Rh Separation Research Articles

Highly Selective Rh(III) Recovery from HCl Solutions Using Aromatic Primary Diamines via Formation of Three-Dimensional Ionic Crystals.

A new Rh(III) separation method using metal-containing hydrochloric acid (HCl) solutions has been developed. This method includes Rh(III) precipitation with high selectivity using aromatic primary diamines as precipitants. The compound p-phenylene diamine dihydrochloride (PPDA) successfully precipitates only Rh(III) from HCl solutions containing Pd(II), Pt(IV), and Rh(III). Furthermore, highly selective Rh(III) recovery from the simulated spent catalyst leach solution, comprising Pd, Pt, Rh, Ce, Al, Ba, Zr, La, and Y in 5 M HCl, was achieved using PPDA. Single-crystal X-ray analysis revealed that the Rh(III)-containing precipitate using PPDA forms three-dimensional ionic crystals comprising the [RhCl6]3–/ammonium form of PPDA/chloride anion/H2O at a 1:2:1:2 ratio. Formation of these unique ionic crystals plays a key role in the highly selective Rh(III) recovery. This Rh(III) recovery method will be promising for use in the purification process of Rh as well as the practical Rh recovery from spent catalysts.

SEPARATION OF P t (IV), P d (II) AND R h (III) FROM CHLORIDE SOLUTIONS BY MULTISTAGE SOLVENT EXTRACTION USING NITROGEN-CONTAINING EXTRACTANTS

The possibility of Pd (II), Pt (IV), and Rh (III) separation from chloride solutions by solvent extraction in rotating coiled columns (RCC) is demonstrated. The reagents most frequently used in extraction of platinum metals were selected as extractants: trioctylamine (TOA), methyltrialkylammonium chloride (MTAA), tributylphosphate (TBP), N, N, N',N'-tetra-re-octyldiglyTOlamide (TODGA). The completeness of extraction of the platinum group metals from individual and mixed hydrochloric acidic and chloride solutions was studied depending on the nature and concentration of the extractant, acidity of the test solutions and other factors. Optimal conditions for the quantitative extraction of metals from model hydrochloric acidic and chloride solutions and subsequent selective separation at the stripping stage are specified. A scheme of multistaged extraction separation of Pd (II), Pt (IV), and Rh (III) from chloride solutions using a 0.05 M solution of MTAA in toluene as a stationary phase in RCC is proposed. The scheme includes extraction of Pd (II) and Pt (IV) ions from a chloride solution (0, 1 M HCl + 30 g/liter NT) into the organic phase with simultaneous separation of Rh(III) remaining in the aqueous phase, and sequential stripping of Pd (II) and Pt (IV) from the organic phase with a 0.01 M solution of thiourea in 0.1 M HCl and a 1 M solution of thiourea in 0.5 M HCl, respectively. The scheme was tested in separation of the platinum group metals from the technological solution of a given composition. The degree of metal extraction with a 0.05 M MTAA solution in toluene and sequential stripping with thiourea solutions is 99.5% for Rh (III), 99.9% for Pd (II), and 97.4% for Pt (IV). The separated water fractions of rhodium and platinum after leaving the column did not contain impurities of other platinum metals whereas the water fraction of palladium contained 0.5% Pt.

Preferential Precipitation and Selective Separation of Rh(III) from Pd(II) and Pt(IV) Using 4-Alkylanilines as Precipitants.

Rhodium (Rh) is the most expensive platinum group metal (PGM) and is of great industrial importance. Although the recycling of PGMs from secondary sources is in high demand, the preferential and selective separation of Rh from PGM mixtures remains a great challenge. Here, a selective Rh separation method involving the precipitation of Rh from an HCl solution containing palladium (Pd), platinum (Pt), and Rh is reported. 4-Butylaniline and 4-hexylaniline were used as precipitants for Rh, and selective Rh precipitation was achieved at high HCl concentrations. We revealed that Rh in HCl selectively forms a unique and highly stable ion-pair complex comprising [RhCl6]3–/anilinium/chloride ions in a 1:6:3 ratio. The formation and high stability of the Rh complex were found to play important roles in the selective recovery of Rh from PGM mixtures.

