Dimeric Rhodium Research Articles

Rhodium(I) carbonyl complexes of quinoline carboxylic acid: Synthesis, reactivity and catalytic carbonylation reaction

The dimeric rhodium precursor [Rh(CO)2Cl]2 reacts with the ligands (L) quinoline-2-carboxylic acid (a) or quinoline-8-carboxylic acid (b) in 1:2 mole ratio to afford complexes of the type cis-[Rh(CO)2ClL] (1a and 1b). The complexes have been characterized by elemental analysis, Mass spectrometry, FT-IR and NMR (1H, 13C) spectroscopy. 1a and 1b undergo oxidative addition (OA) with different electrophiles such as CH3I, C2H5I and I2 to give Rh(III) complexes of the type [Rh(CO)(COR)ClIL] {R=CH3 (2a and 2b), R=C2H5 (3a and 3b)} and [Rh(CO)ClI2L] (4a and 4b) respectively. OA of the CH3I with 1a forms relatively stable acyl intermediate which is evident from IR spectroscopy. The complexes 1a and 1b show higher catalytic activity for carbonylation of methanol to acetic acid and methyl acetate [Turn over number (TON) upto 1775 in 1h] compared to that of the well known Monsanto's species [Rh(CO)2I2]− (TON=1000 in 1h) under the reaction conditions: temperature 130±2°C, pressure 30±2bar, 450rpm and 1h reaction time.

Surface‐Mediated Synthesis of Dimeric Rhodium Catalysts on MgO: Tracking Changes in the Nuclearity and Ligand Environment of the Catalytically Active Sites by X‐ray Absorption and Infrared Spectroscopies

The preparation of dinuclear rhodium clusters and their use as catalysts is challenging because these clusters are unstable, evolving readily into species with higher nuclearities. We now present a novel synthetic route to generate rhodium dimers on the surface of MgO by a stoichiometrically simple surface-mediated reaction involving [Rh(C(2)H(4))(2)] species and H(2). X-ray absorption and IR spectra were used to characterize the changes in the nuclearity of the essentially molecular surface species as they formed, including the ligands on the rhodium and the metal-support interactions. The support plays a key role in stabilizing the dinuclear rhodium species, allowing the incorporation of small ligands (ethyl, hydride, and/or CO) and enabling a characterization of the catalytic performance of the supported species for the hydrogenation of ethylene as a function of the metal nuclearity and ligand environment. A change in the nuclearity from one to two Rh atoms leads to a 58-fold increase in the catalytic activity for ethylene hydrogenation, a reaction involving unsaturated, but stable, dimeric rhodium species.

Complexation of oxygen ligands with dimeric rhodium(II) tetrakistrifluoroacetate in chloroform: 1H, 13C NMR and DFT studies

The complexation of dimeric rhodium(II) tetrakistrifluoroacetylate with 25 ligands containing oxygen atoms: alcohols, ethers, ketones, aldehydes, carboxylic acids and esters in chloroform solution have been investigated by 1H and 13CNMR spectroscopy and Density Functional Theory (DFT) methods. Investigated ligands form 1:1 adducts in our experimental conditions, with stability constants in the order of several hundred mol−1. The exchange of ligands in solution is fast on the NMR spectroscopic timescale. The decrease of longitudinal relaxation times T1 in ligands in the presence of rhodium salt has been tested as the means of determination of the complexation site in ligands. The influence of complexation on chemical shifts in ligands was evaluated by a parameter complexation shift Δδ (Δδ=δadd−δlig). These parameters were positive (>0ppm) and did not exceed 1ppm for 1H NMR; and varied from ca. −5 to +15ppm in the case of 13CNMR. The calculation by DFT methods using the B3LYP functional (structure optimization, electronic energy) and B3PW91 functional (shielding), and combinations of the (6-31G(2d), 6-311G++(2d,p), and LANL2DZ basis sets, followed by scaling procedures reproduced satisfactorily 1H and 13C chemical shifts and, with some limitations, allowed to estimate Δδ parameters.

Dimeric Rhodium–Ethylene NHC Complexes As Reactive Intermediates for the Preparation of Tetra-heteroleptic NHC Complexes

Dimeric rhodium complexes with various N-heterocyclic carbene (NHC) ligands have been synthesized and fully characterized. X-ray analysis unambiguously confirms the bimetallic nature of these compl...

