Collins Obuah

Tandem ethylene oligomerisation and Friedel–Crafts alkylation of toluene catalysed by bis-(3,5-dimethylpyrazol-1-ylmethyl)benzene nickel(II) complexes and ethylaluminium dichloride

Three ligands, 1,2-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene (L1), 1,3-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene (L2) and 1,4-bis(3,5-dimethylpyrazol-1-ylmethyl)benzene (L3), were reacted with either nickel(II) chloride or nickel(II) bromide to produce four nickel complexes, Ni(L1)Br2 (1), Ni(L1)Cl2 (2), Ni(L2)Br2 (3), and Ni(L1)Br2 (4). The complexes were either mononuclear, 1 and 2, or polymeric, 3 and 4, depending on the positions of the pyrazolyl units on the benzene linker in the ligand. This was established from the crystal structures of 1, 2 and 3. All four complexes upon activation with ethylaluminium dichloride produced a tandem catalyst system that oligomerised ethylene to mainly 1-butene and 1-hexene and subsequently used the olefins present in the reaction medium to alkylate toluene that was used as solvent in the reactions. This led to mono-, di- and tri-alkyltoluenes with ethylene, butene and hexene.

(Ferrocenylpyrazolyl)nickel(II)-catalysed ethylene oligomerisation

Compounds L1–L6 (3-ferrocenylpyrazole (L1), 3-ferrocenyl-5-methylpyrazole (L2), 3-ferrocenylpyrazolyl-methylenepyridine (L3), 3-ferrocenyl-5-pyrazolyl-methylenepyridine (L4), 3-ferrocenylpyrazolyl-ethylamine (L5) and 3-ferrocenyl-5-pyrazolyl-ethylamine (L6)) reacted with [NiBr2(DME)] or [NiCl2·6H2O] to give the mononuclear nickel complexes [NiBr2(κ1-L1)2] (1), [NiBr2(κ1-L2)2] (2), [NiBr2(κ2-L3)] (3), [NiBr2(κ2-L4)] (4), [NiBr2(κ2-L5)] (5), [NiBr2(κ2-L6)] (6), [NiCl2(κ2-L3)] (7) and [NiCl2(κ2-L4)] (8). Because these nickel complexes are paramagnetic, they were characterised by a combination of IR spectroscopy, mass spectrometry, elemental analysis and, in selected cases, single crystal X-ray crystallography. Activation of complexes 1–8 with EtAlCl2 in chlorobenzene produced active species that catalysed ethylene oligomerization to butenes and C16–C64 olefins, showing a non-Schulz–Flory distribution of products. Complexes 2 and 3 were the most active (1989 kg of ethylene oligomer per mol of Ni per h and 1776 kg of ethylene oligomer per mol of Ni per h, respectively) and, in toluene, produced isomers of butene and small amounts of butyltoluenes via Friedel–Crafts alkylation of toluene by the butenes.

Novel bio-friendly and non-toxic thiocarbohydrate stabilizers of gold nanoparticles

Several bio-friendly carbohydrate disulfides and thiocarbohydrates have been synthesized via the reaction of D-(+)-gluconic acid δ-lactone with aminoalkylthiols, leading to n-gluconamidoalkyldisulfides {di-(2-gluconamidoethyl)disulfide (L1), di(3-gluconamidopropyl)-disulfide (L2), di(4-gluconamidobutyl) disulfide (L3) and (2-gluconamidoethyl)thiol (L4)}. Acetylation of hydroxy groups in L1–L3 and subsequent reduction produced the following disulfides and thiols: acetylated di(2-gluconamidoethyl)disulfide (L5), acetylated di(3-gluconamidopropyl)disulfide (L6), acetylated di(4-gluconamidobutyl)disulfide (L7), acetylated di(2-gluconamidoethyl)thiol (L8), acetylated di(3-gluconamidopropyl)thiol (L9) and acetylated di(4-gluconamidobutyl)thiol (L10). Compounds L1–L10 were characterized by combination of NMR and infrared spectroscopy, microanalysis, mass spectrometry and in a selected case X-ray crystallographic data. These thiocarbohydrate compounds were used to stabilize gold nanoparticles to gold glyconanoparticles (AuNPs) of sizes in the range of ca. 2–9 nm. The thiocrabohydrates are non-toxic toward both cancer and normal cell lines and have IC50 values generally ≥200 μM.

cis-Dichlorido[2-(3,5-dimethyl-1H-pyrazol-1-yl-κN2)ethanamine-κN]palladium(II) dichloro­methane monosolvate

In the title compound, [PdCl2(C7H13N3)]·CH2Cl2, the 2-(3,5-dimethyl-1H-pyrazol-1-yl)ethanamine ligand chelates the PdII atom via two N atoms forming a six-membered ring resulting in a distorted square-planar metal coordination environment, highlighted by N—Pd—Cl angles of 172.63u2005(8) and 174.98u2005(9)°. In addition to N—H⋯Cl hydrogen bonds creating infinite chains along [001], several C—H⋯Cl interactions are observed in the crystal structure.