Reaction of nitrosyltribromide with rhodium(I) complexes and with rhodiumtrichloride trihydrate,in the presence of triphenylphosphine and triphenylarsine

Summary Nitrosyltribromide reacts with rhodium(I) complexes and with rhodiumtrichloride trihydrate in the presence of triphenylphosphine and triphenylarsine to give rhodium(III) nitrosyl complexes and rhodium(III) hyponitrite complexes which are characterized by i.r. spectra, magnetic measurements and by elemental analyses.     

Reactivity and equilibrium thermodynamic studies of rhodium tetrakis(3,5-disulfonatomesityl)porphyrin species with H2, CO, and olefins in water

Aqueous (D2O) solutions of tetrakis(3,5-disulfonatomesityl)porphyrin rhodium(III) aquo/hydroxo complexes ([(TMPS)Rh(III)(D2O)2]-7 (1), [(TMPS)Rh(III)(OD)(D2O)]-8 (2), and [(TMPS)Rh(III)(OD)2]-9 (3)) react with hydrogen (D2) to form an equilibrium distribution with a rhodium hydride ([(TMPS)Rh-D(D2O)]-8 (4)) and a rhodium(I) complex ([(TMPS)Rh(I)(D2O)]-9 (5)). Equilibrium constants (298 K) are measured that define the distribution for all five of these (TMPS)Rh species in this system as a function of the dihydrogen (D2) and hydrogen ion (D+) concentrations. The hydride complex [(TMPS)Rh-D(D2O)]-8 is a weak acid in D2O (Ka(298 K) = 4.3 x 10(-8)). Steric demands of the TMPS porphyrin ligand prohibit formation of a Rh(II)-Rh(II)-bonded complex, related rhodium(I)-rhodium(III) adducts, and intermolecular association of alkyl complexes which are prominent features of the rhodium tetra(p-sulfonatophenyl)porphyrin ((TSPP)Rh) system. The rhodium(II) complex ([(TMPS)Rh(II)(D2O)]-8) reacts with water to form hydride and hydroxide complexes and is not observed in D2O. The (TMPS)Rh-OD and (TMPS)Rh-D bond dissociation free energies (BDFE) are virtually equal and have a value of approximately 60 kcal mol(-1). Reactions of [(TMPS)Rh-D(D2O)]-8 in water with CO and olefins produce rhodium formyl and alkyl complexes which have equilibrium thermodynamic values comparable to the values for the corresponding substrate reactions of [(TSPP)Rh-D(D2O)]-4.     

Synthesis and reactions of rhodium compounds containing tellurium donor ligands

This paper describes the synthesis and characterization of a series of rhodium(I) and rhodium(III) complexes containing tellurium-rhodium bonds resulting from the coordination of diorgano telluride or organotelluro ligands. Oxidative addition, metathesis and substitution reactions of these compounds have been examined, and the resulting products are compared with those from the known reactions of rhodium(I) and rhodium(III) compounds containing phosphine ligands.     

Metal complexes of isonicotinic acid hydrazide

Complexes of platinum(IV), ruthenium(III), rhodium(III), iridium(III), gold(III), dioxouranium(II), zinc(II), cadmium(II), mercury(II) and manganese(II) with isonicotinic acid hydrazide were prepared and characterized on the basis of analytical, conductometric, magnetic susceptibility and spectral data. Platinum(IV) ruthenium(III), rhodium(III), iridium(III), dioxouranium(II) and manganese(II) form six-coordinate complexes while gold(III), zinc(II), cadmium(II) and mercury(II) form four coordinate complexes.     

Reactions of ruthenium(III), Rhodium(III) and Iridium(III) chlorides in molten nitrite eutectics

The reactions of ruthenium(III), rhodium(III) and iridium(III) chlorides in molten lithium nitrite—sodium nitrite, lithium nitrite—potassium nitrit and sodium nitrite—potassium nitrite eutectics were studied and compared with those of their first row congeners. Ruthenium(III) reacted to form hexanitroruthenate(II) with the evolution of nitrogen dioxide, whereas rhodium(III) and iridium(III) formed hexanitrorhodate(III) and hexanitroiridate(III), respectively. These complexes decomposed at higher temperatures to form ruthenium(IV), rhodium(III) and iridium(IV) oxides, respectively, with the evolution of nitrogen oxides. The stoichiometries of these reactions were established by thermogravimetry and the products were characterized by their IR, visible and UV spectra, and X-ray diffraction patterns.     

