Hydrogenation of Carbon Dioxide to Formate by Noble Metal Catalysts Supported on a Chemically Stable Lanthanum Rod-Metal-Organic Framework.

The conversion of carbon dioxide to formate is of great importance for hydrogen storage as well as being a step to access an array of olefins. Herein, we have prepared a JMS-5 metal-organic framework (MOF) using a bipyridyl dicarboxylate linker, with the molecular formula [La2(bpdc)3/2(dmf)2(OAc)3]·dmf. The MOF was functionalized by cyclometalation using Pd(II), Pt(II), Ru(II), Rh(III), and Ir(III) complexes. All metal catalysts supported on JMS-5 showed activity for CO2 hydrogenation to formate, with Rh(III)@JMS-5a and Ir(III)@JMS-5a yielding 4319 and 5473 TON, respectively. X-ray photoelectron spectroscopy of the most active catalyst Ir(III)@JMS-5a revealed that the iridium binding energies shifted to lower values, consistent with formation of Ir-H active species during catalysis. The transmission electron microscopy images of the recovered catalysts of Ir(III)@JMS-5a and Rh(III)@JMS-5a did not show any nanoparticles. This suggests that the catalytic activity observed was due to Ir(III) and Rh(III). The high activity displayed by Ir(III)@JMS-5a and Rh(III)@JMS-5a compared to using the Ir(III) and Rh(III) complexes on their own is attributed to the stabilization of the Ir(III) and Rh(III) on the nitrogen and carbon atom of the MOF backbone.

Two novel metal-organic frameworks functionalised with pentamethylcyclopentadienyl iridium(III) chloride for catalytic conversion of carbon dioxide to formate.

Hydrogenation of CO2 to formate is a vital reaction, because formate is an excellent hydrogen carrier, which yields blue hydrogen. Blue hydrogen is comparatively cheaper and attractive as the world envisions the hydrogen economy. In this work, two isostructural lanthanide-based MOFs (JMS-6 and JMS-7 [Ln(bpdc)3/2(dmf)2(H2O)2]n) were prepared and used as support materials for molecular catalysts. The bipyridyl MOF backbone were functionalised using pentamethylcyclopentadienyl iridium(III) chloride to give Ir(III)@JMS-6a and Ir(III)@JMS-7a. XPS of the functionalised MOFs show downfield shifts in the N 1s binding energy indicating successful grafting of the complex to the MOF. Hydrogenation experiments in the presence of an organic base showed that the functionalised MOFs were active towards converting CO2 to formate. Ir(III)@JMS-6a and Ir(III)@JMS-7a exhibited the highest turnover numbers of 813 and 621 respectively. ICP-OES indicated insignificant leaching during catalysis. TEM images and XPS data of the recovered catalyst ruled out the presence of Ir(0), confirming that the activity observed was attributed to the molecular Iridium(III) centres.

Selective Cu and Ni-MOFs as pre-catalysts for the hydrogenation of furfural to furfuryl alcohol.

In this work, we report the design of one-dimensional (1D) metal-organic framework containing Cu(II) and Ni(II) active sites using a N,N'-bis-(4-pyridyl)isophthalamide linker to form MOF 1 [Cu1/2(L1)(NO3-)·DMF] and MOF 2 [Ni1/2L1Cl]. The MOFs were evaluated as heterogeneous catalysts for the hydrogenation of furfural to furfuryl alcohol. MOF 2 catalyst showed impressive performance with conversion of FF (81%) and selectivity towards FA (100%). Post-experimental characterisation showed that the structural integrity of the MOF 2 was not altered after catalysis. The catalyst could also be reused several times without any significant loss in activity and selectivity. Furthermore, a possible plausible reaction mechanism of the reaction over MOF 2 was proposed.

The Transfer Hydrogenation of Cinnamaldehyde Using Homogeneous Cobalt(II) and Nickel(II) (E)-1-(Pyridin-2-yl)-N-(3-(triethoxysilyl)propyl)methanimine and the Complexes Anchored on Fe3O4 Support as Pre-Catalysts: An Experimental and In Silico Approach.

