Rhodium(III) and palladium(II) complexes of some P-heterocycles; synthesis and X-ray structures

Deoxygenation of the syn-3-phosphabicyclo[3.1.0]hexane 3-oxides bearing a 3-phenyl or a 3-(4-methylphenyl) substituent (1a,b) by trichlorosilane took place already at mild condition and resulted in the corresponding phosphines (2a,b) with retention of configuration at phosphorus, while in the case of 3-(2-methylphenyl)-3-phosphabicyclo[3.1.0]hexane (2c), the inversion of the phosphorus atom was observed in solution under ambient conditions that was evaluated by quantum chemical calculations. A further phosphine ligand (5) was obtained by the reduction of 4-dichloromethylene-1,4-dihydrophosphinine oxide (4). The phosphine ligands (2 and 5) were used in the preparation of Rh(III) complexes (3 and 6). A Pd(II) complex of type PdCl₂(5)₂ (7) was also prepared. The stereostructures of a series of Rh(III) complexes of 3-aryl-3-phosphabicyclo[3.1.0]hexanes (3b-syn, 3c-syn and 3c-anti) were elucidated by single crystal X-ray analysis confirming the relative position of the dichlorocyclopropane and the P-substituent.     

Rhodium assisted CH activation of N-(2′-hydroxyphenyl)benzaldimines. Synthesis, structure and electrochemical properties of a group of organorhodium complexes

Reaction of a group of N-(2′-hydroxyphenyl)benzaldimines, derived from 2-aminophenol and five para-substituted benzaldehydes (the para substituents are OCH₃, CH₃, H, Cl and NO₂), with [Rh(PPh₃)₃Cl] in refluxing toluene in the presence of a base (NEt₃) afforded a family of organometallic complexes of rhodium(III). The crystal structure of one complex has been determined by X-ray crystallography. In these complexes the benzaldimine ligands are coordinated to the metal center, via dissociation of the phenolic proton and the phenyl proton at the ortho position of the phenyl ring in the imine fragment, as dianionic tridentate C,N,O-donors, and the two PPh₃ ligands are trans. The complexes are diamagnetic (low-spin d⁶, S = 0) and show intense MLCT transitions in the visible region. Cyclic voltammetry shows a Rh(III)Rh(IV) oxidation within 0.63-0.93 V vs SCE followed by an oxidation of the coordinated benzaldimine ligand. A reduction of the coordinated benzaldimine is also observed within −0.96 to −1.04 V vs SCE. Potential of the Rh(III)Rh(IV) oxidation is found to be sensitive to the nature of the para-substituent.     

Thin-layer chromatographic separation of rhodium(III) and iridium(III, IV) by anion exchange

Summary The TLC behaviour of Rh(III), Ir(III) and Ir(IV) has been investigated in the two systems consisting of DEAE-cellulose or ECTEOLA-cellulose and 5 M HCl media containing H₂O₂. These systems, especially in combination with a simple chemical pretreatment of samples (with LiCl, HCl and H₂O₂), can effectively be applied to the complete separation of mixtures of Rh(III) and Ir(III) or Ir(IV) in a wide range of ratios and amounts (Rh: Ir=1100 to 1001).

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Dünnschicht-chromatographische Trennung von Rhodium(III) und Iridium(III, IV) durch Anionenaustausch

Zusammenfassung Das dünnschicht-chromatographische Verhalten von Rh(III), Ir(III) und Ir(IV) wurde in H₂O₂-haltiger 5 M salzsaurer Lösung auf DEAE-sowie ECTEOLA-Cellulose untersucht. In Kombination mit einer einfachen chemischen Vorbehandlung der Probe (mit LiCl, HCl, H₂O₂) kann eine wirkungsvolle Trennung von Rh(III) und Ir(III) oder Ir(IV) über einen weiten Konzentrationsbereich erzielt werden (Rh: Ir=1100 bis 1001).

     

The rhodium complex of a tris(bipyridine) ligand—Its electrochemical behaviour and function as mediator for the regeneration of NADH from NAD+

The tris-bipyridine ligand3a and its stoichiometric Rh³⁺ complex have been prepared. Cyclovoltammograms of the complex at pH 7.4 using a glassy carbon disk electrode reveal a strong reduction peak at –620 mV and two weak reduction peaks at more negative voltage. The reduction potential of the new complex is shifted by 300 mV to more positive values as compared to [Rh(bipy)₃]³⁺. There is no reversible reoxidation peak of the Rh(I) complex formed due to the decomplexation of one of the three bipyridine units in the course of the transition Rh(III)Rh(I). The Rh(III) complex of3a was also studied with respect to its function as a possible redox mediator for the electrochemical regeneration of NADH from NAD⁺. The preparative electrolysis of the Rh³⁺ complex of3a in the presence of NAD⁺ yields a selective formation of NADH, whereas NAD dimers were not detected. On the other hand, a significant acceleration of this reaction compared to [Rh(bipy)₃]³⁺ was not observed.     