Chloride‐Bridged Dinuclear Rhodium(III) Complexes Bearing Chiral Diphosphine Ligands: Catalyst Precursors for Asymmetric Hydrogenation of Simple Olefins

Efficient rhodium(III) catalysts were developed for asymmetric hydrogenation of simple olefins. A new series of chloride‐bridged dinuclear rhodium(III) complexes 1 were synthesized from the rhodium(I) precursor [RhCl(cod)]₂, chiral diphosphine ligands, and hydrochloric acid. Complexes from the series acted as efficient catalysts for asymmetric hydrogenation of (E)‐prop‐1‐ene‐1,2‐diyldibenzene and its derivatives without any directing groups, in sharp contrast to widely used rhodium(I) catalytic systems that require a directing group for high enantioselectivity. The catalytic system was applied to asymmetric hydrogenation of allylic alcohols, alkenylboranes, and unsaturated cyclic sulfones. Control experiments support the superiority of dinuclear rhodium(III) complexes 1 over typical rhodium(I) catalytic systems.     

Luminescent cyclometalated Rh(III), Ir(III), and (DIP)2Ru(II) complexes with carboxylated bipyridyl ligands: synthesis, X-ray molecular structure, and photophysical properties

Luminescent cyclometalated rhodium(III) and iridium(III) complexes of the general formula [M(ppy) 2(N (wedge)N)][PF 6], with N (wedge)N = Hcmbpy = 4-carboxy-4'-methyl-2,2'-bipyridine and M = Rh ( 1), Ir ( 2) and N (wedge)N = H 2dcbpy = 4,4'-dicarboxy-2,2'-bipyridine and M = Rh ( 3), Ir ( 4), were prepared in high yields and fully characterized. The X-ray molecular structure of the monocarboxylic iridium complex [Ir(ppy) 2(Hcmbpy)][PF 6] ( 2) was also determined. The photophysical properties of these compounds were studied and showed that the photoluminescence of rhodium complexes 1 and 3 and iridium complexes 2 and 4 originates from intraligand charge-transfer (ILCT) and metal-to-ligand charge-transfer/ligand-centered MLCT/LC excited states, respectively. For comparison purposes, the mono- and dicarboxylic acid ruthenium complexes [Ru(DIP) 2(Hcmbpy)][Cl] 2 ( 5) and [Ru(DIP) 2(H 2dcbpy)][Cl] 2 ( 6), where DIP = 4,7-diphenyl-1,10-phenanthroline, were also prepared, whose emission is MLCT in nature. Comparison of the photophysical behavior of these rhodium(III), iridium(III), and ruthenium(II) complexes reveals the influence of the carboxylic groups that affect in different ways the ILCT, MLCT, and LC states.     

Synthesis and characterization of Rhodium(III) dichloro complexes with unsymmetrically bound salen-type ligands

We have synthesized a series of novel octahedral Rh(III) salen-type complexes where the salen ligand is unsymmetrically bound to the Rh(III) dichloride center. This mode of bonding left one intact phenol group coordinating to the rhodium center and has never before been observed in salen-metal chemistry. These remarkably stable complexes possess unique coordination geometry and represent the first time that Rh(III) salen complexes have been successfully isolated from the direct combination of RhCl(3).3H2O and the salen ligand in the absence of a nucleophilic base. The (salen)Rh(III) dichloride complex can be converted to the analogous monochloride complex by reaction with metal carbonate salts.     

Recovery of palladium(II) and rhodium(III) chloride complexes with a complexing S,N-containing sorbent

Specific features of sorption recovery of palladium(II) and rhodium(III) chloride complexes from hydrochloric acid and chloride solutions with MITKhAT S,N-containing sorbent were revealed. The kinetic and capacity characteristics of the sorbent were determined in relation to the solution composition and kind of the metal. The most probable mechanism of sorption recovery and the composition of the forming Pd(II) and Rh(III) complexes were suggested.     

Rhodium‐Mediated Oxygenation of Nitriles with Dioxygen: Isolation of Rhodium Derivatives of Peroxyimidic Acids

Dioxygen is used as the oxygenation agent in the rhodium‐mediated conversion of nitriles into amides. The characterization of intermediate species and model compounds as well as isotope‐labeling studies provided an insight into the reaction mechanism. The conversions of rhodium hydroperoxido or methylperoxido complexes with nitriles into metallacyclic rhodium‐ κ²‐(N,O)‐peroxyimidate compounds represent essential key steps. The former are accessible from a rhodium(III) peroxido complex and the latter represent rhodium derivatives of Payne’s reagent (peroxyimidic acids).     

