Binuclear Rhodium Research Articles

Preparation of binuclear rhodium(II) tetraacetate (initial compound for the coulometric determination of rhodium) under the action of microwave radiation

A rapid method is proposed for the preparation of binuclear rhodium(II) tetraacetate [Rh2(OAc)4(HOAc)2] under the action of microwave radiation. This complex is potentially suitable for the coulometric determination of rhodium. The mechanism of the redox process Rh2(III, II) ⇄ Rh2(II, II) in acetic acid solutions of this complex has been characterized by cyclic voltammetry, controlled-potential coulometry, and spectrophotometry.

Interaction of [Rh2(O2CCH3)4(H2O)2] and [Rh2(O2CCH(OH)Ph)2(phen)2(H2O)2](O2C‐CH(OH)Ph)2 With Sulfhydryl Compounds and Ceruloplasmin

The interaction of binuclear rhodium(II) complexes [Rh2(OOCCH3)4(H2O)2], [Rh2{OOCCH(OH)Ph}2(phen)2(H2O)2] {OOCCH(OH)Ph}2, [Rh2(OOCCH3)2(bpy)2(H2O)2](OOCCH3)2 and [Rh2Cl2(OOCMe)2(bpy)2](3H2O) with ceruloplasmin, cysteine, glutathione and coenzyme A have been investigated using. UV-Vis and CD spectroscopies. The complexes containing phen or bpy at pH = 7.4 and 4.0 are readily reduced with sulfhydryl compounds, while rhodium(II) acetate is relatively stable in these conditions. Complex [Rh2{OOCCH(OH)Ph}2(phen)2(H2O)2] strongly changes structure of ceruloplasmin leading to the decrease of of α-helix content and loss of oxidase activity.

Synthesis of Bi- and Trinuclear Bis(alkynyl) Complexes [PtM (M = Rh, Ir), PtRh2] Starting from [cis-Pt(C6F5)2(C⋮CR)2]2-

The course of the reactions of Q2[cis-Pt(C6F5)2(C⋮CR)2] (Q = PPh3Me, R = Ph 1a; Q = NBu4, R = tBu 1b, SiMe3 1c) with [M(μ-Cl)(COD)]2 (M = Rh, Ir) is strongly influenced by the metal and the substituents, as well as the stoichiometry. Thus, whereas treatment of 1a with either 0.5 or 1 equiv of [Rh(μ-Cl)(COD)]2 gives the chelating-type binuclear highly polar compound (PPh3Me)[cis-Pt(C6F5)2(μ-1κCα:η2-C⋮CPh)2Rh(COD)], 2a, analogous reactions using 1b as the precursor afford only the trinuclear complex (NBu4)[{cis-Pt(C6F5)2(μ-1κCα:η2-C⋮CtBu)2}{Rh2(μ-Cl)(COD)2}], 4b. On the other hand, related bi- and trinuclear SiMe3 derivatives (NBu4)[cis-Pt(C6F5)2(μ-1κCα:η2-C⋮CSiMe3)2Rh(COD)], 2c, and (NBu4)[{cis-Pt(C6F5)2(μ-1κCα:η2-C⋮CSiMe3)2}{Rh2(μ-Cl)(COD)2}], 4c, are easily obtained by treating 1c with the binuclear rhodium substrate in the adequate molar ratio [1:0.5 for 2c; 1:1 for 4c]. Complex 2b and, alternatively, 2a,c derivatives can be produced by reacting 1 with the cationic solvento species [Rh(COD)(Et2O)x]+ (prepared in situ). The molecular structures of 2a and 4b have been confirmed by X-ray diffraction. By contrast, whereas the reactions of 1a,b with [Ir(μ-Cl)(COD)]2 lead to the formation of undefined products, the heterobinuclear σ,π double-alkynyl-bridged complex (NBu4)[cis-Pt(C6F5)2(μ-1κCα:η2-C⋮CSiMe3)(μ-η2:2κCα-C⋮CSiMe3)Ir(COD)], 3c, (X-ray) is isolated from reaction of 1c with the dimer iridium complex regardless of the molar ratio used (1:0.5 or 1:1).

