Preliminary demonstration of benchtop NMR metabolic profiling of feline urine: chronic kidney disease as a case study.

OBJECTIVE: The use of benchtop metabolic profiling technology based on nuclear magnetic resonance (NMR) was evaluated in a small cohort of cats with a view to applying this as a viable and rapid metabolic tool to support clinical decision making. RESULTS: Urinary metabolites were analysed from four subjects consisting of two healthy controls and two chronic kidney disease (CKD) IRIS stage 2 cases. The study identified 15 metabolites in cats with CKD that were different from the controls. Among them were acetate, creatinine, citrate, taurine, glycine, serine and threonine. Benchtop NMR technology is capable of distinguishing between chronic kidney disease case and control samples in a pilot feline cohort based on metabolic profile. We offer perspectives on the further development of this pilot work and the potential of the technology, when combined with sample databases and computational intelligence techniques to offer a clinical decision support tool not only for cases of renal disease but other metabolic conditions in the future.

A New Mode of Chemical Reactivity for Metal-Free Hydrogen Activation by Lewis Acidic Boranes.

We herein explore whether tris(aryl)borane Lewis acids are capable of cleaving H2 outside of the usual Lewis acid/base chemistry described by the concept of frustrated Lewis pairs (FLPs). Instead of a Lewis base we use a chemical reductant to generate stable radical anions of two highly hindered boranes: tris(3,5-dinitromesityl)borane and tris(mesityl)borane. NMR spectroscopic characterization reveals that the corresponding borane radical anions activate (cleave) dihydrogen, whilst EPR spectroscopic characterization, supported by computational analysis, reveals the intermediates along the hydrogen activation pathway. This radical-based, redox pathway involves the homolytic cleavage of H2 , in contrast to conventional models of FLP chemistry, which invoke a heterolytic cleavage pathway. This represents a new mode of chemical reactivity for hydrogen activation by borane Lewis acids.

"Janus" Calixarenes: Double-Sided Molecular Linkers for Facile, Multianchor Point, Multifunctional, Surface Modification.

We herein report the synthesis of novel "Janus" calix[4]arenes bearing four "molecular tethering" functional groups on either the upper or lower rims of the calixarene. These enable facile multipoint covalent attachment to electrode surfaces with monolayer coverage. The other rim of the calixarenes bear either four azide or four ethynyl functional groups, which are easily modified by the copper(I)-catalyzed azide-alkyne cycloaddition reaction (CuAAC), either pre- or postsurface modification, enabling these conical, nanocavity reactor sites to be decorated with a wide range of substrates to impart desired chemical properties. Redox active species decorating the peripheral rim are shown to be electrically connected by the calixarene to the electrode surface in either "up" or "down" orientations of the calixarene.

Novel B(Ar')2(Ar'') hetero-tri(aryl)boranes: a systematic study of Lewis acidity.

A series of homo- and hetero-tri(aryl)boranes incorporating pentafluorophenyl, 3,5-bis(trifluoromethyl)phenyl, and pentachlorophenyl groups, four of which are novel species, have been studied as the acidic component of frustrated Lewis pairs for the heterolytic cleavage of H2. Under mild conditions eight of these will cleave H2; the rate of cleavage depending on both the electrophilicity of the borane and the steric bulk around the boron atom. Electrochemical studies allow comparisons of the electrophilicity with spectroscopic measurements of Lewis acidity for different series of boranes. Discrepancies in the correlation between these two types of measurements, combined with structural characterisation of each borane, reveal that the twist of the aryl rings with respect to the boron-centred trigonal plane is significant from both a steric and electronic perspective, and is an important consideration in the design of tri(aryl)boranes as Lewis acids.

Exploring structural and electronic effects in three isomers of tris{bis(trifluoromethyl)phenyl}borane: towards the combined electrochemical-frustrated Lewis pair activation of H2.

Three structural isomers of tris{bis(trifluoromethyl)phenyl}borane have been studied as the acidic component of frustrated Lewis pairs. While the 3,5-substituted isomer is already known to heterolytically cleave H2 to generate a bridging-hydride; ortho-substituents in the 2,4- and 2,5-isomers quench such reactivity through electron donation into the vacant boron pz orbital and steric blocking of the boron centre; as shown by electrochemical, structural and computational studies. Electrochemical studies of the corresponding borohydrides identify that the two-electron oxidation of terminal-hydrides occurs at more positive potentials than observed for [HB(C6F5)3](-), while the bridging-hydride oxidizes at a higher potential still, comparable to that of free H2.

