Rhodium Carbonyl Research Articles

ChemInform Abstract: Rhodium Carbonyl-Catalyzed Carbonylation of Unsaturated Compounds. Part 5. Cross-Hydrocarbonylation of 1-Alkyne and Ethylene by Rhodium Carbonyl Catalyst Modified with Phosphines.

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ChemInform Abstract: Rhodium-Catalyzed Carbonylation of Acetylenes Under Water-Gas Shift Reaction Conditions. Selective Synthesis of Furan-2(5H)-ones.

Rhodium-catalyzed carbonylation of acetylenes was studied. Under water-gas shift reaction conditions, internal acetylenes are selectively carbonylated to 3,4-disubstituted furan-2(5H)-ones (2). Use of D 2 O gave 5,5-dideuteriofuran-2(5H)-one (3), which indicates that the hydrogen comes from water. Use of molecular hydrogen in place of water gave hydroxymethylated product 4 and stilbene 5, and no furanone was obtained, indicating that water-gas shift reaction conditions are indespensable for the formation of furanones. As catalysts, rhodium carbonyl clusters such as Rh 4 (CO) 12 and Rh 6 (CO) 16 are the best among the transition-metal complexes tested. The presence of amines is essential for the selective synthesis of furanones. Effects of additives, solvents, and the pressure of carbon monoxide were examined

ChemInform Abstract: Liquid Polymer Catalyst Immobilized on Polymer-Coated Silica: Application to Hydroformylation.

α,ω-Bis(diphenylphosphino)-poly(ethylene glycol-400) and its rhodium carbonyl complex have been attached to a poly(2-hydroxyethyl methacrylate) network coating on porous silica; the supported catalytic liquid polymer phase thus obtained has been used in the hydroformylation of ethyl undec-10-enoate.

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.

Synthesis of a rhodium(I) carbonyl complex with a chiral aminodiphosphine ligand and its immobilization onto aminopropyl functionalized silica gel

The reaction of [Rh(CO)2(µ-Cl)]2 with two molar equivalents of a chiral ligand, (R)-N,N-bis(2-diphenylphosphinoethyl)-1-phenylethylamine(PNP*) yield a mono-carbonyl complex, [Rh(CO)Cl(η2-P,P-PNP*)] (1), in which the potentially tridentate PNP* ligand coordinates in a bidentate fashion through P,P bonding. The complex was characterized by elemental analysis, FAB mass, IR, UV-Vis, 1H- and 31P{1H}-NMR spectroscopy. Variable temperature (223–298 K) 31P{1H}-,NMR spectra of 1 showed a mixture of cis and trans isomers in the solution with the trans predominating at room temperature and the cis at lower temperature. Complex 1 was immobilized on silica through axial coordination of amine from 3-aminopropyltriethoxysilane functionalized silica. The immobilized materials were characterized by elemental analysis (N2), FTIR, DTA–TGA, N2-adsorption, XRD, and SEM analysis.

Rhodium-Catalyzed Reductive Allylation of Conjugated Aldehydes with Allyl Acetate

Reductive allylation of aryl and alkenyl aldehydes with allyl acetate catalyzed by the ionic diamine carbonyl rhodium complex, [Rh(TMEDA)(CO)(2)][RhCl(2)(CO)(2)], under a carbon monoxide atmosphere afforded the corresponding homoallylic alcohols in good isolated yields.

Carbonyl Complexes of Rhodium with N-Donor Ligands: Factors Determining the Formation of Terminal versus Bridging Carbonyls

