pH-Triggered Assembly of Organometallic Receptors for Lithium Ions

The reaction of half-sandwich complexes of ruthenium, rhodium, and iridium with amino-substituted 3-hydroxy-2-pyridone ligands in aqueous solution gives monomeric O,O‘-chelate complexes. Upon addition of base, the complexes assemble to form trimeric metallamacrocycles, as evidenced by NMR spectroscopy and single-crystal X-ray analyses. The macrocycles are able to act as highly selective receptors for lithium ions. The binding constants depend on the nature of the half-sandwich complex, the ligand, and the pH. With a commercially available (cymene)Ru complex, a receptor with a Li+ binding constant of Ka = 5.8 (±1.0) × 104 M-1 and a Li+−Na+ selectivity of 10 000:1 can be obtained. The fact that the assembly process of the receptor is pH-dependent can be used to detect the presence of lithium ions by a pH measurement. Furthermore, it is possible to transduce the binding of Li+ into a change of color by means of a chemical reaction with FeCl3. This allows the detection of Li+ in the pharmacologically relevant concentration range of 0.5−1.5 mM by the “naked eye”

Synthesis, Structure, and Reactivity of the Methoxy-Bridged Dimer [Cp^∧Ru(μ-OMe)]₂ (Cp^∧ = η⁵-1-Methoxy-2,4-di<i>-tert</i>-butyl-3-neopentylcyclopentadienyl)

The methoxy-bridged RuII complex [Cp∧Ru(μ-OMe)]2 (Cp∧ = η5-1-methoxy-2,4-di-tert-butyl-3-neopentylcyclopentadienyl) was obtained from the RuIII complex [Cp∧RuCl(μ-Cl)]2 by reaction with K2CO3 in methanol. In the presence of EtOH, the complex was converted into the ethoxy-bridged dimer [Cp∧Ru(μ-OEt)]2. Due to the steric demand of the Cp∧ π-ligand, complex [Cp∧Ru(μ-OMe)]2 behaves differently than the parent complex [Cp*Ru(μ-OMe)]2. Reaction with Me3SiCl in the presence of LiCl gave the electronically unsaturated complex [Cp∧Ru(μ-Cl)]2, whereas a tetrameric structure had been reported for the analogous Cp* complex. In contrast to the expected addition reaction, a monomeric complex [Cp∧Ru(CO)2(CO2Me)] was obtained by ligand insertion of CO in the Ru−OMe bond. Moreover, an unprecedented transformation of cyclooctadiene into ethylbenzene in the coordination sphere of Ru was observed. Complex [Cp∧Ru(μ-OMe)]2 was found to act as a highly active catalyst for atom transfer radical cyclization (ATRC) reactions on a diverse range of substrates such as N-substituted dichloro- and trichloroacetamides, enamides, ethers, and esters

CO₂ and CO/H₂ Conversion to Methoxide by a Uranium(IV) Hydride

Here we show that a scaffold combining siloxide ligands and a bridging oxide allows the synthesis and characterization of the stable dinuclear uranium­(IV) hydride complex [K2{[U­(OSi­(OtBu)3)3]2(μ-O)­(μ-H)2}], 2, which displays high reductive reactivity. The dinuclear bis-hydride 2 effects the reductive coupling of acetonitrile by hydride transfer to yield [K2{[U­(OSi­(OtBu)3)3]2(μ-O)­(μ-κ2-NC­(CH3)­NCH2CH3)}], 3. Under ambient conditions, the reaction of 2 with CO affords the oxomethylene2– reduction product [K2{[U­(OSi­(OtBu)3)3]2(μ-CH2O)­(μ-O)}], 4, that can further add H2 to afford the methoxide hydride complex [K2{[U­(OSi­(OtBu)3)3]2(μ-OCH3)­(μ-O)­(μ-H)}], 5, from which methanol is released in water. Complex 2 also effects the direct reduction of CO2 to the methoxide complex 5, which is unprecedented in f element chemistry. From the reaction of 2 with excess CO2, crystals of the bis-formate carbonate complex [K2{[U­(OSi­(OtBu)3)3]2(μ-CO3)­(μ-HCOO)2}], 6, could also be isolated. All the reaction products were characterized by X-ray crystallography and NMR spectroscopy