Coordinating ability of rhodium(III) porphyrins toward organic bases

Reactions of hydroxo(2,3,7,8,12,13,17,18-octaethylporphyrinato)rhodium(III) and acetylacetato-(5,10,15,20-tetraphenylporphyrinato)rhodium(III) with nitrogen-containing substrates were studied by spectrophotometry. The stability constants and compositions of the resulting molecular complexes were determined, and the effects of the macrocycle nature and substrate basicity on the stability constants were estimated. The structures of the isolated rhodium porphyrin molecules and their complexes with organic bases were optimized by the PM3 quantum chemical method. The degree of macrocycle deformation was found to change in the course of metal–substrate coordination. A correlation between the metal–substrate bond energy and equilibrium constant was revealed.

     

Monohydride-Dichloro Rhodium(III) Complexes with Chiral Diphosphine Ligands as Catalysts for Asymmetric Hydrogenation of Olefinic Substrates

We report full details of the synthesis and characterization of monohydride-dichloro rhodium(III) complexes bearing chiral diphosphine ligands, such as (S)-BINAP, (S)-DM-SEGPHOS, and (S)-DTBM-SEGPHOS, producing cationic triply chloride bridged dinuclear rhodium(III) complexes ( 1 a : (S)-BINAP; 1 b : (S)-DM-SEGPHOS) and a neutral mononuclear monohydride-dichloro rhodium(III) complex ( 1 c : (S)-DTBM-SEGPHOS) in high yield and high purity. Their solid state structure and solution behavior were determined by crystallographic studies as well as full spectral data, including DOSY NMR spectroscopy. Among these three complexes, 1 c has a rigid pocket surrounded by two chloride atoms bound to the rhodium atom together with one tBu group of (S)-DTBM-SEGPHOS for fitting to simple olefins without any coordinating functional groups. Complex 1 c exhibited superior catalytic activity and enantioselectivity for asymmetric hydrogenation of exo-olefins and olefinic substrates. The catalytic activity of 1 c was compared with that of well-demonstrated dihydride species derived in situ from rhodium(I) precursors such as [Rh(cod)Cl]₂ and [Rh(cod)₂]⁺[BF₄]⁻ upon mixing with (S)-DTBM-SEGPHOS under dihydrogen.     

Carbonyl complexes of rhodium(I) and rhodium(III) with 2,2′-biquinoline

Novel carbonyl complexes of rhodium(I) and rhodium(III) containing the bidenate nitrogen donor ligand 2,2′-biquinoline (biq) have been prepared; they are of the types RhX(CO)₂ biq and RhX(CO)biq (X = Cl, Br, I). Cationic carbonyl and substituted carbonyl complexes of the types [Rh(CO)₂biq]ClO₄ and [Rh(CO)biqL₂]ClO₄, where L is tertiary phosphine or arsine have also been isolated. In spite of considerable steric crowding around the nitrogen atoms, 2,2′-biquinoline behaves much like 2,2′-bipyridine in forming carbonyl complexes of rhodium.     

Oxygen-Bridged Carboxylato Complexes of Cobalt,Rhodium, and Iridium

The current state of investigations of homonuclear cobalt(III), rhodium(III), and iridium(III) complexes containing bridging O atoms and bridging carboxylato groups is reviewed.     

Regioselectivity and equilibrium thermodynamics for addition of Rh-OH to olefins in water

Rhodium(III) tetra(p-sulfonato phenyl) porphyrin ((TSPP)Rh) aquo and hydroxo complexes react with a series of olefins in water to form beta-hydroxyalkyl complexes. Addition reactions of (TSPP)Rh-OH to unactivated terminal alkenes invariably occur with both kinetic and thermodynamic preferences to place rhodium on the terminal carbon to form (TSPP)Rh-CH(2)CH(OH)R complexes. Acrylic and styrenic olefins initially react to place rhodium on the terminal carbon to form Rh-CH(2)CH(OH)X as the kinetically preferred isomer but subsequently proceed to an equilibrium distribution of regioisomers where Rh-CH(CH(2)OH)X is the predominant thermodynamic product. Equilibrium constants for reactions of the diaquo rhodium(III) compound ([(TSPP)Rh(III)(H(2)O)(2)](-3)) in water with a series of terminal olefins that form beta-hydroxyalkyl complexes were directly evaluated and used in deriving thermodynamic values for addition of the Rh-OH unit to olefins. The DeltaG degrees for reactions of the Rh-OH unit with olefins in water is approximately 3 kcal mol(-1) less favorable than the comparable Rh-H reactions in water. Comparisons of the regioisomers and thermodynamics for addition reactions of olefins with Rh-H and Rh-OH units in water are presented and discussed.     