Cationic rhodium carbonyl complexes supported by a series of different N3- and N4-donor ligands were prepared, and their ability to form carbonyl-bridged species was evaluated. Complex [Rh(κ3-bpa)(cod)]+ (1+) (bpa = bis(2-picolyl)amine, cod = cis,cis-1,5-cyclooctadiene) reacts with 1 bar of CO to form a tris-carbonyl-bridged species [Rh2(κ3-bpa)2(μ-CO)3]2+ (22+), which in solution slowly decomposes to the terminal monocarbonyl complex [Rh(κ3-bpa)(CO)]+ (3+). Similar conditions lead to direct formation of a terminal monocarbonyl species, [Rh(κ3-Bu-bpa)(CO)]+ (5+), from [Rh(κ3-Bu-bpa)(cod)]+ (4+) (Bu-bpa = N-butylbis(2-picolyl)amine). Treatment of 4+ with 50 bar of CO leads to only partial conversion (∼15%) to the tris-carbonyl-bridged species [Rh2(κ3-Bu-bpa)2(μ-CO)3]2+ (62+). Stabilization of tris-carbonyl bridges can be achieved by cooperative binding. Tethering two bpa moieties with a propylene linker allows cooperative CO binding to [(CO)Rh(μ-(bis-κ3)tppn)Rh(CO)]2+, producing the tetranuclear complex [R...

Reactions of rhodium carbonyl clusters with heterobidentate ligands. Synthesis and structural characterization of the Rh6(CO)15[(C6H5)2PC6H4N(CH3)2] and {Rh6(CO)15[(C6H5)2PC6H4NH(CH3)2]}[GaX4] cluster compounds

The reaction of heterobidentate 4-(dimethylamino)phenyldiphenylphosphine with labile cluster Rh6(CO)15(NCMe) yielding a new monosubstituted cluster Rh6(CO)15(Ph2PC6H4NMe2) was described. The reactions of the resulting cluster with GaX3 compounds were studied. The structure of all obtained compounds was completely characterized both in a solid phase and in a solution by X-ray diffraction analysis, mass spectrometry, and IR and polynuclear NMR spectroscopy.

Coordination chemistry with phosphine and phosphine oxide-substituted hydroxyferrocenes

New unsymmetrical hydroxyferrocenes were synthesised from dibromoferrocene. The oxygen heteroatom was introduced via lithiation and quenching with bis-trimethylsilylperoxide followed by hydrolysis to unmask the hydroxyl functionality. The coordination chemistry of 1'-(diphenylphosphino)-1-hydroxyferrocene 2 was explored with palladium and rhodium precursors. A dinuclear palladium methyl complex with bridging ferrocenyloxo groups was obtained from the reaction between 2 and (cyclooctadiene)methylchloropalladium(II). With tetracarbonyldichlorodirhodium(I), two complexes were isolated. The major product was a bis ligand cis phosphine ligated complex with one ligand bound in a chelating mode and one with a pendant hydroxyl group. A minor product was crystallographically characterised as a dinuclear ferrocenyloxo-bridged rhodium carbonyl complex. The coordination chemistry of 2 and the corresponding phosphine oxide 3 was examined with group 4 metals and the resulting complexes examined as ethylene polymerisation catalysts. The ligands were found to bind in either a chelating fashion or with pendant phosphine donors. In all cases, low to moderately active ethylene polymerisation catalysts were found. The catalysts were very unstable and catalyst residues were observed in the isolated polymer indicating a short catalyst lifetime.

Highly selective silylformylation of internal and functionalised alkynes with a cationic dirhodium(II) complex catalyst

The tetracationic complex [Rh 2(MeCN) 2(Naft) 4](BF 4) 4 (Naft = μ-1,8-naphthyridine) was found to be an efficient catalyst for the silylformylation of internal and functionalised alkynes to yield useful synthetic intermediates. The complex exhibits an unprecedented chemoselectivity towards alkyne silylformylation instead of simple hydrosilylation, as well as a good stereoselectivity. The catalytic efficiency of the complex is markedly superior compared to that of previously reported catalysts such as [ Rh + C 7 H 8 BPh 4 - ] or Rh 4(CO) 12; incidentally, the performance of the latter catalyst was found to vary dramatically with its shelf-life, which indicates that the catalyst evolves with ageing towards other species, most notably higher nuclearity rhodium carbonyl clusters, which are more chemoselective towards silylformylation. Preliminary results on the determination of the catalytically active species in the case of complex [Rh 2(MeCN) 2(Naft) 4](BF 4) 4 indicate that the complex is reduced in situ to a dirhodium(I) species which maintains the dimeric, lantern-shaped structure.

