Rhodium Carbonyl Complexes Research Articles

Oxygenation of aromatic hydrocarbons with hydrogen peroxide catalyzed by rhodium carbonyl complexes

AbstractHexanuclear rhodium carbonyl cluster, Rh6(CO)16, catalyzes benzene hydroxylation with hydrogen peroxide in acetonitrile solution. Phenol and (at lower concentration) quinone are formed with the maximum attained total yield and turnover number 17% and 683, respectively. Certain other rhodium carbonyl complexes, containing cyclopentadienyl ligands, Rh2Cp2(CO)3 and Rh3(CpMe)3(CO)3, are less efficient catalysts. Cyclopentadienyl derivatives of rhodium which do not contain the carbonyl ligands, Rh(CpMe5)(CH2CH2)2, RhCp(cyclooctatetraene) and Rh2Cp2(cyclooctatetraene) turned out to be absolutely inactive in the benzene hydroxylation. Styrene is transformed into benzaldehyde and (at lower concentration) acetophenone and 1‐phenylethanol. Copyright © 2008 John Wiley & Sons, Ltd.

Probing the Mechanism of Carbon−Hydrogen Bond Activation by Photochemically Generated Hydridotris(pyrazolyl)borato Carbonyl Rhodium Complexes: New Experimental and Theoretical Investigations

Fast time-resolved infrared (TRIR) experiments and density functional (DFT) calculations have been used to elucidate the complete reaction mechanism between alkanes and photolytically activated hydridotris(pyrazoly-1-yl)boratodicarbonylrhodium. TRIR spectra were obtained after photolysis of Rh(Tp4-tBu-3,5-Me)(CO)2 in n-heptane, n-decane, and cyclohexane and of Rh(Tp3,5-Me)(CO)2 in n-heptane and cyclohexane. Initial photolysis produces a coordinatively unsaturated, 16-electron monocarbonyl species that vibrationally relaxes to an intermediate with νCO of 1971 cm−1 in n-heptane solution (species A). DFT calculations on Rh(Tp3,5-Me)(CO)−RH (RH = C2H6, C6H12) suggest that A is the triplet state of a five-coordinate, square-pyramidal Rh(κ3-Tp3,5-Me)(CO)−RH, in which the alkane is weakly bound. Within the first 2 ns, a new transient grew in at 1993 cm−1 (species B). The calculations show that the observed species B is the singlet state of a four-coordinate Rh(κ2-Tp3,5-Me)(CO)(RH), in which the alkane is strongly bound and one pyrazolyl ring is rotated, decoordinating one N. The transient due to B grew at the same rate as A partially decayed. However, A did not decay completely, but persisted in equilibrium with B throughout the time up to 2500 ps. The ν(CO) bands due to A and B decayed at the same rate as a band at 2026 cm−1 grew in (τ ca. 29 ns, n-heptane). The latter band can be readily assigned to the final alkyl hydride products, Rh(κ3-Tp4-tBu-3,5-Me)(CO)R(H) and Rh(κ3-Tp3,5-Me)(CO)R(H) (species D). The experimental data do not allow the elucidation of which of the two alkane complexes, A or B, is C−H activating, or whether both of the complexes react to form the final product. The calculations suggest that a third intermediate (species C) is the C−H activating species, that is, the final product D is formed from C and not directly from either A or B. Species C is nominally a five-coordinate, square-pyramidal Rh(κ21/2-Tp3,5-Me)(CO)(RH) complex with a strongly bound alkane and one pyrazolyl partially decoordinated, but occupying the apical position of the square pyramid. Intermediate C is unobserved, as the calculations predict it possesses the same CO stretching frequency as the parent dicarbonyl. The unobserved species is predicted to lie on the reaction path between A and B and to be in rapid equilibrium with the four-coordinate species B.

