the axial 1-bromomethyl group, have been explored by n.m.r. spectroscopy, by X-ray crystallography and by MM3 calculations. Evidence is presented to show that the ax-bromomethyl group exists primarily as those rotamers which site the bromine atom synclinal to the vicinal bromine. The A value for a bromomethyl group in this system is then similar to that of an unsubstituted methyl group.

Synthesis and Characterization of the Nickel(II) Complex of a Macrocyclic Schiff Base Ligand with a Single Pendant Coordinating Hydroxyl Arm

2003 ◽  
Vol 56 (12) ◽  
pp. 1255 ◽  
Author(s):  
Ali Akbar Khandar ◽  
Seyed Abolfazl Hosseini-Yazdi
Keyword(s):  
Synthesis And Characterization ◽  
Monoclinic Space Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Octahedral Environment ◽  
Distorted Octahedral ◽  
Macrocyclic Schiff Base ◽  
Template Reaction ◽  
Pentadentate Ligand

The synthesis and characterization of a nickel(II) complex of the ligand 8,9,18,19-tetrahydro-7H,17H-dibenzo[f,o][1,5,9,13]dioxadiazacyclohexadecin-18-ol (L) is described. Complex [NiL(NO3)]NO3 was prepared by facile template reaction of the appropriate dialdehyde 2-(3-(2-formylphenoxy)-2-hydroxypropoxy)benzaldehyde (1) and 1,3-diaminopropane in the presence of nickel nitrate. X-Ray crystallography indicated that the compound was a six-coordinate complex that contained a pentadentate ligand and an NO3− anion trans to the alcoholic donor. The blue complex contains nickel(II) in a distorted octahedral environment of N2O4 donors, and crystallizes in the monoclinic space group C2/c with a 26.921(10), b 9.075(2), c 21.193(7) Å, β 122.12(2)°, and Z 8. From spectro-scopic and conductivity studies of the complex it has been found that six-coordinate [NiL(NO3)]+ cations and NO3− anions are formed in solution.

Computational, 1H NMR, and X-ray structural studies on 1-arylurazole tetrazane dimers

2017 ◽  
Vol 73 (9) ◽  
pp. 660-666 ◽  
Author(s):  
Kenneth L. Martin ◽  
Gary W. Breton
Keyword(s):  
Methyl Groups ◽  
Structural Studies ◽  
Aromatic Rings ◽  
Nmr Spectrum ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
H Nmr ◽  
Dimeric Form ◽  
Shielding Effects

Nitrogen-centered urazole radicals exist in equilibrium with tetrazane dimers in solution. The equilibrium established typically favors the free-radical form. However, 1-arylurazole radicals bearing substituents at the ortho position favor the dimeric form. We were able to determine the structure of one of the dimers (substituted at both ortho positions with methyl groups), namely 1,2-(2,4-dimethylphenyl)-2-[2-(2,4-dimethylphenyl)-4-methyl-3,5-dioxo-1,2,4-triazolidin-1-yl]-4-methyl-1,2,4-triazolidine-3,5-dione, C24H28N6O4, via X-ray crystallography. The experimentally determined structure agreed well with the computationally obtained geometry at the B3LYP/6-311G(d,p) level of theory. The preferred syn conformation of these 1-arylurazole dimers results in the two aromatic rings being proximate and nearly parallel, which leads to some interesting shielding effects of certain signals in the 1H NMR spectrum. Armed with this information, we were able to decipher the more complicated 1H NMR spectrum obtained from a dimer that was monosubstituted at the ortho position with a methyl group.

Total synthesis of polyoximic acid

2001 ◽  
Vol 79 (11) ◽  
pp. 1812-1826 ◽  
Author(s):  
Stephen Hanessian ◽  
Jian-min Fu
Keyword(s):  
Double Bond ◽  
Carboxylic Acid ◽  
Total Synthesis ◽  
Wittig Reaction ◽  
2D Nmr ◽  
Amino Acid Derivative ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Correct Structure

The structure and stereochemistry of polyoximic acid, a degradation product of polyoxins, was originally designated as trans-3-ethylidene-L-azetidine-2-carboxylic acid. However, total synthesis revealed that the correct structure was in fact cis-3-ethylidene-L-azetidine-2-carboxylic acid, which was confirmed by X-ray crystallography. The synthesis of the trans-isomer was also done and its identity was confirmed by X-ray analysis as well. The key step for constructing the four-membered ring was a rhodium catalyzed carbenoid insertion into the N—H bond of a beta-amino acid derivative. The stereoselectivity of the exo-double bond was controlled by conducting a Horner-Emmons-Wadsworth or a Wittig reaction to generate the trans- and cis-isomers, respectively. Weinreb's amide was used as a latent methyl group for the separation of trans and cis mixtures. The double bond stereochemistry of polyoximic acid in the parent polyoxin was also confirmed to be cis by extensive 2D NMR studies.Key words: diazoinsertion, azetidine, olefination.

Stereoelectronic effects in sulfonyl compounds: axial orientation of an N-methyl group in a six-membered sultam

1998 ◽  
Vol 76 (2) ◽  
pp. 164-170 ◽  
Author(s):  
James Frederick King ◽  
Gay Yuyitung ◽  
Manjinder Singh Gill ◽  
Jeffrey Charles Stewart ◽  
Nicholas Charles Payne
Keyword(s):  
Single Crystal ◽  
Key Words ◽  
Axial Orientation ◽  
Anomeric Effect ◽  
Trans Form ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Stereoelectronic Effects ◽  
Negative Hyperconjugation

The trans form of octahydro-1-methyl-1H-2,1-benzothiazine 2,2-dioxide, in which a six-membered sultam unit is trans-fused to cyclohexane, has been synthesized. The single-crystal X-ray structure shows the molecule to have the N-methyl group in the axial orientation. The generalized anomeric effect believed to be responsible for the axial preference is estimated at =>2 kcal mol-1.Key words: generalized anomeric effect, negative hyperconjugation, sulfonamides, sultams, X-ray crystallography.

Sign in / Sign up

Export Citation Format

Share Document