Metal-free electrocatalytic hydrogen oxidation using frustrated Lewis pairs and carbon-based Lewis acids.

Whilst hydrogen is a potentially clean fuel for energy storage and utilisation technologies, its conversion to electricity comes at a high energetic cost. This demands the use of rare and expensive precious metal electrocatalysts. Electrochemical-frustrated Lewis pairs offer a metal-free, CO tolerant pathway to the electrocatalysis of hydrogen oxidation. They function by combining the hydrogen-activating ability of frustrated Lewis pairs (FLPs) with electrochemical oxidation of the resultant hydride. Here we present an electrochemical-FLP approach that utilises two different Lewis acids - a carbon-based N-methylacridinium cation that possesses excellent electrochemical attributes, and a borane that exhibits fast hydrogen cleavage kinetics and functions as a "hydride shuttle". This synergistic interaction provides a system that is electrocatalytic with respect to the carbon-based Lewis acid, decreases the required potential for hydrogen oxidation by 1 V, and can be recycled multiple times.

A combined "electrochemical-frustrated lewis pair" approach to hydrogen activation: surface catalytic effects at platinum electrodes.

Herein, we extend our "combined electrochemical-frustrated Lewis pair" approach to include Pt electrode surfaces for the first time. We found that the voltammetric response of an electrochemical-frustrated Lewis pair (FLP) system involving the B(C6 F5 )3 /[HB(C6 F5 )3 ](-) redox couple exhibits a strong surface electrocatalytic effect at Pt electrodes. Using a combination of kinetic competition studies in the presence of a H atom scavenger, 6-bromohexene, and by changing the steric bulk of the Lewis acid borane catalyst from B(C6 F5 )3 to B(C6 Cl5 )3 , the mechanism of electrochemical-FLP reactions on Pt surfaces was shown to be dominated by hydrogen-atom transfer (HAT) between Pt, [PtH] adatoms and transient [HB(C6 F5 )3 ](⋅) electrooxidation intermediates. These findings provide further insight into this new area of combining electrochemical and FLP reactions, and proffers additional avenues for exploration beyond energy generation, such as in electrosynthesis.

Photochemical Reactions of Fluorinated Pyridines at Half-Sandwich Rhodium Complexes: Competing Pathways of Reaction.

Irradiation of CpRh(PMe3)(C2H4) (1; Cp = η5-C5H5) in the presence of pentafluoropyridine in hexane solution at low temperature yields an isolable η2-C,C-coordinated pentafluoropyridine complex, CpRh(PMe3)(η2-C,C-C5NF4) (2). The molecular structure of 2 was determined by single-crystal X-ray diffraction, showing coordination by C3-C4, unlike previous structures of pentafluoropyridine complexes that show N-coordination. Corresponding experiments with 2,3,5,6-tetrafluoropyridine yield the C-H oxidative addition product CpRh(PMe3)(C5NF4)H (3). In contrast, UV irradiation of 1 in hexane, in the presence of 4-substituted tetrafluoropyridines C5NF4X, where X = NMe2, OMe, results in elimination of C2H4 and HF to form the metallacycles CpRh(PMe3)(κ2-C,C-CH2N(CH3)C5NF3) (4) and CpRh(PMe3)(κ2-C,C-CH2OC5NF3) (5), respectively. The X-ray structure of 4 shows a planar RhCCNC-five-membered ring. Complexes 2-5 may also be formed by thermal reaction of CpRh(PMe3)(Ph)H with the respective pyridines at 50 °C.

Magnetic relaxation pathways in lanthanide single-molecule magnets.

