Metallomacrocycles as ligands: synthesis and characterisation of aluminium-bridged bisglyoximato complexes of palladium and iron

Dialuminiummacrocycles based on bisglyoximato moieties were prepared and their coordination chemistry with Fe^II and Pd^II was investigated. The bridging aluminium centers were supported by several types of tetradentate diphenoxide diamine ligands. The nature of the ancillary ligands bound to aluminium was found to affect the overall geometry and symmetry of the metallomacrocycles. Enantiopure, chiral diphenoxide ligands based on the (R,R)-trans-1,2-diaminocyclohexane backbone afforded cleanly one metallomacrocycle isomer. The size and electronic properties of remote substituents on aluminium-bound ligands affected the binding mode and electronic properties of the central iron. A structurally characterized iron complex shows trigonal prismatic coordination mode, with phenoxide bridges between iron and aluminium. Increasing the size of the phenoxide substituents led to square bipyramidal coordination at iron. Employing p-NO_2- instead of p-tBu-substituted phenoxide as supporting ligands for aluminium caused a 0.27 V positive shift of the Fe^(III)/Fe^(II) reduction potential. These results indicate that the present synthetic approach can be applied to a variety of metallomacrocycles based on bisglyoximato motifs to affect the chemistry at the central metal

Pyridinethiolate titanocene metalloligands and their self-assembly reactions to yield early–late metallamacrocycles

New titanocene pyridinethiolate compounds [(RCp)2Ti(4-Spy)2] (R = H (1), Me (2); Cp = cyclopentadienyl; 4-Spy = pyridine-4-thiolate) and [Cp2Ti(2-Spy)2] (3; 2-Spy = pyridine-2-thiolate) have been prepared by reaction of the corresponding Li(Spy) salt with the appropriate compound [(RCp)2TiCl2]. Compounds 1 and 2 have been used as metalloligands in self-assembly reactions with the acceptor late-transition-metal compounds [M(H2O)2(dppp)](OTf)2 (M = Pd (a) Pt (b); dppp = 1,3-bis(diphenylphosphino)propane), and the series of early–late tetranuclear metallamacrocycles [{(RCp)2Ti(4-Spy)2}{M(dppp)}]2(OTf)4 (R = H, M = Pd (12a2); R = H, M = Pt (12b2); R = Me, M = Pd (22a2); R = Me, M = Pt (22b2)) arising from the anti isomer of the titanocene metalloligands have been obtained. Only ligand transfer reactions from Ti to either Pd or Pt atoms have been observed when the pyridine-2-thiolate derivative 3 has been assayed in self-assembly processes. The obtained species have been characterized by NMR spectroscopy and ESI(+) mass spectrometry. The supramolecular assemblies have shown to be nonrigid in solution, and their fluxional behavior has been studied by VT 1H NMR spectroscopy. A DFT study including ab initio molecular dynamics in order to elucidate the structures and the relative stability of the isomers has been performed.Financial support for this work was provided by the Ministerio de Economía y Competitividad (MINECO/FEDER) of Spain (CTQ2013-42532-P and CTQ2012-31335), Diputación General de Aragón (Group E07) and Fondo Social Europeo. E.R. thanks Generalitat de Catalunya for an ICREA Academia fellowship.Peer reviewe

Platinum(II) and palladium(II) metallomacrocycles derived from cationic 4,4 '-bipyridinium, 3-aminopyrazinium and 2-aminopyrimidinium ligands

A series of cationic, ditopic N-donor ligands based on 4,4-bipyridine (4,4-bipy), 3-aminopyrazine (apyz) and 2-aminopyrimidine (apym), each incorporating two positively-charged N-heterocycles linked by a conformationally-flexible spacer unit, have been synthesised and treated with palladium(II) or platinum(II) precursors [M(2,2-bipy)(NO3)2] (M = Pd(II) or Pt(II)) to form highly cationic metallocyclic species. Treatment of 1,6-bis(4,4-bipyridinium)hexane nitrate with [M(2,2-bipy)(NO3)2] in aqueous solution, followed by the addition of KPF6, resulted in the formation of the [2+2] species [M2(2,2-bipy)2{4,4-bipy(CH2)64,4-bipy}2](PF6)8. Treatment of [Pd(PhCN)2Cl2] with 1,3-bis(4,4-bipyridinium)propane hexafluorophosphate in MeCN afforded [Pd2Cl4{4,4-bipy(CH2)34,4-bipy}2](PF6)4. When the cationic apyz or apym ligands were used in aqueous solution, the analogous metallomacrocycles did not form. Instead, deprotonation of the exocyclic amino group occurred upon coordination of the ligand to afford a tetranuclear [4+2] species in the case of platinum(II), with Pt(II)Pt(II) bonding supported by strong UV-vis absorption at = 428 nm which was assigned to a metal-metal-to-ligand charge transfer (MMLCT) band. Thus, treatment of 1,6-bis(3-aminopyrazinium)hexane nitrate with [Pt(2,2-bipy)(NO3)2], followed by the addition of KPF6, led to the formation of the red species [Pt4(2,2-bipy)4{apyz(CH2)6apyz–2H}2](PF6)8. No related products could be identified with palladium(II), consistent with the low propensity for this metal ion to form strong Pd(II)Pd(II) bonding interaction

Polymer membrane based electrolytic cell and process for the direct generation of hydrogen peroxide in liquid streams