Synthesis and structure of a dinuclear NiIIIrIII hydride complex supported by a N3S2 bridging ligand: Comparison of property and reactivity of dinuclear NiII(μ-H)MIII units (M = Rh, Ir) in aqueous media

A water-soluble dinuclear NiIIIrIII complex with a bridging hydride, [Cp*Ir(μ-H)Ni(TsTACN(C2H4S)2)]NO3 (TsTACN(C2H4SH)2 = 1,4-bis(2-mercaptoethyl)-7-tosyl-1,4,7-triazacyclononane, Cp* = η5-penta-methylcyclopentadienyl, [2b]NO3), was synthesized by reacting a dinuclear NiIIIrIII complex [Cp*Ir(NO3)Ni(TsTACN(C2H4S)2)]NO3 ([1b]NO3) with HCOONa in water. The structure of [2b]NO3 was unequivocally determined by an X-ray analysis to allow comparing its structure, property, and reactivity in aqueous media to those of the corresponding rhodium counterpart, [Cp*Rh(μ-H)Ni(TsTACN(C2H4S)2)]NO3 ([2a]NO3). The Ni⋯Ir distance (av. 2.721 Å) is slightly longer than the Ni⋯Rh separation (av. 2.691 Å). The hydrido ligand of NiII(μ-H)IrIII complex ([2b]NO3) bears protic character and is stable in water above pH 2, which is contrasted to the fact that the hydrido ligand of NiII(μ-H)RhIII ([2a]NO3) has no protic character and is stable in water only above pH 6. The difference of the hydride stability in water may lead to a difference of their reductivity, in which [2b]NO3 barely reduced benzaldehyde to benzyl alcohol only in acidic media (pH 3) although the rhodium analog [2a]NO3 did promote the reaction in neutral water. Theoretical calculations with DFT methods on model compounds [Cp*M(μ-H)Ni(HTACN(CH2CH2S)2)]+ (M = Rh ([3a]+), Ir ([3b]+)) revealed that the hydrido ligand of the Ni(μ-H)Ir has less bridging character with a stronger interaction with the IrIII center than that with the RhIII center in the Ni(μ-H)Rh unit.

Thermodynamics of Water Confined in Porous Calcium-Silicate-Hydrates

Water within pores of cementitious materials plays a crucial role in the damage processes of cement pastes, particularly in the binding material comprising calcium-silicate-hydrates (C-S-H). Here, we employed Grand Canonical Monte Carlo simulations to investigate the properties of water confined at ambient temperature within and between C-S-H nanoparticles or "grains" as a function of the relative humidity (%RH). We address the effect of water on the cohesion of cement pastes by computing fluid internal pressures within and between grains as a function of %RH and intergranular separation distance, from 1 to 10 Å. We found that, within a C-S-H grain and between C-S-H grains, pores are completely filled with water for %RH larger than 20%. While the cohesion of the cement paste is mainly driven by the calcium ions in the C-S-H, water facilitates a disjoining behavior inside a C-S-H grain. Between C-S-H grains, confined water diminishes or enhances the cohesion of the material depending on the intergranular distance. At very low %RH, the loss of water increases the cohesion within a C-S-H grain and reduces the cohesion between C-S-H grains. These findings provide insights into the behavior of C-S-H in dry or high-temperature environments, with a loss of cohesion between C-S-H grains due to the loss of water content. Such quantification provides the necessary baseline to understand cement paste damaging upon extreme thermal, mechanical, and salt-rich environments.

Separation of concentrated platinum(IV) and rhodium(III) in acidic chloride solution via liquid–liquid extraction using tri-octylamine

This research dealt with the intensification of Pt–Rh separation via liquid–liquid extraction (LLE). The stock solution contained Pt(IV) and Rh(III) at high concentration level in hydrochloric solution: 625 ppm and 104 ppm, respectively. Tri-octylamine (TOA) in toluene was used as an extractant. For single stage extraction, the separation factor was 135 with 8 wt% TOA. The percentage of extraction was 97% for Pt(IV) and 21% for Rh(III). Soybean oil as a solvent in LLE provided good extraction performance comparable to that of toluene. Pt(IV) was almost completely removed from the organic phase when stripped by 8 M nitric acid. Multi-stage extraction with direct recycling of organic phase after stripping significantly decreased the separation factor to 13 during the 5th stage. When the organic phase was washed with 1 M NaOH prior to be used in the next extraction stage, the separation factor increased to 818 during the 5th stage. Finally, the Pt–Rh continuous separation process scheme is presented.