The imino pyridine Schiff base cobalt(II) and nickel(II) complexes (C1 and C2) and their functionalised γ-Fe3O4 counterparts (Fe3O4@C1 and Fe3O4@C2) were synthesised and characterised using IR, elemental analysis, and ESI-MS for C1 and C2, and single crystal X-ray diffraction for C1, while the functionalised materials Fe3O4@C1 and Fe3O4@C2 were characterized using IR, XRD, SEM, TEM, EDS, ICP-OES, XPS and TGA. Complexes C1, C2 and the functionalised materials Fe3O4@C1 and Fe3O4@C2 were tested as catalysts for the selective transfer hydrogenation of cinnamaldehyde and all four pre-catalysts showed excellent catalytic activity. Complexes C1 and C2 acted as homogeneous catalysts with high selectivity towards the formation of hydrocinnamaldehyde (88.7% and 92.6%, respectively) while Fe3O4@C1 and Fe3O4@C2 acted as heterogeneous catalysts with high selectivity towards cinnamyl alcohol (89.7% and 87.7%, respectively). Through in silico studies of the adsorption energies, we were able to account for the different products formed using the homogeneous and the heterogeneous catalysts which we attribute to the preferred interaction of the C=C moiety in the substrate with the Ni centre in C2 (-0.79 eV) rather than the C=O (-0.58 eV).

New Triazolyl N

Cisplatin and other metallodrugs have realised great success in clinical chemotherapeutic applications as anticancer drugs. However, severe toxicity to healthy cells and non-selectivity to cancer cells remains a challenge, warranting the further search for alternative agents. Herein, we report the anticancer potential of a series of complexes of the general formula [MCl(p-cym)(k2-N^N-L)]+ X− and [MCl(Cp*)(k2-N^N-L)]+ X−, where M is the metal centre (Ru(II), Os(II), Rh(III) or Ir(III)), L = 1-benzyl-4-pyridinyl-1-H-1,2,3-triazole for L1 and 1-picolyl-4-pyridinyl-1-H-1,2,3-triazole for L2 and X− = Cl−, BF4−, BPh4−. When evaluated for activity against some cancerous and non-cancerous cell lines (namely, HeLa, HEK293, A549 and MT4 cancer cells and the normal healthy kidney cells (BHK21)), most of the compounds displayed poor cytotoxicities against cancer cells except for complexes C2 ([RuCl(p-cym)(k2-N^N-L1)]+ BPh4−, EC50 = 9−16 µM and SI = 14), C7 ([RuCl(p-cym)(k2-N^N-L2)]+ BPh4−, EC50 = 17−53 µM and SI = 4) and C11 ([IrCl(Cp*)(k2-N^N-L2)]+ BF4−, EC50 < 5 µM and SI > 10). Selected complexes C1 ([RuCl(p-cym)(k2-N^N-L1)]+ BF4−), C5 ([IrCl(Cp*)(k2-N^N-L1)]+ BF4−) and C11 showed significant interactions with model biomolecules such as guanosine-5'-monophosphate (5'-GMP), bovine serum albumin (BSA) and amino acids under physiological conditions, possibly through carbenylation and N-coordination with 5'-GMP, N-coordination with L-Histidine and L-proline. While the compounds showed good activities in reducing pyruvate to lactate, there was no direct correlation between catalytic transfer hydrogenation of pyruvate and the observed cytotoxic activities. As observed in this work, the marked influence of single atom replacement in ligand may provide a pivotal approach to improving the cytotoxicity and fine-tuning the selectivity to cancer cells.

Investigating cyanogen rich Manihot esculenta efficacy for Ru phytomining and application in catalytic reactions.