Rhodium(I) carbonyl complexes of quinoline carboxaldehyde ligands and their catalytic carbonylation reaction

The dimeric rhodium precursor [Rh(CO) 2Cl] 2 reacts with quinoline ( a) and its three isomeric carboxaldehyde ligands [quinoline-2-carboxaldehyde ( b), quinoline-3-carboxaldehyde ( c), and quinoline-4-carboxaldehyde ( d)] in 1:2 mole ratio to afford complexes of the type cis-[Rh(CO) 2Cl(L)] ( 1a– 1d), where L = a– d. The complexes 1a– 1d have been characterised by elemental analyses, mass spectrometry, IR and NMR ( 1H, 13C) spectroscopy together with a single crystal X-ray structure determination of 1c. The X-ray crystal structure of 1c reveals square planar geometry with a weak intermolecular pseudo dimeric structure (Rh⋯Rh = 3.573 Å). 1a– 1d undergo oxidative addition ( OA) with different electrophiles such as CH 3I, C 2H 5I and I 2 to give Rh(III) complexes of the type [Rh(CO)(COR)Cl(L)I] {R = –CH 3 ( 2a– 2d), R = –C 2H 5 ( 3a– 3d)} and [Rh(CO)Cl(L)I 2] ( 4a– 4d) respectively. 1b exhibits facile reactivity with different electrophiles at room temperature (25 °C), while 1a, 1c and 1d show very slow reactivity under similar condition, however, significant reactivity was observed at a temperature ∼40 °C. The complexes 1a– 1d show higher catalytic activity for carbonylation of methanol to acetic acid and methyl acetate [Turn Over Frequency (TOF) = 1551–1735 h −1] compared to that of the well known Monsanto’s species [Rh(CO) 2I 2] − (TOF = 1000 h −1) under the reaction conditions: temperature 130 ± 2 °C, pressure 33 ± 2 bar, 450 rpm and time 1 h. The organometallic residue of 1a– 1d was also isolated after the catalytic reaction and found to be active for further run without significant loss of activity.

Influence of phosphorus and oxygen donor diphosphine ligands on the reactivity of rhodium(I) carbonyl complexes

The dimeric rhodium precursor [Rh(CO) 2Cl] 2 reacts with two molar equivalent of 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene [xantphos] ( a), bis(2-diphenylphosphinophenyl)ether [DPEphos] ( b) and their corresponding dioxide analogues xantphos dioxide ( c), DPEphos dioxide ( d) to afford the mono- and dicarbonyl complexes of the type [Rh(CO)Cl(L)] ( 1a, 1b) and [Rh(CO) 2Cl(L)] ( 1c, 1d) respectively, where L = a– d. The complexes 1a– 1d have been characterized by elemental analyses, IR and NMR ( 1H, 31P and 13C) spectroscopy, and the structure of the ligand d was determined by single crystal X-ray diffraction. 1a– 1d undergo oxidative addition (OA) reactions with different electrophiles such as CH 3I, C 2H 5I and I 2 to give Rh(III) complexes of the types [Rh(CO) y (COR)ClXL] {R = –CH 3 ( 2a– 2d), –C 2H 5 ( 3a– 3d); X = I and y = 0, L = a, b; y = 1, L = c, d} and [Rh(CO)ClI 2L] ( 4a– 4d) respectively. Kinetic data for the reactions of 1a– 1d with CH 3I indicate a pseudo-first-order reaction. The catalytic activity of 1a– 1d for the carbonylation of methanol to acetic acid and its ester was evaluated at different CO pressure 15, 20 and 33 bar at 130 °C and a higher Turn Over Number (TON) (679–1768) were obtained compared to that of the well-known commercial species [Rh(CO) 2I 2] − (TON = 463–1000) in each case under the similar experimental conditions.