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.

High-yield syntheses of [Rh 7(CO) 16] 3− and [Rh 14(CO) 25] 4− working in ethylene glycol solution under 1 atm of CO

The anionic rhodium carbonyl clusters [Rh 7(CO) 16] 3− and [Rh 14(CO) 25] 4− can be easily prepared by a new simple and high yield one-pot synthesis starting from RhCl 3· nH 2O dissolved in ethylene glycol and involving two steps: (i) treatment of RhCl 3· nH 2O under 1 atm of CO at 50 °C to give [Rh(CO) 2Cl 2] −; (ii) addition of a base (CH 3CO 2Na or Na 2CO 3) followed by reductive carbonylation under 1 atm of CO at an adequate temperature (50 °C for [Rh 7(CO) 16] 3−; 150 °C for [Rh 14(CO) 25] 4−). These new syntheses are more convenient than those previously reported, especially since such clusters are not accessible via silica surface-mediated reactions. This different behavior is due to the particular stabilization on the silica surface and under 1 atm of CO of an anionic carbonyl cluster, called A, which does not allow the formation of a higher nuclearity carbonyl cluster, called B, which was shown to be the key-intermediate in the synthesis of [Rh 14(CO) 25] 4− working in ethylene glycol solution. Although it was not possible to isolate crystals of A and B suitable for X-ray structural determination, a combination of cyclovoltammetry, one of the few examples so far available of the use of this technique for anionic rhodium carbonyl clusters, infrared spectroscopy and elemental analyses suggest that A and B are probably the never reported [Rh 7(CO) 14] − and [Rh 15(CO) 28] 3− clusters, respectively. In particular the tentative formulation of the two clusters was carried out by a non-conventional method based on the existence of a linear correlation between carbonyl frequencies of the main band and the [(charge/Rh atoms)/CO number] ratio.

Synthesis of rhodium–carbonyl complexes bearing a novel P,N-chelating ligand of Schiff-base type

Schiff-base type N,P-chelating ligands, phosphorus analogues of imino–anilido ligands, were designed and synthesized as a new type of ligands toward transition metals, and the rhodium–carbonyl complexes bearing the novel imino–phosphido and phosphaalkenyl-anilido ligands were synthesized as stable crystalline compounds. Their structures were definitively revealed by X-ray crystallographic analysis, showing the unique electronic features of the ligands. In addition, the effective trans-influence of the phosphorus atom was suggested on the basis of the structural parameters and spectroscopic features of the isolated complexes.

Carbonyl rhodium(I) complexes containing (H)PNX (X = O or N) ligands deriving from natural aminoacid–amides. Synthesis, X-ray structure and spectroscopic characterization

The polyfunctional (H)PNX (X = O or N) ligands 1 and 2 react with [Rh(CO) 2Cl] 2 to give the corresponding chloro carbonyl complexes {Rh[κ 2-(H)PN](CO)Cl} ( 1a and 2a), where the neutral ligands coordinate in a κ 2-PN bidentate fashion, the square planar coordination being completed by the CO trans to N and the chloride trans to P. In chloroform solution 1a maintains its original structure, while 2a partially transforms into the cationic species {Rh[κ 3-(H)PNO](CO)}Cl. The chloroform solutions of 1a and 2a react with AgPF 6 to give the purely cationic species {Rh[κ 3-(H)PNO](CO)}PF 6 ([ 1a] + and [ 2a] +), while addition of Et 3N originates the neutral species {Rh[κ 3-PNN′](CO)} ( 1b and 2b). All the complexes have been characterized by microanalysis, IR, 1H NMR as well as 31P{ 1H} NMR spectroscopy. The X-ray structures of ligand 1 and complex 1b are also reported.