Phytomining is a newly developing alternative green technology. This technology has been applied for recovering precious metals from mine tailings that are low-grade ores. In this study, effective catalytic transfer hydrogenation of furfural to furfural alcohol was investigated using a ruthenium (Ru) bio-based catalyst, Ru@CassCat. The catalyst was prepared from Ru rich bio-ore recovered during laboratory scale phytomining as a model of mining tailing using the cassava plant (Manihot esculenta). Pre-rooted cassava cuttings were propagated and watered with Ru rich solutions for ten weeks before harvest. Harvested cassava roots were calcined to produce the bio-ore used as an in situ bio-based catalyst. The properties of the catalyst were characterized by various techniques, which include transmission electron microscopy (TEM), Fourier transform infrared (FT-IR) spectroscopy, scanning electron microscopy coupled to energy-dispersive X-ray spectroscopy (SEM-EDS), powder X-ray diffraction (pXRD), ultraviolet-visible (UV-Vis) spectroscopy, thermogravimetric analysis (TGA) and Brunauer-Emmett-Teller (BET) theory. Characterization by FTIR, SEM and TEM revealed that RuCassCat has spherical component particles, loosely arranged around a cellulose/lignin-like matrix of the biocatalyst. It was also found that calcination strengthened the structure and texture of the support carbon matrix to distribute the Ru particles evenly. An ICP-MS analysis showed that up to 295 µg g-1 of Ru was detected in cassava roots. The variation of test conditions, namely, temperature, time, base, catalyst load, and a hydrogen source, was investigated. Optimally, a 0.00295 wt% ruthenium loading on the Ru@CassCat catalyst resulted in 100% furfural conversion with a turnover frequency of 0.0114 million per hour at 160 °C for 24 h using triethylamine as a base and formic acid as a hydrogen source. The catalyst remained active for up to three recycles, consecutively and produced furfural alcohol in high turnover numbers.

Chiral-at-Metal: Iridium(III) Tetrazole Complexes With Proton-Responsive P-OH Groups for CO2 Hydrogenation.

A rise in atmospheric CO2 levels, following years of burning fossil fuels, has brought about increase in global temperatures and climate change due to the greenhouse effect. As such, recent efforts in addressing this problem have been directed to the use of CO2 as a non-expensive and non-toxic single carbon, C1, source for making chemical products. Herein, we report on the use of tetrazolyl complexes as catalyst precursors for hydrogenation of CO2. Specifically, tetrazolyl compounds bearing P-S bonds have been synthesized with the view of using these as P∧N bidentate tetrazolyl ligands (1-3) that can coordinate to iridium(III), thereby forming heteroatomic five-member complexes. Interestingly, reacting the P,N'-bidentate tetrazolyl ligands with [Ir(C5 Me 5)Cl 2]2 led to serendipitous isolation of chiral-at-metal iridium(III) half-sandwich complexes (7-9) instead. Complexes 7-9 were obtained via prior formation of non-chiral iridium(III) half-sandwich complexes (4-6). The complexes undergo prior P-S bond heterolysis of the precursor ligands, which then ultimately results in new half-sandwich iridium(III) complexes featuring monodentate phosphine co-ligands with proton-responsive P-OH groups. Conditions necessary to significantly affect the rate of P-S bond heterolysis in the precursor ligand and the subsequent coordination to iridium have been reported. The complexes served as catalyst precursors and exhibited activity in CO2 and bicarbonate hydrogenation in excellent catalytic activity, at low catalyst loadings (1 µmol or 0.07 mol% with respect to base), producing concentrated formate solutions (ca 180 mM) exclusively. Catalyst precursors with proton-responsive P-OH groups were found to influence catalytic activity when present as racemates, while ease of dissociation of the ligand from the iridium center was observed to influence activity in spite of the presence of electron-donating ligands. A test for homogeneity indicated that hydrogenation of CO2 proceeded by homogeneous means. Subsequently, the mechanism of the reaction by the iridium(III) catalyst precursors was studied using 1H NMR techniques. This revealed that a chiral-at-metal iridium hydride species generated in situ served as the active catalyst.

