{1,2-Bis[(3,5-dimethyl-1H-pyrazol-1-yl- ĸN²)methyl]benzene}dichloridozinc(II)
- Guzei, Ilia A., Spencer, Lara C., Budhai, Asheena, Darkwa, James
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Budhai, Asheena , Darkwa, James
- Date: 2011
- Subjects: Zinc compounds , Atomic distortions
- Type: Article
- Identifier: uj:5859 , ISSN 1600-5368 , http://hdl.handle.net/10210/7956
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Budhai, Asheena , Darkwa, James
- Date: 2011
- Subjects: Zinc compounds , Atomic distortions
- Type: Article
- Identifier: uj:5859 , ISSN 1600-5368 , http://hdl.handle.net/10210/7956
- Description: Please refer to full text to view abstract
- Full Text:
Synthesis, characterization and evaluation of bulky bis(pyrazolyl)palladium complexes in Suzuki– Miyaura cross-coupling reactions
- Ocansey, Edward, Darkwa, James, Makhubela, Banothile C. E.
- Authors: Ocansey, Edward , Darkwa, James , Makhubela, Banothile C. E.
- Date: 2018
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/294578 , uj:32055 , Citation: Ocansey, E., Darkwa, J. & Makhubela, B.C.E. 2018. Synthesis, characterization and evaluation of bulky bis(pyrazolyl)palladium complexes in Suzuki– Miyaura cross-coupling reactions. RSC Advances, 8, 13826–13834. DOI: 10.1039/c8ra01430b
- Description: Abstract: Pyrazole-containing compounds have been used in recent times as ligands to stabilize metal complexes used as pre-catalysts in cross-coupling reactions. With various substituents at various positions in the pyrazole ring, the overall electrophilic and steric properties of the metal complexes can be fine-tuned. Herein, we report the synthesis of bulky pyrazole-based ligands by condensation of methyl 4- (bromomethyl)benzoate or benzyl bromide with various substituted pyrazole compounds. These ligands were utilised in the synthesis of bis(pyrazolyl)palladium(II) complexes. The complexes' catalytic activity in Suzuki–Miyaura cross-coupling reactions was evaluated. Phenyl bearing pre-catalyst 7, at a catalyst loading of 0.33 mol%, successfully converted 98% of bromobenzene and phenylboronic acid to biphenyl in 4 h at 140 o C, while the tertiary butyl bearing pre-catalyst 8 converted up to 81% of the same substrates to biphenyl. An increase in conversion was seen for all pre-catalysts when an electron- withdrawing substituent was present on the aryl halide substrate, and the opposite was observed when the electron-withdrawing group was present on the phenyl boronic acid.
- Full Text:
- Authors: Ocansey, Edward , Darkwa, James , Makhubela, Banothile C. E.
- Date: 2018
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/294578 , uj:32055 , Citation: Ocansey, E., Darkwa, J. & Makhubela, B.C.E. 2018. Synthesis, characterization and evaluation of bulky bis(pyrazolyl)palladium complexes in Suzuki– Miyaura cross-coupling reactions. RSC Advances, 8, 13826–13834. DOI: 10.1039/c8ra01430b
- Description: Abstract: Pyrazole-containing compounds have been used in recent times as ligands to stabilize metal complexes used as pre-catalysts in cross-coupling reactions. With various substituents at various positions in the pyrazole ring, the overall electrophilic and steric properties of the metal complexes can be fine-tuned. Herein, we report the synthesis of bulky pyrazole-based ligands by condensation of methyl 4- (bromomethyl)benzoate or benzyl bromide with various substituted pyrazole compounds. These ligands were utilised in the synthesis of bis(pyrazolyl)palladium(II) complexes. The complexes' catalytic activity in Suzuki–Miyaura cross-coupling reactions was evaluated. Phenyl bearing pre-catalyst 7, at a catalyst loading of 0.33 mol%, successfully converted 98% of bromobenzene and phenylboronic acid to biphenyl in 4 h at 140 o C, while the tertiary butyl bearing pre-catalyst 8 converted up to 81% of the same substrates to biphenyl. An increase in conversion was seen for all pre-catalysts when an electron- withdrawing substituent was present on the aryl halide substrate, and the opposite was observed when the electron-withdrawing group was present on the phenyl boronic acid.