CO₂ and CO/H₂ Conversion to Methoxide by a Uranium(IV) Hydride

Here we show that a scaffold combining siloxide ligands and a bridging oxide allows the synthesis and characterization of the stable dinuclear uranium­(IV) hydride complex [K2{[U­(OSi­(OtBu)3)3]2(μ-O)­(μ-H)2}], 2, which displays high reductive reactivity. The dinuclear bis-hydride 2 effects the reductive coupling of acetonitrile by hydride transfer to yield [K2{[U­(OSi­(OtBu)3)3]2(μ-O)­(μ-κ2-NC­(CH3)­NCH2CH3)}], 3. Under ambient conditions, the reaction of 2 with CO affords the oxomethylene2– reduction product [K2{[U­(OSi­(OtBu)3)3]2(μ-CH2O)­(μ-O)}], 4, that can further add H2 to afford the methoxide hydride complex [K2{[U­(OSi­(OtBu)3)3]2(μ-OCH3)­(μ-O)­(μ-H)}], 5, from which methanol is released in water. Complex 2 also effects the direct reduction of CO2 to the methoxide complex 5, which is unprecedented in f element chemistry. From the reaction of 2 with excess CO2, crystals of the bis-formate carbonate complex [K2{[U­(OSi­(OtBu)3)3]2(μ-CO3)­(μ-HCOO)2}], 6, could also be isolated. All the reaction products were characterized by X-ray crystallography and NMR spectroscopy

pH-Triggered Assembly of Organometallic Receptors for Lithium Ions

The reaction of half-sandwich complexes of ruthenium, rhodium, and iridium with amino-substituted 3-hydroxy-2-pyridone ligands in aqueous solution gives monomeric O,O‘-chelate complexes. Upon addition of base, the complexes assemble to form trimeric metallamacrocycles, as evidenced by NMR spectroscopy and single-crystal X-ray analyses. The macrocycles are able to act as highly selective receptors for lithium ions. The binding constants depend on the nature of the half-sandwich complex, the ligand, and the pH. With a commercially available (cymene)Ru complex, a receptor with a Li+ binding constant of Ka = 5.8 (±1.0) × 104 M-1 and a Li+−Na+ selectivity of 10 000:1 can be obtained. The fact that the assembly process of the receptor is pH-dependent can be used to detect the presence of lithium ions by a pH measurement. Furthermore, it is possible to transduce the binding of Li+ into a change of color by means of a chemical reaction with FeCl3. This allows the detection of Li+ in the pharmacologically relevant concentration range of 0.5−1.5 mM by the “naked eye”

Beyond Click-Chemistry: Transformation of Azides with Cyclopentadienyl Ruthenium Complexes

The cyclopentadienyl Ru complexes Cp*RuCl(cod) (cod = 1,5-cyclooctadiene), Cp*RuCl(PPh3)2, and [Cp∧RuCl2]2 (Cp∧ = η5-1-methoxy-2,4-di-tert-butyl-3-neopentylcyclopentadienyl) are able to catalyze the decomposition of benzyl azides to give 1,3,5-triphenyl-2,4-diazapenta-1,4-diene (“hydrobenzamide”), benzyl-benzylideneamine, and benzonitrile. Reactions with the catalyst precursor [Cp∧RuCl2]2 are particularly fast and give hydrobenzamide with high selectivity. A similar coupling reaction is observed for other benzylic azides but not for (2-azidoethyl)benzene and ethyl-4-azidobutanoate. If the reactions are performed in the presence of water, benzylic azides are converted into aldehydes. Mononuclear tetrazene complexes are formed in stoichiometric reactions of [Cp∧RuCl2]2 with benzyl azide and (2-azidoethyl)benzene