Mono- and binuclear complexes of rhodium involving a new series of hemilabile o-phosphinoaniline ligands

Monophosphines of the type Ph(x)PAr(3-x) (x = 0, 1 or 2, Ar = o-N-methylanilinyl) and the diphosphine, Ar(2)PCH(2)PAr(2) (mapm) have been synthesized for use as chelating and/or bridging P,N-ligands within mono- and binuclear rhodium(i) complexes, respectively. The previously prepared phosphines, Ph(x)PAr'(3-x) (x = 0, 1 or 2, Ar' = o-N,N-dimethylanilinyl) and Ar'(2)PCH(2)PAr'(2) (dmapm), have also been used to prepare analogous mono- and binuclear complexes. Variable temperature (1)H NMR spectroscopy of the mononuclear complexes, [RhCl(CO)(L)] (L = PhPAr(2), PhPAr'(2), PAr(3) and PAr'(3)), and line-shape analyses of the resultant spectra indicate the substantially increased lability of the N,N-dimethylanilinyl donors relative to the related monomethylanilinyl groups. X-Ray structural analyses of the mononuclear complexes suggest that the enhanced Type II hemilability in the dimethylanilinyl complexes compared to their monomethyl analogues results from increased steric interactions involving the coordinated dimethylanilinyl substituents. In the case of the binuclear, dmapm-bridged compound [Rh(2)Cl(2)(CO)(2)(micro-dmapm)], there are additional transannular repulsions between the chloro ligand on one metal and the coordinated dimethylanilinyl group on the other, which result in a Rh-Rh separation of over 4.1 A. For the analogous mapm-bridged species, the transannular interactions between the chloro ligands and the amine hydrogens are in fact attractive, resulting in a much closer Rh-Rh separation (3.450 A). The chloride substituents of [Rh(2)Cl(2)(CO)(2)(micro-mapm)] can be replaced to generate the complexes, [Rh(2)(X)(2)(CO)(2)(micro-mapm)] (X = I, CF(3)SO(3), CH(3)CO(2)), the last of which also exhibits pronounced transannular hydrogen-bonding interactions in the solid state.

Rhodium Dimers with 2,2-Dimethyl-1,3-diisocyano and Bis(diphenylphosphino)methane Bridging Ligands

Four rhodium dimers have been synthesized with a bridging diisocyanide ligand, dmb (2,2-dimethyl-1,3-diisocyanopropane): [Rh2(dmb)4](BPh4)2, [Rh2(dmb)4Cl2]Cl2, [Rh2(dmb)4I2](PF6)2, and [Rh2(dmb)2(dppm)2](BPh4)2 (dppm = bis(diphenylphosphino)methane). The complexes have been characterized by elemental analysis and mass spectrometry, as well as UV-visible, IR, and 1H NMR spectroscopies. X-ray crystal structures of the rhodium(I) complexes, [Rh2(dmb)4](BPh4)2 . 1.5CH3CN (3.2330(4), 3.2265(4) A) and [Rh2(dmb)2(dppm)2](BPh4)2.0.5CH3OH . 0.2H2O (3.0371(5) A), confirm the existence of short Rh...Rh interactions. The metal-metal separation for the rhodium(II) adduct, [Rh(2)(dmb)4Cl2]Cl2.6CHCl3 (2.8465(6) A), is consistent with a formal Rh-Rh bond. For the two luminescent rhodium(I) dimers and six previously investigated diisocyano-bridged dimers with and without dppm ligands, the intense spin-allowed dsigma-->psigma absorption band maximum shifts to longer wavelengths with decreasing Rh...Rh separation, and there is an approximate correlation between band energy and the inverse of the metal-metal separation cubed. Both [Rh2(dmb)4]2+ and [Rh2(dmb)4(dppm)2]2+ undergo oxidative addition in the presence of iodine. In the conversion of [Rh2(dmb)4]2+ to [Rh2(dmb)4I2]2+, the observed intermediate is tentatively assigned to a tetramer composed of two rhodium dimers. In the case of [Rh2(dmb)2(dppm)2]2+, no intermediate was detected.

Permeation of Iridium(IV) and Metal Impurity Chlorocomplexes through a Supported Liquid Membrane Designed for Rhodium Separation

