67913-10-4

Upstream product

• 122924-43-0 Rh{(C₆H₅)2P(CH₂)2P(C₆H₅)2}(CO)I 
• 74-88-4 methyl iodide 
• 122924-42-9 Rh(CO)I₂(P(C₆H₅)2CH₂CH₂P(C₆H₅)2)(methyl) 
• 1663-45-2 1,2-bis-(diphenylphosphino)ethane 
• 58675-42-6 [Rh(CO)Cl(1,4-bis(diphenylphosphino)butane)2] 
• 15024-81-4 [Rh(CO)Cl(1,2-bis(diphenylphosphino)ethane)] 
• 756480-18-9 [rhodium(III)diiodide(acetyl)(carbonyl)(NCMe)]2 
• 122924-42-9 Rh(CO)(CH₃)I₂((C₆H₅)2PCH₂CH₂P(C₆H₅)2) 

Relevant academic research and scientific papers

Insights into the ligand effects of rhodium catalysts toward reductive carbonylation of methanol to ethanol

Methanol reductive carbonylation to ethanol catalyzed by diphosphine ligand modified Rh-based catalysts has been studied. All the catalysts show ligand effects toward the turnover frequency and selectivity. Four Rh-diphosphine complexes were isolated and single crystals were obtained. These complexes were characterized by X-ray single-crystal diffraction, NMR, FTIR, and XPS. The X-ray crystal structure of [Rh2(μ-I)(μ-CO)(CO)2(dppm)2]+ was reported for the first time in this work. Based on the analysis of crystal structures, we unraveled the origin of the ligand effects of rhodium catalysts toward reductive carbonylation of methanol to ethanol. The diphosphine ligand with the appropriate number of methylene groups between two phosphorus atoms can improve the catalytic activity. The steric congestion around the empty coordination site in the Rh-diphosphine complexes led to a preferential reaction of rhodium with H2, which promoted ethanol/acetaldehyde formation.

A mechanistic investigation into the elimination of phosphonium salts from rhodium-TRIPHOS complexes under methanol carbonylation conditions

Phosphine modified rhodium complexes are currently the topic of considerable research as methanol carbonylation catalysts, but often suffer from poor stability. This paper reports on an investigation into how coordination mode affects the elimination of phosphonium salts from rhodium complexes, namely [trans-RhCl(CO)(PPh3)2] 1, [RhCl(CO)(dppe)] 2, [RhCl(CO)(dppb)]23, [Rh(TRIPHOS)(CO)2]Cl 4. These complexes are all potential pre-catalysts for methanol carbonylation. The reaction of these complexes with methyl iodide at 140 °C under both N 2 and CO atmospheres has been studied and has revealed clear differences in the stability of the corresponding Rh(iii) complexes. In contrast to both monomeric 2 and dimeric 3 that react cleanly with CH3I to give stable Rh(iii) acetyl complexes, 4 forms a novel bidentate complex after the elimination of the one arm of the ligand as a quaternised phosphonium salt. The structure of this complex has been determined spectroscopically and using X-ray crystallography. The mechanism of formation of this novel complex has been investigated using 13CH3I and strong evidence that supports a dissociative mechanism as the means of phosphine loss from the rhodium centre is provided.

Oxidative addition of methyl iodide to [Rh(CO)2I]2: Synthesis, structure and reactivity of neutral rhodium acetyl complexes, [Rh(CO)(NCR)(COMe)I2]2

Reaction of [Rh(CO)2I]2 (1) with MeI in nitrile solvents gives the neutral acetyl complexes, [Rh(CO)(NCR)(COMe)I 2]2 (R=Me, 3a; tBu, 3b; vinyl, 3c; allyl, 3d). Dimeric, iodide-bridged structures have been confirmed by X-ray crystallography for 3a and 3b. The complexes are centrosymmetric with approximate octahedral geometry about each Rh centre. The iodide bridges are asymmetric, with Rh-(μ-I) trans to acetyl longer than Rh-(μ-I) trans to terminal iodide. In coordinating solvents, 3a forms mononuclear complexes, [Rh(CO)(sol) 2(COMe)I2] (sol=MeCN, MeOH). Complex 3a reacts with pyridine to give [Rh(CO)(py)(COMe)I2]2 and [Rh(CO)(py)2(COMe)I2] and with chelating diphosphines to give [Rh(Ph2P(CH2)nPPh2)(COMe)I 2] (n=2, 3, 4). Addition of MeI to [Ir(CO)2(NCMe)I] is two orders of magnitude slower than to [Ir(CO)2I2] -. A mechanism for the reaction of 1 with MeI in MeCN is proposed, involving initial bridge cleavage by solvent to give [Rh(CO)2(NCMe)I] and participation of the anion [Rh(CO)2I2]- as a reactive intermediate. The possible role of neutral Rh(III) species in the mechanism of Rh-catalysed methanol carbonylation is discussed.