Reaction of a rhodium(I) carbonyl complex of a para-dimethylaminophenyl substituted diphosphine with methyl iodide and hydrogen iodide

Reaction of [Rh(CO) 2](μ-Cl)] 2 with bis-1,2-(di{4 -dimethylaminophenyl)phosphino-ethane (L) gives the monomeric Rh(I) complex of type cis-[RhCl(L)(CO)] that was separated from a side product of type [Rh(L) 2]Cl, and characterised by X-ray crystallography. This complex reacts with methyl iodide at high temperature to give the Rh(III) acetyl complex, [Rh(I) 2(C(O)Me)(L)], which was also structurally characterised by X-ray crystallography. There is no sign of quaternisation of the dimethylamino groups under these conditions. This complex is soluble in organic solvent and insoluble in the polar media used in methanol carbonylation (AcOH/H 2O/MeOH). However, in the presence of HI, this complex is readily soluble in AcOH/H 2O/MeOH, in contrast to [Rh(I) 2(C(O)Me)(dppe)] and most other Rh-acetyl complexes of diphosphine ligands.

Structure, Activity, and Stability of Triphenyl Phosphine-Modified Rh/SBA-15 Catalyst for Hydroformylation of Propene: A High-Resolution Solid-State NMR Study

A ligand (triphenyl phosphine, PPh3)-modified heterogeneous PPh3−Rh(CO)/SBA-15 catalyst and supported Wilkinson complex HRh(CO)(PPh3)3/SBA-15 catalyst were prepared and examined in the hydroformylation of propene. Heterogeneous PPh3−Rh(CO)/SBA-15 catalyst showed much higher activity and stability in this reaction. Multinuclear 1H, 29Si, 31P, and 17O MAS NMR and two-dimensional 17O MQ MAS NMR together with XRD and N2 adsorption were employed to study the local structures of these two catalysts. Quantitative 1H and 29Si MAS NMR and qualitative one- and two-dimensional 17O MAS and MQ MAS NMR indicate that in the presence of CO the silanols on the surface of SBA-15 can react with rhodium carbonyls to form the Si−O−Rh bonds at the interface between the catalyst and the support. 31P MAS NMR spectra demonstrate a similar Wilkinson complex structure is produced on the heterogeneous PPh3−Rh(CO)/SBA-15 catalyst. The formation of Si−O−Rh bonds at the interface may immobilize the Rh complex during the long reaction. These may be correlated to the higher performances of heterogeneous PPh3−Rh(CO)/SBA-15 catalyst in propene hydroformylation.

Activation of Carbon Monoxide by (Me3tpa)Rh and (Me3tpa)Ir

Cationic iridium and rhodium carbonyl complexes supported with the tetradentate N-donor ligand Me3tpa (Me3tpa = N,N,N-tri(6-methyl-2-pyridylmethyl)amine) were synthesized. Their structures were investigated using X-ray diffraction, NMR, and IR, and their redox properties were probed using cyclic voltammetry and EPR spectroscopy. Iridium forms a trigonal bipyramidal 18 VE biscarbonyl complex, while rhodium forms a square-planar 16 VE monocarbonyl species. In both compounds the Me3tpa ligand coordinates in a κ3 rather than the expected κ4 mode and is fluxional on the NMR time scale. Complex [Ir(κ3-Me3tpa)(CO)2]PF6 (2+) reacts at room temperature with methanol and water to form the methoxycarbonyl iridium compound [Ir(κ3-Me3tpa)(CO)(H)(COOMe)]PF6 (4+) and the hydroxycarbonyl iridium compound [Ir(κ3-Me3tpa)(CO)(H)(COOH)]PF6 (5+), respectively. The hydroxycarbonyl iridium complex 5+ is not stable and decomposes to bis-hydride iridium complex [Ir(κ3-Me3tpa)(CO)(H)2]PF6 (6+), thus illustrating subsequent steps o...