- Full Text:
Tetra-µ-acetato-κ⁸O:O'-bis[(3,5-dimethyl-1H-pyrazole-κN²)copper(II)]
- Van Wyk, Juanita, Omondi, Bernard, Darkwa, James
- Authors: Van Wyk, Juanita , Omondi, Bernard , Darkwa, James
- Date: 2011
- Subjects: X-ray crystallography , Crystallography , Pyrazolyl ligands , Palladium compounds
- Type: Article
- Identifier: uj:5908 , ISSN 1600-5368 , http://hdl.handle.net/10210/8067
- Description: Pyrazolyl ligands containing a carbonyl linker has been utilized to prepare a number of coordination compounds with palladium salts (Guzei et al., 2003; Mohlala et al., 2005, Ojwach et al., 2005). In these compounds the pyrazolyl carbonyl moiety appear to be robust enough to avoid hydrolysis. However in a few instances the presence of metal ions like Cu(II) (Deka et al., 2006) and Pd(II) (Nelana et al., 2008) appear to catalyze the hydrolysis of the benzoyl fragments. We have observed similar hydrolysis when reacting copper(II) acetate with (3,5-dimethyl-pyrazol-1-yl)-o-benzoyl-methane. The title compound formed from this reaction is the subject of this report. The half "solvent" molecule excluded from the structure had a total number of 30.7 electrons which is approximately half the total number of electrons that acetophenone has. Compound (I) crystallizes with two half molecules in the assymetric unit. The compound is dinuclear with each of the Cu atoms coordinated to four O atoms and a N atom from the pyrazole ligand. The O atoms are from acetate ions, all in the equatorial positions of a slightly distorted octahedral geometry around the Cu atoms. The N atom is bound trans to the Cu—Cu vector completing a the distorted octahedral geometry as axial ligands. The crystal structure of (I) is composed of two N—H···O hydrogen bonded chains (Table 1) that extend in the crystallographic b axis (Fig. 2).
- Full Text:
- Authors: Van Wyk, Juanita , Omondi, Bernard , Darkwa, James
- Date: 2011
- Subjects: X-ray crystallography , Crystallography , Pyrazolyl ligands , Palladium compounds
- Type: Article
- Identifier: uj:5908 , ISSN 1600-5368 , http://hdl.handle.net/10210/8067
- Description: Pyrazolyl ligands containing a carbonyl linker has been utilized to prepare a number of coordination compounds with palladium salts (Guzei et al., 2003; Mohlala et al., 2005, Ojwach et al., 2005). In these compounds the pyrazolyl carbonyl moiety appear to be robust enough to avoid hydrolysis. However in a few instances the presence of metal ions like Cu(II) (Deka et al., 2006) and Pd(II) (Nelana et al., 2008) appear to catalyze the hydrolysis of the benzoyl fragments. We have observed similar hydrolysis when reacting copper(II) acetate with (3,5-dimethyl-pyrazol-1-yl)-o-benzoyl-methane. The title compound formed from this reaction is the subject of this report. The half "solvent" molecule excluded from the structure had a total number of 30.7 electrons which is approximately half the total number of electrons that acetophenone has. Compound (I) crystallizes with two half molecules in the assymetric unit. The compound is dinuclear with each of the Cu atoms coordinated to four O atoms and a N atom from the pyrazole ligand. The O atoms are from acetate ions, all in the equatorial positions of a slightly distorted octahedral geometry around the Cu atoms. The N atom is bound trans to the Cu—Cu vector completing a the distorted octahedral geometry as axial ligands. The crystal structure of (I) is composed of two N—H···O hydrogen bonded chains (Table 1) that extend in the crystallographic b axis (Fig. 2).
