Irvin Noel Booysen

Coordination behavior of chromone Schiff bases towards the [ReVO]3+ and [ReI(CO)3]+ cores

Herein, we describe the coordination behavior of chromone Schiff bases towards [ReVO]3+ and [ReI(CO)3]+. The reaction between 2-(2-thiolphenyliminomethyl)-4H-chromen-4-one (Htch) and [Re(CO)5Cl] led to fac-[Re(CO)3(bsch)Cl] (1) (bsch = 2-benzothiazole-4H-chromen-4-one). The square pyramidal [ReO(Hns)] (2) {H2ns=bis-[(2-phenylthiolate)iminomethyl]-methyl-1-(2-hydroxyphenyl)prop-2-en-1-one} and octahedral [ReO(OCH3)(PPh3)(Huch)] (3) complexes were isolated from reactions of trans-[ReVOBr3(PPh3)2] with Htch and H3uch [(5Z)-5-((4-hydroxy-2-methoxy-2H-chromen-3-yl)methyleneamino)-6-amino-1,3-dimethylpyrimidine-2,4(1H, 3H)-dione], respectively. The chromone Schiff bases and their metal complexes were fully characterized via NMR-, IR- and UV–Vis spectroscopy, single crystal XRD analysis and conductivity measurements. In addition, DFT studies were conducted to compare selected optimized and experimental parameters of the complexes.

Synthesis, characterization and electrocatalytic behavior of cobalt and iron phthalocyanines bearing chromone or coumarin substituents

Cobalt and iron phthalocyanines (Pcs) bearing peripherally tetra-substituted chromone (chr) or coumarin (cou) moieties were formulated and characterized by UV–Vis and FTIR spectroscopy, ESI-TOF mass spectrometry, and elemental analysis. The structural elucidations of the ligands, 4-(chromone-7-oxy)phthalonitrile (1) and 4-(4-(trifluoromethyl)-coumarin-7-oxy)phthalonitrile (2) were complemented by NMR spectroscopy and single crystal X-ray analysis (for 1). The redox properties of the complexes were investigated via voltammetry and the subsequent voltammetric assignments were corroborated by UV–Vis spectroelectrochemistry. Each metal complex displayed four redox processes of which their Pc ring oxidations are irreversible and the remaining redox couples are quasi-reversible. Utilizing the respective metallophthalocyanines, modified working electrodes were prepared by electropolymerization and their electrocatalytic activities toward nitrite oxidation were explored. All the metal complexes showed an increase in nitrite oxidation currents and a minor decrease in oxidation potentials which is indicative of electrocatalysis. The trend of electrocatalytic activity was found to be as follows: CoPc–chr (3) > FePc–cou (4) > CoPc–cou (5).

Ruthenium(II/IV) complexes with potentially tridentate Schiff base chelates containing the uracil moiety

Herein we report the synthesis and characterization of trans-[RuIICl2(PPh3)3] with potentially tridentate Schiff bases derived from 5,6-diamino-1,3-dimethyl uracil (H2ddd) and two 2-substituted aromatic aldehydes. In the diamagnetic ruthenium(II) complexes, trans-[RuCl(PPh3)2(Htdp)] (1) {H2tdp = 5-((thiophen-3-yl)methyleneamino)-6-amino-1,3-dimethyluracil} and trans-[RuCl(PPh3)2(Hsdp)] (2) {H2sdp = 5-(2-(methylthio)benzylideneamino)-6-amino-1,3-dimethyluracil}, the Schiff base ligands (i.e. Htdp and Hsdp) act as mono-anionic tridentate chelators. Upon reacting 5-(2-hydroxybenzylideneamino)-6-amino-1,3-dimethyluracil (H3hdp) with the metal precursor, the paramagnetic complex, trans-[RuIVCl2(ddd)(PPh3)2] (3), was isolated, in which the bidentate dianionic ddd co-ligand was formed by hydrolysis. The metal complexes were fully characterized via multinuclear NMR-, IR-, and UV–Vis spectroscopy, single crystal XRD analysis and conductivity measurements. The redox properties were probed via cyclic voltammetry with all complexes exhibiting comparable electrochemical behavior with half-wave potentials (E½) at 0.70 V (for 1), 0.725 V (for 2), and 0.68 V (for 3) versus Ag|AgCl, respectively. The presence of the paramagnetic metal center for 3 was confirmed by ESR spectroscopy.

6-Amino-1,3-dimethyl-5-[(E)-2-(methyl-sulfan-yl)benzyl-idene-amino]-pyrimidine-2,4(1H,3H)-dione.

The title compound, C14H16N4O2S, is a Schiff base derivative of 2-(methylsulfanyl)benzaldehyde. The configuration about the C=N double bond is E. The heterocyclic ring is essentially planar (τ = 3.1°) and makes a dihedral angle of 12.24 (7)° with the benzene ring. An intramolecular N—H⋯S hydrogen bond is observed. In the crystal, N—H⋯O and C—H⋯O hydrogen bonds link molecules into layers perpendicular to [101]. The closest distance between the centroids of two heterocyclic rings was found to be 3.5268 (8) Å.