Rhodium(I) carbonyl complexes of chalcogen functionalized tripodal phosphines, [CH 3C(CH 2P(X)Ph 2) 3] {X = O, S, Se} and their reactivity

The reaction of dimeric rhodium precursor [Rh(CO) 2Cl] 2 with two molar equivalent of 1,1,1-tris(diphenylphosphinomethyl)ethane trichalcogenide ligands, [CH 3C(CH 2P(X)Ph 2) 3](L), where X = O( a), S( b) and Se( c) affords the complexes of the type [Rh(CO) 2Cl(L)] ( 1a–1c). The complexes 1a–1c have been characterized by elemental analyses, mass spectrometry, IR and NMR ( 1H, 31P and 13C) spectroscopy and the ligands a–c are structurally determined by single crystal X-ray diffraction. 1a–1c undergo oxidative addition (OA) reactions with different electrophiles such as CH 3I, C 2H 5I and C 6H 5CH 2Cl to give Rh(III) complexes of the types [Rh(CO)(COR)ClXL] {R = –CH 3 ( 2a–2c), –C 2H 5 ( 3a–3c); X = I and R = –CH 2C 6H 5 ( 4a–4c); X = Cl}. Kinetic data for the reaction of a–c with CH 3I indicate a first-order reaction. The catalytic activity of 1a–1c for the carbonylation of methanol to acetic acid and its ester is evaluated and a higher turn over number (TON = 1564–1723) is obtained compared to that of the well-known commercial species [Rh(CO) 2I 2] − (TON = 1000) under the reaction conditions: temperature 130 ± 2 °C, pressure 30 ± 2 bar and time 1 h.

NMR studies on interaction of rhodium(II) tetratrifluoroacetate with the ligands containing nitrile, isonitrile, isothiocyanate or isocyanate functional groups

The complexation in CDCl 3 solution of rhodium(II) tetratrifluoroacetate Rh 4TFA 4 and tetraacetate Rh 2AcO 4 with ligands having nitrile, isonitrile, isothiocyanate and isocyanate functional groups has been investigated by means of 1H, 13C and 15N nuclear magnetic resonance (NMR) and absorption spectroscopy in the visible range. Dimeric rhodium(II) salts in CDCl 3 solution form 1:1 or/and 1:2 axial adducts with nitriles ( 1) via nitrogen and isonitriles ( 2) via carbon atom. The complexation decreases NMR shielding of the atom bonded to rhodium salt (C or N atoms), by several dozen ppm. According to NMR results, DFT energy calculation and UV/vis spectroscopy the complexation via sulfur atom is preferred in case of isothiocyanates 3 and 4. In contrast, the energy calculations performed for isocyanate 5 suggest the complexation by nitrogen atom to be more stable. Spectroscopic data did not provide unambiguous answer in this case. The calculations satisfactory reproduce known from X-ray structural parameters of adducts and allow to predict experimental 13C and 15N NMR chemical shifts qualitatively.

Rh complexes of 1-(2,4,6-triisopropylphenyl-)3-methyl-1H-phosphole: preparation and use as catalysts in the hydroformylation of styrene

In the series of 1-(2,4,6-trialkylphenyl-)3-methyl-1H-phospholes (1a–c) that are to a certain extent of aromaticity, only the isopropyl substituted one (1a) entered into reaction with dimeric (pentamethylcyclopentadienyl)rhodium dichloride to afford Rh(III) complex (2a) in a reversible manner. After a careful workup, (2a) could be prepared and characterized whose stereostructure was elucidated by B3LYP/3–21G*, B3LYP/6–31G* and LANL2DZ calculations. Complex (2a) as a preformed catalyst, as well as the Rh(acac)(CO)2 + 2(1a) in situ catalytic system were useful in the hydroformylation of styrene and gave the branched aldehyde in regioselectivities of 65–96%.

Tetrakis(tert-butyl isocyanide-2κC)dichloro-1κCl,3κCl-di-μ-cyano-1κN:2κC;2κC:3κN-bis[1,3(η4)-cycloocta-1,5-diene]dirhodium(I)ruthenium(II)

The title compound, [Rh2Ru(CN)2Cl2(C8H12)2(C5H9N)4], was obtained from the reaction of the chloro­(1,5-cyclo­octa­diene)rhodium(I) dimer with trans-dicyano­tetra­(tert-butyl isocyanide)ruthenium(II) by cleavage of the chloro bridges in the dimeric rhodium starting complex. The mol­ecular structure shows the Ru atom in a nearly ideal octa­hedral coordination geometry, whereas the Rh atoms are situated in square-planar ligand environments. The central ruthenium ion is located on a crystallographic twofold axis. The crystal structure is realized by infinite chains of the trinuclear complex units which are connected by C—H⋯Cl inter­actions. These chains are further linked by another C—H⋯Cl inter­action to produce the observed three-dimensional structure.

