Browsing by Author "Friedrich, Holger B."

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Application of arene ruthenium(II) complexes with pyridine-2-carboxaldimine ligands in the transfer hydrogenation of ketones
(Elsevier, 2016-05) Gichumbi, Joel M.; Friedrich, Holger B.; Omondi, Bernard
The reaction of various pyridine-2-carboxaldimine ligands with the [(η6-arene)Ru(μ-Cl)Cl]2 dimer followed by a metathesis reaction with ammonium hexaflourophosphate, yielded the ruthenium(II) arene complex salts [(η6-arene)RuCl(C5H4N-2 CH N-Ar]PF6; where (arene = C6H6 (1), p-cymene (2), Ar = 3, 5-dimethyl phenyl (a), 2,3-dimethyl phenyl (b), 2,5-dimethyl phenyl (c), 3,4-dimethyl phenyl (d)). The compounds were characterized by elemental analysis, FT- IR, UV–vis and 1H and 13C NMR. Single crystal X-ray structures for compounds 1a, 1d and 2e were also determined and showed that the ruthenium(II) centre has a pseudo-octahedral geometry and the molecule adopted a three legged piano stool geometry in which the arene ring occupies the apex and the nitrogen atoms of the N,N′-bidentate ligand and the chloride atom the base of the stool. The Ru(II) complex salts were active for the catalytic transfer hydrogenation of ketones into alcohols in the presence of NaOH using 2-propanol as the hydrogen source at 82 °C. The complexes were suitable for a wide range of aliphatic, cyclic and aromatic ketones giving good turn over numbers.
Crystal structure of chlorido-(η5-pentamethylcyclopenta dienyl)-((bis-pyrazol-1-yl) methane-κ2N, N′) rhodium (III) hexafluorophosphate
(2019-11-13) Gichumbi, Joel M.; Zamisa, Sizwe J.; Friedrich, Holger B.
C17H23ClN4RhF6P, monoclinic, P21/c (no. 14), a = 10.6954(2) Å, b = 15.3868(3) Å, c = 12.6130(2) Å, β = 90.5590(10)°, V = 2075.60(7) Å3, Z = 4, Rgt(F) = 0.0296, wRref(F2) = 0.0727, T = 100(2) K.
Crystal structure of chlorido-(η6 - toluene)(2,2′-bipyridine-κ2 N,N′)ruthenium(II) hexafluorophosphate, C17H16ClN2RuPF6
(De Gruyter, 2022) Gichumbi, Joel M.; Zamisa, Sizwe J.; Friedrich, Holger B.
C17H16ClN2RuPF6, monoclinic, P21/c (no. 14), a = 14.4426(9) Å, b = 8.3311(5) Å, c = 16.413(1) Å, β = 109.2690°, V = 1864.2(2) Å3 , Z = 4, Rgt(F) = 0.0309, wRref(F2 ) = 0.0697, T = 173 K.
Crystal structure of chlorido-(η6-p-cymene)-(N- (2-fluorophenyl)-1-(pyridin-2-yl) methanimine-κ2N, N′) ruthenium (II)–acetone (1/1), C22H23ClN2F7OPRu.
(2010-01) Gichumbi, Joel M.; Omondi, Bernard *; Friedrich, Holger B.
C 22 H 23 ClN 2 F 7 OPRu, monoclinic, P 2 1 / c (no. 14), a = 7.30480(10) Å, b = 12.9540(3) Å, c = 28.7076(6) Å, β = 96.6990(10)°, V = 2697.95(9) Å ³ , Z = 4, Rgt ( F ) = 0.0196, wRref ( F² ) = 0.0479, T = 100(2) K.
Crystal structure of η 6 -p-cymene-iodido-(N-isopropyl-1-(pyridin-2-yl) methanimine-κ 2N,N′)ruthenium(II) hexafluorophosphate(V), C19H26IN2F6Ru
(De Gruyter, 2019-12-07) Gichumbi, Joel M.; Omondi, Bernard; Friedrich, Holger B.