Synthesis and Characterization of 2D Metal-Organic Frameworks for Adsorption of Carbon Dioxide and Hydrogen.

The reaction of Cd(NO3)2·4H2O and Zn(NO3)2·6H2O with the bipyridyl dicarboxylate ligand H2bpydc (2,2'-bipyridine-4,4'-dicarboxylic acid) afforded two porous metal organic frameworks [Cd(bpydc)2(DMF)2·2DMF]n (JMS-3) and [Zn(bpydc)(DMF)·DMF]n (JMS-4). X-ray diffraction studies revealed that both JMS-3 and JMS-4 crystallize in the monoclinic crystal. The MOFs possess 2D interdigited networks with (sql) topology. Sorption studies showed that the activated phase of JMS-3 had CO2 volumetric uptakes of 26.50 and 30.89 cm3 (STP) g-1 (1.18 and 1.39 mmol g-1) whist JMS-4 gave 10.96 and 16.08 cm3 (STP) g-1 (0.49 and 0.71 mmol g-1) at 298 and 273 K respectively.

Synthesis and anti-cancer activity of bis-amino-phosphine ligand and its ruthenium(II) complexes.

The development of both chemotherapeutic drug resistance as well as adverse side effects suggest that the current chemotherapeutic drugs remain ineffective in treating the various types of cancers. The development of new metallodrugs presenting anti-cancer activity is therefore needed. Ruthenium complexes have gained a great deal of interest due to their promising anti-tumour properties and reduced toxicity in vivo. This study highlighted the effective induction of cell death in a malignant melanoma cell by two novel bis-amino-phosphine ruthenium(II) complexes referred to as GA105 and GA113. The IC50 concentrations were determined for both the complexes, the ligand and cisplatin, for comparison. Both complexes GA105 and GA113 displayed a high anti-cancer selectivity profile as they exhibited low IC50 values of 6.72 µM and 8.76 µM respectively, with low toxicity towards a non-malignant human cell line. The IC50 values obtained for both complexes were lower than that of cisplatin. The new complexes were more effective compared to the free ligand, GA103 (IC50 = >20 µM). Morphological studies on treated cells induced apoptotic features, which with further studies could indicate an intrinsic cell death pathway. Additionally, flow cytometric analysis revealed that the mode of cell death of complex GA113 was apoptosis. The outcomes herein give further insight into the potential use of selected Ru(II) complexes as alternative chemotherapeutic drugs in the future.

Palladium(II) Immobilized on Metal-Organic Frameworks for Catalytic Conversion of Carbon Dioxide to Formate.

In this work, we report the design of a two-dimensional (2D) isostructural metal-organic framework containing Pd(II) active sites, using a bipyridyl dicarboxylate linker (Mg(bpdc)(DMF)2PdCl2]n (Pd@Mg:JMS-2) and [Mn(bpdc)(DMF)2PdCl2]n(Pd@Mn:JMS-2)). The activated MOFs Pd@Mg:JMS-2a and Pd@Mn:JMS-2a were evaluated as heterogeneous catalysts for the hydrogenation of carbon dioxide (CO2) to formate. Under optimal conditions, the MOFs exhibited impressive catalytic activity with formate turnover numbers of 7272 and 9808 for Pd@Mg:JMS-2a and Pd@Mn:JMS-2a, respectively, after 24 h. These catalysts exhibited higher catalytic activity when compared to its homogeneous counterpart that was used as a linker during MOF synthesis. Post-experimental characterization showed that the structural integrity of the MOFs was not altered after catalysis. This work demonstrates that the catalytic activity of homogeneous systems can be enhanced under heterogeneous conditions by anchoring them on MOFs.

Cyclometalation of lanthanum(iii) based MOF for catalytic hydrogenation of carbon dioxide to formate.