New anionic and dianionic polydentate systems featuring ancillary phosphinosulfides as ligands in coordination chemistry and catalysis

This article provides an overview of the chemistry of monoanionic S–P–S and dianionic S–C–S ligands featuring two phosphinosulfide ligands as pendant groups. These new pincer-type structures are easily assembled from phosphinines and the bis-sulfide derivative of the bis(diphenylphosphino)methane, respectively. Monoanionic S–P–S pincer ligands easily coordinate group 10 and group 9 metal fragments through displacement reactions. Palladium(II) complexes of S–P–S ligands efficiently catalyze cross-coupling processes, allowing the formation of boronic esters and biphenyl derivatives. Rh(I) complexes of S–P–S ligands react in a regioselective way with small molecules (O₂, SO₂, CS₂, MeI) to afford the corresponding Rh(I) or Rh(III) derivatives. S–C–S dianonic ligands, which are readily obtained through a bis-metallation at the central carbon atom of Ph₂P(S)CH₂P(S)Ph₂, react with Pd(II) and Ru(II) precursors to afford new carbene complexes. Samarium and thulium alkylidene complexes of these S–C–S dianionic ligands were synthesized in a similar way. Reaction of the lanthanide derivatives with ketones or aldehydes yields olefinic derivatives through a ‘Wittig-like’ process.     

Forms of Rh(III) in Nitric Acid Solutions

The forms of Rh(III) in nitric acid solutions are studied by ¹⁴N, ¹⁵N, ¹⁷O, and ¹⁰³Rh NMR and electronic absorption spectra. At HNO₃concentrations below 5 mol/l, rhodium mainly exists as low-nuclear oligomers with a bridging fragment Rh(-OH)(-ONO₂)Rh; terminal positions of the central atoms are occupied by water molecules. It was found that the isotopic equilibrium ¹⁴NO^– ₃/¹⁵NO^– ₃of the bridging ligand sets in at an abnormally high rate, at which the isotopic exchange H₂ ¹⁷O/H₂ ¹⁶O of the terminal ligands also occurs in the dimers and trimers. The formation of low-nuclear oligomers is a common feature of Rh(III) complexes in aqueous solutions with ligand deficiency in the system. The possibility of isolating rhodium from nitric acid solutions using different methods is predicted.     

Cyclic voltammetric behavior of Pd–Pt–Rh ternary alloys

The electrochemical behavior of Pd–Pt–Rh alloys has been investigated using cyclic voltammetry (CV). The alloys were prepared by electrochemical codeposition as limited volume electrodes (less than 1 m in thickness). The morphology of the alloy surface and bulk compositions were examined by the SEM/EDAX method. Surface oxides generation (oxygen adsorption) and oxides reduction (oxygen desorption) currents together with hydrogen adsorption and hydrogen absorption signals can be distinguished on CV curves. During potential cycling through the full hydrogen–oxygen potential range Rh and Pd are preferentially dissolved, which is reflected in a dramatic transformation in the voltammogram shape. The composition changes involve not only the surface but also some atomic layers beneath the surface.     

Anion-exchange TLC of rhodium(III) and iridium(III,IV) on DEAE-cellulose or ECTEOLA-cellulose

Summary The TLC behaviour and separation of Rh(III), Ir(III) and Ir(IV) has been investigated in the two systems composed of DEAE-cellulose or ECTEOLA-cellulose using 3 M or 5 M HCl containing NaClO₃ as solvent. These systems, especially in combination with a sample treatment with LiCl, HCl and H₂O₂ solutions, allow the clean-cut separations of Rh(III) from Ir(III) as well as Ir(IV), coexisting in an extremely wide range of amounts and ratios (RhIr=1500 to 2001). A brief discussion on the characteristic adsorption behaviour of Rh(III), dependent on the previous history of the sample solutions, is also included.

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Anionenaustausch-Dünnschicht-Chromatographie von Rhodium(III) und Iridium(III, IV) auf DEAE- oder ECTEOLA-Cellulose

Zusammenfassung Zur dünnschicht-chromatographischen Trennung von Rh und Ir wurden DEAE- bzw. ECTEOLA-Cellulose mit 3 M bzw. 5 M NaClO₃-haltiger Salzsäure als Lösungsmittel benutzt. Besonders in Verbindung mit einer Probevorbehandlung mit LiCl, HCl und H₂O₂ konnten mit diesen Systemen scharfe Trennungen von Rh(III), Ir(III) und Ir(IV) in einem weiten Konzentrationsbereich erzielt werden (RhIr=1500 bis 2001). Das Adsorptionsverhalten des Rh(III) in Abhängigkeit von der Vorbehandlung der Probelösung wird diskutiert.