An electrolytic cell for generating hydrogen peroxide is provided including a cathode containing a catalyst for the reduction of oxygen, and an anode containing a catalyst for the oxidation of water. A polymer membrane, semipermeable to either protons or hydroxide ions is also included and has a first face interfacing to the cathode and a second face interfacing to the anode so that when a stream of water containing dissolved oxygen or oxygen bubbles is passed over the cathode and a stream of water is passed over the anode, and an electric current is passed between the anode and the cathode, hydrogen peroxide is generated at the cathode and oxygen is generated at the anode

Synthesis and coordination chemistry of 2-(di-2-pyridylamino)pyrimidine; structural aspects of spin crossover in an Fe(II) complex

This paper was accepted on February 26 20122-(Di-2-pyridylamino)pyrimidine (L), a potentially ditopic tetradentate ligand, was synthesized from commercially available di-2-pyridylamine and 2-chloropyrimidine. Despite being capable of bridging two metal atoms with bidentate chelation of both metal centres, L prefers to chelate or bridge through the more basic pyridyl donors of the di-2-pyridylamine moiety. Mononuclear trans-[Fe(NCS)2(L)2] and [Cu(L)2(H2O)](BF4)2•H2O complexes, and a discrete [Ag2(L)4](PF6)2 metallomacrocycle were isolated and structurally characterized by X-ray crystallography. A mononuclear palladium complex [PdCl2(L)]•(solvate), where solvate = ½H2O or CH2Cl2, was also readily obtained in 71% yield. One example of the ligand acting as a bis(bidentate) bridging ligand was observed in a dinuclear [(PdCl2)2(L)]•¾H2O complex that was obtained only in very low yield (ca. 3%) from the reaction that produced [PdCl2(L)]•½H2O. trans-[Fe(NCS)2(L)2] undergoes a temperature dependent HS-LS (HS = high spin; LS = low spin) crossover at ca. 205 K that was 2 observed by X-ray crystallography and magnetic measurements and attempts were made to understand the structural basis of this process. Despite efforts to isolate examples of L bridging two iron(II) centres, only the mononuclear trans-[Fe(NCS)2(L)2] species could be obtained.Rachel S. Crees, Boujemma Moubaraki, Keith S. Murray, and Christopher J. Sumb

Molecular recognition by multiple metal coordination inside wavy-stacked macrocycles

AbstractMost biological and synthetic receptors for small organic molecules employ a combination of relatively weak intermolecular interactions such as hydrogen bonds. A host compound that utilizes stronger yet reversible bonding in a synergistic manner could realize precise recognition, but the regulation and spatial arrangement of such reactive interaction moieties have been a challenge. Here, we show a multinuclear zinc complex synthesized from a macrocyclic ligand hexapap, which inwardly arranges labile metal coordination sites for external molecules. The metallomacrocycle forms a unique wavy-stacked structure upon binding a suitable length of dicarboxylic acids via multipoint coordination bonding. The saddle-shaped deformation and dimerization realize the differentiation of the interaction moieties, and change of guest-binding modes at specific metal coordination sites among the many present have been achieved utilizing acid/base as external stimuli.</jats:p

A self-assembled luminescent host that selectively senses ATP in water.

Metal-ion-directed self-assembly has been used to construct kinetically inert, water-soluble heterometallic Ru2Re2 hosts that are potential sensors for bioanions. A previously reported metallomacrocycle and a new derivative synthesised by this approach are found to be general sensors for bioanions in water, showing an “off–on” luminescent change that is selective for nucleotides over uncharged nucleobases. Through a change in the ancillary ligands coordinated to the ruthenium centres of the host, an “off–on” sensor has been produced. Whilst this host only shows a modest enhancement in binding affinities for nucleotides relative to the other two host systems, its sensing response is much more specific. Although a distinctive “off–on” luminescence response is observed for the addition of adenosine triphosphosphate (ATP), related structures such as adenine and guanosine triphosphate (GTP) do not induce any emission change in the host. Detailed and demanding DFT studies on the ATP- and GTP-bound host–guest complexes reveal subtle differences in their geometries that modulate the stacking interactions between the nucleotide guests and the ancillary ligands of the host. It is suggested that this change in stacking geometries affects solvent accessibility to the binding pocket of the host and thus leads to observed difference in the host luminescence response to the guests

Self-assembly of an imidazolate-bridged FeIII/CuII heterometallic cage

A rare, discrete, mixed-valent, heterometallic Fe(III)/Cu(II) cage, [CuFeL](ClO)χ solvent (HL = tris{[2-{(imidazole-4-yl)methylidene}amino]ethyl} amine), was designed and synthesized via metal-ion-directed self-assembly with neutral tripodal metalloligands. The formation of this coordination cage was demonstrated by X-ray crystallography, ESI mass spectrometry, FT-IR, and UV-vis-NIR spectroscopy

Switchable counterion gradients around charged metallic nanoparticles enable reception of radio waves

Mechanically flexible, easy-to-process, and environmentally benign materials capable of current rectification are interesting alternatives to &quot;hard&quot; silicon-based devices. Among these materials are metallic/charged-organic nanoparticles in which electronic currents though metal cores are modulated by the gradients of counterions surrounding the organic ligands. Although layers of oppositely charged particles can respond to both electronic and chemical signals and can function even under significant mechanical deformation, the rectification ratios of these &quot;chemoelectronic&quot; elements have been, so far, low. This work shows that significantly steeper counterion gradients and significantly higher rectification ratios can be achieved with nanoparticles of only one polarity but in contact with a porous electrode serving as a counterion &quot;sink.&quot; These composite structures act as rectifiers even at radio frequencies, providing a new means of interfacing counterions&apos; dynamics with high-frequency electronic currents