Coordination Sphere Of Rhodium Research Articles

Cyclobutadiene Arene Complexes of Rhodium and Iridium

Reactions of [(C2H4)2RhCl]2 or [(coe)2RhCl]2 (coe = cyclooctene) with AgPF6 and arenes, followed by addition of 3-hexyne, give the cyclobutadiene complexes [(C4Et4)Rh(arene)]+ in 40–65% yield (arene = tert-butylbenzene, p-xylene, mesitylene, 4-mesitylbutanoic acid). In the absence of arenes, the hexaethylbenzene complex [(C4Et4)Rh(C6Et6)]+ is formed in 70% yield as a result of cyclotrimerization of 3-hexyne in the coordination sphere of rhodium. Similar reaction of [(coe)2IrCl]2 with AgPF6 and 3-hexyne leads to [(C4Et4)Ir(C6Et6)]+, which is apparently the first reported cyclobutadiene iridium complex. DFT calculations suggest that formation of the model cyclobutadiene complex [(C4Me4)Rh(C6H6)]+ from bis(alkyne) intermediate [(C2Me2)2Rh(C6H6)]+ can proceed via a metallacycle transition state with a low energy barrier of 14.5 kcal mol–1.

Dynamic ligand reactivity in a rhodium pincer complex.

Ligand cooperativity provides (transition) metal complexes with new reactivities in substrate activation and catalytic reactions, but usually the ligand acts as an internal (Brønsted) base, while the metal acts as a (Lewis) acid. We describe the synthesis and stepwise activation of a new phosphane-pyridine-amide ligand PNN(H2) in combination with Rh(I) . The ligand is susceptible to stepwise proton and hydride loss from the nitrogen arm (imine formation) and deprotonation at the pyridylphosphine arm (dearomatization), giving rise to amine complex 1, amido species 2, imine complex 3 and dearomatized compound 4. Complex 4 bears a dual-mode cooperative PNN' ligand containing both a (nucleophilic) basic methine fragment and a reactive (electrophilic) imine moiety. The basic ligand arm enables substrate deprotonation while the imine ligand arm enables reversible "storage" of the activated (nucleophilic) form of a sulfonamide substrate at the ligand. In combination with metal-based reactivity, this allows for the mono-alkylation of o-toluenesulfonamide with iodomethane. Compounds 1, 3 and 4 are structurally characterized. We also report the first structurally characterized example of an aminal in the coordination sphere of rhodium, complex 5, [Rh(CO)(PNN'')], formed by sequential NH activation of sulfonamide by the dearomatized ligand PNN' and follow-up nucleophilic attack of anionic sulfonamide onto the imine fragment.

Liquid-liquid extraction of rhodium(III) from hydrochloric acid solutions with 1,2,4-triazole derivative

Liquid-liquid extraction of rhodium(III) from hydrochloric acid solutions with a 1,2,4-triazole derivative was studied. Optimal conditions for its recovery were found. Rhodium(III) was shown to be recovered in extraction system by ion-exchange reaction at the time of phase contact not longer than 5 min. When phase contact time increased, rhodium(III) is extracted by a mixed mechanism with simultaneous insertion of two extractant molecules into the inner coordination sphere of rhodium(III) ion. Composition of coordination species of recovered compounds was established by electronic, IR, 1H and 13C NMR spectroscopy and functional analysis, the structure of the coordination species is proposed.

Catalytic hydroformylation in the presence of rhodium complexes with homo- and heterocombination of two monodentate P-ligands

Activity of the complex containing both a phosphine and an amidophosphite ligand in the coordination sphere of rhodium was determined for the first time in the hydroformylation of styrene and oct-1-ene in supercritical carbon dioxide and benzene. The efficiency of this “mixed” heteroligand complex was compared with that of its analogs each containing the same two phosphine or two amidophosphite ligands.