State of Supported Rhodium Nanoparticles for Methane Catalytic Partial Oxidation (CPO): FT-IR Studies

The effect of pretreatments as well as of rhodium precursor and of the support over the morphology of Rh nanoparticles were investigated by Fourier transform infrared (FT-IR) spectroscopy of adsorbed CO. Over a Rh/alumina catalyst, both metallic Rh particles, characterized by IR bands in the range 2070-2060 cm-1 and 1820-1850 cm-1, and highly dispersed rhodium species, characterized by symmetric and asymmetric stretching bands of RhI(CO)2 gem-dicarbonyl species, are present. Their relative amount changes following pretreatments with gaseous mixtures, representative of the catalytic partial oxidation (CPO) reaction process. The Rh metal particle fraction decreases with respect to the Rh highly dispersed fraction in the order CO approximately CO/H2 > CH4/H2O, CH4/O2 > CH4 > H2. The metal particle dimensions decrease in the order CH4/O2 > H2 > CH4/H2O > CO > CO/H2. Grafting from a carbonyl rhodium complex also increases the amount and the dimensions of Rh0 particles at the catalyst surface. Increasing the ratio (extended rhodium metal particles/highly dispersed Rh species) allows a shorter conditioning process. The surface reconstruction phenomena going on during catalytic activity are related to this effect.

Rhodium(I) carbonyl complexes of mono selenium functionalized bis(diphenylphosphino)methane and bis(diphenylphosphino)amine chelating ligands and their catalytic carbonylation activity

The chelate complexes of the types ▪ ( 1) and ▪ ( 2) have been synthesized and characterized by IR and NMR spectroscopy. The lower shift of the ν(P–Se) bands and downfield shift of the 31P–{ 1H}NMR signals for both P(III) and P(V) atoms in 1 and 2 compared to the corresponding free ligands indicate chelate formation through selenium donor. 1 and 2 show terminal ν(CO) bands at 1977 and 1981 cm −1, respectively, suggesting high electron density at the metal center. The molecular structure of 2 has been determined by single-crystal X-ray diffraction. The rhodium atom is at the center of a square planar geometry having the phosphorus and selenium atoms of the chelating ligand at cis-position, one carbonyl group trans- to selenium and one chlorine atom trans- to phosphorus atom. 1 and 2 undergo oxidative addition (OA) reaction with CH 3I to produce acyl complexes ▪ ( 3) and ▪ ( 4), respectively. The kinetics of the OA reactions reveal that 1 undergoes faster reaction by about 4.5 times than 2. The catalytic activity of 1 and 2 in carbonylation of methanol was higher than that of the well known species [Rh(CO) 2I 2] − and 2 shows higher catalytic activity compared to 1.

Oxidative addition of different electrophiles with rhodium(I) carbonyl complexes of unsymmetrical phosphine–phosphine monoselenide ligands

Dimeric chlorobridge complex [Rh(CO) 2 Cl] 2 reacts with two equivalents of a series of unsymmetrical phosphine-phosphine monoselenide ligands, Ph 2 P(CH 2 ) n P(Se)Ph 2 {n = 1(a), 2(b), 3(c), 4(d)}to form chelate complex [Rh(CO)CKPnSe)] (la) (PnSe = η 2 -(P,Se) coordinated} and non-chelate complexes [Rh(CO) 2 Cl(P∼Se)] (1b-d) {P∼Se = η 1 -(P) coordinated}. The complexes 1 undergo oxidative addition reactions with different electrophiles such as CH 3 I, C 2 H 5 I, C 6 H 5 CH 2 Cl and I 2 to produce Rh(III) complexes of the type [Rh(COR)ClX(PnSe)] {where R = -C 2 H 5 (2a), X = I; R = -CH 2 C 6 H 5 (3a), X = Cl}, [Rh(CO)ClI 2 (Pnse)] (4a), [Rh(CO)(COCH3)ClI(P∼Se)] (5b-d), [Rh(CO)(COH 5 )ClI-(P∼Se)] (6b-d), [Rh(CO)(COCH2C6H5)Cl2(P∼Se)] (7b-d) and [Rh(CO)ClI 2 (P∼Se)] (8b-d). The kinetic study of the oxidative addition (OA) reactions of the complexes 1 with CH 3 I and C 2 H 5 I reveals a single stage kinetics. The rate of OA of the complexes varies with the length of the ligand backbone and follows the order la > 1b > 1c > 1d. The CH 3 I reacts with the different complexes at a rate 10-100 times faster than the C 2 H 5 I. The catalytic activity of complexes 1b-d for carbonylation of methanol is evaluated and a higher turnover number (TON) is obtained compared with that of the well-known commercial species [Rh(CO) 2 I 2 ] - .