C19H26IN2F6Ru, triclinic, P¯1 (no. 2), a = 9.240(2) Å, b = 10.019(3) Å, c = 12.689(3) Å, α = 78.921°, β = 81.596(10)°, γ = 83.654°, V = 1136.30(5) Å3 , Z = 2, Rgt(F) = 0.0174, wRref(F 2 ) = 0.0440, T = 173 K.
Crystal structure of η6-p-cymene-iodido- (N-isopropyl-1-(pyridin-2-yl) methanimine-κ2N, N′) ruthenium (II) hexafluorophosphate (V), C19H26IN2F6Ru
(2019-12-07) Gichumbi, Joel M.; Omondi, Bernard; Friedrich, Holger B.
C19H26IN2F6Ru, triclinic, P1̄ (no. 2), a = 9.240(2) Å, b = 10.019(3) Å, c = 12.689(3) Å, α = 78.921°, β = 81.596(10)°, γ = 83.654°, V = 1136.30(5) Å3, Z = 2, Rgt(F) = 0.0174, wRref(F2) = 0.0440, T = 173 K.
Synthesis and characterization of half-sandwich ruthenium(II) complexes with N-alkyl pyridyl-imine ligands and their application in transfer hydrogenation of ketones
(2016-08-24) Gichumbi, Joel M.; Friedrich, Holger B.; Omondi, Bernard
A series of new arene ruthenium(II) complexes were prepared by reaction of ruthenium(II) precursors of the general formula [(η6-arene)Ru(μ-Cl)Cl]2 with N,N′-bidentate pyridyl-imine ligands to form complexes of the type [(η6-arene)RuCl(C5H4N-2-CH=N-R)]PF6, with arene = C6H6, R = iso-propyl (1a), tert-butyl (1b), cyclohexyl (1c), cyclopentyl (1d) and n-butyl (1e); arene = p-cymene, R = iso-propyl (2a), tert-butyl (2b). The complexes were fully characterized by 1H NMR and 13C NMR, UV–Vis and IR spectroscopies, elemental analyses, and the single-crystal X-ray structures of 2a and 2b have been determined. The single-crystal molecular structure revealed both compounds with a pseudo-octahedral geometry around the Ru(II) center, normally referred to as a piano stool conformation, with the pyridyl-imine as a bidentate N,N ligand. The activity of all complexes in the transfer hydrogenation of cyclohexanone in the presence of NaOH and iso-propanol is reported, the compounds showing turnover numbers of close to 1990 and high conversions. Complex 2b was also shown to be very effective for a range of aliphatic and cyclic ketones, giving conversions of up to 100 %.
Synthesis and characterization of piano-stool ruthenium complexes with N,N′-pyridine imine bidentate ligands and their application in styrene oxidation
(Elsevier, 2016-04) Gichumbi, Joel M.; Friedrich, Holger B.; Omondi, Bernard
The new complexes [(η6-arene)RuCl(C5H4N-2-CH N-R)]PF6 (arene = C6H6 with R = 4- flourophenyl (1), 4-chlorophenyl (2), 4-bromophenyl (3), 4 -iodophenyl (4), 2, 5-dichlorophenyl (5) or p-cymene with R = 4-flourophenyl (6), 4-chlorophenyl (7), 4-bromophenyl (8), 4- iodophenyl (9), 2, 5 - dichlorophenyl (10)) have been synthesized by reacting the ruthenium arene precursors [(η6-arene)Ru(μ-Cl)Cl]2, with the N,N′-bidentate ligands in a 1:2 ratio. Full characterization of all complexes was accomplished using 1H and 13C NMR, elemental analyses, UV-Vis spectroscopy, thermal analysis, IR spectroscopy and single crystal x-ray structures for compounds 7 and 10. The single crystal structures confirmed coordination of the ligand to the ruthenium(II) centre. The Ru(II) centre has a pseudo-octahedral three legged piano stool geometry in which the arene ring occupies the apex of the stool and the ruthenium is coordinated to the N,N′-bidentate ligand and a chloride ligand at the base of the stool. Two polymorphs of 7 were identified. The synthesized Ru(II) complexes were tested as catalysts for the oxidation of styrene to benzaldehyde using NaIO4 as a co-oxidant. All complexes were active catalysts for styrene oxidation and they gave high yields of benzaldehyde as the major product.