Chemical conversions of rhodium selenochloride Rh2Se9Cl6

Rhodium selenochloride Rh2Se9Cl6 (1) reacts with aqueous solutions of KCN and CsCl and 4-cyanopyridine (4-CNPy) to give complexes KCs2Rh(CN)6 (2) and RhCl3(4-CNPy)3 (3). According to X-ray diffraction data, 2 and 3 have mononuclear structures in which the rhodium atoms are in the oxidation state III and six-coordinate environment. Reactions 1 with CN-containing ligands lead to complete displacement of selenium-containing ligands from the rhodium coordination sphere.

O-Semiquinonato and o-iminosemiquinonato rhodium complexes. EPR study of the reactions in coordination sphere of rhodium

The number of dicarbonyl-o-semiquinonato (o-iminosemiquinonato) rhodium complexes was isolated and characterized. Some reactions of these compounds with tertiary phosphines (substitution, addition) were studied by EPR in solution using o-semiquinones (o-iminosemiquinones) as spin labels.

Asymmetric hydrogenation of methyl (Z)-2-acetamido-3-(3,4-dimethoxyphenyl)acrylate catalyzed by Rh complexes with available amidophosphite ligands

A convenient express procedure for the preparation of methyl (Z)-2-acetamido-3-(3,4-dimethoxyphenyl)acrylate was developed. Asymmetric hydrogenation of this substrate in the presence of rhodium catalysts involving synthetically available amidophosphite ligands was carried out, which is characterized by high enantioselectivity (to 99.5% ee) and complete conversion. An approach to the selective formation of cationic complexes containing two ligands of different nature in one coordination sphere of rhodium was suggested.

Rhodium(I) mediated arylation of aldehydes with arylboronic acids under base and water free conditions: A computational study

The mechanism for rhodium(I) mediated arylation of aromatic aldehydes by arylboronic acids under base and water free conditions was investigated with DFT methods. The detailed picture resulting from the calculations is that the reaction proceeds via an internal base mechanism, whereby the initially formed alcoholate (obtained by aryl migration to the aldehyde) attacks the electrophilic boron atom of the coordinated arylboronic acid substrate to facilitate the aryl transfer to the metal. Alternative pathways involving B–C oxidative addition or internal proton transfer followed by β-aryl transfer from thus resulting Rh–O–BPh(OH) moieties are kinetically disfavored. The rhodium atom does not change its oxidation state throughout this whole process, and all steps proceed smoothly within the coordination sphere of rhodium(I). Aldehyde migratory insertion into the Rh I-aryl bond appears to be the rate limiting step (Δ G † = +19.4 kcal mol −1) of the catalytic cycle. The subsequent elementary steps involved in the transmetallation process proceed with lower barriers (<+16.3 kcal mol −1). The cis-[Rh(OH-CHPh 2)(OBOHPh)(PNH 2(OH) 2) 2] species R.S. should be the resting state species under the catalytic conditions according to the DFT calculations.

Homogeneous catalytic hydrogenolysis of chlorodifluoromethane

Abstract CHF 2 Cl has been converted to CHF 3 and CH 4 as main products when hydrogenolyzed in the presence of RhCl 3 (py) 3 and other homogeneous catalysts modified with bases (amines and fluoride ion). Pyridine additive was partly hydrogenated and then alkylated to N -alkylpiperidines. Nucleophilic attack of fluoride ion on the substrate as well as difluorocarbene formation and hydrogenolysis in the coordination sphere of rhodium are the possible crucial steps leading to the gaseous products.