The hydrogenation of carbon dioxide (CO2) to formic acid is of great importance due to its useful properties in the chemical industry. In this work, we have prepared a novel metal-organic framework (MOF), JMS-1, using bipyridyl dicarboxylate linkers, with molecular formula [La2(bpdc)3(DMF)3] n . Network analysis of JMS-1 revealed a new 7-connected topology (zaz). The MOF backbone of the activated phase (JMS-1a) was functionalized by cyclometalation using [RuCl2(p-cymene)]2 to produce Ru(ii)@JMS-1a. Both JMS-1a and Ru(ii)@JMS-1a were able to convert CO2 in the presence of hydrogen to formate. Ru(ii)@JMS-1a displayed outstanding conversion evidenced by a yield of 98% of formate under optimized conditions of total pressure 50 bar (CO2/H2 = 1 : 4, temperature 110 °C, time 24 h, 5 mmol KOH, 8 mL ethanol). This work is significant in providing new strategies of incorporating active catalytic centres in MOFs for efficient and selective conversion of CO2 to formate.

A Novel Series of N-aryltriazole and N-acridinyltriazole Hybrids as Potential Anticancer Agents.

BACKGROUND: Triazoles are a class of aza-heterocycles with broad spectrum of biological importance. The synthetic tunability of the triazole moiety allows for the development of new pharmacophores with applications as drugs to contend with the burden of cancer. OBJECTIVE: In this study, we aimed to develop a series of N-aryltriazole and N-acridinyltriazole molecular hybrids and evaluate their potential as anticancer agents. METHODS: The triazole derivatives (1-10) were synthesized via a tandem nucleophilic substitution of aryl chlorides with sodium azide followed by 1,3-dipolar cycloaddition of the resulting organic azides with terminal/internal alkynes. From terminal alkynes, the well established copper(I) catalyzed azide-alkynes 1,3- dipolar cycloaddition, a premier example of click chemistry, was employed to access the 1,4-regioisomers of N-benzyl-1H-1,2,3-triazoles and N-acridynyl-1H-1,2,3-triazoles. All the compounds thus synthesized were characterized by 1D and 2D NMR spectroscopy and high resolution mass spectrometry. RESULTS: Thermally controlled 1,3-dipolar cycloaddition was used to deliver N-aryl-1H-1,2,3-triazoles with 1,4,5-substitution on the triazole framework. The unprecedented high regioselectivity promoted by the sterically-strained silylated 1,4,5-trisubstituted moiety 4a offers a useful synthetic precursor with the silyl group being a synthetic handle for further structural elaboration to the desired 1,(4),5-di(tri)substituted 1,2,3- triazoles. Notably, anticancer evaluation revealed good cytotoxic activities of the novel acridinyltriazole hybrids (6-10) at micromolar concentrations in the range of 12.5 µM-100 µM against cervical cancer HeLa, kidney cancer HEK293, lung cancer A549 and leukemic MT4 cancer cell lines (p < 0.05). CONCLUSION: A series of novel triazole-based acridine hybrids have been developed as potential leads for the development of multifaceted anticancer agents.

Water-soluble SNS cationic palladium(II) complexes and their Suzuki-Miyaura cross-coupling reactions in aqueous medium.

Unlike their SCS analogues, SNS pincer complexes are poorly studied for their use in coupling reactions. Accordingly, a series of water soluble cationic Pd(II) SNS pincer complexes have been successfully synthesised and investigated in detail for their catalytic activity in Suzuki-Miyaura coupling reactions. By using only 0.5 mol % loading of the complexes, the coupling of inactivated aryl bromides and activated aryl chlorides with various boronic acids in water was achieved in excellent yields and the catalysts were found to be reusable for three cycles without a significant loss of activity. The investigation of the mechanism of the reaction revealed that a Pd(II) to Pd(IV) route is the more likely pathway which was further supported by computational studies.

Synthesis, characterization and evaluation of bulky bis(pyrazolyl)palladium complexes in Suzuki-Miyaura cross-coupling reactions.

