Rh Moiety Research Articles

An unusual reaction in nitromethane solution: use of the Cp*Rh moiety to form Prussian blue analogues

The direct decomposition of nitromethane into nitrile compounds is a significant challenge due to the occurrence of severe side-reactions.

Understanding the nature of Pt-Rh synergy for three-way conversion catalysis

A series of Al2O3 supported Pt, Rh and Pt-Rh catalysts was investigated for TWC catalysis. Profound synergy between Pt and Rh was found on all Pt-Rh compositions relative to their single metal references with significantly reduced light-off temperatures. The nature of this synergy was probed using various characterization techniques. CO chemisorption, CO-DRIFTS and XPS results show that the surface Rh concentrations on aged Pt-Rh catalysts are much higher than that of the Rh reference. In addition, on the bimetallic catalysts the Rh species is in a more reduced state as indicated by XPS and XANES. AC-STEM/EDS results clearly illustrate that there are two types of Rh species on an aged Pt-Rh catalyst in terms of its location: one sitting on Pt particles as Rh nanoparticles and the other associated with the Al2O3 support as sub-nano Rh moieties. The Pt-Rh bimetallic particles contain a certain degree of Pt-Rh alloy as evidenced by the upshift of the metal XRD peaks and the Pt-Rh coordination from the EXAFS measurement. All structural and microscopy analyses suggest that Rh is surface enriched on the Pt-Rh particles, and it is the surface enriched Rh species that plays a primary role in enhancing the activity of Pt-Rh catalysts.

Multicolor Mechanochromic Epoxy Thermosets That Recognize the Intensity, Type, and Duration of Mechanical Stimulation.

Mechanochromic polymers that exhibit multiple color changes under external mechanical stimulation show great potential for sensor applications. Herein, an epoxy thermoset that can reveal the intensity, type, and duration of mechanical stimulation via a combination of disulfide (DS) and rhodamine (Rh) mechanochromophores is reported. A unique multicolor transition occurs upon ball mill or manual grinding because of the different activation energies of DS and Rh. The epoxy changes color depending on the ball mill grinding duration. Simultaneous activation occurs with a mechanochromic time lag between DS and Rh, and the collision energy strongly affects the relative intensity. A more dramatic multicolor response is observed using a mortar and pestle, as sequential activation occurs upon gentle and strong grinding. Various types of mechanical stimulation can cause different aggregates of the activated Rh moiety and vary the relative mechanosensitivities of Rh and DS, which lead to a different color response.

A Facile Fabrication of Lysosome-Targeting pH Fluorescent Nanosensor Based on PEGylated Polyester Block Copolymer.

A novel lysosome-targeting PEGylated polyester-based fluorescent pH nanosensor is fabricated by the combination of ring-opening copolymerization (ROCOP), side-group modification and subsequent self-assembly. First, a key target amphiphilic copolymer carrier for rhodamine (Rh) pH indicator is synthesized in a facile manner by the ROCOP of phthalic anhydride with allyl glycidyl ether using mPEG-OH and t-BuP1/Et3B as the macroinitiator and binary catalyst, respectively. Subsequently, Rh moieties are covalently attached on the polymer chain with controllable grafting degree via an efficient thiol-ene click reaction. Concurrently, the effect of catalyst systems and reaction conditions on the catalytic copolymerization performance is presented, and the quantitative introduction of Rh is described in detail. Owing to its amphiphilic characteristics, the rhodamine-functionalized polyester-based block copolymer can self-assemble into micelles. With the covalent incorporation of Rh moieties, the as-formed micelles exhibit excellent absorption and fluorescence-responsive sensitivity and selectivity towards H+ in the presence of various metal cations. Moreover, the as-prepared micelles with favorable water dispersibility, good pH sensitivity and excellent biocompatibility also display appreciable cell-membrane permeability, staining ability and pH detection capability for lysosomes in living cells. This work provides a new strategy for the facile synthesis of novel biocompatible polymeric fluorescent pH nanosensors for the fluorescence imaging of lysosomal pH changes.

Inside Cover: An Isolated Nitridyl Radical-Bridged {Rh(N.)Rh} Complex (Angew. Chem. Int. Ed. 26/2014)

Breaking news: The first example of an isolated “nitridyl radical” (.N2−) complex is described by S. Schneider, B. de Bruin, and co-workers in their Communication on page 6814 ff. Formally, the paramagnetic, binuclear [(PNN)Rh Rh(PNN)] complex is also a rare example of a Group 9 transition-metal (bridging) nitrido complex. Its spin density is delocalized over the Rh Rh moiety, but the complex has a prevailing nitridyl radical character.