Studies of antibacterial activity of binuclear rhodium(II) complexes with heterocyclic nitrogen ligands

Binuclear rhodium(II) complexes, [Rh 2(OOCPh) 2(phen) 2(H 2O) 2](OOCPh) 2 ( 1), [Rh 2(OOCPh) 2(bpy) 2(H 2O) 2] (OOCPh) 2 ( 2), [Rh 2(OOCBu n) 2(bpy) 2(H 2O) 2](OOCBu n) 2 ( 3), and [Rh 2(OOCPr n) 2(phen) 2(H 2O) 2](OOCPr n) 2 ( 4) (phen = 1,10-phenanthroline and bpy = 2,2′-bipyridine), have been synthesized and characterized using NMR, IR and electronic spectra. Activity of these compounds against Gram-positive bacteria decreases in the order: 1? 2? 3 > 4. Complex 1 is active against many Staphylococcus strains resistant to commonly used antibiotics. The complexes 1–4 are much less active agents against Gram-negative bacteria.

Infinite sheet structure of disodium tetra-μ-acetato- dichlorodirhodate(II) tetrahydrate

The binuclear rhodium(II) complex Na2[Rh2Cl2(OAc)4]· 4H2O has an infinite sheet structure. Binuclear anionic complexes [Rh2Cl2(OAc)4]2− are bound with cationic entities. The Na+ cation has pseudooctahedral coordination and is surrounded by two chloro ligands and two oxygen atoms of bridging acetato ligands of two [Rh2Cl2(OAc)4]2− anions and two water molecules. Both Cl and H2O are bridging ligands involved in formation of the Na+ chains. The remaining water molecules are located between sheets.

Preparation and catalytic properties of resin bound binuclear rhodium tetracarboxylate complexes

4-(4′-Polystyrylmethyloxy)-3-carboxylatomethyloxy-1-phenylacetate bis- μ-coordinated rhodium(II) diacetate complex, a resin-bound analogue of dirhodium tetraacetate in which two adjacent μ-bridging acetate moieties are covalently linked, serves as an efficient, stable and re-useable immobilised alkene hydrofomylation and hydrogenation catalyst.

Oxidative addition of methyl iodide and iodine to new binuclear rhodium(I) and iridium(I) compounds containing diaminoanthraquinonate-bridging ligands. Crystal structure of [Rh 2(μ-1,4-DA)(CO) 2(PPh 3) 2] (1,4-H 2DA = 1,4-diaminoanthraquinone)

The binuclear rhodium and irridum complexes containing the 1,4-diaminoanthraquinonate ligand (1,4-DA) [M 2(μ-1,4-DA)L 2] (L = COD, M = Rh ( 1), Ir ( 2); L = (CO) 2, M = Rh ( 3), Ir ( 4) L = (CO)(PPh 3), M = Rh ( 5), Ir, ( 6)) have been prepared and oxidative addition of the electrophiles MeI and I 2 has been investigated. The molecular structure of an isomer of compound 5 has been determined by X-ray diffraction methods. Complex 5a crystallised in the triclinic space group P-1, with a = 9.711(5), b = 13.701(7), c = 17.990(9) A ̊ . a = 68.53(2), β = 76.98(3), γ = 79.72(3)°, and Z = 2. The molecule is binuclear with the metals bridged by an approximately planar tetradentate dianionic 1,4-DA ligand. Both rhodium centres exhibit slightly distorted square-planar coordinations with both phosphine groups rans disposed to the aminic nitrogen atoms. Addition of MeI to the rhodium complex 5 leads to the diacyl-dirhodium(III) derivative [Rh 2(μ-1,4-DA)(COMe) 2] 2(PPh 1) 2] ( 7). However, addition MeI to the isoelectronic iridium compound 6 yields the dimethyldiiridium(III) compound [Ir 2(μ-1,4-DA)] 2(Me) 2(CO) 2(PPh 3) 2] ( 8). Reaction of iodine with compounds 5 and 6, in a molar ratio M/I 2 = 1/1, yields the symmetrical complexes [M 2(μ-1,4-DA)I 4(CO) 2(PPh 4) 2] (M = Rh ( 9, Ir( 10)).

Binuclear rhodium(II) complexes with leucine and proline

The dimeric rhodium(II) complexes [Rh2(leu)4(H2O)2]- (ClO4)4 and [Rh2(pro)4(H2O)2](ClO4)4 have been prepared and characterized by elemental analyses, i.r., u.v.–vis. and 1H-n.m.r. spectroscopy. The amino acid molecules are coordinated as bridging ligands via their carboxylato groups. Cyclic voltammetry in DMF has shown that the complexes undergo a quasi-reversible reduction to yield dimers containing a Rh23+ core. Oxidation processes within the 0–1.5V range were not observed.