- Full Text:
Dichlorido[2-(3,5-dimethyl-1H-pyrazol-1-yl-ĸN²)ethanamine-ĸN]zinc(II)
- Guzei, Ilia A., Spencer, Lara C., Segapelo, Tebogo V., Darkwa, James
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Segapelo, Tebogo V. , Darkwa, James
- Date: 2011
- Subjects: Amines
- Type: Article
- Identifier: uj:5845 , ISSN 1600-5368 , http://hdl.handle.net/10210/7917
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Segapelo, Tebogo V. , Darkwa, James
- Date: 2011
- Subjects: Amines
- Type: Article
- Identifier: uj:5845 , ISSN 1600-5368 , http://hdl.handle.net/10210/7917
- Description: Please refer to full text to view abstract
- Full Text:
Ethyl 3-ferrocenyl-1-(pyridin-2-ylmethyl)-1H-pyrazole-5-carboxylate
- Guzei, Ilia A., Spencer, Lara C., Munyaneza, Apollinaire, Darkwa, James
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Munyaneza, Apollinaire , Darkwa, James
- Date: 2012
- Subjects: Pyrazole , Crystallization
- Type: Article
- Identifier: uj:5858 , ISSN 1600-5368 , http://hdl.handle.net/10210/7955
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Munyaneza, Apollinaire , Darkwa, James
- Date: 2012
- Subjects: Pyrazole , Crystallization
- Type: Article
- Identifier: uj:5858 , ISSN 1600-5368 , http://hdl.handle.net/10210/7955
- Description: Please refer to full text to view abstract
- Full Text:
{1-[1-(3-Carboxypropanamido)ethyl]- 1',2-bis(diphenylphosphino)ferrocenek²P,P'}dichloridoplatinum(II) dichloromethane 1.25-solvate
- Spencer, Lara C., Bjelosevic, Haris, Darkwa, James, Elmroth, Sofi K. C., Persson, Tina
- Authors: Spencer, Lara C. , Bjelosevic, Haris , Darkwa, James , Elmroth, Sofi K. C. , Persson, Tina
- Date: 2008
- Subjects: Ferrocenyl compounds , Platinum complexes , Crystallography
- Type: Article
- Identifier: http://ujcontent.uj.ac.za8080/10210/389837 , uj:5961 , ISSN 1600-5368 , http://hdl.handle.net/10210/8167
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Spencer, Lara C. , Bjelosevic, Haris , Darkwa, James , Elmroth, Sofi K. C. , Persson, Tina
- Date: 2008
- Subjects: Ferrocenyl compounds , Platinum complexes , Crystallography
- Type: Article
- Identifier: http://ujcontent.uj.ac.za8080/10210/389837 , uj:5961 , ISSN 1600-5368 , http://hdl.handle.net/10210/8167
- Description: Please refer to full text to view abstract
- Full Text:
Constructor graph description of the hydrogen-bonding supramolecular assembly in two ionic compounds:2-(pyrazol-1-yl)ethylammonium chloride and diaquadichloridobis(2-hydroxyethylammonium)cobalt(II) dichloride
- Guzei, Ilia A., Spencer, Lara C., Darkwa, James, Ainooson, Michael K.
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Darkwa, James , Ainooson, Michael K.
- Date: 2010
- Subjects: Hydrogen bonding , Crystallography , Metal ions , Ionic compounds
- Type: Article
- Identifier: uj:5869 , ISSN 0108-2701 , http://hdl.handle.net/10210/7967
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Darkwa, James , Ainooson, Michael K.