Preparation and performance of anchored heterogenized rhodium complex catalyst for hydroformylation

In order to solve the difficult problem in separation of homogeneous catalyst from the reaction mixture, heterogenized rhodium carbonyl complex catalyst for hydroformylation of olefins was prepared by copolymerization of functionalized 3-aminopropyltriethoxysalane with tetraethoxysalane (TEOS) via the sol–gel method. The catalyst was characterized by FT-IR, X-ray photoelectron spectroscopy (XPS), ICP and N 2 absorption. The activity, selectivity and stability of this catalyst for 1-hexene hydroformylation have been examined. It was concluded the activity depended on the surface area of the catalyst matrix, which varied according to the pH in the sol–gel process. The conversion of 1-hexene reached 98.8%, with a selectivity of 99.6% of aldehydes and the n/ i ratio of 0.86 under optimized conditions. Furthermore, it showed excellent stability and reusability, the catalyst was used for six times without obvious loss of activity.

Hydroesterification versus hydroformylation–acetalization of 1-hexene catalyzed by soluble carbonylrhodium complexes of pyridine ligands

The rhodium(I) complexes, cis-[Rh(CO) 2(amine) 2](PF 6) (amine = pyridine, 2-picoline, 3-picoline, 4-picoline, 3,5-lutidine or 2,6-lutidine) dissolved in methanol under carbon monoxide atmosphere are effective catalysts for the hydroesterification and hydroformylation–acetalization of 1-hexene. In the presence of these soluble complexes, 1-hexene, CO and methanol give methyl-heptanoate and 1,1-dimethoxy-heptane as major products, and minor amounts of heptanal. The acetal product comes from the nucleophilic addition reaction of the methanol with the formed heptanal. Gaseous by-products (H 2 and CO 2) from the catalysis of the water–gas shift reaction (WGSR) are also observed. The reaction products distribution depends on the nature of the coordinated amine to the rhodium center. The effects of the reaction variables such as CO pressure, temperature, catalyst concentration, 1-hexene/Rh molar ratio and reaction medium, were also examined. These data are discussed in terms of catalytic cycles, and it is concluded that common Rh–H catalytic species are involved.

Rhodium‐Catalyzed Acylation of Vinylsilanes with Acid Anhydrides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Rhodium-Catalyzed Acylation of Vinylsilanes with Acid Anhydrides

Abstract A catalytic acylation of vinylsilane with acid anhydride is accomplished by the use of [RhCl(CO)2]2, in which the transmetalation between vinylsilane and rhodium(I) carbonyl complex plays a key role. The application of this acylation reaction to (1-acyloxyvinyl)silanes provides synthetic methods for α-acyloxy enones, α-diketones, and their derivatives.

5+1] Cocyclization of (Cyclopropylmethylene)cyclopropanes and other Vinylcyclopropanes with Carbon Monoxide Catalyzed by Octacarbonyldicobalt

Vinylcyclopropanes react with octacarbonyldicobalt stoichiometrically under mild conditions to give cyclohex-3-enones in moderate to good yields (51-75%). Catalytic amounts of the cobaltcarbonyl complex or a rhodiumcarbonyl complex also mediate [5+1] cocyclizations of vinylcyclopropanes with carbon monoxide (under CO balloon pressure) to give cyclohex-3-enones in good yields (up to 95%;).

Synthesis and structural characterization of a series of high-hydride content osmium–rhodium carbonyl complexes by the hydrogenation of arene-coordinated clusters