A quantum-chemical study of the possibility to synthesize nuclear spin isomers of water by homogeneous catalytic hydrogenation of compounds containing semipolar X → O bonds (X = N, P, S) with hydrogen

The mechanism of catalytic hydrogenation of compounds with semipolar bonds RnX → O (RnX = N2, Me2S, C5H5N, and Ph3P) on the (Ph3P)3RhCl Wilkinson catalyst with para-hydrogen was modeled quantum-chemically by the density functional theory method with the gradient-corrected nonempirically constructed PBE functional and the TZ2p basis set. The reaction was shown to involve a reaction channel in which the sequential transfer of two hydrogen atoms to oxygen occurred intramolecularly in the coordination sphere of rhodium with the conservation of the spin correlation of protons. This opens up the possibility in principle of using this reaction to prepare para-H2O, one of the nuclear spin isomers of water in which proton spins are antiparallel.

C–C coupling reactions in the coordination sphere of rhodium(i) and rhodium(iii): New routes for the di- and trimerization of terminal alkynes

The alkynyl(vinylidene)rhodium(I) complexes trans-[Rh(C[triple bond, length as m-dash]CR)(=C=CHR)(PiPr3)2] 2, 5, 6 react with CO by migratory insertion to give stereoselectively the butenynyl compounds trans-[Rh{eta1-(Z)-C(=CHR)C[triple bond, length as m-dash]CR}(CO)(PiPr3)2](Z)-7-9, of which (Z)-7 (R=Ph) and (Z)-8 (R=tBu) rearrange upon heating or UV irradiation to the (E) isomers. Similarly, trans-[Rh{eta1-C(=CH2)C[triple bond, length as m-dash]CPh}(CO)(PiPr3)2] 12 and trans-[Rh{eta1-(Z)-C(=CHCO2Me)C[triple bond, length as m-dash]CR}(CO)(PiPr3)2](Z)-15, (Z)-16 have been prepared. At room temperature, the corresponding "non-substituted" derivative trans-[Rh{eta1-C(=CH2)C[triple bond, length as m-dash]CH}(CO)(PiPr3)2] 18 is in equilibrium with the butatrienyl isomer trans-[Rh(eta1-CH=]C=C=CH2)(CO)(PiPr3)2] 19 that rearranges photochemically to the alkynyl complex trans-[Rh(C[triple bond, length as m-dash]CCH=CH2)(CO)(PiPr3)2] 20. Reactions of (Z)-7, (E)-7, (Z)-8 and (E)-8 with carboxylic acids R'CO2H (R'=CH3, CF3) yield either the butenyne (Z)- and/or (E)-RC[triple bond, length as m-dash]CCH=CHR or a mixture of the butenyne and the isomeric butatriene, the ratio of which depends on both R and R'. Treatment of 2 (R=Ph) with HCl at -40 degrees C affords five-coordinate [RhCl(C[triple bond, length as m-dash]CPh){(Z)-CH=CHPh}(PiPr3)2] 23, which at room temperature reacts by C-C coupling to give trans-[RhCl{eta2-(Z)-PhC[triple bond, length as m-dash]CCH=CHPh}(PiPr3)2](Z)-21. The related compound trans-[RhCl(eta2-HC[triple bond, length as m-dash]CCH=CH2)(PiPr3)2] 27, prepared from trans-[Rh(C[triple bond, length as m-dash]CH)(=C=CH2)(PiPr3)2] 17 and HCl, rearranges to the vinylvinylidene isomer trans-[RhCl(=C=CHCH=CH2)(PiPr3)2] 28. While stepwise reaction of 2with CF3CO2H yields, via alkynyl(vinyl)rhodium(III) intermediates (Z)-29 and (E)-29, the alkyne complexes trans-[Rh(kappa1-O2CCF3)(eta2-PhC[triple bond, length as m-dash]CCH=CHPh)(PiPr3)2](Z)-30 and (E)-30, from 2 and CH3CO2H the acetato derivative [Rh(kappa2-O2CCH3)(PiPr3)2] 33 and (Z)-PhC[triple bond, length as m-dash]CCH=]CHPh are obtained. From 6 (R=CO2Me) and HCl or HC[triple bond, length as m-dash]CCO2Me the chelate complexes [RhX(C[triple bond, length as m-dash]CCO2Me){kappa2(C,O)-CH=CHC(OMe)=O}(PiPr3)2] 34 (X=Cl) and 35 (X=C[triple bond, length as m-dash]CCO2Me) have been prepared. In contrast to the reactions of [Rh(kappa2-O2CCH3)(C[triple bond, length as m-dash]CE)(CH=CHE)(PiPr3)2] 37(E=CO2Me) with chloride sources which give, via intramolecular C-C coupling, four-coordinate trans-[RhCl{eta2-(E)-EC[triple bond, length as m-dash]CCH=CHE}(PiPr3)2](E)-36, treatment of 37with HC[triple bond, length as m-dash]CE affords, via insertion of the alkyne into the rhodium-vinyl bond, six-coordinate [Rh(kappa2-O2CCH3)(C[triple bond, length as m-dash]CE){eta1-(E,E)-C(=CHE)CH=CHE}(PiPr3)2] 38. The latter reacts with MgCl2 to yield trans-[RhCl{eta2-(E,E)-EC[triple bond, length as m-dash]CC(=CHE)CH=CHE}(PiPr3)2] 39, which, in the presence of CO, generates the substituted hexadienyne (E,E)-EC[triple bond, length as m-dash]CC(=CHE)CH=CHE 40.