ABSTRACT A supported liquid membrane (SLM) system previously designed for Rh separation has been examined for its capability to reject the metal impurities which are commonly encountered in industrial Rh chloride solutions. Special attention was paid to Ir(IV) chlorocomplexes and their extraction/transport behavior against both conventional solvent extraction and supported liquid membrane systems of Kelex 100. A lab-scale SLM cell with an effective membrane area of 44 cm2 was used to conduct the SLM permeation tests. The SLM was composed of a Gore-Tex polymer substrate impregnated with an organic solution of Kelex 100, tridecanol, and kerosene. The impurities tested [in addition to Ir(IV)] were Ag(I), As(V), Bi(III), Cd(II), Co(II), Cu(II), Fe(III), Ni(II), Pb(II), Pd(II), Pt(IV), Se(IV), Te(IV), and Zn(II). These impurities, based on their response against the SLM, were classified into three groups, i.e., those permeated through [Zn(II), Pb(II), Cd(II), Bi(III), Te(IV), and Ir(IV)], those nonpermeated at all [Ni(II), Co(II), As(V), Se(IV), Cu(II), and Fe(III)], and those blocking the membrane [Pt(IV), Pd(II), Ag(I), Pb(II), and Bi(III)]. The SLM was not capable of discriminating between Rh(III) and Ir(IV) transport at the optimum operating conditions. Complementary upstream and downstream processes are required to separate the impurities from the feed and the product solutions, respectively. Overall, this work revealed the great limitations of SLMs as effective and potentially useful separation media for the extraction of metals from industrial-like multicomponent aqueous feed solutions.

Protonation of the CoRh bond in CoRh( μ- CO)( CO) 2( μ- dppm) 2

The electronic structure of CoRh(μ-CO)(CO) 2(μ-H 2PCH 2PH 2) 2 and CoRh(μ-H)(μ-CO)(CO) 2(μ-H 2PCH 2PH 2) 2 has been investigated by means of density functional calculations (DFT). The tetrahedral environment around the cobalt atom is the origin of the lack of direct metal-metal interaction in the former complex. In the protonated form a three-center, two-electron interaction emerges, inducing a slight lessening of the CoRh separation. The fluxionality process has also been investigated. The energy barrier for the exchange of the semibridging carbonyl with the terminal CoCO carbonyl has been computed to be 19 kcal mol −1. A second pathway involving the terminal RhCO group appears 18 kcal mol −1 above.

Hydrido(1,4,8,11,15,18,22,25-octa-n-pentylphthalocyaninato)- rhodium Dimers: Single-Crystal X-ray Structure and the Isomerization of the Four Isomers

The hydrido(phthalocyaninato)rhodium dimer [(R8Pc)RhH]2 (1; R8Pc2- = dianion of 1,4,8,11,15,18,22,25-octa-n-pentylphthalocyanine) was synthesized from the reaction of [(R8Pc)(MeOH)2Rh]Cl with H2 at 110 °C in 1-pentanol. A single-crystal X-ray diffraction study shows that 1 is a dimer. The two Pc ligands are essentially planar and staggered by 35(2)°. The two Rh atoms are not significantly displaced from the planes of the ligands; they are separated by 3.347(3) A. This long Rh−Rh separation suggests that 1 has a bridging hydride ligand. The dimeric structure of 1 is maintained in benzene solution. The 1H NMR spectra show that 1 contains one Rh−H and one N−H moiety for every two R8Pc2- ligands. The νNH band at 3373 cm-1 (the νND band at 2478 cm-1) supports the presence of an N−H moiety in 1. Our belief that protonation occurs on a meso (or peripheral) nitrogen, rather than a pyrrolic nitrogen, is derived from X-ray structural data and 1H NMR results. (1) No uniquely long Rh−N bond is present, and all four p...

Cofacial and antarafacial indenyl bimetallic isomers: a descriptive MO picture and implications for the indenyl effect on ligand substitution reactions

The hetero-bimetallic Ind complexes (Ind=indenyl anion) with the formula (CO) 3Cr(μ-Ind)RhL 2 (L=CO, ethylene; L 2=COD, COT, NBD) have two possible conformers, one with the metals at antipodal sides of the condensed bicyclic polyene (antarafacial, anti) and the other with both metals on the same side (cofacial, syn). These systems can be considered to contain 34 valence electrons by assuming that Ind is capable of donating all of its ten π electrons to the metals. A qualitative MO analysis, based on EHMO calculations, is presented. The anti conformer is compared to the homometallic 34e species, namely [CpRu(μ-Ind)RuCp] +. Here, the pseudo-symmetrical relationship between the two identical metal fragments strongly suggests that one Ind σ-bonding MO donates part of its electron density to each of the two metals, which thus become formally saturated (36e). This argument is extended to the anti CrRh derivative in which a critical role is played by an empty FMO of the (CO) 2Rh(I) fragment with π ‖ symmetry (i.e. lying in the molecular mirror plane). The latter, in spit the large π CO ∗ contributions, has good acceptor capabilities at the metal.The calculations suggest that the so-called indenyl effect, namely the increased rate of substitution of one CO ligand by another σ donor (e.g. a phosphine), although a structurally dynamic process, also depends on the electron density which accumulates on the aforementioned π ‖ FMO. In the series ( η 5-C 5H 5)Rh(CO) 2, ( η 5-C 7H 9Rh(CO) 2 and { η 5-[(CO) 3CrC 7H 9]}-Rh(CO) 2 the progressively reduced donor capabilities of the cyclic polyene toward the (CO) 2Rh(I) fragment induce a larger electrophilicity in rhodium, in good agreement with the experimental data on substitution reactivity. Finally, the electronic features of the cofacial conformer (CO) 3Cr(μ-Ind)Rh(CO) 2 are examined. In spite of the long CrRh separation ( > 3 A ̊ ) the graphically illustrated MO analysis indicates a direct, heterodox, intermetallic linkage, which helps the metals to achieve a formal electronic saturation. In this case, the limited propensity of the complex toward any CO substitution reactions is likely attributable to the hindered mobility of the (CO) 2Rh(I) fragment.

