Synthesis and characterization of poly(proyleneimine)-based Rhodium(I) Metallodendrimers and their evaluation as Hydroformylation catalysts

A series of new iminopyridyl- and iminophosphine-functionalized dendritic ligands were synthesized by reacting the commercially available first and second-generation DAB poly(propyleneimine) (PPI) dendrimers with 4-pyridinecarboxaldehyde and 2-(diphenylphosphino)benzaldehyde respectively via a Schiff-base condensation reaction. The ligands were characterized using NMR and IR spectroscopies, elemental analyses and mass spectrometry. Model monomeric analogues of these multimeric ligands were synthesized to aid with interpreting the more complex spectra of the dendritic ligands. The iminopyridyl-functionalized ligands were reacted with [RhCl(COD)]2 to yield a set of new mononuclear and multinuclear rhodium(I) complexes that coordinated selectively to the pyridyl nitrogen in a monodentate coordination mode. The iminophosphine functionalized ligands were reacted with [RhCl(CO)2]2. These reactions yielded a set of new mononuclear and multinuclear iminophosphine rhodium(I) complexes, where the P,N-donor iminophosphine ligands coordinated to the rhodium metal center in a heterobidentate coordination mode to form chelate complexes. The complexes were characterized using NMR and IR spectroscopies, elemental analyses and mass spectrometry. Crystals of the mononuclear iminophosphine rhodium(I) complex were obtained and the molecular structure solved using single crystal X-ray diffraction analysis. Chemical reactivity studies were conducted on the mononuclear and multinuclear iminopyridyl and iminophosphine complexes. The iminopyridyl rhodium(I) complexes were reacted with triphenylphosphine. These reactions yielded similar results to that of the reaction between the iminopyridylfunctionalized ligands and [RhCl(PPh3)3]. Methyl iodide was reacted with the mononuclear and multinuclear iminophosphine rhodium(I) complexes. Reactions of methyl iodide with the mononuclear iminophosphine rhodium(I) complex yielded a mixture of the oxidative addition and the acyl product, where the acyl product results from a subsequent alkyl migration into the metal carbonyl bond after oxidative addition has occurred. Reaction of methyl iodide with the multinuclear metallodendritic iminophosphine rhodium(I) complexes yielded the oxidative addition product exclusively. Reaction products were monitored using IR spectroscopy. Selected mononuclear and multinuclear iminopyridyl and iminophosphine rhodium(I) complexes were evaluated as catalysts in the hydroformylation of 1-octene. The complexes showed moderate hydroformylation rates under mild conditions. The multinuclear metallodendritic rhodium(I) complexes compare favorably to that of the mononuclear rhodium(I) complexes showing slightly enhanced catalytic activity and regioselectivity in certain cases. Hydroformylation results obtained when using these complexes compare well to results obtained when using [Rh(acac)(CO)2] under similar conditions, a rhodium(I) complex commonly used in literature

(Acetylacetonato-j2O,O0)carbonyl[tris(4- chlorophenyl)phosphane-jP]rhodium(I)

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Imino-phospine palladium (II) and platinum (II) complexes: Synthesis, molecular structures and evaluation as antitumor agents

The imino-phosphine ligands L1 and L2 were prepared via condensation reaction of 2-(diphenylphosphino) benzaldehyde with substituted anilines and obtained in very good yields. An equimolar reaction of L1 and L2 with either PdCl2(cod) or PtCl2(cod) gave new palladium(II) and platinum(II) complexes 1–4. The compounds were characterized by elemental analysis, IR, 1H and 31P NMR spectroscopy. The molecular structures of 2, 3 and 4 were confirmed by X-ray crystallography. All the three molecular structures crystallized in monoclinic C2/c space system. The coordination geometry around the palladiumand platinumatoms in respective structures exhibited distorted square planar geometry at the metal centers. The complexes were evaluated in vitro for their cytotoxic activity against human breast (MCF-7) and human colon (HT-29) cancer cells, and they exhibited growth inhibitory activities and selectivity that were superior to the standard compound cisplatin.Web of Scienc

The evaluation of dendrimer encapsulated ruthenium nanoparticles, immobilised on silica, as catalysts in various catalytic reactions and the effect of ionic liquids on the catalytic activity

Ph.D. (Chemistry)This study discusses the preparation of various sized dendrimer encapsulated ruthenium nanoparticles (RuDEN) with the use of the generation 4 (G4), generation 5 (G5) and generation 6 (G6) hydroxyl-terminated poly(amidoamine) (PAMAM-OH) dendrimers as templating agents. The size of the nanoparticles ranges from 1.1-2.2 nm. The RuDENs were used as nanoparticle solutions in catalytic reactions or immobilised on amorphous silica 60 and silica 100 and subsequently referred to as RuSil catalysts. These catalysts were evaluated in the reduction of 4-nitrophenol, toluene hydrogenation, citral hydrogenation, cinnamaldehyde hydrogenation and styrene oxidation..

