Pascual Lahuerta

Heterogeneous Dinuclear Rhodium(II) Hydroformylation Catalysts—Performance Evaluation and Silsesquioxane‐Based Chemical Modeling

Supported, air stable, and reusable hydroformylation catalysts have been prepared by immobilizing dinuclear rhodium(II) complexes bearing ortho-metalated arylphosphane ligands on amorphous silica and mesoporous MCM-41 supports by phosphane tethers. The oligosilsesquioxane model complex of the catalytic site 1 has been prepared analogously and characterized by single-crystal X-ray diffraction analysis.

The structure of a dinuclear silver(I) complex: Ag2[S2C2(CN)2] [P(C6H5)3]4

Abstract The crystal structure of the dimeric Ag maleonitriledithiolate complex, Ag2[S2C2(CN)2] [P(C6- H5)3]4 (1), has been performed. Complex 1 crystallizes in the space group P21/c with a = 12.2898(77), b = 23.8325(91), c = 23.1790(118) A, β = 101.315(43)° and Z = 4. Refinement using 3253 reflections with Fo2>3σ(Fo2) yielded R = 0.0662, Rw= 0.0669. The most interesting aspect of the structure is the strong bridging interaction of the chelating maleonitriledithiolate ligand with the second Ag center, where a Ag-S distance of 2.478 A is observed. The residual bonding capability of the sulfur atoms in the chelating anion [Ag(S2C2(CN)2)(PPh3)2]− for [Ag(PPh3)2]+ is demonstrated.

Reactions of dirhodium(II) monometallated compounds with phosphines. Factors affecting the reactivity and the structure of the doubly-metallated compounds. Molecular structure of Rh2(O2CCH3)2[(C6H4)P(C6H5)2][(p-ClC6H3)P(p-ClC6H4)2] · (HO2CCH3)2·(C6H6), a compound with two different metallated phosphines

Abstract Monometallated compounds of formula Rh2(O2CCH3)3[(p-XC6H3)P(p-XC6H4)2](HO2CCH3)2 (X=CH3, Cl) have been prepared in good yield. The reactions with p-substituted triarylphosphines P(p-X′C6H4)3 (X′=CH3, H, Cl) have been studied. For X=X′ and [P]/[Rh2]=1 all the resulting doubly metallated compounds Rh2(O2CCH3)2[(p- XC6H3)P(p-XC6H4)2](HO2CCH3)2 (X=CH3, Cl) have head-to-tail (H-T) structure. For [P]/[Rh2]=3 reaction progress is observed at room temperature. When X=X′ a 1:1 mixture of H-T and H-H compounds is formed for X=Cl but only the H-H compound is obtained for X=CH3. For X ≠ X′ mixtures of H-T and H-H compounds are obtained. The entering phosphine, and to a less extent the phosphine in the monometallated compound, seems to influence the rate of the process and the product distribution. The crystal structure of Rh2(O2CCH3)2[(C6H4)P(C6H5)][(p-ClC6,H3)P(p-ClC6H4)2] (HO2CCH3)2· 1 2 (C6H6) a doubly metallated compound with two different metallated phosphines in a head-to-tail configuration, is also described.

ortho-metallation of P(m-MeC6H4)3 in dirhodium(II) tetraacetate. Molecular structure of Rh2(O2CCH3)2[(m-MeC6H3)P(m-MeC6H4)2]2(HO2CCH3)2·CH3CO2H

Abstract The thermal reaction of Rh2(O2CCH3)4(MeOH)2 and P(m-MeC6H4)3 in a 1:2 molar ratio in acetic acid yielded Rh2(O2CCH3)2[(m-MeC6H3)P(m -MeC6H4)2]2(HO2CCH3)2. Purple monoclinic crystals of this compound and one molecule of acetic acid, space group P21/c, were obtained by evaporation of a solution of the original reaction product in acetic acid/CH2Cl2 mixture. The unit cell parameters are a = 21.346(3), b = 11.909(2), c = 20.071 A, β = 97.98(1)° and Z = 4. The structure consists of a dinuclear rhodium core bridged by cisoid acetate groups and two ortho-metallated phosphine ligands. The ortho-metallation occurs at the least sterically hindered carbon atom which is trans to the methyl substituent. If the reaction is performed in a 1:1 molar ratio, a monometallated species Rh2(O2- CCH3)3[(m-MeC6H3)P(m-MeC6H4)2](HO2CCH3)2 is obtained in high yield, with the above mentioned doubly metallated compound as a minor reaction product.