     

Thin-layer chromatographic separation of noble metals on ECTEOLA-cellulose in hydrochloric acid and aqueous chloride solutions

Summary The thin-layer chromatographic behaviour of the noble metals on ECTEOLA-cellulose has been examined in HCl and aqueous chloride solutions of Li, Na, Mg, Ca, Sr and Al. The R_f-values decrease in the order Ir(III) Rh(III) > Ru(III) > Pd(II) > Pt(IV) > Ir(IV) > Au(III) in all of the media of higher chloride concentrations (3M to 5M), in which there are sufficiently large differences in R_f-values of adjacent metals to resolve them clearly. Especially, the HCl solutions with or without H₂O₂ are very suitable for multi-component separations of the noble metals.

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DC-Trennung von Edelmetallen auf ECTEOLA-Cellulose in salzsauren und wäßrigen Chloridlösungen

Zusammenfassung Das Verhalten von Edelmetallen wurde in salzsauren Lösungen sowie in Lösungen der Chloride von Li, Na, Mg, Ca, Sr und Al geprüft. Die R_f-Werte nehmen in allen Medien mit höherer Chlorid-konzentration (3M bis 5M) in folgender Reihenfolge ab: Ir(III) Rh(III) > Ru(III) > Pd(II) > Pt(IV) > Ir(IV) > Au(III). Die Unterschiede in den R_f-Werten sind groß genug, um eine deutliche Trennung zu gewährleisten. Salzsaure Lösungen mit oder ohne H₂O₂-Zusatz sind besonders gut für die Trennung von Vielkomponenten-Gemischen geeignet.

     

Rhodium(I) complexes with bidentate nitrogen heterocycles and their reactions with tin(II) chloride and carbon monoxide

Summary Cleavage of [{Rh(diolefin)Cl}₂] by bidentate heterocyclic chelating ligands (LL) has been studied, and diolefin neutral, ionic or ion-pair type compounds are formed depending on the ligands and/or the Rh: (LL) ratio employed. When the reactions are performed in media saturated with CO and with Rh: (LL)=21, only carbonylated ion-pair complexes are formed. The diolefin compounds react with tin(II) chloride yielding species containing trichlorostannato-groups. Subsequent reaction with CO leads to displacement of the diolefin and formation of the corresponding dicarbonyl species.     

EQCM Study of Rhodium Anodic Dissolution in Sulfuric Acid

Rh anodic dissolution is studied in 0.5 M H₂SO₄ solution in the E range from 0.2 to 1.2 V (RHE) by means of EQCM, cyclic voltammetry, photometry, and XPS. Bright pure Rh electroplate 0.5 m thick on a gold sputtered quartz crystal electrode is used for electrochemical and microgravimetrical studies. It is found that the increase in Rh electrode weight during the anodic process is lesser than its decrease during the cathodic one. The difference is 120 ± 60 ng cm^–2. The electrode weight also decreases under open-circuit conditions, i.e. at E _{I = 0}. A linear relationship between the weight change and the charge exists for the anodic process. The presence of Rh(III) compounds in the solution and on the electrode surface is confirmed by a photometrical analysis and XPS measurements. It is assumed that the formation and reduction of Rh(OH)₃ phase on Rh electrode surface within E range investigated proceed according to equation Rh + 3H₂O [Rh(OH)₃]_s + 3H⁺ + 3e, where [Rh(OH)₃]_s is a surface layer of Rh(OH)₃ phase. is evaluated to be 0.6 V. Rh(OH)₃ partly dissolves in the electrolyte.     