Reactions of a Hydroxy Phosphonite Ligand in the Coordination Sphere of Rhodium(I)

The complexation behavior of 6-(3,3‘-di-tert-butyl-5,5‘-dimethoxy-2-hydroxy-2‘-oxybiphenyl)-6H-[c,e]-1,2-oxaphosphorine, which generates an active and n-regioselective rhodium(I) catalyst for the i...

NO bond cleavage and various bonding modes of the nitrato ligand in rhodium complexes: syntheses and structures of [Cp*Rh(η 1-NO 3)(μ-Cl)] 2, {[Cp*RhCl(PPh 3)(CNC 6H 11)] 2(NO 2)(NO 3)}·2H 2O, [Cp*Rh(η 1-NO 3)(η 1,μ-N 3)] 2, [Cp*Rh(η 2-NO 3)(O 3SCF 3)], trans-{[Rh(PPh 3) 2(CN2,6-Me 2C 6H 3) 2](NO 3)}·H 2O, and {[Cp* 2Rh 2(η 2,μ-NO 2- N, O) 2(η 1,μ-N

The addition of 2 equiv. of AgNO 3 to a dinuclear chloro-bridged Rh(III) compound, [Cp*RhCl 2] 2, resulted in the replacement of the terminal chloro ligand to give [Cp*Rh(η 1-NO 3)(μ-Cl)] 2 ( 1). On the other hand, the reaction of [Cp*RhCl 2] 2 with 4 equiv. of AgNO 3 led to the formation of a mononuclear bis(nitrato)-rhodium compound, [Cp*Rh(η 1-NO 3)(η 2-NO 3)] ( 2). Compound 1 reacted with PPh 3 and cyclohexyl isocyanide (CNC 6H 11) to give a chiral compound, {[Cp*RhCl(PPh 3)(CNC 6H 11)] 2(NO 2)(NO 3)}·2H 2O ( 3·2H 2O), which shows an unusual example of the nitrate-to-nitrite reduction in the rhodium coordination sphere. The reaction of compound 2 with either NaN 3 or N 3SiMe 3 gave a dinuclear (η 1-nitrato)-rhodium compound, [Cp*Rh(η 1-NO 3)(η 1,μ-N 3)] 2 ( 4). On the other hand, on addition of silver triflate (AgOTf), compound 2 underwent replacement to give a mononuclear (η 2-nitrato)-rhodium compound, [Cp*Rh(η 2-NO 3)(OTf)] ( 5). In addition, compound 2 reacted with a mixture of PPh 3 and 2,6-dimethylphenyl isocyanide (CN2,6-Me 2C 6H 3) to give trans-{[Rh(PPh 3) 2(CN2,6-Me 2C 6H 3) 2](NO 3)}·H 2O ( 6·H 2O), which exhibits the complete elimination of all ligands in compound 2 and indicates the formal reduction of the rhodium metal from +3 to +1. The nitro-rhodium compound, {[Cp* 2Rh 2(η 2,μ-NO 2- N, O) 2(η 1,μ-N 3)](PF 6)}·0.5H 2O ( 7·0.5H 2O), was prepared by the reaction of [Cp*RhCl(dppf)](PF 6) (dppf=Fe(η 5-C 5H 4PPh 2) 2) with a mixture of N 3SiMe 3 and AgNO 3, which also displays the NO bond cleavage of nitrate (NO 3 − ) to nitrite (NO 2 − ). The structures of 1, 3·2H 2O, 4, 5, 6·H 2O, and 7·0.5H 2O were determined by X-ray diffraction.