- Date: 2010
- Subjects: Hydrogen bonding , Crystallography , Metal ions , Ionic compounds
- Type: Article
- Identifier: uj:5869 , ISSN 0108-2701 , http://hdl.handle.net/10210/7967
- Description: Please refer to full text to view abstract
- Full Text:
Metals at your service
- Authors: Darkwa, James
- Date: 2008-11-03T07:12:38Z
- Subjects: Metals , Metals as catalysts , Catalysis , Chemistry
- Type: Inaugural
- Identifier: uj:14897 , http://hdl.handle.net/10210/1447
- Description: Inaugural lecture--Dept. of Chemistry, University of Johannesburg, 4 October 2006
- Full Text:
- Authors: Darkwa, James
- Date: 2008-11-03T07:12:38Z
- Subjects: Metals , Metals as catalysts , Catalysis , Chemistry
- Type: Inaugural
- Identifier: uj:14897 , http://hdl.handle.net/10210/1447
- Description: Inaugural lecture--Dept. of Chemistry, University of Johannesburg, 4 October 2006
- Full Text:
The role of noble metal catalysts in conversion of biomass and bio-derived intermediates to fuels and chemicals : a review of promising approaches on plant based biomass as a renewable alternative feedstock
- Makhubela, Banothile C. E., Darkwa, James
- Authors: Makhubela, Banothile C. E. , Darkwa, James
- Date: 2018
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/294591 , uj:32057 , Citation: Makhubela, B.C.E. & Darkwa, J. 2018. The role of noble metal catalysts in conversion of biomass and bio-derived intermediates to fuels and chemicals : a review of promising approaches on plant based biomass as a renewable alternative feedstock. Johnson Matthey Technol. Rev, 62(1), 4–31. https://doi.org/10.1595/205651317X696261
- Description: Abstract: In the face of growing oil demand the use of renewable feedstocks for the potential to supply transportation fuels, electricity, chemicals and materials is increasingly attractive. This review covers novel technologies and pathways to produce liquid fuels and chemical intermediates in an efficient and cost-effective way. Several commercial and pilot scale projects by companies including Anellotech, USA; Johnson Matthey, UK; GFBiochemicals, Italy; Quaker Oats, USA; Changchun Dacheng Group, China; Avantium, The Netherlands; BASF, Germany and Rennovia, USA are highlighted. The review focuses on the use of non-food competing biomass, namely cellulose and hemicellulose biomass, and the use of precious metals to effect the key reaction steps: hydrolysis, dehydration, hydrodeoxygenation, hydrogenation and oxidation. The value added products achieved include fine chemicals and functional materials...
- Full Text:
- Authors: Makhubela, Banothile C. E. , Darkwa, James
- Date: 2018
- Language: English
- Type: Article
- Identifier: http://hdl.handle.net/10210/294591 , uj:32057 , Citation: Makhubela, B.C.E. & Darkwa, J. 2018. The role of noble metal catalysts in conversion of biomass and bio-derived intermediates to fuels and chemicals : a review of promising approaches on plant based biomass as a renewable alternative feedstock. Johnson Matthey Technol. Rev, 62(1), 4–31. https://doi.org/10.1595/205651317X696261
- Description: Abstract: In the face of growing oil demand the use of renewable feedstocks for the potential to supply transportation fuels, electricity, chemicals and materials is increasingly attractive. This review covers novel technologies and pathways to produce liquid fuels and chemical intermediates in an efficient and cost-effective way. Several commercial and pilot scale projects by companies including Anellotech, USA; Johnson Matthey, UK; GFBiochemicals, Italy; Quaker Oats, USA; Changchun Dacheng Group, China; Avantium, The Netherlands; BASF, Germany and Rennovia, USA are highlighted. The review focuses on the use of non-food competing biomass, namely cellulose and hemicellulose biomass, and the use of precious metals to effect the key reaction steps: hydrolysis, dehydration, hydrodeoxygenation, hydrogenation and oxidation. The value added products achieved include fine chemicals and functional materials...
- Full Text:
[Bis(pyridin-2-ylmethyl) ether]- trichloridorhodium(III) dichloromethane monosolvate : unusual hydrolysis of the methylene bridge in (pyrazolylmethyl)- pyridine
- Ojwach, Stephen O., Omondi, Bernard, Darkwa, James
- Authors: Ojwach, Stephen O. , Omondi, Bernard , Darkwa, James
- Date: 2011
- Subjects: X-ray crystallography , Crystallography , Transition metal compounds
- Type: Article
- Identifier: uj:5887 , ISSN 1600-5368 , http://hdl.handle.net/10210/8003
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Ojwach, Stephen O. , Omondi, Bernard , Darkwa, James
- Date: 2011
- Subjects: X-ray crystallography , Crystallography , Transition metal compounds
- Type: Article
- Identifier: uj:5887 , ISSN 1600-5368 , http://hdl.handle.net/10210/8003
- Description: Please refer to full text to view abstract
- Full Text:
Detailed example of the identification and crystallographic analysis of a pseudo-merohedrally twinned crystal.
- Guzei, Ilia, Herbst-Irmer, Regine, Munyaneza, Apollinaire, Darkwa, James
- Authors: Guzei, Ilia , Herbst-Irmer, Regine , Munyaneza, Apollinaire , Darkwa, James
- Date: 2012
- Subjects: Crystallography , X-ray structural determination , Twinned crystals
- Type: Article
- Identifier: uj:5852 , ISSN 0108-7681 , http://hdl.handle.net/10210/7939
- Description: A detailed description of the procedures utilized in the nonroutine X-ray single-crystal structural determination and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallography how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and atomic positional disorder.