Single-molecule magnets are compounds that exhibit magnetic bistability caused by an energy barrier for the reversal of magnetization (relaxation). Lanthanide compounds are proving promising as single-molecule magnets: recent studies show that terbium phthalocyanine complexes possess large energy barriers, and dysprosium and terbium complexes bridged by an N2(3-) radical ligand exhibit magnetic hysteresis up to 13 K. Magnetic relaxation is typically controlled by single-ion factors rather than magnetic exchange (whether one or more 4f ions are present) and proceeds through thermal relaxation of the lowest excited states. Here we report polylanthanide alkoxide cage complexes, and their doped diamagnetic yttrium analogues, in which competing relaxation pathways are observed and relaxation through the first excited state can be quenched. This leads to energy barriers for relaxation of magnetization that exceed 800 K. We investigated the factors at the lanthanide sites that govern this behaviour.

Magnetic cooling at a single molecule level: a spectroscopic investigation of isolated molecules on a surface.

A sub-monolayer distribution of isolated molecular Fe14 (bta)6 nanomagnets is deposited intact on a Au(111) surface and investigated by X-ray magnetic circular dichroism spectroscopy. The entropy variation with respect to the applied magnetic field is extracted from the magnetization curves and evidences high magnetocaloric values at the single molecule level.

Pentametallic lanthanide-alkoxide square-based pyramids: high energy barrier for thermal relaxation in a holmium single molecule magnet.

Pentametallic Ln complexes of formula [Ln(5)O(O(i)Pr)(13)] have been made, where Ln(III) = Sm, Gd, Tb, Ho and Er; slow magnetisation relaxation to 33 K is observed for the Ho complex with an energy barrier of ca. 400 K.

The oxidative conversion of the N,S-bridged complexes [{RhLL'(µ-X)}2] to [(RhLL')3)(µ-X)2]+ (X = mt or taz): a comparison with the oxidation of N,N-bridged analogues.

The structures of [{RhLL'(µ-X)}(2)] [LL' = cod, (CO)(2), (CO)(PPh(3)) or {P(OPh)(3)}(2); X = mt or taz], prepared from [{RhLL'(µ-Cl)}(2)] and HX in the presence of NEt(3), depend on the auxiliary ligands LL'. The head-to-tail arrangement of the two N,S-bridges is accompanied by a rhodium-eclipsed conformation for the majority but the most hindered complex, [{Rh[P(OPh)(3)](2)(µ-taz)}(2)], uniquely adopts a sulfur-eclipsed structure. The least hindered complex, [{Rh(CO)(2)(µ-mt)}(2)], shows intermolecular stacking of mt rings in the solid state. The complexes [{RhLL'(µ-X)}(2)] are chemically oxidised to trinuclear cations, [(RhLL')(3)(µ-X)(2)](+), most probably via reaction of one molecule of the dimer, in the sulfur-eclipsed form, with the fragment [RhLL'](+) formed by oxidative cleavage of a second.

Isomerism in rhodium(I) N,S-donor heteroscorpionates: ring substituent and ancillary ligand effects.

The heteroscorpionate ligands [HB(taz)(2)(pz(R))](-) (pz(R) = pz, pz(Me2), pz(Ph)) and [HB(taz)(pz)(2)](-), synthesised from the appropriate potassium hydrotris(pyrazolyl)borate salt and 4-ethyl-3-methyl-5-thioxo-1,2,4-triazole (Htaz), react with [{Rh(cod)(µ-Cl)}(2)] to give [Rh(cod)Tx] {Tx = HB(taz)(2)(pz), HB(taz)(2)(pz(Me2)), HB(taz)(2)(pz(Ph)), HB(taz)(pz)(2)}; the heteroscorpionate rhodaboratrane [Rh{B(taz)(2)(pz(Me2))}{HB(taz)(2)(pz(Me2))}] is the only isolable product from the reaction of [{Rh(nbd)(µ-Cl)}(2)] with K[HB(taz)(2)(pz(Me2))]. Carbonylation of the cod complexes gave a mixture of [Rh(CO)(2)Tx] and [(RhTx)(2)(µ-CO)(3)] which reacts with PR(3) to give [Rh(CO)(PR(3))Tx] (R = Cy, NMe(2), Ph, OPh). In the solid state the complexes are square planar with the particular structure dependent on the steric and/or electronic properties of the scorpionate and ancillary ligands. The complex [Rh(cod){HB(taz)(pz)(2)}] has the heteroscorpionate κ(2)[N(2)]-coordinated to rhodium with the B-H bond directed away from the rhodium square plane while [Rh(cod){HB(taz)(2)(pz(Me2))}] is κ(2)[SN]-coordinated, with the B-H bond directed towards the metal. The complexes [Rh(CO)(PPh(3)){HB(taz)(2)(pz)}] and [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Me2))}] are also κ(2)[SN]-coordinated but with the pyrazolyl ring cis to PPh(3); in the former the B-H bond is directed towards rhodium while in the latter the ring is pseudo-parallel to the rhodium square plane, as also found for [Rh(CO)(2){HB(taz)(2)(pz(Me2))}]. The analogues [Rh(CO)(PR(3)){HB(taz)(2)(pz(Me2))}] (R = Cy, NMe(2)) have the phosphines trans to the pyrazolyl ring. Uniquely, [Rh(CO)(PPh(3)){HB(taz)(2)(pz(Ph))}] is κ(2)[S(2)]-coordinated. A qualitative mechanism is given for the rapid ring-exchange, and hence isomerisation, observed in solution.