A novel binuclear rhodium complex with two mercapto bridges and two terminal thioether groups

The cyclic thioether–thioester ligand [7,8-µ-SCH2C(O)S-7,8-C2B9H10]-, [L1]-, is a source of strongly co-ordinating mercapto and thioether groups. Upon reaction with complexes with metal ions in oxidation state higher than+1, [L1]- modifies to the dianionic ligand [7-S,8-SCH2C(O)OMe-7,8-C2B9H10]2-, [L2]2-. Reaction of [NMe4][L1] with [M2(C5Me5)2Cl4] (M=RhIII or IrIII) in MeOH produces [M2(C5Me5)2(L2)2], a molecule with an earmuff shape.

Carbonylation of aryl and alkyl halides catalyzed by a binuclear rhodium hydroxide complex

The binuclear rhodium complex [(Ph 3P) 4Rh 2(μ-OH) 2]·2C 6H 6 is an effective catalyst for the carbonylation of aryl iodides to acids. This Rh-catalyzed carbonylation is applicable to the synthesis of diacids. Iodoalkanes also undergo carbonylation, but in low yields.

Bridged Hemilabile Allylphosphonate Ligand: Synthesis and Crystal Structure of a New Binuclear Rhodium Complex

The reaction of 2 equiv of the allylphosphonate CH2CHCH2P(O)(OEt)2 with [Rh(Cl)(CO)2]2 results in the formation of a new binuclear rhodium complex with two bridged bidentate allylphosphonate ligands in cis positions, reaction with carbon monoxide induces the lability of the phosphonate moiety, which is reversible.

Reductive carbonylation of nitrobenzenes catalyzed by a new binuclear rhodium complex

The binuclear rhodium complex [(Ph 3P) 4Rh 2(μ-OH) 2] · 2C 6H 6 is an effective catalyst for the reductive carbonylation of nitrobenzenes to carbamate esters. Electron-withdrawing groups at the para-position enhance the reactivity of the substrate in comparison with electron-donating groups.

Pyramidality effect on metal–metal single bonds

G. Aullón and S. Alvarez, J. Chem. Soc., Dalton Trans., 1997, 2681 DOI: 10.1039/A702022H

Binuclear Rhodium(II) Complexes With Selective Antibacterial Activity

Binuclear rhodium(II) complexes [Rh2Cl2(μ-OOCR)2(N-N)2] {R = H, Me; N-N = 2,2'-bipyridine (bpy), 1,10-phenanthroline (phen)} and [Rh2(μ-OOCR)2(N-N)2(H2O)2](RCOO)2 (R = Me, Et;) have been synthesized and their structure and properties have been studied by electronic, IR and 1H NMR spectroscopy. Antibacterial activity of these complexes against Escherichia coli and Staphylococcus aureus has been investigated. The most active antibacterial agents against E. coli were [Rh2Cl2(μ-OOCR)2(N-N)2] and [Rh2(μ-OOCR)2(N-N)2(H2O)2](RCOO)2 {R = H and Me} which were considerably more active than the appropriate nitrogen ligands. The complexes show low activity against S. aureus. The activity of the complexes [Rh2(OOCR)2(N-N)2(H2O)2](OOCR)2 against E. coli decreases in the series: R=H≅CH3>C2H5>C3H7≅C4H9. The reverse order was found in the case of S. aureus.

Properties of Binuclear Rhodium(II) Complexes and TheirAntibacterial Activity

Binuclear rhodium(II) complexes [Rh2Cl2(μ-OOCR)2(N-N)2], [Rh2(μ-OOCR)2(N-N)2(H2O)2](RCOO)2 and [Rh2Cl2(μ-OOCCH3)(terpy)2](H3O)Cl2.9H2O (R = H, Me, Bun, ph, PhCHOH; N-N = 2,2′-bipyridine (bpy), 1,10-phenanthroline (phen), 2,9-dimethyl-1,10-phenanthroline (dmp) and 6,7-dimethyl-2,3- di(2-pyridyl)quinoxaline (dmpq); terpy 2,2′:6′,2′′-terpyridine) have been synthesized and their structure and properties have been studied by electronic, IR and 1H NMR spectroscopy. Antibacterial activity of these complexes against Staphylococcus aureus and Escherichia coli has been investigated. The most active antibacterial agents against S. aureus were [Rh2(OOCPh)2(phen)2(H2O)2]2+, [Rh2(OOCPh)2(dmpq)2(H2O)2]2+, [Rh2(OOCBu)2(phen)2(H2O)2]2+ and [Rh2-(OOCBu)2(bpy)2(H2O)2]2+ which were considerably more active than the appropriate nitrogen ligands. The complexes show rather low activity against E. coli.