- Full Text:
- Authors: Guzei, Ilia , Herbst-Irmer, Regine , Munyaneza, Apollinaire , Darkwa, James
- Date: 2012
- Subjects: Crystallography , X-ray structural determination , Twinned crystals
- Type: Article
- Identifier: uj:5852 , ISSN 0108-7681 , http://hdl.handle.net/10210/7939
- Description: A detailed description of the procedures utilized in the nonroutine X-ray single-crystal structural determination and refinement of a pseudo-merohedrally twinned crystal of an Fe/Ni organometallic complex is presented. It illustrates to the practitioners of crystallography how to properly handle such cases and describes the logic and concrete steps necessary to account for the twinning, pseudo-symmetry and atomic positional disorder.
- Full Text:
Phosphinogold(I) dithiocarbamate complexes : effect of the nature of phosphine ligand on anticancer properties
- Keter, Frankline K., Guzei, Ilia A., Nell, Margo, van Zyl, Werner E., Darkwa, James
- Authors: Keter, Frankline K. , Guzei, Ilia A. , Nell, Margo , van Zyl, Werner E. , Darkwa, James
- Date: 2014
- Subjects: Phosphinogold(I) dithiocarbamate complexes , Phosphine ligands
- Type: Article
- Identifier: uj:5432 , http://hdl.handle.net/10210/12057
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Keter, Frankline K. , Guzei, Ilia A. , Nell, Margo , van Zyl, Werner E. , Darkwa, James
- Date: 2014
- Subjects: Phosphinogold(I) dithiocarbamate complexes , Phosphine ligands
- Type: Article
- Identifier: uj:5432 , http://hdl.handle.net/10210/12057
- Description: Please refer to full text to view abstract
- Full Text:
Chlorido{N-[2-(diphenylphosphanyl)- benzylidene]-2-(2-thienyl)ethanamine-ĸ²N,P}methylpalladium(II) dichloromethane hemisolvate
- Onani, Martin O., Motswainyana, William M., Iwuoha, Emmanuel I., Darkwa, James, Lalancette, Roger A.
- Authors: Onani, Martin O. , Motswainyana, William M. , Iwuoha, Emmanuel I. , Darkwa, James , Lalancette, Roger A.
- Date: 2010-04
- Subjects: Dichloromethane , Ligands (Biochemistry)
- Type: Article
- Identifier: uj:5830 , ISSN 1600-5368 , http://hdl.handle.net/10210/7847
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Onani, Martin O. , Motswainyana, William M. , Iwuoha, Emmanuel I. , Darkwa, James , Lalancette, Roger A.
- Date: 2010-04
- Subjects: Dichloromethane , Ligands (Biochemistry)
- Type: Article
- Identifier: uj:5830 , ISSN 1600-5368 , http://hdl.handle.net/10210/7847
- Description: Please refer to full text to view abstract
- Full Text:
Intramolecular hydrogen bonding in dichloridobis(3,5-di-tert-butyl-1Hpyrazole-kN²)cobalt(II) as a consequence of ligand steric bulk
- Guzei, Ilia A., Spencer, Lara C., Ainooson, Michael K., Darkwa, James
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Ainooson, Michael K. , Darkwa, James
- Date: 2010
- Subjects: Hydrogen bonding , Crystallography , Pyrazole ligands , Chloride ligands
- Type: Article
- Identifier: uj:5870 , ISSN 0108-2701 , http://hdl.handle.net/10210/7968
- Description: Please refer to full text to view abstract
- Full Text:
- Authors: Guzei, Ilia A. , Spencer, Lara C. , Ainooson, Michael K. , Darkwa, James
- Date: 2010
- Subjects: Hydrogen bonding , Crystallography , Pyrazole ligands , Chloride ligands
- Type: Article
- Identifier: uj:5870 , ISSN 0108-2701 , http://hdl.handle.net/10210/7968
- Description: Please refer to full text to view abstract
- Full Text:
- «
- ‹
- 1
- ›
- »