A New More Sulfur-Resistant Rhodium Complex as an Alternative to the Traditional Wilkinson's Catalyst

A new rhodium complex was obtained using tridecylamine as the ligand. The procedure was carried out with relatively simple equipment and under mild conditions of pressure and temperature. The complex so obtained showed similar activity and higher sulfur resistance than the Wilkinson's complex in heterogeneous conditions for the hydrogenation of cyclohexene to cyclohexane at low values of pressure and temperature. Fourier transform infrared (FTIR) results indicated that the tridecylamine molecule is present in the coordination sphere of the rhodium complex. Elemental microanalysis and X-ray photoelectron spectroscopy (XPS) results suggested that the complex formula is [RhCl(NH2(CH2)12CH3)3]; XPS also suggested that the complex suffered an insertion of a sulfur atom into the rhodium coordination sphere after poisoning with tetrahydrothiophene.

Indication of water in the coordination sphere of rhodium by conversions of 2,5-dimethoxy-2,5-dihydrofuran with syngas

2,5-Dimethoxy-2,5-dihydrofuran did not form the expected aldehydes when water-soluble rhodium-catalysts were used for the conversion with syngas. Instead of hydroformylation, hydrogenation was the main reaction path in water, where 2,5-dimethoxytetrahydrofuran and its hydrolysis product, succinic dialdehyde, were obtained. The formation of hydrogenation products indicates water in the coordination sphere of rhodium. This may provide us with information on the environment of an active metal in aggregated structures like micelles and vesicles which are gaining in importance in biphasic catalysis.

An Unprecedented

Mono- and dinuclear organometallic rhodium(I) complexes such as 1 are obtained in excellent yields by the reaction of trans-[RhF{=C=C=C(Ph)R}(PiPr3)2] with triphenylstannanes PhC≡CSnPh3 and Ph3SnC≡CC≡CSnPh3. Compound 1 undergoes an unprecedented [C2+C1+C1] coupling reaction with CO to produce the highly unsaturated cyclobutenone derivative 2. R=Ph, tBu; L=iPr3.

Supported Wilkinson's complex used as a high active hydrogenation catalyst

Supporting Wilkinson's complex on γ-Al 2O 3 rendered a high active catalyst for cyclohexene to cyclohexane hydrogenation. The activity was higher than that of the same complex unsupported, in the presence or absence of a S-containing poison (tetrahydrothiophene). XPS results suggested that, after poisoning, there was an insertion of a sulfur atom into the rhodium coordination sphere. Comparison of Wilkinson's complex with other palladium and nickel complexes was also made. The Wilkinson's complex proved to be more active and sulfur resistant than the Pd and Ni complexes in both homogeneous and heterogeneous conditions. For the Pd and Ni complexes there was a change in the coordination sphere after poisoning, as shown by the XPS results.