pH-Triggered Assembly of Organometallic Receptors for Lithium Ions

The reaction of half-sandwich complexes of ruthenium, rhodium, and iridium with amino-substituted 3-hydroxy-2-pyridone ligands in aqueous solution gives monomeric O,O‘-chelate complexes. Upon addition of base, the complexes assemble to form trimeric metallamacrocycles, as evidenced by NMR spectroscopy and single-crystal X-ray analyses. The macrocycles are able to act as highly selective receptors for lithium ions. The binding constants depend on the nature of the half-sandwich complex, the ligand, and the pH. With a commercially available (cymene)Ru complex, a receptor with a Li+ binding constant of Ka = 5.8 (±1.0) × 104 M-1 and a Li+−Na+ selectivity of 10 000:1 can be obtained. The fact that the assembly process of the receptor is pH-dependent can be used to detect the presence of lithium ions by a pH measurement. Furthermore, it is possible to transduce the binding of Li+ into a change of color by means of a chemical reaction with FeCl3. This allows the detection of Li+ in the pharmacologically relevant concentration range of 0.5−1.5 mM by the “naked eye”

pH-Triggered Assembly of Organometallic Receptors for Lithium Ions

The reaction of half-sandwich complexes of ruthenium, rhodium, and iridium with amino-substituted 3-hydroxy-2-pyridone ligands in aqueous solution gives monomeric O,O‘-chelate complexes. Upon addition of base, the complexes assemble to form trimeric metallamacrocycles, as evidenced by NMR spectroscopy and single-crystal X-ray analyses. The macrocycles are able to act as highly selective receptors for lithium ions. The binding constants depend on the nature of the half-sandwich complex, the ligand, and the pH. With a commercially available (cymene)Ru complex, a receptor with a Li+ binding constant of Ka = 5.8 (±1.0) × 104 M-1 and a Li+−Na+ selectivity of 10 000:1 can be obtained. The fact that the assembly process of the receptor is pH-dependent can be used to detect the presence of lithium ions by a pH measurement. Furthermore, it is possible to transduce the binding of Li+ into a change of color by means of a chemical reaction with FeCl3. This allows the detection of Li+ in the pharmacologically relevant concentration range of 0.5−1.5 mM by the “naked eye”

The Enigmatic Nature of Rh^ICl(cyclopentadienone) Complexes: Dimers, Trimers, and Tetramers

Although RhICl(cyclopentadienone) complexes have been known for more than 40 years, structural data were so far not available. We have investigated the complexes [RhCl(tetraphenylcyclopentadienone)]n (1), [RhCl(2,5-diethyl-3,4-diphenylcyclopentadienone)]n (4), and [RhCl(phencyclone)]n (5) by single-crystal X-ray crystallography. Contrary to what has been observed for simple olefin complexes such as [RhCl(1,5-cyclooctadiene)]2, they crystallize as trimers (4 and 5) or tetramers (1), in which the RhCl(cyclopentadienone) fragments are aggregated via Rh−(μ-Cl) and Rh−(μ-OC) bonds. When crystallized from acetonitrile, however, complex 4 was found to form the dimeric adduct [Rh(μ-Cl)(CH3CN)(2,5-diethyl-3,4-diphenylcyclopentadienone)]2 (6), whereas the phencyclone complex gave an ionic structure (7) resulting from chloride transfer. In solution, all complexes form solvent- and concentration-dependent dynamic equilibria

Syntheses and Structures of the Trinuclear Ruthenium Complexes [RuCl₂(PAd₂Bu)]₃ and [RuCl₂(P<i>^t</i>Bu₂Cy)]₃

The trinuclear ruthenium complexes [RuCl2-(PAd2Bu)]3 and [RuCl2(PtBu2Cy)]3 have been obtained by reaction of [(cymene)RuCl2]2 with 2 equiv of the respective phosphine. Crystallographic analyses show that the three metal fragments are connected by strong Ru−Ru bonds and bridging chloro ligands