A novel route to rhodaboratranes [Rh(CO)(PR3){B(taz)3}]+ via the redox activation of scorpionate complexes [RhLL'Tt].

The reaction of a mixture of the sodium salts of dihydrobis(4-ethyl-3-methyl-5-thioxo-1,2,4-triazolyl)borate, NaBt, and hydrotris(4-ethyl-3-methyl-5-thioxo-1,2,4-triazolyl)borate, NaTt, with [{Rh(cod)(mu-Cl)}2] gave [Rh(cod)Bt] and [Rh(cod)Tt], which separately react with CO gas to give the unstable dicarbonyl [Rh(CO)2Bt] and an equilibrium mixture of two isomers of [Rh(CO)2Tt] and [(RhTt)2(mu-CO)3], respectively. Tertiary phosphorus donor ligands react with the mixture of [Rh(CO)2Tt] and [(RhTt)2(mu-CO)3] to give [Rh(CO)(PR3)Tt] (R = Cy, NMe(2), Ph or OPh) and [Rh{P(OPh)3}2Tt] in which rhodium is bound to two sulfur atoms of the scorpionate ligand; the B-H bond is directed towards the metal to give an agostic-like B-H...Rh interaction. Dinuclear [(RhTt)2(mu-CO)3] has kappa3[S3]-bound Tt ligands with a rhodium-rhodium bond bridged by three carbonyls. In solution the mononuclear Tt complexes undergo rapid dynamic interchange of the three thioxotriazolyl rings, probably via kappa3[S3]-coordinated intermediates. The monocarbonyls [Rh(CO)(PR3)Tt] (R = Cy, NMe2 or Ph) react with two equivalents of [Fe(eta-C5H5)2][PF6] in the presence of triethylamine to give the monocationic rhodaboratranes [Rh(CO)(PR3){B(taz)3}]+, with boron NMR spectroscopy providing evidence for the boron-rhodium bond. In the solid state, rhodium is bound to the three sulfur atoms and the boron of the B(taz)3 fragment, forming a tricyclo[3.3.3.0] cage. The phosphine is trans to the Rh-B bond, the long Rh-P bond indicating a pronounced trans influence for the coordinated boron. The cation [Rh(CO)(PPh3){B(taz)3}]+ reacts with [NBu(n)(4)]I to give [Rh(PPh3)I{B(taz)3}], in which the halide is trans to the Rh-B bond, and a second species, possibly [Rh(CO)I{B(taz)3}]. The dirhodaboratrane [Rh2(PCy3){B(taz)3}2][PF6]2, a minor byproduct in the synthesis of [Rh(CO)(PCy3){B(taz)3}][PF6], has a distorted square pyramidal rhodium atom with a vacant site trans to the Rh-B bond. The second metal has four coordination sites filled by the sulfur and boron atoms of a second B(taz)3 unit, the remaining octahedral sites occupied by two of the sulfur atoms of the first B(taz)3 unit which therefore bridges the two rhodium atoms.

Redox activation of a B-H bond: a new route to metallaboratrane complexes.

Oxidative activation of a B-H bond of a coordinated scorpionate ligand provides an unprecedented route to rhodaboratranes.