Transfer of Amido Groups from Isolated Rhodium(I) Amides to Alkenes and Vinylarenes

The reaction of monomeric and dimeric rhodium(I) amido complexes with unactivated olefins to generate imines is reported. Transamination of {(PEt(3))(2)RhN(SiMePh(2))(2)} (1a) or its -N(SiMe(3))(2) analogue 1b with p-toluidine gave the dimeric [(PEt(3))(2)Rh(mu-NHAr)](2) (Ar = p-tolyl) (2a) in 80% isolated yield. Reaction of 2a with PEt(3) generated the monomeric (PEt(3))(3)Rh(NHAr) (Ar = p-tolyl) (3a). PEt(3)-ligated arylamides 2a and 3a reacted with styrene to transfer the amido group to the olefin and to form the ketimine Ph(Me)C=N(p-tol) (4a) in 48-95% yields. The dinuclear amido hydride (PEt(3))(4)Rh(2)(mu-NHAr)(mu-H) (Ar = p-tolyl) (5a) was formed from reaction of 2a in 95% yield, and a mixture of this dimeric species and the (PEt(3))(n)RhH complexes with n = 3 and 4 was formed from reaction of 3a in a combined 75% yield. Propene reacted with 2a to give Me(2)C=N(p-tol) (4b) and 5a in 90 and 57% yields. Propene also reacted with 3a to give 4b and 5a in 65 and 94% yields. Analogues of 2a and 3a with varied electronic properties also reacted with styrene to form the corresponding imines, and moderately faster rates were observed for reactions of electron-rich arylamides. Kinetic studies of the reaction of 3a with styrene were most consistent with formation of the imine by migratory insertion of olefin into the rhodium-amide bond to generate an aminoalkyl intermediate that undergoes beta-hydrogen elimination to generate a rhodium hydride and an enamine that tautomerizes to the imine.

Rhodium(III) pentamethyl cyclopentadienyl complexes incorporating 1-(4-cyanophenyl)-imidazole: role of solvent in ligand substitution reactions

Reaction of the dimeric rhodium complex [{(η 5-C 5Me 5)Rh(μ-Cl)Cl} 2] with an excess of 1-(4-cyanophenyl)-imidazole in dichloromethane afforded neutral mononuclear complex [(η 5-C 5Me 5)RhCl 2(CPI)] (CPI = 1-(4-cyanophenyl)-imidazole) 1. The complex 1 reacted with EPh 3 (E = P, As, Sb) and N–N donor bases 2,2′-bipyridine and 1,10-phenanthroline in different solvents to give substitution products wherein, nature of the product was governed by polarity of the solvents employed in the reaction. Resulting complexes have been characterized by elemental analyses, spectral (FAB-MS, IR, 1H, 13C, 31P NMR, UV–Vis, Emission) and electrochemical studies. Coordination of CPI through imidazole nitrogen and the presence of pendant nitrile group have been supported by spectral studies.

Bis(imino)carbazolide Complexes of Rhodium: Highly Nucleophilic Ligands Exerting a Dramatic Accelerating Effect on MeI Oxidative Addition

Rhodium(I) complexes bearing a bis(imino)carbazolide ligand L and an additional neutral donor [LRh(C2H4), 2; LRh(CO), 3] have been prepared via a salt metathesis reaction between NaL and the dimeric rhodium precursors [RhCl(C2H4)2]2 and [RhCl(CO)2]2, respectively. Complex 3 was also prepared by reaction of the free ligand with [RhCl(CO)2]2, whereas a related reaction with [RhCl(C2H4)2]2 afforded the dinuclear RhI−RhIII ethyl complex 4. The X-ray crystal structure of 4 showed octahedral [bis(imino)carbazolide]RhIII(Cl)Et linked to square-planar bis(ethylene)RhICl via chloride bridges. Kinetic studies on the oxidative addition of MeI to 3 to form the LRhIIII(CO)Me complex 5 revealed a second-order rate constant of 1.66 M-1 s-1 in CH2Cl2 at 25 °C, which corresponds to a reaction rate approximately 50 000 times faster than that observed for [RhI2(CO)2]-.