Bulky pyrazole as ligands in rhodium(I) complexes. Crystal structure of chlorodicarbonyl (3- p-methoxyphenylpyrazole)rhodium(I)

A new family of complexes containing bulky pyrazoles substituted in the 3 or the 3 and 5 positions, [RhCl(L 2)(Hpz R′,R″)] (L 2  NBD, 2CO; R′  Bu t, Ph, p-CH 3OC 6H 4 (An), R″  H; R′  Bu t, Ph, R″  CH 3; R′  R″  H, CH 3), has been obtained. A dynamic behaviour has been observed only in complexes with the less demanding pyrazole ligands, relating with a metallotropic equilibrium when R′  R″  H, Me, or a diolefin reorientation when R′  Bu t, Ph, An, R″  H. The X-ray crystal structure of [RhCl(CO) 2(Hpz An)] has been solved, showing a molecular stacking with a RhRh separation of 3.398(3) Å along the one-dimensional chain.

Binuclear rhodium alkyl and acyl A-frame complexes: synthesis, structure and reactivity

The electrophilic alkylation of Rh 2(CO) 3(dppm) 2 ( 2) with CH 3SO 3CF 3 yields the μ-acyl A-frame complex Rh 2(μ- CH 3CO)(CO) 2(dppm) 2 + ( 3). Complex 3 is unstalbe and at 70 °C forms the A-frame species Rh 2(CH 3)(μ- CO)(CO)(dppm) 2 + ( 4) via CO loss. Between 40 and 70 °C, both complexes 3 and 4 are observed in solution. Complex 3 reacts with CO to yield the terminal acyl complex Rh 2(CH 3CO)(CO) 3(dppm) 2 + generated in situ. The characterization of complexes 3, 4 and Rh 2(CH 3CO)(CO) 3(dppm) 2 + is based on NMR and IR spectroscopies, and single crystal X-ray diffraction methods for complexes 3 and 4. The crystals of 3 are monoclinic (space group P2 1/ c) having a unit cell of dimensions a=11.953(3), b=24.127(7), c=22.490(12) Å, β=103.00(3)°, V=6310.1 Å 3 and Z=4, with one molecule per asymmetric unit along with acetone and diethyl ether as solvents of crystallization. Complex 3 possesses an A-frame structure in which the Rh centers are bridged by two dppm ligands, and an acyl group occupies the bridgehead position with the carbonyl carbon bonded to Rh1 and the oxygen bonded to Rh2. The RhRh separation of 2.952(3) Å 3 suggests a weak RhRh interaction and the absence of a formal RhRh single bond. The crystals of 4 are monoclinic (space group P2 1/ n) having a unit cell of dimensions a=13.919(4), b=15.682(3), c=23.758(9) Å, β=96.76(3)°, V=5149.8 Å 3 and Z=4, with one molecule per asymmetric unit. Complex 4 possesses an unsymmetrical A-frame structure with the two Rh centers bridged by two dppm ligands and CO located in the bridgehead position. The RhRh bond distance is 2.811(2) Å. The reactivity of these complexes with H 2, phenyl acetylene and CO is also examined.