Steric and electronic effects on the reactivity of Rh and Ir complexes containing P-S, P-P, and P-O ligands. Implications for the effects of chelate ligands in catalysis

Kinetic studies of the reactions of [M(CO)(L-L)I] [M = Rh, Ir; L-L = Ph2PCH2P(S)Ph2 (dppms), Ph2PCH2CH2PPh2 (dppe), and Ph2PCH2P(O)Ph2 (dppmo)] with methyl iodide have been undertaken. All the chelate ligands promote oxidative addition of methyl iodide to the square planar M(I) centers, by factors of between 30 and 50 compared to the respective [M(CO)2I2]- complexes, due to their good donor properties. Migratory CO insertion in [Rh(CO)(L-L)I2Me] leads to acetyl complexes [Rh(L-L)I2(COMe)] for which x-ray crystal structures were obtained for L-L = dppms (3a) and dppe (3b). Against the expectations of simple bonding arguments, methyl migration is faster by a factor of ca. 1500 for [Rh(CO)(dppms)I2Me] (2a) than for [Rh(CO)(dppe)I2Me] (2b). For M = Ir, alkyl iodide oxidative addition gives stable alkyl complexes [Ir(CO)(L-L)I2R]. Migratory insertion (induced at high temperature by CO pressure) was faster for [Ir(CO)-(dppms)I2Me] (5a) than for its dppe analogue (5b). Reaction of methyl triflate with [Ir(CO)(dppms)I] (4a) yielded the dimer [{Ir(CO)(dppms)(μ-I)Me}2]2+ (7), which was characterized crystallographically along with 5a and [Ir(CO)(dppms)I2Et] (6). Analysis of the x-ray crystal structures showed that the dppms ligand adopts a conformation which creates a sterically crowded pocket around the alkyl ligands of 5a, 6, and 7. It is proposed that this steric strain can be relieved by migratory insertion, to give a five-coordinate acetyl product in which the sterically crowded quadrants flank a vacant coordination site, exemplified by the crystal structure of 3a. Conformational analysis indicates similarity between M(dppms) and M2(μ-dppm) chelate structures, which have less flexibility than M(dppe) systems and therefore generate greater steric strain with the "axial" ligands in octahedral complexes. Ab initio calculations suggest an additional electronic contribution to the migratory insertion barrier, whereby a sulfur atom trans to CO stabilizes the transition state compared to systems with phosphorus trans to CO. The results represent a rare example of the quantification of ligand effects on individual steps from catalytic cycles, and are discussed in the context of catalytic methanol carbonylation. Implications for other catalytic reactions utilizing chelating diphosphines (e.g., CO/alkene copolymerization and alkene hydroformylation) are considered.

Rhodium-catalyzed reductive carbonylation of methanol

In the presence of diphosphine ligands, CH3I, and synthesis gas, rhodium catalyzes the reductive carbonylation of methanol. With diphosphine = Ph2P(CH2)3PPh2, acetaldehyde is produced in selectivities approaching 90%; the remaining product is acetic acid. The reaction rates for the rhodium-diphosphine catalysts (up to 6 M h-1) rival those for the best previously reported catalysts. More importantly, these rates are achieved at much lower temperatures (130-150°C) and pressures (ca. 1000 psi) than normally employed for this chemistry (e.g., 175-220°C, 4000-8000 psi). If ruthenium is employed as a cocatalyst, acetaldehyde is hydrogenated in situ and ethanol is produced with the same high selectivity and rate. Thus, this catalyst is readily tuned to produce either acetaldehyde or ethanol under relatively mild conditions. The five-coordinate acetyl complexes Rh(diphosphine) (COCH3) (I)2 [diphosphine = R2PYPR2, where R = Ph, p-tol, or P-ClC6H5 and Y = (CH2)2, (CH2)3, CH(CH3) (CH2)2, or (CH2)2C(CH2)2] are the only rhodium and diphosphine-containing species detected at the end of catalysis experiments. They are isolable in nearly quantitative yield and have been characterized by standard methods. These complexes can, in turn be employed successfully as catalysts (e.g., no loss in rate or selectivity) and again be isolated quantitatively. Rh[Ph2P(CH2)3PPh2](COCH 3)(I)2 reacts quantitatively with H2 (100°C, 100 psi) yielding CH3CHO and the hydride Rh[Ph2P(CH2)3PPh2](H)(I) 2. Rh[Ph2P(CH2)3PPh2](H)(I)2 is converted to Rh[Ph2P-(CH2)3PPh2](COCH 3)(I)2 upon treatment with CO in CH3OH. This reaction likely proceeds via reductive elimination of HI to form Rh(I), followed by oxidative addition of CH3I (from HI + CH3OH) and migratory CO insertion. This possibility is verified by the observation that CH3I adds to Rh(diphosphine)(CO)(I) (diphosphine = Ph2P(CH2)nPPh2, n = 2 or 3) at room temperature, yielding the transient but detectable (1H, 31P NMR; IR) complexes Rh[Ph2P(CH2)nPPh2](CO)(I) 2(CH3) (two isomers). These Rh(III) methyl complexes are converted into Rh[Ph2P(CH2)nPPh2] (COCH3)(I)2 at a rate competitive with oxidative addition. Alternatively, treating Rh[Ph2P(CH2)3PPh2] (COCH3)(I)2 with CO in CH3OH results in the catalytic formation of CH3CO2H. Analysis of products from catalytic reactions employing the labeled compounds CH313CO2H, 13CH313CHO, and 13CH3I are consistent with a reaction sequence involving conversion of CH3OH to CH3I, followed by irreversible conversion of CH3I to CH3CHO or CH3CO2H. Kinetic studies on the catalytic reaction indicate a first-order dependence on acetyl concentration and zero-order dependence on CH3I. These results are discussed in terms of a catalytic cycle wherein the acetyl complexes are involved in a rate and selectivity determining reaction with either H2 or CO.