Pyrazole-containing compounds have been used in recent times as ligands to stabilize metal complexes used as pre-catalysts in cross-coupling reactions. With various substituents at various positions in the pyrazole ring, the overall electrophilic and steric properties of the metal complexes can be fine-tuned. Herein, we report the synthesis of bulky pyrazole-based ligands by condensation of methyl 4-(bromomethyl)benzoate or benzyl bromide with various substituted pyrazole compounds. These ligands were utilised in the synthesis of bis(pyrazolyl)palladium(ii) complexes. The complexes' catalytic activity in Suzuki-Miyaura cross-coupling reactions was evaluated. Phenyl bearing pre-catalyst 7, at a catalyst loading of 0.33 mol%, successfully converted 98% of bromobenzene and phenylboronic acid to biphenyl in 4 h at 140 °C, while the tertiary butyl bearing pre-catalyst 8 converted up to 81% of the same substrates to biphenyl. An increase in conversion was seen for all pre-catalysts when an electron-withdrawing substituent was present on the aryl halide substrate, and the opposite was observed when the electron-withdrawing group was present on the phenyl boronic acid.

Aqueous-phase hydroformylation of 1-octene using hydrophilic sulfonate salicylaldimine dendrimers.

Water-soluble dendritic ligands based on tris-2-(5-sulfonato salicylaldimine ethyl)amine (5) and DAB-(5-sulfonato salicylaldimine) (6) (DAB = diaminobutane) were synthesized by means of Schiff base condensation and sulfonation reactions. These dendritic ligands were fully characterized by (1)H NMR, (13)C NMR and FT-IR spectroscopy, elemental analysis and mass spectrometry. Dendritic ligands (5 and 6) in combination with [RhCl(COD)](2) (COD = 1,5-cyclooctadiene) were evaluated in aqueous biphasic hydroformylation of 1-octene. New water-soluble mononuclear 5-sulfonato propylsalicylaldimine Rh(i) complexes (7 and 8) were synthesized and characterized using (1)H NMR, (13)C NMR and FT-IR spectroscopy, elemental analysis as well as mass spectrometry. These complexes were applied as catalyst precursors in aqueous biphasic hydroformylation reactions. All the catalyst precursors were active in the hydroformylation of 1-octene under the investigated conditions. Optimal conditions were realized at 75 °C (40 bars), where the best selectivity for aldehydes was noticed. Catalyst recycling was achieved up to 5 times with minimal loss in conversion and consistent chemoselectivities and regioselectivities. Less Rh leaching was observed in the dendritic systems (5 and 6)/[RhCl(COD)](2) as compared to mononuclear catalyst precursors (7 and 8) as determined by inductively coupled plasma-mass spectrometry (ICP-MS).

Hydroformylation of 1-octene using low-generation Rh(I) metallodendritic catalysts based on a tris-2-(2-pyridyliminoethyl)amine scaffold.

The synthesis and characterization of low-generation pyridylimine Rh(I) metallodendrimers is described. These metallodendrimers were obtained via a Schiff base condensation of tris-2-(aminoethyl)amine with 2-pyridinecarboxaldehyde to afford the tris-2-(2-pyridylimine ethyl) amine ligand (1). Subsequent complexation reactions with [RhCl(CO)(2)](2) and [RhCl(COD)](2) yielded the corresponding metal-containing dendrimers containing -RhCl(CO) and -Rh(COD) moieties on the periphery. These new rhodium metallodendrimers (2 and 3) and their precursor ligand (1) are thermally stable and have been characterized using (1)H NMR, (13)C NMR, (31)P NMR, FT-IR spectroscopy, elemental analysis as well as mass spectrometry. The Rh(I) metallodendrimers are highly active and chemo- and regioselective in the hydroformylation of 1-octene. Aldehydes were favoured at moderate to high temperatures (95 °C and 75 °C) and pressure (30 bars), while more iso-octenes were formed at low temperature (55 °C) and pressures (5 and 10 bars). The mononuclear analogues (5 and 6) also produced more aldehydes (albeit showing catalyst decomposition at 95 °C and 75 °C, 30 bars) and these aldehydes were mostly branched.