The reaction of [Os3Rh(mu-H)3(CO)12] with an excess amount of 4-vinylphenol (as hydride acceptor) in refluxing m-xylene, chlorobenzene or benzene yielded the three new clusters [Os5Rh2(mu-CO){eta6-C6H4(CH3)2}(CO)16] 1, [Os5Rh2(mu-CO)(eta6-C6H5Cl)(CO)16] 2 and [Os5Rh2(mu-CO)(eta6-C6H6)(CO)16] 3. The treatment of [Os3Rh(mu-H)3(CO)12] 4 in refluxing toluene with an excess amount of 4-vinylphenol afforded a new complex, [Os4Rh(mu-H)(eta6-C6H5CH3)(CO)12], which was isolated as a brown complex in 20% yield together with two known compounds, [Os5Rh2(eta6-C6H5CH3)(mu-CO)(CO)16] in 10% yield and [Os3Rh4(mu3-eta1:eta1:eta1-C6H5CH3)(CO)13] in 5% yield. Complexes 1-4 were fully characterized by IR, 1H NMR spectroscopy, mass spectroscopy, elemental analysis and X-ray crystallography. The molecular structures of compounds 1-3 are isomorphous, and only differ in the arene-derivatives that attach to the same metal core. Their metal cores can be viewed as a monocapped octahedral, in which an osmium atom caps one of the Os-Os-Os triangular faces of the Os4Rh2 metal framework. Complex 4 has a trigonal-bipyramidal metal core with a C6H5Me ligand that is terminally bound to the Rh atom that lies in the trigonal plane of the metal core. The hydrogenation of [Os5Rh2(eta6-C6H5CH3)(mu-CO)(CO)16] with [Os3(mu-H)2(CO)10] in chloroform under reflux resulted in two hydrogen-rich compounds: [Os7Rh3(mu-H)11(CO)23] 5 and [Os5Rh3Cl(mu-H)8(CO)18] 6, both in moderate yields. The reaction of [Os5Rh2(eta6-C6H5CH3)(mu-CO)(CO)16] with hydrogen in refluxing chloroform yielded a new cluster compound, [Os5Rh(mu-H)5(CO)18] 7, in 20% yield, together with a known osmium-rhodium cluster, [Os6Rh(mu-H)7(mu-CO)(CO)18], as a major compound. Clusters 5, 6, and 7 have been fully characterized by both spectroscopic and crystallographic methods. Additionally, a deuterium-exchange experiment was performed on [Os7Rh3(mu-H)11(CO)23] 5 and [Os5Rh3Cl(mu-H)8(CO)18] 6. Both the compounds proved to be able to exchange the H atom with D in the presence of D2SO4, and the absence of the hydride signal in the 1H NMR spectrum is consistent with this. Therefore, clusters 5 and 6 may serve as appropriate new hydrogen storage models.

A Ruthenium Olefin Metathesis Catalyst with a Four-Membered N-Heterocyclic Carbene Ligand

The first ruthenium olefin metathesis catalyst bearing a four-membered N-heterocyclic carbene (5) was synthesized and characterized by NMR spectroscopy and X-ray crystallography. The synthesis of a (carbene)carbonylrhodium complex (6) was also reported, allowing the study of the electronic properties of this new carbene ligand. The complex 5 was screened toward different olefin metathesis reactions, and it showed a slow reactivity.

Oxidative addition reaction of rhodium(I) carbonyl complexes of the pyridine-aldehyde ligands and their catalytic activity in carbonylation reaction

Rhodium(I) carbonyl complexes [Rh(CO) 2 ClL] ( 1 ) where L = Py-2-CHO ( a ), Py-3-CHO ( b ) and Py-4-CHO ( c ) have been synthesized and characterized by elemental analyses, IR, 1 H and 13 C NMR spectroscopy. The complexes 1 undergo oxidative addition reactions with different types of electrophiles such as CH 3 I, C 2 H 5 I, C 6 H 5 CH 2 Cl and I 2 to yield [Rh(CO)(COCH 3 )ClIL] ( 2 ), [Rh(CO)(COC 2 H 5 )ClIL] ( 3 ), [Rh(CO)(COCH 2 C 6 H 5 )Cl 2 L] ( 4 ) and [Rh(CO)ClI 2 L] ( 5 ) complexes, respectively. The kinetic study of the complexes 1 with CH 3 I reveals a two-stage kinetics and the second-stage reactions are faster than that of the first stage by about 80–100 times. The rate of reaction of 1a is higher than that of 1b and 1c . The catalytic activity of complexes 1 in carbonylation of methanol, in general, is higher (TON 800 – 1250) than that of the well-known species [Rh(CO) 2 I 2 ] − (TON 650). Rhodium(I) carbonyl complexes [Rh(CO) 2 ClL] (L = Py-2-CHO, Py-3-CHO and Py-4-CHO) have been synthesized and their oxidative reactivity towards different electrophiles like CH 3 I, C 2 H 5 I, C 6 H 5 CH 2 Cl and I 2 were studied. The catalytic activity of the complexes in carbonylation of methanol, in general, is higher than that of the well-known species [Rh(CO) 2 I 2 ] − .