Effect of ring methylation on the photophysical, photochemical and photobiological properties of cis-dichlorobis(1,10-phenanthroline)rhodium(III)Chloride

Methylated analogues of cis-dichlorobis(1,10-phenanthroline)rhodium(III)chloride (BISPHEN) have been prepared in order to increase the hydrophobicity of the parent compound, and thus create octahedral rhodium (III) complexes suitable for use as anticancer and antiviral agents that can be photoactivated. The parent complex has been shown in earlier work to be unable to cross through cell membranes. Octamethylation, as in the case of cis-dichlorobis(3,4,7,8-tetramethyl-1,10-phenanthroline)rhodium(III)chloride (OCTBP), provides enough hydrophobicity to be taken up by KB tumor cells. It also provides a higher level of ground-state association with double-stranded DNA and increases the quantum efficiency of photoaquation by greater than 10-fold, relative to BISPHEN. OCTBP forms covalent bonds to deoxyguanosine when irradiated with the nucleoside, as has been seen with the parent complex. Irradiation of OCTBP in the presence of the KB or M109 tumor cell lines using narrow-band UVB (lambda = 311 nm) irradiation initiates a considerable amount of phototoxicity. There is evidence that OCTBP acts as a prodrug (i.e. after passing through the cell membrane the metal complex is photolyzed to cis-chloro aquo OCTBP, which may be the active phototoxic agent). OCTBP and the tetramethyl analogue cis-dichlorobis(4,7-dimethyl-1,10-phenanthroline)rhodium(III)chloride (47TMBP) also show photoaquation upon excitation with visible light (lambda > 500 nm), and indeed, some phototoxicity of KB cells is observed at these wavelengths as well. This is attributed to direct population of photoactive triplet-excited states. These results, together with our earlier studies of cis-dichloro[dipyrido(3,2-a: 2',3'-c)phenazine (1,10-phenanthroline)rhodium(III)chloride (DPPZPHEN) demonstrate that such octahedral rhodium complexes are viable "photo-cisplatin" reagents.     

Synthesis of N-confused tetraphenylporphyrin rhodium complexes having versatile metal oxidation states

A variety of N-confused tetraphenylporphyrin rhodium complexes were synthesized, and their structures and physical properties were investigated. Depending on the reaction conditions, the rhodium(I), -(III), and -(IV) complexes were produced, which exemplified the versatile coordination mode of N-confused porphyrin ligands.     

The Spectropolarimetric Back-Titration of Rhodium(III) with the Chiral Ligand (R,R)-(-)-Trans-1, 2-Cyclohexanediaminetetraacetic Acid

Abstract

Spectropolarimetric back-titrations are described for rhodium(III); the optically active ligand (R, R)-(-)-t?ans-l, 2-cyclohexanediaminetetraacetic acid (R, R(-)CDTA) is used as the complexing agent and cadmium(II) ion as the back-titrant. The optical rotation is monitored throughout the titration, and the optically active ligand and stereospecifically formed complexes serve as self-indicators. The end points are determined graphically by straight-line extrapolations from a plot of volume-corrected observed rotations versus ml of titrant. The rhodium(III) titration plots are representative of normal spectro-polarimetric back-titrations. The range of analyses of rhodium(III) was from 40–0.5 mg.     

The first (<Superscript>31</Superscript>P, <Superscript>17</Superscript>O,and <Superscript>103</Superscript>Rh) NMR observation complex formation of rhodium(III) with phosphoric acid

³¹P, ¹⁷O, and ¹⁰³Rh NMR spectroscopy shows that rhodium(III) reacts with phosphoric acid to generate polynuclear aquaphosphate complexes in which phosphate ions mostly have a bridging function. Assignment of ¹⁰³Rh NMR signals in dominant rhodium complexes is suggested.