Regiospecific insertion into the Co–Co bond of the mixed-metal cluster Co2Rh2(CO)12 by an electron-poor alkyne: X-ray diffraction structure of the butterfly cluster Co2Rh2(CO)10(μ-HCCCO2Me)

The reaction between the mixed-metal tetrahedral cluster Co₂Rh₂(CO)₁₂ (1) and the electron-poor alkyne methyl propiolate in hexane at room temperature furnishes a mixture of products consisting of Co₃Rh(CO)₁₂ (2), Co₃Rh(CO)₁₀(μ-HCCCO₂Me) (3), Co₂Rh₂(CO)₁₀(μ-HCCCO₂Me) (4), and CoRh₃(CO)₉(μ-HCCCO₂Me)₃ (5). The isolation and solution spectroscopic data of these compounds are described, and the solid-state structure of Co₂Rh₂(CO)₁₀(μ-HCCCO₂Me) determined by X-ray diffraction analysis. The title cluster crystallizes in the triclinic space group. The solid-state structure of Co₂Rh₂(CO)₁₀(μ-HCCCO₂Me) provides proof for the regiospecific insertion of the methyl propiolate ligand into the Co–Co bond of the starting cluster Co₂Rh₂(CO)₁₂. The stability of clusters 3 and 4 in the presence of added methyl propiolate is discussed.     

Organometallic chemistry and homogeneous catalysis of Rh and Rh-Co mixed metal carbonyl clusters

The reactions of hydrosilane and/or alkyne as well as isonitriles with rhodium and rhodium cobalt mixed metal carbonyl clusters, e.g., Rh₄(CO)₁₂ and Co₂Rh₂(CO)₁₂, are studied. Novel mixed metal complexes, e.g., CoRh(CO)₅ (HCCBu ⁿ ), (R₃Si)₂Rh(CO) _n Co(CO)₄, Rh(R–NC)₄Co(CO)₄, Co₂Rh₂(CO)₁₀(HCCR), and Co₂Rh₂(CO)₉(HCCBu ⁿ ), are synthesized and identified. The catalytic activities of these rhodium and rhodium-cobalt mixed metal complexes are examined in hydrosilyation, silylformylation, and novel silylcarbocyclization reactions. Possible mechanisms for these reactions are proposed and discussed.     

Hydroformylation of 1, 1, 1-d3-2-butene. Isotope Effect on the Product Composition

In the hydroformylation of 1,1,1-trideuterio-2-butene with Rh₄ (CO)₁₂ the deuterated pentanals formed contain 75% of 5,5,5-trideuterio-pentanal, the rest being substantially 2,2-dideuterio-pentanal. On the contrary, using Co₂ (CO)₈ as the catalyst precursor, position 1 and 4 are formylated to the same extent.     

The formation of a new mixed cobalt rhodium carbonyl from Co2(CO)8 and Rh4(CO)12: Infrared spectroscopic characterization under carbon monoxide pressure

The formation of a new compound, the most characteristic IR absorption bands of which appear at 2007 cm^-1 and 1956 cm^-1, has been in the reaction between Co₂(CO)₈ and Rh₄(CO)₁₂ under carbon monoxide pressure in a hydrocarbon medium. The same compound is also formed either by the reaction of Co₂(CO)₈ with [Rh(CO)₂Cl]₂ or by the reaction of Co₃Rh(CO)₁₂ with carbon monoxide. The new complex has not been isolated in a pure state, but the formula CoRh(CO)₇ is proposed on the basis of the stoichiometry of its formation and its physico-chemical properties. Equilibrium constants and thermo-dynamic parameters for the reaction 2 Co₂(CO)₈ + Rh₄(CO)₁₂  4 CoRh(CO)₇ have been estimated. Possible structures for the new complex are discussed on the basis of its IR spectrum.     

Synthesis and reactivity of rhodium(I) complexes of the type Rh(L-L)(CO)[P(OPh)3] and Rh(L-L)[P(OPh)3]2

Summary The carbonyl ligands in the Rh¹ complexes Rh(L-L)(CO)₂ [L-L=anthranilate (AA) orN-phenylanthranilate(FA) ions] are replaced by P(OPh)₃ to form the mono-or disubstituted products, Rh(L-L)(CO)[P(OPh)₃] and Rh(L-L)[P(OPh)₃]₂ respectively depending on the [P(OPh)₃]/[Rh] molar ratio, at room temperature and in air. Under argon at [P(OPh)₃]/[Rh]4 theortho-metallated Rh¹ complex Rh[P(OPh)₃]₃[P(OC₆H₄)-OPh)₂] is formed. The new route forortho-metallated Rh¹ complex synthesis is described.The Rh(AA)(CO)₂ complex was used as a catalyst precursor in hydroformylation of olefins.     