New rhodium complexes of the tetradentate ligand bis(diacetylmonoxime-imino)propane 1,3 (H 2dopn): synthesis and crystal structure of trans-[Rh(Hdopn)Cl] 2 and trans-[Rh(Hdopn)(I) 2

The reaction between [Rh(H 2O) 6](ClO 4) 3 and the monoanion Hdopn − (H 2dopn=bis(diacetylmonoxime-imino)propane 1,3=3,9-dimethyl-4,8-diazaundeca-3,8-diene-2,10-dione dioxime) afforded a new dimeric rhodium(II) compound of formula [Rh(Hdopn)(H 2O)] 2(ClO 4) 2 · H 2O ( 1). Treatment of methanolic solution of 1 with NaX (X=Cl −, Br −, I −) results in the replacement of water with halides in 1, leading to the formation of [Rh(Hdopn)X] 2 rhodium(II) dimers. The X-ray crystal structure of [Rh(Hdopn)Cl] 2 · 0.5H 2O ( 2) was determined showing a [Rh(II)–Rh(II)] core. Upon the reaction of 1 with NaI carried out in air, [Rh(Hdopn)(I) 2] ( 3) was isolated and characterized by a single-crystal X-ray diffraction analysis.

Cationic carbonyl complexes of rhodium(I) and rhodium(III): syntheses, vibrational spectra, NMR studies, and molecular structures of tetrakis(carbonyl)rhodium(I) heptachlorodialuminate and -gallate, [Rh(CO)4][Al2Cl7] and [Rh(CO)4][Ga2Cl7

Dimeric rhodium(I) bis(carbonyl) chloride, [Rh(CO)(2)(mu-Cl)](2), is found to be a useful and convenient starting material for the syntheses of new cationic carbonyl complexes of both rhodium(I) and rhodium(III). Its reaction with the Lewis acids AlCl(3) or GaCl(3) produces in a CO atmosphere at room temperature the salts [Rh(CO)(4)][M(2)Cl(7)] (M = Al, Ga), which are characterized by Raman spectroscopy and single-crystal X-ray diffraction. Crystal data for [Rh(CO)(4)][Al(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.705(3), b = 9.800(2), c = 10.268(2) A; alpha = 76.52(2), beta = 76.05(2), gamma = 66.15(2) degrees; V = 856.7(5) A(3); Z = 2; T = 293 K; R(1) [I > 2sigma(I)] = 0.0524, wR(2) = 0.1586. Crystal data for [Rh(CO)(4)][Ga(2)Cl(7)]: triclinic, space group Ponemacr; (No. 2); a = 9.649(1), b = 9.624(1), c = 10.133(1) A; alpha = 77.38(1), beta = 76.13(1), gamma = 65.61(1) degrees; V = 824.4(2) A(3); Z = 2; T = 143 K; R(1) [I > 2sigma(I)] = 0.0358, wR(2) = 0.0792. Structural parameters for the square planar cation [Rh(CO)(4)](+) are compared to those of isoelectronic [Pd(CO)(4)](2+) and of [Pt(CO)(4)](2+). Dissolution of [Rh(CO)(2)Cl](2) in HSO(3)F in a CO atmosphere allows formation of [Rh(CO)(4)](+)((solv)). Oxidation of [Rh(CO)(2)Cl](2) by S(2)O(6)F(2) in HSO(3)F results in the formation of ClOSO(2)F and two seemingly oligomeric Rh(III) carbonyl fluorosulfato intermediates, which are easily reduced by CO addition to [Rh(CO)(4)](+)((solv)). Controlled oxidation of this solution with S(2)O(6)F(2) produces fac-Rh(CO)(3)(SO(3)F)(3) in about 95% yield. This Rh(III) complex can be reduced by CO at 25 degrees C in anhydrous HF to give [Rh(CO)(4)](+)((solv)); addition of SbF(5) at -40 degrees C to the resulting solution allows isolation of [Rh(CO)(4)][Sb(2)F(11)], which is found to have a highly symmetrical (D(4)(h)()) [Sb(2)F(11)](-) anion. Oxidation of [Rh(CO)(2)Cl](2) in anhydrous HF by F(2), followed in a second step by carbonylation in the presence of SbF(5), is found to be a simple, straightforward route to pure [Rh(CO)(5)Cl][Sb(2)F(11)](2), which has previously been structurally characterized by us. All new complexes are characterized by vibrational and NMR spectroscopy. Assignment of the vibrational spectra and interpretation of the structural data are supported by DFT calculations.