Preparation of (1,4,7-triazacyclononane)Rh(hydrocarbyl)3 Compounds and Their Derivatives. Strong Donor Labilization of RhCl Bonds toward Alkylation and Preparation of Unusually Stable Alkyl Hydride Complexes of Rhodium

(tacn)Rh(R)3 compounds (tacn = 1,4,7-triazacyclononane; R = Me, Et, Ph, vinyl) have been prepared in 65−86% yields by treatment of (tacn)RhCl3·H2O with more than a 7-fold molar quantity of RLi in THF, followed by protonation by methanol. The product before protonation is (Li3tacn)RhR3 (Li3tacn = 1,4,7-trilithio-1,4,7-triazacyclononane) which can be isolated. The alkylation is complete in a few minutes to a couple of hours, depending on R, which compares with 3−4 days for CnRhCl3 with MeLi (Cn = 1,4,7-trimethyl-1,4,7-triazacyclononane) and suggests that the presumably first-formed (Li3tacn)RhCl3 is highly activated toward Cl- dissociation by the strong donor effect of the three LiNR2 groups in the rhodium coordination sphere. Protonation of (Li3tacn)RhR3 by methanol gives the neutral products (tacn)RhR3. X-ray structure determinations of (tacn)RhEt3 and (tacn)RhPh3 have been carried out. Protonolysis of (tacn)RhR3 (R = Me, Et, Ph) by 2 HSO3CF3 (HOTf) affords (tacn)RhR(OTf)2. Dissolution of the latter in D2...

An ab Initio MO Study on the Transformation of Acetylene to Vinylidene in the Coordination Sphere of Rhodium(I). The Intra- and Intermolecular Proton Transfer Mechanism

The transformation of a rhodium(I) η2-alkyne model complex RhCl(PH3)2(HC⋮CH) (A) into the vinylidene form RhCl(PH3)2(CCH2) (E) has been examined by ab initio theoretical calculations using MP2 level geometry optimizations and localized molecular orbital (LMO) analysis. The vinylidene form E has been found to be 7.8 kcal/mol more stable than A. The previously found intraligand 1,2-hydrogen shift mechanism in the Ru(II)-coordinated alkyne−vinylidene isomerization is not relevant for the present Rh system. The reaction proceeds via the oxidative addition product RhCl(PH3)2(H)(C⋮CH) (C), followed by a bimolecular hydrogen shift from the metal to the terminal carbon of a second molecule rather than by intramolecular 1,3-hydrogen transfer. The LMO analysis of the transition state of the unimolecular 1,3-hydrogen shift indicates that the hydrogen moves as a proton while it interacts with the three centers simultaneously, i.e., Rh, Cα, and Cβ in the transition state. The hydrogen was analyzed to migrate also as a proton in the bimolecular mechanism. The barrier of the bimolecular pathway has been further calculated for a more realistic system with substituted phosphines, RhCl(PiPr3)2(H)(C⋮CH), using the integrated MO + MM (MP2:MM3) method. It was concluded that in the real system with substituents on both the phosphines and the alkyne, RhCl(PiPr3)2(HC⋮CR), the bimolecular hydrogen shift is still favored by ca. 15 kcal/mol in free energy of activation; unimolecular 1,3-H migration should become important in special cases like solid state isomerizations.

Supramolecular approach to metal-support interactions: reactivity of silica-supported bis(allyl)rhodium(III) and the influence of surface hydroxyl groups

The structure and stoichiometric reactivity of a surface organometallic fragment, bis(allyl)rhodiuim(III) on silica, has been studied in order to identify concepts of molecular chemistry which can be applied to mechanisms of heterogeneous catalysis. The reactions with electrophiles and Lewis bases are examined. The similarity of the ‘supramolecular’ surface chemistry to molecular chemistry was limited since the surface hydroxyl groups of silica were found to participate. A hydroxyl group in the coordination sphere of rhodium is a source of electrophilic protons, and neighbouring hydroxyl groups facilitate surface mobility of grafted organometallic fragments.