Hydroformylation of olefins catalyzed by rhodium complex anchored on clay matrices

Investigations on the catalytic activity of a transient Rh(I) triphenylphosphine complex1 anchored on montmorillonite clay have been carried out with respect to hydroformylation of olefins at 70°C and 60 atm of CO+H₂ (1:1). The analysis has shown that aldehydes and hydrocarbons of the corresponding olefins result under hydroformylation conditions. In limonene, reaction proceeds with double hydroformylation and hydrogenation to give the respective oxo products. The catalytic activities of1 are compared with Wilkinson's Rh^I (H) (CO) (PPh₃)₂ (6) complex in solution under the same hydroformylation conditions.     

C−N Coupling through Hydroaminoalkylation on a Single-Atom Rh Heterogeneous Catalyst

C−N coupling is significant for the synthesis of fine chemicals toward various applications. Hydroaminoalkylation of olefins is a tandem reaction of C−N coupling involving first the formation of an aldehyde through hydroformylation of an olefin and then the production of amine through reductive amination of the aldehyde. Here we report a stable, supported catalyst of singly dispersed Rh₁ atoms anchored on TiO₂ (P25) nanoparticles designated as Rh₁/P25. Its high activity for C−N coupling was demonstrated by six hydroaminoalkylations of olefins and amines with selectivity of higher than 90% for producing tertiary amines. The singly dispersed Rh₁O₄ on P25 exhibit activity and selectivity for hydroaminoalkylation comparable or even higher than some reported molecular catalysts. In contrast to molecular catalysts, the Rh-based single-atom Rh heterogeneous catalysis (Rh₁/P25) can be readily separated from reactants and products, reused for multiple runs of hydroaminoalkylation, and recycled with a low cost.     

Theoretical investigation on hydroformylation reactions : I. Structures and reactivities of cobalt carbonyls and hydrocarbonyls

Extended Hückel Theory calculations have been carried out in a study of the most important cobalt carbonyls and hydrocarbonyls involved in the hydroformylation reaction. The geometries of the stable isomers of Co₂(CO)₈, Co₂(CO)₇, Co(CO)₄, Co(CO)₃ have been calculated and used to interpret the changes in the IR spectrum of Co₂(CO)₈ observed on varying the temperature. The reaction paths for the interconversions of the stable isomers have also been investigated. The optimized geometry of HCo(CO)₄ agrees well with the experimental structure. The C_s symmetry found for the most stable isomer of HCo(CO)₃ is of much interest, serves to explain the formation of the complex with olefins.     

Unsaturation in binuclear cyclopentadienylrhodium carbonyls: Comparison with their cobalt analogs

The Cp₂Rh₂(CO)_n (n = 4, 3, 2, 1) derivatives have been examined by density functional theory using the BP86 and MPW1PW91 functionals. The known tricarbonyl Cp₂Rh₂(CO)₃ is predicted to have a singly bridged structure with a predicted Rh–Rh single bond distance of ～2.70 Å in close agreement with the experimental value of 2.68 Å, determined by X-ray crystallography. In contrast to the cobalt analog, no evidence for a triply bridged Cp₂Rh₂(μ-CO)₃ structure was found. The known dicarbonyl Cp₂Rh₂(CO)₂ is predicted to have a doubly bridged structure with a predicted RhRh double bond distance of 2.58 Å in close agreement with the experimental RhRh double bond distance of 2.564 Å, found by X-ray crystallography for the permethylated derivative (η⁵-Me₅C₅)₂Rh₂(μ-CO)₂. The monocarbonyl Cp₂Rh₂(CO) is predicted to have a four-electron donor bridging carbonyl group with a Rh–O distance of ～2.5 Å and a RhRh double bond distance of ～2.54 Å. This differs from Cp₂Co₂(CO) which was previously predicted to have only a two-electron donor bridging carbonyl group with a long Co?O distance and a short CoCo distance of ～2.0 Å suggesting a formal triple bond. For Cp₂Rh₂(CO)₄ doubly bridged trans and cis isomers were found within ～1.0 kcal/mol in energy with non-bonding Rh?Rh distances of ～3.2 Å. However, these Cp₂Rh₂(CO)₄ isomers are predicted to be unstable with respect both to CO loss to give Cp₂Rh₂(CO)₃ and to fragmentation into two CpRh(CO)₂ units.     