Chemistry of polynuclear metal complexes with bridging carbene or carbyne ligands. Part 89. Tetra- and penta-nuclear tungsten–rhodium complexes: crystal structures of [W3Rh2(µ-CO)2(µ-CMe){µ-C(Me)C(O)}(µ-PPh2)2(µ3-CMe)(CO)2(η-C5H5)3] and [W3Rh2(µ-CO)3(µ-CMe){µ-C(Me)PPh2}(µ3-CMe)-(CO)2(ηC5H5)3

Treatment of [Rh2(µ-PPh2)2(cod)2](cod = cyclo-octa-1,5-diene) in thf (tetrahydrofuran) at room temperature with 2 equivalents of [W(CMe)(CO)2(η-C5H5)] rapidly affords the tetranuclear metal complex [W2Rh2(µ-CMe)2(µ-PPh2)2(CO)4(η-C5H5)2](4). If the same reaction is carried out using an excess of the ethylidynetungsten complex two metal cluster compounds are obtained: [W2Rh2(µ-CO){µ-C(Me)C(O)}(µ-PPh2)2(µ3-CMe)(CO)2(η-C5H5)2](5)(formed as a separable mixture of two diastereoisomers) and [W3Rh2(µ-CO)2(µ-CMe){µ-C(Me) C(O)}(µ-PPh2)2(µ3-CMe)(CO)2(η-C5H5)3](6). The structure of the latter was established by X-ray diffraction. The molecule has an essentially planar W(1), Rh(1), W(2), Rh(2), W(3) framework. Carbonyl groups bridge the Rh(1)–W(1) and Rh(2)–W(2) bonds, and PPh2 ligands span the Rh(1)–W(2) and Rh(2)–W(3) linkages. Ethylidyne groups edge-bridge the Rh(1)–W(1) bond and triply bridge the atoms Rh(1)W(2)Rh(2), but the Rh(1)⋯ Rh(2) separation [3.115(4)A] is non-bonding. The Rh(2)–W(3) bond is bridged by a C(Me)C(O) ketenyl group, and the terminal W atoms in the chain each carry a CO ligand and a C5H5 ring. A third C5H5 group ligates W(2). The metal–metal distances fall into two groups [Rh(1)–W(2) 2.791(6), Rh(2)– W(3) 2.813(4); and Rh(1)–W(1) 2.696(5), Rh(2)–W(2) 2.664(5)A], with the shorter separations corresponding to double bonds and the longer to single bonds. Compound (6) is produced by addition of a molecule of [W(CMe)(CO)2(η-C5H5)] to (5), while the latter is formed by isomerisation of (4), a process necessitating migration of µ-CMe and µ-PPh2 between the metal centres. After several hours solutions of (6) in thf afford quantitatively the complex [W3Rh2(µ-CO)3(µ-C(Me){µ-C(Me)PPh2}(µ-PPh2)(µ-CMe)(CO)2(η-C5H5)3](7) an isomer of (6). The structure of (7) was established by X-ray diffraction. An essentially planar metal atom chain W(1), Rh(1), W(2), Rh(2), W(3) forms the spine of the molecule. The various ligands ligate the rhodium and tungsten atoms in a similar manner to those in (6), with the exception of the groups which span the Rh(2)–W(3) bond. This bond is now bridged by a λ5- phospha-alkyne C(Me) PPh2 fragment such that the phosphorus atom ligates W(3) and the carbon atom CMe is bonded to Rh(2) and W(3). The Rh(2)–W(3) bond is also bridged by a CO ligand. Thus the conversion of (6) into (7) involves a novel interchange of CO and PPh2 fragments such that in the former a µ-C(Me)C(O) group is present and in the latter a µ- C(Me)PPh2 moiety. The n.m.r. data (1H, 13C-{1H), and 31P-{1H}) for the new compounds are reported and discussed.

Reaction of [Rh2{µ-1,8-(NH)2C10H6}(CO)2(PPh3)2] with [M(PPh3)]+(M = Au, Ag, or Cu): formation of unusual 44-electron Rh2M clusters. Crystal structure of [Rh2{µ-Au(PPh3)}{µ-1,8-(NH)2C10H6}(CO)2(PPh3)2]ClO4·2CH2Cl2

The complex trans-[Rh2{µ-1,8-(NH)2C10H6}(CO)2(PPh3)2](1) reacts with [M(PPh3)]+(M = Au, Ag, or Cu) to give [Rh2{µ-M(PPh3)}{µ-1,8-(NH)2C10H6}(CO)2(PPh3)2]ClO4(2)–(4). Compound (2) was analysed by single-crystal X-ray diffraction: triclinic, space group Pa= 14.358(4), b= 20.775(6), c= 13.184(3)A, α= 105.65(3), β= 115.66(2), γ= 69.96(3)°, Z= 2, and R= 0.071. The basic skeleton consists of a Rh2Au triangle, the two Rh–Au distances [2.797(2) and 2.690(2)A] being consistent with Rh–Au bonds. The co-ordination geometry around the rhodium atoms is square pyramidal. The Rh–Rh separation [2.815(2)A] is at the upper part of the range of distances for a single Rh–Rh bond. Phosphorus-31 n.m.r. and i.r. data for compounds (2)–(4) are described, and are consistent with a bridging disposition of the M (PPh3) group in all the complexes.

