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Containers and Vessels for Supramolecular Catalysis
Published in Jubaraj Bikash Baruah, Principles and Advances in Supramolecular Catalysis, 2019
The confinement provided by ligands changes the hydrophobic or hydrophilic microenvironment. It has a large influence on the performance of a catalyst. The labiality associated with a metal—ligand bond and the coordination unsaturation provide access to exchange ligands. The exchanges of ligands in solution contribute to catalytic reactivity. However, it is important that the ligand fields of different ligands decide the electronic configuration of central metal ions and control reactivity. The trans-effect and back-bonding properties of a ligand control the reactivity of a complex by influencing the strength of the metal—ligand bond located at another coordination site within the same metal complex. Hence, the performance of a metal complex in catalytic activity depends on the surrounding environment of the ligand. If a metalcentric reaction is focused, the metal site should have access to a reactant. However, there are exceptions of metal complexes where the reactions may not require direct interaction of substrate with the metal ion. Energy and electron transfer occurring through mediators, space or a part of the ligands perform redox processes. Most importantly, there are ligands that do not directly participate in a catalytic reaction but dictate the course of the redox reaction by changing the rate and selectivity. Those ligands are known as spectator ligands. In the chemistry of mononuclear complexes, spectator ligands contribute significantly to product selectivity.
Structural characterization of ((9-fluorenylidene) (ferrocenyl)methyl)palladium iodide as the catalytic intermediate in the synthesis of 9-(ferrocenyl (ferrocenylethynyl)methylene)-9H-fluorene
Published in Journal of Coordination Chemistry, 2022
The 1H NMR spectra of ferrocenyl containing compounds are identified by the singlet of the Cp entity and the pseudo-triplets of the substituted cyclopentadienyl ring in the region between 4 and 5 ppm. The restricted rotation in fluorenylidenes 4 and 8 results in pseudo E-/Z-configurations of the respective 9H-fluorenylidene entities. The protons in close proximity to the ethynyl group (position 1) show a low-field shift towards 8.96 ppm, due to the ring current cone of the triple bond. Contrary, resonances at the second phenylene entity (positions 5 to 8) do not appear above 7.68 ppm. The 31P{1H} NMR spectrum of 13 displays doublets at 20.0 ppm (2JP,P = 46.1 Hz) and 7.0 ppm (2JP,P = 46.1 Hz). Notably, the latter appeared significantly broadened, probably caused by the increased trans-effect/influence (vide infra) of the vinyl compared to the iodo ligand, resulting in a weaker P–Pd bond more likely to dissociate.
Synthesis, density functional theory, molecular docking and antioxidant studies of ruthenium(II) carbonyl complex of N-dehydroacetic acid-4-aminoantipyrene
Published in Journal of Coordination Chemistry, 2022
P. S. Jaget, P. K. Vishwakarma, M. K. Parte, R. C. Maurya
The optimized molecular structures of 1 and 2 are presented in Figures 6 and 7, respectively, and selected geometrical parameters of 2 are listed in Table S3. The coordination environment around the Ru ion is a slightly distorted octahedron. The angles in trans positions [C(27)–Ru–N(10) = 174.97°; H(26)–Ru–P(29) = 178.05° and O(5)–Ru–O(13) = 174.97°] confirm distortion. An ONO-donor Schiff base monoanionic tridentate ligand chelates ruthenium with bite angles of O(5)–Ru–N(10) (= 87.67°) and N(10)–Ru–O(13) (= 81.82°). The basal plane contains O, N, and O of the monobasic tridentate Schiff ligand and the carbonyl carbon. The carbonyl is trans to the N donor (N(10)–Ru–C(27) 172.441°). The hydride is trans to PPh3 ligand. Ru-P bond distance is longer due to the trans effect of the hydride ligand. The Ru–P distance at 2.697 Å is comparable with other ruthenium complexes, and the interatomic Ru–H, Ru–C, Ru–N and Ru–O distances are expected [33–35]. In 1, the (>C = O), (˗C = N˗) and (C–O–) distances are 1.224, 1.341 and 1.263 Å, while after complexation, the bond distances are 1.285, 1.347 and 1.304 Å, increased due to coordination.
The effect of substituents on the reactivity of dichloridotriphenylphosphinoruthenium(II) complexes: kinetic and mechanistic study
Published in Journal of Coordination Chemistry, 2021
Meshack K. Sitati, Gershom Kyalo Mutua, Daniel O. Onunga, Deogratius Jaganyi, Allen Mambanda
The trend in the rate of substitution increases in the same way as the electron donor strength, indicating that the reactivity is driven by σ-trans-effect where electron density donated to Ru(II) repels the electrons in the chloro ligand and thus weakening the Ru-Cl bond resulting in increased reactivity. The strength of the trans-effect increases from 1 to 3 in line with the trend in the reactivity. Evidence in support of increase in electron donation going from 1 to 3 is further indicated by decrease in DFT calculated NBO charges on the Ru metal center in the order 0.171 (1) > 0.164 (2) > 0.151 (3), confirming that 3 is the least electrophilic. Further evidence of electron donation in these complexes is seen in the raising of the HOMO energy as donor effect increases (–5.488 (1) < −5.471 (2) < −5.360 (3)). It has been reported that strong electron donors raise the HOMO energy [31–33]. The very high σ-trans-effect in 3 results in unusually high reactivity compared to 1 and 2 which is due to donation of electrons from both cis and trans positions. The trans-effect has been observed in a number of studies [29].