(Acetylacetonato-κ2O,O′)carbonyl[tris(4-chlorophenyl)phosphane-κP]rhodium(I)

The title compound, [Rh(C5H7O2)(C18H12Cl3P)(CO)], contains the bidentate acetylacetonate ligand coordinated to the RhI atom, forming a chelate ring [Rh—O = 2.0327 (15) and 2.0613 (14) Å]. The RhI atom is additionally coordinated by one P [Rh—P = 2.2281 (6) Å] and one carbonyl C [Rh—C = 1.812 (2) Å] atom, resulting in a slightly distorted square-planar geometry. The molecules are packed to minimize steric hindrance with the phosphanes positioned above and below the slightly distorted square geometrical plane

Preparation of Well-Defined Dendrimer Encapsulated Ruthenium Nanoparticles and Their Evaluation in the Reduction of 4‑Nitrophenol According to the Langmuir–Hinshelwood Approach

This study discusses the preparation of various sized dendrimer encapsulated ruthenium nanoparticles (RuDEN) with the use of the generation 4 (G4), generation 5 (G5), and generation 6 (G6) hydroxyl-terminated poly­(amidoamine) (PAMAM-OH) dendrimers as templating agents. The size of the nanoparticles ranges from 1.1 to 2.2 nm. These catalysts were fully characterized using UV/vis spectrophotometry, infrared (IR) spectroscopy, and transmission electron microscopy (TEM). The RuDEN catalysts were evaluated in the reduction of 4-nitrophenol (4NP) in the presence of sodium borohydride (BH₄^–) for various concentrations of either. The kinetic data obtained were modeled to the Langmuir–Hinshelwood equation. The model allows the relation of the apparent rate constant to the total surface area <i>S</i> of the nanoparticle, the kinetic constant <i>k</i> which is related to the rate-determining step, and the adsorption constants <i>K</i>_4NP and <i>K</i>_BH₄ for 4NP and borohydride, respectively. These parameters were calculated for each of the RuDENs, proving the Langmuir–Hinshelwood model to be suitable for the kinetic evaluation of RuDENs in the catalytic reduction of 4NP

Anticancer activity of multinuclear arene ruthenium complexes coordinated to dendritic polypyridyl scaffolds

The rational development of multinuclear arene ruthenium complexes (arene = p-cymene, hexamethylbenzene) from generation 1 (G1) and generation 2 (G2) of 4-iminopyridyl based poly(propyleneimine) dendrimer scaffolds of the type, DAB-(NH2)n (n = 4 or 8, DAB = diaminobutane) has been accomplished in order to exploit the ‘enhanced permeability and retention’ (EPR) effect that allows large molecules to selectively enter cancer cells. Four compounds were synthesised, i.e. [{(p-cymene)RuCl2}4G1] (1), [{(hexamethylbenzene)RuCl2}4G1] (2), [{(p-cymene)RuCl2}8G2] (3), and [{(hexamethylbenzene)RuCl2}8G2] (4), by first reacting DAB-(NH2)n with 4-pyridinecarboxaldehyde and subsequently metallating the iminopyridyl dendrimers with [(p-cymene)RuCl2]sub>2 or [(hexamethylbenzene)RuCl2]2. The related mononuclear complexes [(p-cymene)RuCl2(L)] (5) and [(hexamethylbenzene)RuCl2 (L)] (6) were obtained in a similar manner from N-(pyridin-4-ylmethylene)propan-1-amine (L). The molecular structure of 5 has been determined by X-ray diffraction analysis and the in vitro anticancer activities of the mono-, tetra- and octanuclear complexes 1–6 studied on the A2780 human ovarian carcinoma cell line showing a close correlation between the size of the compound and cytotoxicity