Hydroformylation of styrene catalyzed by a rhodium thiolate binuclear catalyst supported on a cationic exchange resin

The binuclear complex [Rh₂(μ-S(CH₂)₂NMe₂)₂(cod)₂] 1 (cod=1,5-cyclooctadiene) was anchored to a sulfonic exchange resin through the residual amine groups. The reaction of the immobilized complex with CO and PPh₃ yielded the catalytically active complex [Rh₂(μ-S(CH₂)₂NHMe₂)₂(CO)₂(PPh₃)₂]²⁺ supported in the polymer matrix. When methanol was used as solvent, the metal complex loaded cationic resin behaved as a multifunctional catalyst, since it was active in the hydroformylation of styrene and the subsequent formation of the acetals, directly rendering 1,1-dimethoxy-2-phenylpropane in 85% selectivity. Furthermore, the immobilized catalyst can be separated from the reaction mixture and recycled. A homogeneous model of the supported catalyst was generated by reacting complex 1 with HTsO, PPh₃, and CO. Thus, the methanol soluble complex [Rh₂(μ-S(CH₂)₂NHMe₂)₂(CO)₂(PPh₃)₂](TsO)₂ was also found to be active in the hydroformylation of styrene yielding identical selectivity in the branched isomer to that of the immobilized catalyst, although the latter is much slower (20-fold) than the homogeneous catalyst.     

Bidentate amines as bridges between M(CO)2Cl (M = Rh OR Ir) units

The preparation and characterization by elemental analysis, electronic and infrared spectroscopy are reported for the monomeric complexes cis-(amine)-M(CO)₂Cl (M = Ir or Rh, amine = 1,8-naphthyridine or pyridazine; M = Ir, amine = o-phenylenediamine) and the binuclear species (1,8-naphthyridine)Rh₂(CO)₄Cl₂, (1,8-naphthyridine)IrRh(CO)₄Cl₂, (pyrazine)Rh₂(CO)₄Cl₂ and (1,3-di-4-pyridylpropane)Rh₂(CO)₄Cl₂.     

Thermal decomposition of a series of tetranuclear carbonyl clusters Rh4(CO)12, Rh2Co2(CO)12, RhCo3(CO)12 and Co4(CO)12

Decarbonylation of the unsupported clusters Rh₄(CO)₁₂, Rh₂Co₂(CO)₁₂, RhCo₃(CO)₁₂ and Co₄(CO)₁₂ in a stream of hydrogen has been investigated by temperature programmed decomposition. Kinetic parameters for the thermal decomposition are presented, and the stabilities of the clusters are discussed. The profile for evolution of CO from Rh₄(CO)₁₂ indicates that a stable intermediate is formed. In all four cases methane is formed stepwise until most of the CO groups are evolved.     

[Fec3(μ3-CR)(CO)10]− Cluster anions as building blocks for the synthesis of mixed-metal clusters: II. Synthesis of HFe3Rh(μ4-η2-CCHR)(CO)11 clusters (R = H or C6H5) and study of their catalytic activity (R = C6H5) under hydroformylation and hydrogenation conditions

The mixed-metal vinylidene clusters HFe₃Rh(CO)₁₁(CCHR) (R = H, C₆H₅) have been synthesized via the reaction of [HFe₃(CO)₃CCHR][P(C₆H₅)₄] with [RhCl(CO)₂]₂ in the presence of a thallium salt. The reaction initially gives the [Fe₃Rh(CO)₁₁]CCHR][P(C₆H₅)₄] cluster which leads to the final products by protonation. Spectroscopic data indicate a μ₄-η² mode of bonding for the vinylidene ligand. A structure with a Fe₃Rh core in a butterfly configuration and in which the rhodium atom occupy a wing-tip site is proposed. The catalytic activity of HFe₃Rh(CO)₁₁(CCH(C₆H₅)) (80% yield) has been checked in hydroformylation and hydrogenation. In hydroformylation the cluster shows the same activity as Rh₄(CO)₁₂, whereas in hydrogenation the mixed-metal system shows specific activity; isomerization of 1-heptene to cis and trans 2-heptene takes place with no more than 14% heptane formation. The cluster is broken down during the catalysis, and some H₃Fe₃CO)₉(μ₃-CCH₂(C₆H₅)) is formed. The latter cluster is not an active catalyst, and under the same conditions use of Rh₄(CO)₁₂ results mainly in hydrogenation of 1-heptene. These observations suggest that the active species is a mixed iron-rhodium system.     

On hydrogen activation in the hydroformylation of olefins with Rh4(CO)12 or Co2(CO)8 as catalyst precursors

In the hydroformylation of ethylene with approximately equimolar H₂/D₂ mixtures and Rh₄(CO)₁₂ or Co₂(CO)₈ as the catalyst precursor about 50% of propionaldehyde-d₁ was formed. The propionaldehyde-d₀/d₂ ratio was ～ 3 for rhodium and ～ 2.6 for the cobalt catalyst. On the basis of the results and assuming that there is no rapid M(H)₂/M(D)₂ scrambling, activation of hydrogen through M(H)₂ or M(H)₂(olefin) complexes can be excluded.     

Reduction des halogenures de titane(IV) par les metaux: une nouvelle methode de synthese de Cp2 Ti(CO)2 et de CpTi(C7H7

A ready intermolecular ligand exchange process occurs when solutions of Co₂Rh₂(CO)₁₂ and Co₂Rh₂(CO)₈(PF₃)₄ are mixed at room temperature.     