Synthetic, structural, spectroscopic, and electrochemical studies of mixed sandwich Rh(III) and Ir(III) complexes involving Cp* and tridentate macrocycles

The syntheses, structures, spectroscopy, and electrochemistry for six Ir(III) and Rh(III) mixed sandwich mononuclear complexes involving tridentate macrocycles and pentamethylcyclopentadienide (Cp*) are reported. The complexes are readily prepared by direct ligand substitution reactions from the dichloro bridged binuclear complexes, [{M(Cp*)(Cl)₂}₂]. All complexes have the general formula [M(L)(Cp*)]X₂ (M = Ir(III) or Rh(III), L = macrocycle, or Cl⁻) and exhibit a distorted octahedral structure involving three donor atoms from the macrocycle and the facially coordinating carbocyclic Cp* ligand. The complex cations include: [Rh(η⁵ -Cp*)(9S3)]²⁺ (1), [Rh(η⁵-Cp*)(9N3)]²⁺ (2), [Rh(η⁵-Cp*)(10S3)]²⁺ (3), [Ir(η⁵-Cp*)(9S3)]²⁺ (4), [Ir(η⁵-Cp*)(9N3)]²⁺ (5), and [Ir(η⁵-Cp*)(10S3)]²⁺ (6), where 9S3 = 1,4,7-trithiacyclononane, 9N3 = 1,4,7-triazacyclononane, and 10S3 = 1,4,7-trithiacyclodecane. The structures for all six complexes are supported by ¹H and ¹³C{¹H} NMR spectroscopy, and five complexes are also characterized by single-crystal X-ray crystallography (complexes 1-5). The ¹H NMR splittings between the two sets of methylene protons for both the Rh(III) and Ir(III) 9S3 complexes are much larger (0.4 vs. 0.2 ppm) compared to those in the two 9N3 complexes. Similarly, the ¹³C{¹H} NMR spectra in all four thioether complexes show that the ring carbons in the Cp* ligand are shifted by over 10 ppm downfield compared to the azacrown complexes. The electrochemistry of the complexes is surprisingly invariable and is dominated by a single irreversible metal-centered reduction near −1.2 V vs. Fc/Fc⁺.     

Synthesis of tris(β-diketonato) technetium(III) and its adsorption behaviour on silica gel

Tris (benzoylacetonato) technetium(III) and tris (2-thenoyltrifluoroacetonato) technetium(III) were synthesized by the direct reduction of pertechnetate with dithionite in the presence of excess ligands. The geometrical isomers of the benzoylacetonate were further separated by means of a silica gel column chromatography. In the silica gel system, the adsorption distribution coefficient of the tris (-diketonato) technetium(III) decreases in the order of Tc(acac)₃>fac-Tc(bzac)₃>mer-Tc(bzac₃)>Tc(tta)₃.     

14N, 17O, 103Rh NMR Studies of Rh(III) State in Diluted Nitric Acid Solutions

The state of rhodium(III) in nitric acid solutions diluted with 3M HNO₃ or water was studied by ¹⁴N, ¹⁷O, and ¹⁰³Rh NMR methods. The ¹⁰³Rh NMR chemical shifts significantly depend on the ionic background of the solution. Concentrated nitric acid solutions (c _Rh = 0.5–1 mol/l) diluted 100 to 200 times retain the polynuclear Rh(III) forms with double (-NO₃, -OH) bridges. The predominant form in the diluted solutions is a dimer.     

MHNAMT,a new locating and chelating agent in thin-layer chromatographic determination of Cu(II), Co(II), Ni(II), Pd(II), Pt(IV), and Rh(III)

Summary Synthesis of MHNAMT [3-methyl-4-(2-hydroxy-1 naphthalideneamino)-5-mercapto-1,2,4-triazole] and its IR and NMR spectral data are reported. The high stability of the characteristically coloured chelates with Cu(II), Co(II), Ni(II), Pd(II), Pt(IV) and Rh(III) has been made the basis for their efficient ascending TLC separations on silica gel G layers, when present together. Results of three different solvent systems are included to assess efficient resolution of the chelates.     

Crystal Structure of [M(NH3)5Cl]2[IrCl6]Cl2 (M = Co, Rh, Ir) Binary Complex Salts

Binary complex salts of M(NH₃)₅Cl]₂[IrCl₆]Cl₂ composition, where M = Co(III), Rh(III), or Ir(III), have been studied. All phases are isostructural with [M(NH₃)₅Cl]₂[PtCl₆]Cl₂ complexes [M = Rh(III) and Ir(III)]; Xray structural and crystallochemical analysis have been performed.     

Synthesis and structure of N-heterocyclic carbene complexes of rhodium and iridium derived from an imidazolium-linked cyclophane

This paper describes the synthesis, spectroscopic and structural characterisation, and electrochemical behaviour of some rhodium and iridium complexes of the form LM(X₁)(X₂)⁺, where L is a chelating bis(carbene) derived from an imidazolium-linked ortho-cyclophane. The complexes where X₁/X₂ = 1,5-cycooctadiene or norbornadiene were prepared from the imidazolium-linked cyclophane and the appropriate metal source. In these complexes, the M-L bonding was quite robust, but the diene could be displaced by CO to give the dicarbonyl complexes , from which one or both carbonyl ligands could be displaced by monodentate or bidentate phosphines, respectively. Structural studies revealed only minor variations in the cyclophane unit upon exchange of the ancillary ligands, in each case the rhodium complex being isomorphous with its iridium analogue. In cyclovoltammetric studies of LRh(dppe)⁺, reversible Rh(I/II) and Rh(II/III) redox couples were observed. The other rhodium complexes displayed more complex electrochemical behaviours and did not undergo simple reversible redox reactions.     