Rhodium-carbonyl complexes with a quinolyl functionalized Cp-ligand: synthesis and photochemical activation

Dicarbonyl[η 5-2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadienyl]rhodium(I) ( 1) was prepared by the reaction of [Rh(CO) 2Cl] 2 with 2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadienyl-potassium. Irradiation of 1 in chloroform or dichloromethane as solvent leads to the formation of dichloro[η 5-2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadienyl]rhodium(III) ( 2). When Rh 6(CO) 16 is present, the cluster adds to the 8-quinolyl-cp-rhodium fragment and the compound [η 5-2,3,4,5-tetramethyl-1-(8-quinolyl)cyclopentadienyl]rhodium-di-μ-carbonyl-hexarhodiumtetradecacarbonyl ( 3) is formed in 65% yield. The coordination sphere of the rhodium(III) atom in compound 2 and of the rhodium(I) atom in 3 is completed by a coordination of the quinolyl moiety. This was revealed by NMR spectroscopy as well as by X-ray analyses.

Rh4(CO)12-Catalyzed Hydroformylation of Cyclopentene Promoted with HMn(CO)5. Another Example of Rh4(CO)12/HMn(CO)5 Bimetallic Catalytic Binuclear Elimination

A detailed in situ high-pressure FTIR spectroscopic study was performed to investigate the bimetallic origins of catalytic synergism in homogeneous catalysis. The reaction chosen was the homogeneous catalyzed hydroformylation of cyclopentene to cyclopentanecarboxaldehyde, starting with unmodified rhodium and manganese carbonyls as catalyst precursors in n-hexane as solvent. The spectra were analyzed by an advanced signal processing and statistical technique. Only four organometallic spectra could be found. These were RCORh(CO)4, Rh4(CO)12, HMn(CO)5, and Mn2(CO)10. A very significant increase in aldehyde formation was observed in the experiments when both rhodium carbonyl and manganese carbonyl complexes were used simultaneously. The kinetics of product formation shows a distinct linear−bilinear form in observable organometallics; k1[RCORh(CO)4][H2][CO]-1 + k2[RCORh(CO)4][HMn(CO)5][CO]-1.6. The determined activation parameters for the bilinear term were ΔH⧧ = 47 ± 8 kJ/mol and ΔS⧧ = −88 ± 28 J/(mol K). The...

Reactions of the hexaaquarhodium(III) cation with bis(benzimidazol-2-ylmethyl)methylamine and PPh 3: syntheses and properties of new hydrido- and carbonylrhodium complexes

Hexaaquarhodium(III) perchlorate has been found to be an interesting starting material for the preparation of rhodium compounds. New mononuclear hydrido- and carbonylrhodium compounds with bis(benzimidazol-2-ylmethyl)methylamine (L) and PPh 3 of the type [Rh(H)L(PPh 3) 2](ClO 4) 2 ( 1) and [Rh(CO)L(PPh 3) 2](ClO 4) ( 2) have been synthesized. The monomeric Rh(II) compound was identified as an intermediate. Complexes 1 and 2 were characterized by elemental analysis, mass spectrometry and IR, and NMR spectroscopies. The fluxional behaviour of 2 was studied by variable-temperature 1H and 31P{H} NMR experiments.

Reactions of the hexaaquarhodium(III) cation with bis(benzimidazol-2-ylmethyl)methylamine and PPh3: syntheses and properties of new hydrido- and carbonylrhodium complexes

Reactions of [Rh(H 2 O) 6 ] 3+ with bis(benzimidazol-2-ylmethyl)methylamine (L) and PPh 3 yielded novel hydrido- and carbonylrhodium compounds [Rh(H)L(PPh 3 ) 2 ](ClO 4 ) 2 ( 1 ) and [Rh(CO)L(PPh 3 ) 2 ](ClO 4 ) ( 2 ). The stdies revealed the formation of a metalloradical Rh(II) species as an intermediate and the ability of L to adopt its geometry to the electronic and geometric preferences of the metal centre. Hexaaquarhodium(III) perchlorate has been found to be an interesting starting material for the preparation of rhodium compounds. New mononuclear hydrido- and carbonylrhodium compounds with bis(benzimidazol-2-ylmethyl)methylamine (L) and PPh 3 of the type [Rh(H)L(PPh 3 ) 2 ](ClO 4 ) 2 ( 1 ) and [Rh(CO)L(PPh 3 ) 2 ](ClO 4 ) ( 2 ) have been synthesized. The monomeric Rh(II) compound was identified as an intermediate. Complexes 1 and 2 were characterized by elemental analysis, mass spectrometry and IR, and NMR spectroscopies. The fluxional behaviour of 2 was studied by variable-temperature 1 H and 31 P{H} NMR experiments.