The Chemoselective Reactions of Tyrosine-Containing G-Protein-Coupled Receptor Peptides with [Cp*Rh(H2O)3](OTf)2, Including 2D NMR Structures and the Biological Consequences

The bioconjugation of organometallic complexes with peptides has proven to be a novel approach for drug discovery. We report the facile and chemoselective reaction of tyrosine-containing G-protein-coupled receptor (GPCR) peptides with [Cp*Rh(H(2)O)(3)](OTf)(2), in water, at room temperature, and at pH 5-6. We have focused on three important GPCR peptides; namely, [Tyr(1)]-leu-enkephalin, [Tyr(4)]-neurotensin(8-13), and [Tyr(3)]-octreotide, each of which has a different position for the tyrosine residue, together with competing functionalities. Importantly, all other functional groups present, i.e., amino, carboxyl, disulfide, phenyl, and indole, were not prominent sites of reactivity by the Cp*Rh tris aqua complex. Furthermore, the influence of the Cp*Rh moiety on the structure of [Tyr(3)]-octreotide was characterized by 2D NMR, resulting in the first representative structure of an organometallic-peptide complex. The biological consequences of these Cp*Rh-peptide complexes, with respect to GPCR binding and growth inhibition of MCF7 and HT29 cancer cells, will be presented for [(η(6)-Cp*Rh-Tyr(1))-leu-enkephalin](OTf)(2) and [(η(6)-Cp*Rh-Tyr(3))-octreotide](OTf)(2).

Spin State, Structure, and Reactivity of Terminal Oxo and Dioxygen Complexes of the (PNP)Rh Moiety

[Rh(III)H{(tBu(2)PCH(2)SiMe(2)NSiMe(2)CH(2)PtBu{CMe(2)CH(2)})}], ([RhH(PNP*)]), reacts with O(2) in the time taken to mix the reagents to form a 1:1 eta(2)-O(2) adduct, for which O--O bond length is discussed with reference to the reducing power of [RhH(PNP*)]; DFT calculations faithfully replicate the observed O-O distance, and are used to understand the oxidation state of this coordinated O(2). The reactivity of [Rh(O(2))(PNP)] towards H(2), CO, N(2), and O(2) is tested and compared to the associated DFT reaction energies. Three different reagents effect single oxygen atom transfer to [RhH(PNP*)]. The resulting [RhO(PNP)], characterized at and above -60 degrees C and by DFT calculations, is a ground-state triplet, is nonplanar, and reacts, above about +15 degrees C, with its own tBu C--H bond, to cleanly form a diamagnetic complex, [Rh(OH){N(SiMe(2)CH(2)PtBu(2))(SiMe(2)CH(2)PtBu{CMe(2)CH(2)})}].

Dynamic Behaviour of the [(Triphos)Rh(η1:η2‐P4RR′)]n+ Complexes [Triphos = MeC(CH2PPh2)3; R = H, Alkyl, Aryl; R′ = Lone Pair, H, Me; n = 0, 1]: NMR and Computational Studies

AbstractSolution multinuclear and multidimensional NMR analyses of the [(triphos)Rh(η1:η2‐P4RR′)]n+ complex cations [triphos = MeC(CH2PPh2)3; R = H, Me, Ph; R′ = lone pair, H, Me; n = 0, 1] confirm the same primary structure determined by X‐rays in the solid state. In addition, 2D 1H NOESY and 31P{1H} exchange NMR spectroscopy show that these complexes are nonrigid on the NMR time‐scale over the 253–318 K temperature range. A dynamic process that involves the terminal phosphane groups of the triphos ligand is displayed by each compound. The NMR spectroscopic data indicate a slow scrambling motion in which the P4R unit tumbles with respect to the (triphos)Rh moiety. DFT calculations outline a possible turnstile mechanism involving the threefold and twofold rotors into which the complex is subdivided. The process goes through a transition state in which the axial and equatorial dispositions of the PRR′ and P=P donating groups of the P4RR′ ligand are inverted with respect to the ground state. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

A Mismatch-Selective Bifunctional Rhodium−Oregon Green Conjugate: A Fluorescent Probe for Mismatched DNA