Synthetic, spectral and structural aspects of some Rh(III) pentamethylcyclopentadiene complexes containing N, N′-donor bridging ligands

Reactions of the chloro-bridged dimeric rhodium complex [{(η 5-C 5Me 5)Rh(μ-Cl)Cl} 2] with the N, N′-donor bridging ligands pyridine-2-carbaldehyde azine (paa), p-phenylene-bis(picoline)aldamine (pbp) or p-biphenylene-bis(picoline)aldamine (bbp) in 1:1 molar ratio in methanol led in the formation of cationic binuclear complexes [(η 5-C 5Me 5)ClRh(μ-L)RhCl(η 5-C 5Me 5)] 2+ (L=paa, pbp or bbp) in high yield. It was further observed that reactions of the chloro-bridged dimeric rhodium complex [{(η 5-C 5Me 5)Rh(μ-Cl)Cl} 2], with an excess of the above mentioned ligands also, resulted in binuclear complexes. The reaction products have been characterized by microanalyses and spectroscopic studies (IR, 1H-, 13C-NMR, ESMS/FAB mass and electronic spectra). Molecular structure of the representative binuclear complex [(η 5-C 5Me 5)ClRh(μ-paa)RhCl(η 5-C 5Me 5)](BF 4) 2 has been confirmed by single crystal X-ray analysis. Crystal data: monoclinic, P2 1/ n, a=10.2050(7), b=15.4470(7), c=24.959(2) Å, β=97.904(6)°, V=3897.1(5) Å 3, Z=4, R=0.0609.

Dimeric rhodium(III), iridium(III) and ruthenium(II) thiosalicylate complexes

Reactions of the chloride-bridged dimers [LMCl(μ-Cl)] 2 (M=Rh, Ir; L=Cp*=η 5-C 5Me 5; M=Ru, L=η 6- p-cymene) with two mole equivalents of thiosalicylic acid (HSC 6H 4CO 2H, H 2tsal) and excess base gives the dimeric rhodium(III), iridium(III) and ruthenium(II) thiosalicylate complexes [LM(tsal)] 2. Reaction of the complex [Cp*RhCl 2(PPh 3)] with one equivalent of H 2tsal and triethylamine in dichloromethane gives a mixture of the dimer [Cp*Rh(tsal)] 2 and the phosphine complex [Cp*Rh(tsal)(PPh 3)]; upon recrystallisation, pure dimer is obtained. A single-crystal X-ray diffraction study on the rhodium and ruthenium dimers reveals the expected thiolate-bridged M 2(μ-S) 2 unit. Electrospray mass spectrometry (ESMS) is a useful technique in studying the chemistry of the thiosalicylate complexes, all complexes giving strong [M+H] + ions. With added thiosalicylic acid, cations of the type [(LM) 2(Htsal) 3] + were detected in the mass spectra.

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.

Redox investigation and X-ray diffraction structure of the dimeric rhodium maleonitriledithiolate complex [Cp ∗ Rh(mnt)] 2. Confirmation of bridging and chelating mnt ligands in the solid-state structure

The reaction between the pentamethylcyclopentadienyl complex [Cp ∗RhCl 2] 2 and disodium maleonitriledithiolate (Na 2 mnt) in CH 2Cl 2 solvent affords the mnt-substituted compound Cp ∗Rh(mnt) in moderate yield. Cp ∗Rh(mnt) has been isolated and characterized in solution by IR and 1H NMR spectroscopy, and by isopiestic molecular weight measurements, which confirm the monomeric nature of this complex. However, the solid-state structure has been re-determined by X-ray diffraction analysis, revealing the presence of a dimeric structure for Cp ∗Rh(mnt) that possesses both bridging and chelating mnt ligands. The relationship of dimeric [Cp ∗Rh(mnt)] 2 to the previously reported monomeric structure for Cp ∗Rh(mnt) [R. Ziessel, M.-T. Youinou, F. Balegroune, D. Grandjean, J. Organomet. Chem. 441 (1992) 143] is discussed. The electrochemical properties of Cp ∗Rh(mnt) in CH 2Cl 2 and MeCN have been explored, and the redox chemistry is further discussed relative to the results obtained from extended Hückel molecular orbital calculations on monomeric CpRh(mnt).

A rhodium(I) amide dimer: Synthesis, structural characterisation and preliminary reactivity studies

Abstract A rhodium(I) amide complex was synthesised, isolated and crystallographically characterised: this is the first reported molecular structure of a dimeric rhodium amide complex.