Construction of Metal-Centered Chirality: Diastereoselective Addition of the Meerwein Reagent (Me3OBF4) to Rhodium Carbonyl Complexes Having the Cp‘-P Ligand

Reaction of the rhodium(I) carbonyl complexes [η5:η1-{3-(R)Ind-P}n=2]Rh(CO) (1; R = H (a), Et (b), Cy (c), (1‘S,2‘S,5‘R)-neomenthyl (NM) (d), (1‘R,2‘R,5‘R)-neoisomenthyl (NIM) (e)) with the Meerwein reagent (Me3OBF4) afforded the cationic rhodium(III) complexes [[η5:η1-{3-(R)Ind-P}n=2]RhMe(CO)]BF4, having metal-centered chirality, in good to excellent yields. When a bulkier substituent (R) was used, the corresponding cationic complex was obtained with higher diastereoselectivity. In the case of using an optically active substituent such as NM or NIM, complete stereodiscrimination around the rhodium center by the Meerwein reagent occurred to give the cationic complexes with 100% de.

Novel hydrodesulfurization catalysts derived from a supported rhodium carbonyl complex

Abstract The dibenzothiophene hydrodesulfurization (HDS) reactions were carried out over alumina, titania, silica and silica-alumina supported rhodium complex catalysts. First, a series of catalysts containing 1 wt.% Rh was prepared and tested. Whilst in the case of the Rh/Al 2 O 3 catalyst we did not observe any significant variation of the activity with the pretreatment, in the case of the titania, the silica and the silica-alumina supported catalysts, the pre-reduction treatment resulted in an activity twice as high as that obtained after the pre-sulfiding treatment. The use of the various supports slightly affected the overall HDS activity as well as the products selectivities. Whilst the Rh/Al 2 O 3 catalyst exhibited the highest biphenyl (BP) selectivity, the Rh/SiO 2 -Al 2 O 3 catalyst exhibited the highest dibenzothiophene conversion. The Rh supported on TiO 2 , SiO 2 and SiO 2 -Al 2 O 3 catalysts gave high cyclohexylbenzene (CHB) yields, indicating high hydrogenation abilities. Further, the effect of the Rh loading was studied on the titania and the silica supports. Unlike the other supports for which the activity stabilized for Rh loadings higher than 0.5–1.0 wt.%, the DBT conversions of the SiO 2 -supported Rh catalysts increased up to 4 wt.% Rh, exhibiting the highest HDS activity. To precisely elucidate the effect of the pre-activation method on the sulfidation state and on the HDS activity, the 4 wt.% Rh/SiO 2 catalyst was placed under HDS working conditions and [ 35 S ]DBT HDS tracer experiments were performed. We found that, whilst the amount of labile sulfur (S OA ) present on the surface of the prereduced catalyst was slightly lower than that observed for the presulfided catalyst, the labile sulfur atoms created on the prereduced catalyst exhibited a significantly greater mobility ( k RE ). This increase in sulfur mobility induced by the reduction pretreatment facilitated the active sites regeneration during the reaction, which led to an enhancement of the HDS catalytic activity.

Kinetic Evidence of an Arm-Off Mechanism in Complexes of Hemilabile Hybrid Ligands. Oxidative Addition of Methyl Iodide to the Rhodium(I) Complex [Rh(2,6-bis(benzylthiomethyl)pyridine)(CO)]PF6 via Competitive Pathways

Kinetic experiments of the oxidative addition of methyl iodide to the cationic rhodium(I) carbonyl complex [Rh(L)(CO)]PF6 (1; L = 2,6-bis(benzylthiomethyl)pyridine) forming the observable rhodium(III) methyl species [RhI(L)(CO)Me)]PF6 have been performed by FT-IR. The reaction yields the isolable rhodium acyl complex [RhI(L)(COMe)]PF6. Plots of kobs versus concentration of methyl iodide indicate that the reaction proceeds by two parallel pathways, one which is first order in complex 1 and zero order in MeI (k1) and one which is first order in complex 1 and first order in MeI (k2). The first-order pathway displays scarce dependence on the nature of the solvent (k1 (31 °C): 6.7 × 10-6 s-1, acetone; 1.1 × 10-5 s-1, dichloromethane; 1.7 × 10-5 s-1, acetonitrile), while a larger solvent effect is observed for the second-order pathway (k2 (31 °C): 6.4 × 10-6 M-1 s-1, dichloromethane; 5.9 × 10-5 M-1 s-1, acetone; 1.4 × 10-4 M-1 s-1, acetonitrile), in agreement with the dissociative and associative character of...