Orthometalation reactions in trifluoroacetate dirhodium(II) compounds. Molecular structure of Rh2(O2CCF3)2[(C6H4)PPh2]2·(PPh3)2·2(C7H8)

Abstract Rh 2 (O 2 CCF 3 ) 3 [(C 6 H 4 )PPh 2 ]·(HO 2 CCF 3 ) 2 reacts with PPh 3 yielding the doubly metalated compound Rh 2 (O 2 CCH 3 ) 2− [(C 6 H 4 )PPh 2 ] 2 ·(HO 2 CCF 3 ) 2 . The reaction proceeds via a reactive intermediate with an equatorial phosphine, Rh 2 (η 2 -O 2 CCF 3 )(μ-O 2 CCF 3 ) 2 [(C 6 H 4 )PPh 2 ](PPh 3 )·(HO 2 CCF 3 ), which can also be generated in moderate yield under photochemical conditions. The structure of the PPh 3 bis-adduct Rh 2 (O 2 CCF 3 ) 2 [(C 6 H 4 )PPh 2 ] 2 ·(PPh 3 ) 2 ·2(C 7 H 8 ) has been determined by X-ray diffraction. M r =1663.27, orthorhombic, space group Fdd 2, a =41.748(9), b =21.620(5), c =17.375(5) A, V =15683(6) A 3 , Z =8, D x =1.41 g cm −3 . Mo Kα radiation (graphite crystal monochromator, λ=0.71073 A), μ(Mo Kα)=5.57 cm −1 , F (000)=6800, T =293 K. Final conventional R factor=0.035 for 2789 ‘observed’ reflections and 422 variables. The molecule shows crystallographic two-fold axis symmetry through the RhRh bond. One toluene solvent molecule slightly disordered is present in the asymmetric unit.

Mechanism of the acid-catalysed cyclometallation reaction of dirhodium(II) compounds with general formula [Rh2(O2CMe)(µ-O2CMe)2{(C6H4)PPh2}{P(C6H4X)}3}(OH2)]

Compounds of general formula [Rh2(O2CMe)(µ-O2CMe)2{(C6H4)PPh2}{P(C6H4X)3}(OH2)]2(X = H, p-Me, p-Cl, m-Me or m-Cl) have been prepared by photochemical reaction of the corresponding adduct [Rh2(µ-O2CMe)3{(C6H4)PPh2}{P(C6H4X)3}(HO2CMe)]1. These compounds contain one equatorial phosphine which undergoes a facile cyclometallation reaction, catalysed in the presence of protic acids, to give doubly metallated compounds [Rh2(µ-O2CMe)2{(C6H4)PPh2}{(XC6H3)P(C6H4X)2}(HO2CMe)2]3. The kinetics and mechanism of this cyclometallation have been studied in chloroform and toluene solutions. A mechanism in which protons facilitate loss of one of the acetate groups in the starting compounds is proposed. Preliminary experiments showed that the addition of phosphines enhances the cyclometallation rate. The mechanism is fully concerted with a highly ordered transition state as seen by the very negative activation entropies. The values obtained for the deuterium kinetic isotopic effect indicate that, for the acid-catalysed path, the transition state lies in a more advanced position on the reaction coordinate than for the thermal process. The gap between the isokinetic plots for the acid-catalysed and thermal reactions is ca. 20 kJmol–1.

A unified mechanistic view obtained from the temperature and pressure dependence of the spontaneous, acid-, and base-assisted cyclometallation reactions of dirhodium(II) complexes

The reaction of compounds [Rh2(O2CMe)(µ-O2CMe)2{µ-(XC6H3)P(C6H4X-p)2}{P(C6H4X′-p)3}](X = H, X′= H or Me; X = Me, X′= H or Me), having a metallated and an equatorial phosphine in a head-to-tail cisoid configuration, to produce the corresponding doubly metallated compounds [Rh2(µ-O2CMe)2{µ-(XC6H3)P(C6H4X-p)2}2], has been studied in detail. The thermal, acid-, and base-assisted conditions include toluene solution, neat acetic acid, and different bases [PPh3, P(C6H4Me-p)3 or pyridine] in toluene solution and as a function of temperature, pressure and base concentration (when applicable). The doubly metallated compounds always show retention of the head-to-tail cisoid configuration according to 31P NMR spectroscopy. The reported activation parameters allow a clear differentiation between the spontaneous, acid-assisted and base-assisted processes, some of which had been previously studied (ΔH‡= 80 ± 5, 68 ± 1, 38 ± 3 kJ mol–1; ΔS‡=–105 ± 15, –85 ± 3, –150 ± 30 J K–1 mol–1; ΔV‡=–22.7 ± 0.2, –15.3 ± 0.2, –35.0 ± 0.5 cm3 mol–1 respectively, for the compound with X, X′= H). For the reactions under baseassisted conditions, when long reaction times and/or high added Lewis-base concentrations were applied, the non-metallated phosphine was displaced from equatorial to axial co-ordination. Under these conditions a mixture of the bis adducts of the monometallated [Rh2(µ-O2CMe)3{µ-(XC6H3)P(C6H4X-p)2}], and the doubly-metallated compounds was detected by 31P NMR spectroscopy. The activation parameters obtained for this slower process agree with those expected for substitution reactions and are interpreted in terms of the steric demands of the mono and bis adducts formed immediately on mixing the reaction solutions.