A fluorescent metallointercalator conjugate that selectively targets DNA base mismatches has been synthesized by coupling an organic fluorophore to a bulky Rh intercalator containing the chrysenequinone diimine ligand. Ion pairing between the cationic Rh and anionic fluorophore moieties dramatically quenches the fluorescence of the conjugate in solution and in the presence of matched DNA. However, in the presence of mismatched DNA, the fluorescence of the conjugate is increased >300%. This increase in fluorescence is attributed to the loss in intramolecular quenching associated with DNA binding; intercalation of the Rh moiety into the mismatched site can lead to electrostatic repulsion of the anionic fluorophore away from the DNA phosphate backbone and Rh. Denaturing PAGE experiments with 32P-labeled oligonucleotides indicate that the conjugate selectively binds the mismatched DNA with a binding affinity of 6 x 105 M-1 and, upon irradiation, cleaves the DNA backbone neighboring the mismatched site.

Anionic platinum complexes with 2-pyridylphosphines as ligands for rhodium: synthesis of zwitterionic Pt-Rh organometallic compounds.

Bimetallic zwitterionic platinum(II)-rhodium(I) complexes of the type [(C(6)F(5))(3)Pt(micro-PPy(n)Ph(3)(-)(n)Rh(CO)(2))] and [(C(6)F(5))(3)Pt(micro-PPy(n)Ph(3)(-)(n)())Rh(diene))] (n = 2, 3; Py = 2-pyridyl) have been prepared. The P end of the bridging ligands (micro-PPy(n)Ph(3)(-)(n)) is always coordinated to the Pt center, while the N-donor ends chelate the Rh atom, giving metallacycles comparable to pyrazolylborate-Rh complexes. These metallacycles can adopt two conformations, either with the Pt complex in pseudoaxial position approaching the Rh center or with the Pt complex in a remote position. The preferred conformation depends on the steric hindrance at the rhodium center. In less sterically demanding Rh-carbonyl complexes the Pt moiety gets close to the Rh moiety as this brings closer the opposite charges of the zwitterion. For diene complexes mixtures of conformers are obtained. The X-ray structures of [(C(6)F(5))(3)Pt(micro-PPhPy(2))Rh(COD)] (COD = 1,5-cyclooctadiene) and [(C(6)F(5))(3)Pt(micro-PPhPy(2))Rh(CO)(2)] are reported.

Dithioethers as ligands in pentamethylcyclopentadienylrhodium(III) and iridium(III) complexes. Crystal structures of [{(η 5-C 5Me 5)Rh} 2(μ-Cl) 2{μ-(MeS) 2CH 2}](BF 4) 2·H 2O and [(η 5-C 5Me 5)IrCl 2{η 1-(PhS) 2CH 2}

Reactions of complexes [{(η 5-C 5Me 5)MCl 2} 2] (M=Rh, Ir) with the ligand (MeS) 2CH 2 in CH 2Cl 2 solution led to the neutral dinuclear complexes of the general formula [{(η 5-C 5Me 5)MCl 2} 2{μ-(MeS) 2CH 2}] [M=Rh ( 1), Ir ( 2)]. Compound 1 reacts in CH 2Cl 2 solution with silver tetrafluoroborate in 1:2 molar ratio to yield the dinuclear cationic complex [{(η 5-C 5Me 5)Rh} 2(μ-Cl) 2{μ-(MeS) 2CH 2}](BF 4) 2·H 2O ( 3). Compound 2 reacts with silver salts in analogous conditions to give the mononuclear cationic complex [(η 5-C 5Me 5)IrCl{η 2-(MeS) 2CH 2}]BF 4 ( 4). Reactions of the starting complexes [{(η 5-C 5Me 5)MCl 2} 2] with the ligand (PhS) 2CH 2 afforded the mononuclear complexes [(η 5-C 5Me 5)MCl 2(η 1-(PhS) 2CH 2)] [M=Rh ( 5), Ir ( 6)]. All the complexes have been characterised by analytical and spectroscopic means, and the fluxional behaviour of 4, in solution, has been studied. The crystal structures of complexes 3 and 6 have been established by X-ray crystallography. Complex 3 crystallised in space group P2 1/ n, a=11.848(2), b=12.693(2), c=21.608(4) Å, β=95.18(2)° and Z=4. The complex cation consists of two (η 5-C 5Me 5)Rh moieties connected by two chloride atoms and one dithioether group. The two rhodium atoms are separated by 3.6093(10) Å. Complex 6 crystallised in space group P2 1/ c, a=8.366(1), b=16.011(3), c=17.911(2) Å, β=100.28(1)° and Z=4. The iridium atom has a distorted octahedral co-ordination with a η 5-C 5Me 5 group occupying the centre of three octahedral sites, two chloride atoms and a sulphur of a monodentate bis(phenylthio)methane ligand.