Coordination of di- and triimine ligands at ruthenium(II) and ruthenium(III) centers: structural, electrochemical and radical scavenging studies

Abstract Herein, we explore the coordination of di- and triimine chelators at ruthenium(II) and ruthenium(III) centers. The reactions of 2,6-bis-((4-tetrahydropyranimino)methyl)pyridine (thppy), N1,N2-bis((3-chromone)methylene)benzene-1,2-diamine (chb), and tris-((1H-pyrrol-2-ylmethylene)ethane)amine (H3pym) with trans-[RuIICl2(PPh3)3] afforded the diamagnetic ruthenium(II) complex cis-[RuCl2(thppy)(PPh3)] (1) and the paramagnetic complexes [mer-Ru2(μ-chb)Cl6(PPh3)2] (2), and [Ru(pym)] (3), respectively. The complexes were characterized by IR, NMR, and UV–vis spectroscopy and molar conductivity measurements. The structures were confirmed by single crystal X-ray diffraction studies. The redox properties of the metal complexes were probed via cyclic- and squarewave voltammetry. Finally, the radical scavenging capabilities of the metal complexes towards the NO and 2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl (DPPH) radicals were investigated

(E)-6-Amino-1,3-dimethyl-5-[(pyridin-2-yl­methyl­idene)amino]­pyrimidine-2,4(1H,3H)-dione

In the title compound, C12H13N5O2, a Schiff-base-derived chelate ligand, the non-aromatic heterocycle and its substituents essentially occupy one common plane (r.m.s. of fitted non-H atoms = 0.0503 Å). The N=C bond is E-configured. Intracyclic angles in the pyridine moiety cover the range 117.6 (2)–124.1 (2)°. Intra- and intermolecular N—H⋯N and N—H⋯O hydrogen bonds are observed in the crystal structure, as are intra- and intermolecular C—H⋯O contacts which, in total, connect the molecules into a three-dimensional network. The shortest ring-centroid-to-ring-centroid distance of 3.5831 (14) Å is between the two different types of six-membered rings.

A second monoclinic polymorph of 6-amino-1,3-dimethyl-5-[(E)-2-(methyl-sulfan-yl)benzyl-idene-amino]-pyrimidine-2,4(1H,3H)-dione.

A new monoclinic form of the title compound, C14H16N4O2S, has been identified unexpectedly during an attempt to synthesize a coordination compound. The heterocyclic ring is essentially planar (r.m.s. deviation = 0.005 Å) and makes a dihedral angle of 8.77 (5)° with the benzene ring. This is in contrast to 12.24 (7)° reported for the first monoclinic polymorph [Booysen et al. (2011 ▶). Acta Cryst. E67, o1592]. An intramolecular N—H⋯S hydrogen bond is observed. In the crystal, intermolecular N—H⋯O hydrogen bonds link the molecules into zigzag chains along the b axis. The closest distance between the centroids of symmetry-related heterocyclic rings is 3.5161 (6) Å.

Oxorhenium(V) complexes with bidentate carbohydrazide Schiff bases: synthesis, characterization and DNA interaction studies

The respective coordination reactions of trans-[ReOCl3(PPh3)2] with N-[(4-oxo-4H-chromen-3-yl)methylidene]thiophene-2-carbohydrazide (Hchrtc) and N-[1,3-benzothiazol-2-ylmethylidene]thiophene-2-carbohydrazide (Hbztc) afforded two novel oxorhenium(V) complexes, cis-[ReOCl2(chrtc)(PPh3)] (1) and cis-[ReOCl2(bztc)(PPh3)] (2). These metal compounds were elucidated spectroscopically and their solid-state structures determined by single-crystal X-ray diffraction. The redox properties of the metal complexes were probed using cyclic and square wave voltammetry. The DNA interaction capabilities of 1 and 2 were gauged via UV/Vis spectroscopy DNA titrations and gel electrophoresis studies. A correlation is identified between the DNA cleavage observations and the redox potentials of the metal complexes.

N-[(E)-Thio­phen-2-yl­methyl­idene]-1,3-benzothia­zol-2-amine

In the title thiophene-derived Schiff base compound, C12H8N2S2, the thiophene ring is slighty rotated from the benzothiazole group mean plane, giving a dihedral angle of 12.87 (6)°. The largest displacement of an atom in the molecule from the nine-atom mean plane defined by the non-H atoms of the benzothiazole ring system is 0.572 (1) Å, exhibited by the C atom at the 3-position of the thiophene ring. In the crystal, weak C—H⋯S hydrogen bonds involving the thiophene group S atom and the 4-position thiophene C—H group of a symmetry-related molecule lead to an infinite one-dimensional chain colinear with the c axis. The structure is further stabilized by π–π interactions; the distance between the thiazole ring centroid and the centroid of an adjacent benzene ring is 3.686 (1) Å. The crystal studied was an inversion twin with the ratio of components 0.73 (3):0.27 (3).

Effects of a Ruthenium Schiff Base Complex on Glucose Homeostasis in Diet-Induced Pre-Diabetic Rats

Pre-diabetes is a condition that precedes type 2 diabetes mellitus (T2DM) that is characterised by elevated glycated haemoglobin (HbA1c). The management of pre-diabetes includes the combination of dietary and pharmacological interventions to increase insulin sensitivity. However, poor patient compliance has been reported with regard to dietary interventions, therefore, new alternative drugs are required that can be effective even without the dietary intervention. In our laboratory, we have synthesised a novel ruthenium complex that has been shown to have elevated biological activity. This study investigated the effects of this complex in both the presence and absence of dietary intervention on glucose handling in a diet-induced pre-diabetes rat model. Pre-diabetic animals were randomly assigned to respective treatment groups. The ruthenium complex was administered to pre-diabetic rats once a day every third day for 12 weeks. The administration of the ruthenium complex resulted in reduced fasting blood glucose, food intake, and body weight gain which was associated with decreased plasma ghrelin, insulin, and HbA1c levels in both the presence and absence of dietary intervention. The administration of the ruthenium complex ameliorated glycaemic control and insulin sensitivity in pre-diabetic rats. The results of this study warrant further investigations as this compound could potentially be able to re-sensitize insulin resistant cells and reduce the incidence of T2DM.