ortho-Metalated dirhodium(II)-catalyzed α-diazocarbonyl transformation. Diastereoselective cyclopropanation of menthyl-α-diazo-β-keto ester and CH insertion of α-diazo ester

Abstract ortho-Metalated rhodium(II) compound (1d1) containing two metalated P(C6H5)2(C6F5) and two acetates has successfully catalyzed cyclopropanation of menthyl-2-diazo-3-oxo-6-heptanoate (4) to form cyclopropanes 6 and 7 with significant cis–trans (30:70) diastereoselectivity. An enhanced performance of methyl-2-diazoundecanoate (5) cyclization has been achieved mediated by 2d1 and 2d4 catalysts, obtaining 71 and 85%, respectively, of the 1,5-CH insertion product, trans-2-pentylcyclopentanecarboxylate (8) versus 1,2-elimination product, (Z)-2-undecenoate (9) (29 and 15%, respectively). The three possible diastereomers of catalyst (1d) which possess two ortho-metalated P(C6H5)2(C6F5) ligands in a head-to-tail configuration, with the two pentafluorophenyl groups in an endo–endo, endo–exo or exo–exo disposition have been separated by standard column chromatography. The X-ray structure analysis for two of these isomers 1d3endo–exo and 1d1endo–endo allows their structural assignment.

Reactions of rhodium trifluoroacetate with triphenylphosphine and pyridine. Molecular structure of Rh2(O2CCF3)4(py)4

Abstract Rh 2 (O 2 CCF 3 ) 4 reacts with two mol of triphenylphosphine forming the adduct Rh 2 (O 2 CCF 3 ) 4 (PPh 3 ) 2 . This compound in solution, even at room temperature, undergoes slow stepwise orthometalation of the phosphine ligands forming the doubly metalated compound Rh 2 (O 2 CCF 3 ) 2 [(C 6 H 4 )P(C 6 H 5 ) 2 ] 2 . This reaction has been monitored by 31 P NMR spectroscopy detecting in solution three reaction intermediates. Rh 2 (O 2 CCF 3 ) 4 reacts with excess of pyridine to form the compound Rh 2 (O 2 CCF 3 ) 4 (py) 4 that can be structurally classified as a class III adduct. It contains two bridging and two monodentate equatorial carboxylates and two equatorial and two axial pyridine ligands. The structure of this compound has been determined by X-ray diffraction. M r =974.3, monoclinic, space group P 2 1 / n , a =10.504(1), b =18.108(1), c =35.377(1) A, β=96.416(8)°, V =6686.6(8) A 3 , Z =8, D x =1.94 Mg/m 3 . Mo Kα radiation (graphite crystal monochromator, λ=0.71073 A), μ(Mo Kα)=10.89 cm −1 , F(000)=3824, T =293 K. Final conventional R factor=0.12 for 2258 ‘observed’ reflections and 312 variables. The structure was solved by Patterson interpretation using the program SHELXS86 and the Fourier synthesis.

Dinuclear palladium(II) compounds with bridging cyclometalated phosphines. Synthesis, crystal structure and electrochemical study

The structural characterization of bis-cyclometalated palladium(II) compounds of formula Pd2[(micro-(C6X4)PPh2]2(micro-O2CR)2 [X = H, R = CH3 (3), CF3 (4), C(CH3)3 (5) and C6F5 (6); X = F, R = CH3 (7) and CF3 (8)], has confirmed its paddle wheel structure with two palladium atoms bridged by two acetates and two metalated phosphines in a head-to-tail arrangement. The Pd...Pd distances are in the range 2.6779(16)-2.7229(8) A. Under cyclic voltammetric conditions, compounds 3-6, in CH2Cl2 solution, were found to undergo a reversible oxidation peak in the range of potential values 0.84-1.25 V. A second partially-reversible oxidation is observed at more positive potentials (1.37-1.55 V). For compounds 3-5 in the presence of chlorides, the first oxidation becomes a two-electron process presumably leading to a neutral [Pd(III)-Pd(III)] species with a metal-metal bond.