Reduction–oxidation properties of organotransition-metal complexes. Part 30. Triazenido-bridged carbonylrhodium bipyridyl complexes with [Rh2]2+, [Rh2]3+, and [Rh2]4+cores, and the X-ray structures of [Rh2(CO)2(bipy)(µ-RNNNR)2][BF4]·CH2Cl2and [{Rh2I(CO)(bipy)(µ-RNNNR)2}2][PF6]2·2.5CH2Cl2(R =p-tolyl)

The reaction of [{Rh(CO)2(µ-RNNNR)}2](1; R =p-tolyl) with 2,2′-bipyridyl (bipy) in boiling n-heptane gives [Rh2(CO)2(bipy)(µ-RNNNR)2](2) which undergoes two one-electron oxidations at a platinum-bead electrode in CH2Cl2. Chemical oxidation of (2) with [Fe(η-C5H5)2]+ gives [Rh2(CO)2(bipy)(µ-RNNNR)2]+(2+) the X-ray structure of which, as a dichloromethane solvate of the [BF4]– salt, shows a Rh–Rh separation of 2.646(1)A consistent with a formal metal–metal bond order of 0.5. The cation (2+) undergoes carbonyl substitution reactions with PPh3 or P(OPh)3 to give [Rh2(CO)L(bipy)(µ-RNNNR)2][PF6](3+), and with iodide ion to yield [Rh2l(CO)(bipy)(µ-RNNNR)2](4) which may also be prepared directly from (2) and iodine at –78 °C. The cyclic voltammogram of (4) in CH2Cl2 shows one reduction and three oxidation waves; chemical oxidation of (4) with [Fe(η-C5H5)2][PF6] gives the tetranuclear complex [{Rh2l(CO)-(bipy)(µ-RNNNR)2}2][PF6]2(5). X-ray structural studies on the CH2Cl2 solvate of (5) show that the dication is centrosymmetric, having two binuclear (4+) units [Rh–Rh distance within each, 2.544(1)A] linked by asymmetric iodide bridges, Rh–laxial, 2.760(1)A and Rh–lequatorial 2.670(1)A. Complex (5) reacts with I– to give [Rh2l2(CO)(bipy)(µ-RNNNR)2](6), which may also be made directly from (2) and iodine, and with Na[S2CNMe2] to yield [Rh2(CO)(S2CNMe2)(bipy)-(µ-RNNNR)2][PF6](7). The complexes [3+; L = PPh3 or P(OPh)3] react with chloride ion in the presence of [Fe(η-C5H5)2][PF6] giving [Rh2Cl(CO)L(bipy)(µ-RNNNR)2][PF6][8; L = PPh3 or P(OPh)3]. Both (7) and (8) undergo one-electron oxidation and reduction at a platinum electrode. The mechanism of the oxidative addition of iodine to (2) to give (5) and the low-temperature e.s.r. spectra of the paramagnetic [Rh2]3+ complexes (2+), (3+), and (4) are discussed.

Binuclear methylene- and alkyne-bridged complexes of rhodium not containing accompanying metalmetal bonds