Synthesis and spectral properties of novel laser copolymers based on modified rhodamine 6G and 1,8­naphthalimide

The excellent photostability of the trichromophoric rhodamine dyes (TCR-1 and TCR-2) containing two 1,8-naphthalimides as antennas had been observed for the solid lasing operation using the dyes in methacrylate. Further understanding of the stabilization mechanism operating in these compounds would require a study of photophysical properties. The fluorescence lifetimes of TCR-1 and TCR-2 have been measured by the single-photon counting technique and the intramolecular singlet energy transfer from the naphthalimide moiety (NA) to the rhodamine moiety (Rh) has been observed. In order to obtain laser dye polymer materials with a high laser-radiation-damage threshold, modified rhodamine 6G molecules (Rh-Al or Rh-Aln) with polymerizable double bonds have been copolymerized with 1,8-naphthalimide derivatives. The absorption spectra of these new copolymers indicate there is little or no interaction between the two NA and the Rh moieties in their ground state, however, the fluorescent spectra indicate that energy transfer from the NA group to the Rh-Al or Rh-Aln group in the copolymers does occur. In comparison, energy transfer was not observed in an equal molar mixture of monomers corresponding to the copolymers, which demonstrated that intramolecular energy transfer in the copolymer synthesized in this study occurred mainly along the polymeric chain.

Binuclear pentamethylcyclopentadienyl dirhodium complexes with pyrazolato and diphenylphosphido bridging ligands

The reaction of [{Rh(C5Me5)}2(µ-L)(µ-OMe)2]BF4[L = pyrazolate (pz), 3-methylpyrazolate, 3,5-dimethylpyrazolate or 3(5)-bromo-5(3)-methylpyrazolate] with HPPh2 has been studied. Complexes of general formulae [{Rh(C5Me5)}2(µ-L)(µ-OH)(µ-PPh2)]BF4, [{Rh(C5Me5)}2(µ-L)(µ-PPh2)2]BF4 and [{Rh(C5Me5)}2(µ-OH)2(µ-PPh2)]BF4 were prepared and characterized by analytical and spectroscopic means. The crystal structure of [{Rh(C5Me5)}2(µ-pz)(µ-PPh2)2] BF4·CHCl3 was determined. The rhodium atoms show pseudo-octahedral geometry and are separated by 3.473(1)A. The µ-hydroxo complexes [{Rh(C5Me5)}2(µ-L)(µ-OH)(µ-PPh2)] BF4 react with hydrochloric acid affording the corresponding µ-chloride compounds [{Rh(C5Me5)}2(µ-L)(µ-Cl)(µ-PPh2)] BF4, which in turn have been also prepared from [{Rh(C5Me5)}2(µ-OH)3] BF4, HL, HPPh2 and HCl in 1 : 1 : 1 : 1 ratio. The crystal structure of [{Rh(C5Me5)}2(µ-pz)(µ-Cl)(µ-PPh2)] BF4·CHCl3 has been determined. Two (C5Me5)Rh moieties are connected by three different anionic ligands, pz, Cl and PPh2. The rhodium atoms are separated by 3.432(1)A. Aged solutions of reaction mixtures of [{Rh(C5Me5)}2(µ-L)(µ-OMe)2] BF4 and HPPh2 contain [{Rh(C5Me5)}2(µ-Ph2PO2)2(µ-PPh2)] BF4, the diphenylphosphinato ligands arising from Ph2P(O)OH, an oxidation product of HPPh2. The crystal structure of the solvate has been established. Two Ph2PO2 groups and a PPh2 ligand bridge two (C5Me5) Rh units. The rhodium–rhodium distance is 4.049(1)A. The µ-hydrido complex [{Rh(C5Me5)}2(µ-H)(µ-pz)(µ-PPh2)] has been prepared by treating [{Rh(C5Me5)}2(µ-OH)3] BF4 with Hpz and HPPh2 in refluxing propan-2-ol.