Synthesis and characterization of some new half-sandwich ruthenium(II) complexes with bidentate N,N′-ligands and their application in alcohol oxidation
(2016) Gichumbi, Joel M.; Friedrich, Holger B.; Omondi, Bernard
Graphical abstract New ruthenium (II) pyridine-imine complexes have been prepared and characterized. They show good catalytic activity in the oxidation of alcohols to carbonyl products using NaIO4 in a H2O/tert-butanol mixture.
Synthesis and characterization of water-soluble arene- ruthenium complexes and their application in biphasic olefin oxidation
(2018-12-25) Gichumbi, Joel M.; Friedrich, Holger B.; Omondi, Bernard
New water-soluble complexes [(η6-C6H6)RuCl(C5H4N-2-CH = N-R)]Cl (1) (with R = 4-hydroxymethylphenyl (a), 2,4-dichlorophenyl (b), 2-fluorophenyl (c), 3-carboxyphenyl (d)) have been synthesized by reacting [(η6-C6H6)Ru(μ-Cl)Cl]2 with the N,N′-bidentate ligands in a 1:2 ratio. Full characterization of all complexes was accomplished using 1H and 13C NMR, elemental analyses, UV-Vis spectroscopy, IR spectroscopy and single crystal X-ray crystallography for determination of the structure of 1d, as 1d•4H2O. The single crystal structure confirmed coordination of the ligand to the ruthenium(II) center leading to a structure commonly described as a pseudo-octahedral, three-legged piano stool. The geometry around the Ru(II) center is such that the arene ring occupies the apex of the stool while the N,N′-bidentate ligand and a chloride occupy the base of the stool. The synthesized Ru(II) complexes were tested as catalysts for oxidation of styrene using NaIO4 as a co-oxidant in a biphasic system. All complexes were active, giving good yields of benzaldehyde. Catalyst 1c was later investigated for olefin oxidation and gave high yields of the corresponding aldehydes as the major products in all cases.
Synthesis, characterization, and antimicrobial studies of half-sandwich η6-toluene ruthenium complexes with N,N′-bidentate ligands
(Taylor and Francis, 2020-07-29) Gichumbi, Joel M.; Friedrich, Holger B.; Omondi, Bernard; Chenia, Hafizah Y.
Nine new complexes [(η6-C6H5-CH3)RuLCl]+(PF6)ˉ (where L = N,N′-bidentate ligand; (C5H4NCH = N-Ar) where Ar = 4-methylphenyl (C20H20ClF6N2PRu, 1); 3,4-dimethylphenyl (C21H22ClF6N2PRu, 2); 2,4,6-trimethylphenyl (C21H24ClF6N2PRu, 3); 4-bromophenyl (C19H17ClBrF6N2PRu, 4); 2,5-dimethylphenyl (C21H22ClF6N2PRu, 5); 2-flourophenyl (C19H17ClF7N2PRu, 6), (4-methoxyphenyl)methylene (C21H22ClF6N2OPRu, 7); phenylmethylene (C20H20ClF6N2PRu, 8); and 3,5-dimethylphenyl (C21H22ClF6N2PRu, 9) were synthesized by reacting the corresponding N,N′-bidentate ligands with the ruthenium arene dimer in a 2:1 ratio. The compounds were fully characterized via 1H NMR and 13C NMR, IR, and UV-vis spectroscopy and elemental analyses. The molecular structures of representative complexes (1, 7, and 8) were established by single-crystal X-ray diffraction studies. In the molecular structures of the complexes, the ligands coordinate to the Ru (II) centers via the pyridine nitrogen atom and the imine N atom in a bidentate manner. The other coordination sites of the Ru(II) center are occupied by the tolyl system in an η6 manner resulting in geometry often referred to as “pseudo-octahedral piano-stool.” All compounds were evaluated for their in vitro antibacterial activity by the disk diffusion method against a panel of Gram-negative and Gram-positive bacteria. The complexes showed promising bactericidal activity against methicillin-resistant Staphylococcus aureus ATCC 43300.