Direct synthesis of acetals by rhodium catalysed hydroformylation of alkenes in the presence of orthoformate

The two catalyst precursors [Rh₂(μ-penicillamine)₂(CO)₄][OTf]₂ and [Rh₂(μ-cysteine)₂(CO)₄][OTf]₂ in the presence of 4 equivalents of P(OPh)₃ in triethyl orthoformate as solvent and reactant, permit the low pressure hydroformylation of various alkenes into the corresponding acetals. Apart from a few low-yield by-products resulting from isomerization of the substrates, the carbonylated products obtained directly and exclusively are acetals.     

Novel α-fluorinated cyclic phosphite and phosphinite ligands and their Rh-complexes as suitable catalysts in hydroformylation

Asymmetrical cyclic phosphite and phosphinite ligands of a novel type bearing either trifluoromethyl or pentafluorophenyl group were synthesized using >PCl or >PN< species and racemic fluorinated alcohols. The P-ligands were converted to complexes of Rh^III(L)(Cp^∗)Cl₂ type (where L = phosphite or phosphinite) and, in two instances, their stereostructures were evaluated by X-ray analysis. These complexes along with in situ systems, formed from Rh(CO)₂(acac) precursor and the corresponding ligand, were tested in the hydroformylation of styrene. Both systems provided excellent hydroformylation activities at 100 °C. Using the Rh^I in situ systems, moderate and high regioselectivities towards the branched aldehyde (2-phenyl-propanal) were obtained at 100 and 40 °C, respectively.     

Hydroformylation of Olefins Catalyzed by Rhodium Trichloride Anchored on Ti-HMS

Rhodium trichloride supported on Ti-hexagonal mesoporous silica (Ti-HMS), via a bipyridyl group, is an efficient catalyst for the hydroformylation of olefins at 120 °C and 40.8 atm of CO/H₂ (CO/H₂=2/1). The catalyst is selective leading to high ratios of linear or branched aldehydes from functionalized olefins, and high activity in the case of propene which gave a turnover frequency of 6209 mol/mol(Rh)/h.     

Surface supported metal cluster carbonyls. Chemisorption decomposition and reactivity of Rh4(CO)12 supported on silica and alumina

Chemisorption of Rh₄(CO)₁₂ on to a highly divided silica (Aerosil “0” from Degussa), Leads to the transformation: 3 Rh₄(CO)₁₂ → 2 Rh₆(CO)₁₆ + 4 CO. Such an easy rearrangement of the cluster cage implies mobility of zerovalent rhodium carbonyl fragments on the surface. Carbon monoxide is a very efficient inhibitor of this reaction, and Rh₄(CO)₁₂ is stable as such on silica under a CO atmosphere. Both Rh₄(CO)₁₂ and Rh₆(CO)₁₆ are easily decomposed to small metal particles of higher nuclearity under a water atmosphere and to rhodium(I) dicarbonyl species under oxygen. From the Rh^I(CO)₂ species it is possible to regenate first Rh₄(CO)₁₂ and then Rh₆(CO)₁₆ by treatment with CO (P_co ? 200 mm Hg) and H₂O (P_H2O ? 18 mm Hg). The reduction of Rh^I(CO)₂ surface species by water requires a nucleophilic attack to produce an hypothetical [Rh(CO)_n]_m species which can polymerize to small Rh₄ or Rh₆ clusters in the presence of CO but which in the absence of CO lead to metal particles of higher nuclearity. Similar results are obtained on alumina.     

Catalytic hydrogenation of 1,3-trans-pentadiene over Rh4(CO)12 supported on γ-Al2O3

Rh₄(CO)₁₂ anchored on γ-Al₂O₃ (Rh₄(CO)₁₂/Al₂O₃) has been studied as a catalyst for the hydrogenation of 1,3-trans-pentadiene. Under mild conditions (1 atm H₂ and temperatures between 60°C and 80°C) hydrogenation occurs at only one of the double bonds of the diene, and analysis of the products shows that the terminal double bond is preferentially hydrogenated. Hydrogenation of the second double bond of the conjugated diene occurring only after all the 1,3-trans-pentadiene has been consumed. In this respect Rh₄(CO)₁₂/Al₂O₃ behaves like toluene solutions of Rh₄(CO)₁₂. Anchoring of Rh₄(CO)₁₂ on the solid support gives a catalyst which is less active but more stable than toluene solutions of Rh₄(CO)₁₂. The effects of CO and of triphenylphosphine on catalytic activity and on specificity of Rh₄(CO)₁₂/Al₂O₃ have also been investigated and both shown to cause a reduction of the rate of hydrogenation of 1,3-trans-pentadiene.