The alkyne-bridged “A-Frame” complex, [Rh 2Cl 2(μ-CF 3C 2CF 3(DPM) 2] (DPM  Ph 2PCH 2PPh 2), reacts with diazomethane to give the unusual species, [Rh 2Cl 2(μ-CH 2(μ-CF 3C 2CF 3)(DPM) 2] ( 2) in which the two DPM ligands, the methylene and the hexafluoro-2-butyne groups bridge the metals with no accompanying RhRh bond. Attempts to produce a methylene-bridged complex from the analogous carbonyl-bridged “A-frame”, [Rh 2Cl 2(μ-CO)(DPM) 2], were unsuccessful as this species did not react with diazomethane. An X-ray structure determination has been carried out on compound 2. This complex crystallizes in the tetragonal space group P4 1 with a 21.334(3), c 14.574(2) Å, V=6633.2 Å 3 and Z = 4. On the basis of 3669 unique observations and 291 parameters varied the structure has converged to R = 0.034 and R w = 0.039. The RhRh separation of 3.466(1) Å indicates that there is no RhRh bond and the wide RhCRh angle at the bridged methylene group (119.5(5)°) is also consistent with the absence of metalmetal bonding. The methylene group in compound 2 is found to be unreactive towards CO, H 2 and protic acids, probably in part because it is protected in the pocket between the two metals, however compound 2 did react with PMe 3 to yield a complex mix of products, from which [Rh 2Cl(μ-Cl)(μ-CH 2)(μ-CF 3C 2CF 3)(PMe 3) 5] ( 3) crystallized in low yield. This complex crystallizes with two molar equivalents of CH 2Cl 2 in the monoclinic space group P2 1/ n with a 11.519(2), b 14.689(7), c 25.250(5) Å, β 93.00(2)°. V 4266.7 Å 3 and Z = 4. Based on 4614 unique observations and 396 parameters varied the structure has converged to R = 0.063 and R w = 0.095. Compound 3 is unusual in that it has resulted from the replacement of the two bridging bidentate DPM groups in 2 by five monodentate PMe 3 ligands. Both rhodium atoms have octahedral geometries in which they share a common face, bridged by the methylene, the alkyne and one chloro group. The RhRh separation of 3.1338(7) Å is consistent with the absence of metalmetal bonding, which is substantiated by the relatively large RhCH 2Rh angle of 100.1(3)°.

Binuclear rhodium(I) compounds bridged by the bifunctional 2-mercaptothiazolinate anion

Reaction of [Rh(μ-S 2NC 3H 4)(COD)] 2 ( 1) with carbon monoxide yields the wine-red species [Rh(μ-S 2NC 3N 4)(CO) 2] 2 ( 2). Addition of phosphine or phosphite ligands to solutions of 2 results in replacement of one carbonyl group on each metal to give [Rh(μ-S 2NC 3H 4)(CO)(L)] 2 (L = PPh 3 ( 3), PMe 3 ( 4), P(OPh) 3 ( 5), P(OMe) 3 ( 6)). Only the trans isomers of these compounds are observed. The structures of 3 and 4 have been determined by X-ray crystallography. Compound 3 crystallizes with two equivalents of THF in the triclinic space group P 1 with a 10.973(1) Å, b 12.142(2) Å, c 20.611(3) Å, α 76.62(1)°, β 80.41(1)°, γ 80.78(1)°, V 2613.0 Å 3 and Z = 2. On the basis of 7098 independent observations and 570 parameters varied the structure has refined to R = 0.035 and R w = 0.057. In 3 the two square planar rhodium(I) centers are bridged in a head-to-tail arrangement by the two 2-mercaptothiazolinate groups, which are bound to the metals through the exocyclic sulfur and the nitrogen. The square planes are tilted to each other by 38.5° and the RhRh separation is 3.2435(3) Å. Compound 4 crystallizes in the orthorhombic space group Pbca with a 10.032(2) Å, b 28.335(5) Å, c 17.126(2) Å, V 4868.1 Å 3 and Z = 8 and has refined to R = 0.031 and R w = 0.046 on the basis of 3682 independent observations and 235 parameters varied. The structure of 4 closely resembles that of 3 except that the tilt of the square planes is 30.0° and the RhRh separation has decreased to 3.0524(4) Å.

ChemInform Abstract: A Rhodium A‐Frame Complex: Crystal Structure of (Rh2(dppm)2(μ‐OH)(CO)2) (PF6)·(CH3)2CO

The crystal structure of [Rh 2 (dppm) 2 (/gm-OH)- (CO) 2 ] [PF 6 ]·(CH 3 ) 2 CO has been determined. The crystal and structure data are, M r = 1250.7, mono- clinic, P 2 1 / n , a = 10.165(3), b = 21.084(4), c = 25.85(1) A, β = 95.69(3)°, V = 5513(3) A 3 , Z = 4, D m (295 K) = 1.48, D x = 1.51 g cm −3 , Mo Kα, λ = 0.71069 A, μ = 5.03 cm −1 , F (000) = 2348, R = 0.0433, R w = 0.0462, 6257 observed reflections I >3/gs (I) . This molecule was found to be hydrogen- bonded to an acetone molecule in the lattice and has a Rh⋯Rh separation of 3.139(1) A, and a Rh(1) O(3)Rh(2) angle of 99.1(1)°. No other unusual structural features were observed.