The cyclometallation of benzoic acid to give rhodium, iridium, and osmium C,O-benzoates. X-Ray structure determination of the dibenzoate [(C5Me5)Rh(OOCPh)2(H2O)

The cyclometallated benzoate complexes [(C5Me5)[graphic omitted]H4)(Me2SO)][M = Rh (1a) or Ir (1b)] and [(p-MeC6H4CHMe2)O[graphic omitted]C6H4)(Me2SO)] were prepared by reaction of [(C5Me5)MMe2(Me2SO)] or [(p-MeC6H4CHMe2)OsMe(Cl)(Me2SO)] with benzoic acid or silver benzoate respectively. Methane was formed in these reactions. Complex (1b) was also prepared from [(C5Me5)IrCl2( Me2SO)] with silver benzoate. Complex (1a) reacted with water to give [{(C5Me5)Rh}2(µ-OH)3][OOCPh] and the dibenzoate hydrate [(C5Me5)Rh(OOCPh)2(H2O)](5a). Complex (5a) was also formed when (1a) was reacted with benzoic acid or when [(C5Me5)RhCl2(Me2SO)] reacted with two equivalents of silver benzoate. The structure of (5a) was determined by an X-ray study which showed two benzoates attached in a monodentate manner to the (C5Me5)Rh moiety; the rhodium also bore a co-ordinated water, which was also hydrogen-bonded to the two benzoate carbonyl oxygens. Both the rhodium and the iridium complexes (1a) and (1b), reacted with methyl iodide to give the cyclometallated methyl benzoate complexes [(C5Me5)[graphic omitted]H4}(I)]. They also underwent carbonylation to give phthalic anhydride and [(C5Me5)]Rh(CO)2 from (1a), and [(C5Me5)I[graphic omitted]H4)(CO)] from (1b). Mechanismsofthe various transformations are discussed.

Fluorescein and tetramethyl rhodamine as haptens in enzyme immunohistochemistry.

Fluorescein (Fl) and tetramethyl rhodamine (Rh) were evaluated as possible candidates for a double hapten sandwich system in enzyme immunohistology. Monoclonal antibodies were raised against Fl and Rh. Their fine-specificity was tested with a competition-like assay. A pair of Mab's was selected for immunohistology in which they functioned as a bridge between Fl/Rh conjugated antibodies and Fl/Rh labeled peroxidase and alkaline phosphatase, respectively. The binding of fluorescein labeled antibodies could be successfully demonstrated in histological slides. A large variability in the efficacy of staining was observed in the case of rhodamine labeled antibodies. The phenomenon is explained by assuming that tetramethyl rhodamine isothiocyanate reacts preferentially with lysine residues near to, or embedded in, hydrophobic regions in a protein. This condition may reduce the accessibility of the Rh moiety for anti-Rh antibodies.

Cleavage of P4S3and P4Se3cage molecules controlled by transition metal–ligand systems. X-Ray crystal structure of [{MeC(CH2PPh2)3}Rh(P3S3)]˙C6H6

The reaction of tetraphosphorus trisulphide and tetraphosphorus triselenide with [RhCl(cod)]2(cod = cycloocta-1,5-diene) in the presence of triphos [triphos = 1,1,1-tris(diphenylphosphinomethy)ethane]yields the compounds [(triphos)Rh(P3X3)]˙C6H6, X = S or Se, which have been shown by X-ray analysis to contain the (triphos)Rh moiety replacing a basal P atom in the cage molecule.

Crystal structure of di-µ-carbonyl-nonacarbonyl-(π-cyclopentadienyl-rhodio)tri-iron(3Rh–Fe)(3Fe–Fe), (π-C5H5)RhFe3(CO)11

The crystal and molecular structure of the title compound has been elucidated. The compound crystallizes in the centrosymmetric monoclinic space group P21/n(C2h5, No. 14) with a= 12·298(9), b= 11·928(15), c= 13·341(17)A, β= 95·9 (0·1)° and Z= 4. The structure was solved by a full three-dimensional X-ray diffraction study, using counter data and all non-hydrogen atoms were located. The structure has been refined by least-squares techniques to R 6·98% for 1227 independent non-zero reflections. To a first approximation the molecule consists of three Fe(CO)3 groups and a (π-C5H5)Rh moiety which are mutually connected via metal–metal bonds [Fe–Fe 2·553(3)–2·594(3) and Fe–Rh 2·568(3)–2·615(3)A] along with two bridging [Rh–(CO)–Fe] carbonyl groups. However, crowding of ligands around the surface of the tetrahedral metal cluster results in further metal–carbonyl contacts which appear to be of a bonding nature.