Synthesis and Structure of the Diphenyl Binuclear Rhodium A-Frame Complex Rh(2)(&mgr;-CO)(Ph)(2)(dmpm)(2).

Addition of the Grignard reagent C6H5MgCl to [RhCl(CO)dmpm]2 yields the diphenyl binuclear rhodium A-frame complex Rh2(μ-CO)(C6H5)2(dmpm)2 (dmpm = bis(dimethylphosphino)methane). The formally Rh(I) complex possesses a carbonyl bridgehead ligand, terminal phenyl groups, a metal−metal single bond with a distance of 2.8254(5) A, and trans bridging dmpm ligands in a coordination geometry that is slightly distorted from planarity at each rhodium.

Parahydrogen Induced Polarization: A New Magnifying Glass for Examining Reactions with Hydrogen

Parahydrogen-included polarization (PHIP), its occurrence and mechanistic implications in homogeneous hydrogenation chemistry, and its appearance in the oxidative addition of H2 to transition metal centers are described and analyzed. The PHIP phenomenon, which is characterized by unusual NMR absorptions and emissions in product spectra, arises when para-enriched H2 is employed in hydrogenation of unsaturated organic substrates with a homogeneous metal catalyst or when para-enriched H2 is added to a metal complex to form a metal dihydride. Examples of PHIP are found in ruthenium phosphine-catalyzed hydrogenations, catalysis by binuclear rhodium complexes, and in H2 oxidative addition to Ir(I) complexes. The decay of polarization has been shown in the case of asymmetric hydrogenation catalyzed by Rh(chiraphos)+ to correlate well with the measured rate of reaction. For asymmetric hydrogenation of aprotic substrates using Noyori's Ru(BINAP)(OAc)2 catalyst (1), PHIP is observed indicating a pairwise hydrogen transfer mechanism. Through the signal enhancement of PHIP, it has been possible to observe Rh hydride species never previously detected including binuclear complexes in the reaction of H2 with RhCl(CO)(PR3)2 (R = Ph, Me) and in hydrogenation catalysis promoted by RhCl(PPh3)3. Also observed in the hydrogenation catalysis is the putative olefin dihydride catalytic intermediate.

An Unprecedented Bending of a Bridging Diynyl Ligand in an Unsymmetrical Binuclear Rhodium(I) Complex

An Unprecedented Bending of a Bridging Diynyl Ligand in an Unsymmetrical Binuclear Rhodium(I) Complex

Synthesis, structure and reactivity of binuclear rhodium dicationic carbonyl complexes

The reaction of Rh 2(CO) 3(dppm) 2 ( 1) with an excess of triflic acid, HSO 3CF 3, yields the dicationic tricarbonyl complex Rh 2(CO) 3(dppm) 2 +2 ( 3). Complex 3 is fluxional and undergoes terminal and bridging CO exchange as well as coordination and dissociation of CF 3SO 3 − in solution. The crystal structure of the η 1-acetone complex Rh 2(η 1-OC(CH 3) 2)(μ- CO)(CO)(SO 3CF 3(dppm) 2 + ( 4) has been determined. Complex 4 crystallizes in the triclinic space group P 1 as its triflate salt with a benzene of crystallization in a unit cell of dimensions a = 12.087(4) Å, b = 15.268(4) Å, c = 20.602(4) Å, α= 87.06(2), β = 73.61(2), γ = 72.56(2)°, V = 3477.7 Å 3 and Z = 2. Complex 4 possesses a binuclear structure in which the Rh centers are bridged by two dppm ligands and an asymmetrically bound CO ligand. The RhRh bond distance is 2.778(2) Å while the RhO(acetone) distance is 2.09(1) Å. The RhO(triflate) distance is 2.37(1) indicating a weak interaction. Complex 3 reacts readily and reversibly under a CO atmosphere to form the tetracarbonyl complex Rh 2(CO) 4(dppm) 2 +2 ( 5). Upon heating under vacuum, complex 3 undergoes facile CO loss to form the dicarbonyl species Rh 2(μ-SO 3CF 3)(CO) 2(dppm) 2 +2 ( 6), in situ. Complex 6 is thought to possess an A-frame structure with triflate coordinated in the bridgehead position. Complex 3 promotes H/D exchange with acetone- d 6 and catalyzes the hydrogenation of acetone under 3 atm of H 2 at 70°C at the rate of 1 turnover per day. The reaction of 3 with H 2 leads to the generation of a moderately strong Bronsted acid whereas complex 5 reacts with H 2 to produce the known cationic species Rh 2(μ-H)(μ-CO)(CO) 2(dppm) 2 + ( 2).

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.