Anion-exchange separation of rhodium and iridium by ECTEOLA-cellulose column

Summary The separation of Rh(III) and Ir(IV) in amounts of 20–5300 and 20–7700 g, respectively, and in ratios of RhIr=1100 to 1001 was achieved without cross-contamination by use of a 3 g ECTEOLA-cellulose column. Rh was first eluted with 40 ml of a 3 mol/l HCl-1% (w/v) NaClO₃ solution. Ir(IV) was desorbed with 60 ml of a 6 mol/l HCl-0.1% (w/v) NaClO₃ solution. Quantitative recoveries were obtained for each metal. The present method provides much better resolution than the other existing anion-exchange methods and can effectively be applied to the separations and recoveries of Rh and Ir(III or IV) present in a more extensive range of amounts and ratios.

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Anionenaustausch-Trennung von Rhodium und Iridium mit Hilfe einer ECTEOLA-Cellulose-Säule

     

Spectrophotometric and derivative spectrophotometric study of the reaction of palladium (II) and rhodium (III) with 5-(3,4-methoxyhydroxybenzylidene)rhodanine and cationic surfactants

Spectrophotometric and derivative spectrophotometric methods for the determination of Pd(II) and Rh(III) are proposed. Pd(II) forms with 5-(3,4-methoxyhydroxybenzylidene)rhodanine [3,4-MHBR], in the absence and presence of cetylpyridinium bromide [CPB], 14 binary and 134 ternary complexes having molar absorptivities of 5.77 × 10⁴ and 7.46 × 10⁴ M ^–1cm^–1 at 525 and 530 nm, respectively. Rh(III) forms a 14 complex with 3,4-MHBR in the presence of cetyltrimethylammonium bromide [CTAB], which gives a maximum absorbance at 445 nm with a molar absorptivity of 5.13 × 10⁴ M ^–1cm^–1. Derivative spectrophotometric methods are employed for the determination of Pd(II) and Rh(III) at ng ml^–1 levels utilizing these complexes. Under the optimum conditions the calibration lines for Pd(II) and Rh(III) determination fit the equations d⁴ A/d⁴ = 1.10 × 10⁶ [Pd] – 0.018 (r = 0.9967) and d⁴ A/d⁴ = 2.25 × 10⁶ [Rh] + 0.03 (r = 1.0426) and have detection limits of 5.6 and 1.2 ng ml^–1, respectively. The influences of experimental variables and foreign ions are studied. The methods are free of interference from most common metal ions and anions. The results of the analysis of some synthetic mixtures of Pd(II) and Rh(III) are reported.     

On the electrochemical reduction of some Cr(III) complexes inDMSO investigated by cyclic voltammetry

The compounds investigated were: [Cr(en)₃]³⁺, [Cr(ur)₆]³⁺, [Cr(DMSO)₆]³⁺, [Cr(dien)₂]³⁺, [Cr(en)₂(acac)]²⁺, [Cr(en) (acac)₂]⁺ and Cr(acac)₃.A distinctly different behaviour is caused by the introduction of one or moreacac ligands into the molecule. The first step is much more cathodic and quite irreversible, while it is reversible or quasi reversible for the first group of ions. This is due to a -type interaction between theacac ligand and the central ion. This interaction is responsible for a third peak occurring for the second group of compounds and may be attributed to the reduction of the Cr(I) ion.Some correlations were found e.g. between the extinction of thed-d band of the first group of ions and the potential of the first peak, and the number ofacac groups introduced in the second group of compounds and the shift of the potential of the first peak.The determined electrochemical data are tabulated.

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Untersuchungen zur elektrochemischen Reduktion einiger Cr(III)-Komplexe in DMSO mittels zyklischer Voltammetrie

Zusammenfassung Die elektrochemischen Daten einer Reihe von Cr(III)-Komplexen miten-, ur-, DMSO-, dien- undacac-Liganden werden präsentiert und einige Möglichkeiten der Korrelation der physikalischen Eigenschaften der Komplexe werden aufgezeigt.Die erste Stufe bei der Einführung vonacac-Liganden ist auf Grund einer -Wechselwirkung zwischen Ligand und Zentralion irreversibel.