Mechanistic Insights into the Rhodium-Catalyzed Intramolecular Ketone Hydroacylation

[Rh((R)-DTBM-SEGPHOS)]BF(4) catalyzes the intramolecular hydroacylation of ketones to afford seven-membered lactones in large enantiomeric excess. Herein, we present a combined experimental and theoretical study to elucidate the mechanism and origin of selectivity in this C-H bond activation process. Evidence is presented for a mechanistic pathway involving three key steps: (1) rhodium(I) oxidative addition into the aldehyde C-H bond, (2) insertion of the ketone CO double bond into the rhodium hydride, and (3) C-O bond-forming reductive elimination. Kinetic isotope effects and Hammett plot studies support that ketone insertion is the turnover-limiting step. Detailed kinetic experiments were performed using both 1,3-bis(diphenylphosphino)propane (dppp) and (R)-DTBM-SEGPHOS as ligands. With dppp, the keto-aldehyde substrate assists in dissociating a dimeric precatalyst 8 and binds an active monomeric catalyst 9. With [Rh((R)-DTBM-SEGPHOS)]BF(4), there is no induction period and both substrate and product inhibition are observed. In addition, competitive decarbonylation produces a catalytically inactive rhodium carbonyl species that accumulates over the course of the reaction. Both mechanisms were modeled with a kinetics simulation program, and the models were consistent with the experimental data. Density functional theory calculations were performed to understand more elusive details of this transformation. These simulations support that the ketone insertion step has the highest energy transition state and reveal an unexpected interaction between the carbonyl-oxygen lone pair and a Rh d-orbital in this transition state structure. Finally, a model based on the calculated transition-state geometry is proposed to rationalize the absolute sense of enantioinduction observed using (R)-DTBM-SEGPHOS as the chiral ligand.

Binuclear homoleptic rhodium carbonyls: Structures, energetics, and vibrational spectra

The binuclear homoleptic rhodium carbonyls Rh2(CO)n (n = 8, 7, 6, 5) have been examined theoretically. Three energetically low-lying equilibrium structures of Rh2(CO)8 were found, i.e., one doubly bridged C2v singlet structure and two unbridged singlet structures with D(3d) and D(2d) symmetry. The doubly bridged structure is the global minimum predicted to lie 3.4 kcal/mol below the D(2d) structure and 6.4 kcal/mol below the D(3d) structure. For Rh2(CO)7 the global minimum is either a singlet C2v unbridged structure or a singlet doubly bridged C(s) structure within 1.8 kcal/mol depending upon the theoretical method. For Rh2(CO)6, the global minimum is either a singlet doubly bridged D(2) structure or a singlet unbridged D(2d) structure depending upon the method. Triplet structures for Rh2(CO)7 and Rh2(CO)6 are predicted to be of high energies relative to the low energy singlet structures. For Rh2(CO)5 the C2v singlet singly bridged structure lies below the C2 or C2v triplet structures.

A novel hemilabile calix[4],quinoline-based P,N-ligand: coordination chemistry and complex characterisation

The synthesis of the calix[4]arene-based P,N-ligand 3 (5,11,17,23-tetra-tert-butyl-25-[(2-quinolylmethyl)oxy]-26,27,28-(mu3-phosphorustrioxy)calix[4]arene), in which the nitrogen atom-containing moiety has been introduced at the lower rim of the cavity prior to P-functionalisation, is described and its coordination properties investigated. In the crystal structure, the calix[4]-cavity adopts a cone conformation with an exo orientation of the phosphorus lone pair enabling P-N chelation. 1H, 13C, 31P and 1H{15N} HMQC NMR spectra indicated that, in complexes [PdCl(CH3)(3)] (4) and [Rh(CO)Cl(3)] (5), ligand 3 coordinates in a chelating fashion, while in cis-[PtC12(3)2] (6) and [Rh(acac)(CO)(3)] (7) it behaves as a monodentate ligand, coordinating via the phosphorus atom only. X-Ray crystal structure determinations were performed for [PdCl(CH3)(3)] (4) and cis-[PtCl2(3)2] (6). The cationic Pd complex [Pd(CH3)(CH3CN)(3)][PF5] (8) was found to be active in a CO/ethylene copolymerisation reaction. Good selectivities were observed for the Pd-catalysed allylic alkylation of cinnamyl acetate with in situ prepared catalysts. [Rh(acac)(CO)2] modified with ligand 3 catalyses the hydroformylation of 1-octene with low selectivities towards linear aldehydes. High-pressure NMR experiments on the hydrido carbonyl rhodium(3) were inconclusive, different species were formed.