Rhodium Carbonyl Research Articles

Rhodium carbonyl complexes containing pyridine carboxylic acid ligands: Reactivity towards various electrophiles and catalytic activity

The complex [Rh(CO) 2Cl] 2 reacts with two molar equivalent of pyridine carboxylic acids ligands Py-2-COOH( a), Py-3-COOH( b) and Py-4-COOH( c) to yield rhodium(I) dicarbonyl chelate complex [Rh(CO) 2(L /)]( 1a) {L / = η 2-(N,O) coordinated Py-2-COO −( a / )} and non-chelate complexes [Rh(CO) 2ClL //]( 1b,c) {L // = η 1-(N) coordinated Py-3-COOH( b), Py-4-COOH( c)}. The complexes 1 undergo oxidative addition ( OA) reactions with different electrophiles such as CH 3I, C 2H 5I, C 6H 5CH 2Cl and I 2 to give penta coordinated Rh(III) complexes of the types [Rh(CO)(COR n)XL /], { n = 1,2,3; R 1 = CH 3( 2a); R 2 = C 2H 5( 3a); X = I and R 3 = CH 2C 6H 5 ( 4a); X = Cl}, [Rh(CO)I 2L /]( 5a), [Rh(CO)(COR n)ClXL //] {R 1 = CH 3( 6b,c); R 2 = C 2H 5( 7b,c); X = I and R 3 = CH 2C 6H 5 ( 8b,c); X = Cl} and [Rh(CO)ClI 2L //]( 9b,c). The complexes have been characterized by elemental analysis, IR and 1H NMR spectroscopy. Kinetic data for the reaction of 1a–b with CH 3I indicate a first order reaction. The catalytic activity of 1a–c for the carbonylation of methanol to acetic acid and its ester is evaluated and a higher turn over number (TON = 810–1094) is obtained compared with that of the well-known commercial species [Rh(CO) 2I 2] − (TON = 653) at mild reaction conditions (temperature 130 ± 5 °C, pressure 35 ± 5 bar).

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.

The Effect of Charge on CO Binding in Rhodium Carbonyls: From Bridging to Terminal CO

The structures of cationic rhodium carbonyl cluster compounds containing one to six Rh atoms are established by infrared multiple photon dissociation spectroscopy. Comparison with their well-known neutral analogues reveals that ionization of the neutral compounds destabilizes bridge bound CO ligands in Rh2(CO)8 and Rh4(CO)12, leading to cationic complexes with only terminally bound CO. The destabilization is associated with removal of charge from a highest occupied molecular orbital that is bonding with respect to bridge-bound CO. Density functional theory calculations support this conclusion. The results provide a possible insight into electronic promoter effects in catalysis.

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.

When is a Nanoparticle a Cluster? An Operando EXAFS Study of Amine Borane Dehydrocoupling by Rh4-6 Clusters

X-ray absorption fine structure (XAFS) is used to determine the structure of the rhodium cluster present during the catalyzed dehydrocoupling of amine boranes under operando conditions. We show how a variety of XAFS strategies can be used in combination with other analytical methods to differentiate homogeneous from heterogeneous systems. Analysis of the in situ XAFS spectra using a series of amine boranes (NH3BH3, R2NHBH3, and RNH2BH3 where R = methyl, isopropyl, tert-butyl, and cyclohexyl) and rhodium catalyst precursor compounds (including chloro-(1,5-cyclooctadiene)rhodium (I) dimer, bis(1,5-cyclooctadiene)rhodium (I) trifluoromethanesulfonate, chlorodicarbonylrhodium (I) dimer, dichloro(pentamethylcylcopentadienyl)rhodium (III) dimer, hexarhodium hexadecacarbonyl, and tetrarhodium dodecacarbonyl) strongly suggest that the active catalyst species for this reaction is a homogeneous rhodium complex. Rhodium clusters containing four or six rhodium atoms (Rh(4-6)) bound to amine boranes are observed as the major (>99%) rhodium containing species during and after the catalyzed anaerobic dehydrocoupling. During the later stages of the reaction a nonmetallic rhodium complex precipitates in which individual Rh(4-6) clusters likely form polymer chains ligated by the reaction products that have two or more ligating sites. The best fits of the XAFS data, using ab initio calculations of FEFF theory, show that the major rhodium species (80%) has each rhodium atom directly bound to three rhodium atoms with an observed bond distance of 2.73 A and to two boron atoms at 2.10 A. A minor (20%) rhodium species has each rhodium atom bound to four rhodium atoms with a bond distance of about 2.73 A and a single rhodium atom at a nonbonding distance of 3.88 A. No metallic rhodium was observed at any time during the anaerobic reaction.

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.

Synthesis and Electrochemistry of New Rh-Centered and Conjuncto Rhodium Carbonyl Clusters. X-ray Structure of [NEt4]3[Rh15(CO)27], [NEt4]3[Rh15(CO)25(MeCN)2]·2MeCN, and [NEt4]3[Rh17(CO)37

A reinvestigation of the redox chemistry of [Rh7(CO)16]3- resulted in the finding of new alternative syntheses for a series of previously reported Rh-centered carbonyl clusters, i.e., [H4-nRh14(CO)25]n- (n = 3 and 4) and [Rh17(CO)30]3-, as well as new species such as a different isomer of [Rh15(CO)27]3-, the carbonyl-substituted [Rh15(CO)25(MeCN)2]3-, and the conjuncto [Rh17(CO)37]3- clusters. All of the above clusters are suggested to derive from oxidation of [Rh7(CO)16]3- with H+, arising from dissociation either of [M(H2O)n]2+ aquo complexes or nonoxidizing acids. The nature of the previously reported species has been confirmed by IR, electrospray ionization mass spectrometry, and complete X-ray diffraction studies. Only the molecular structures of the new clusters are reported in some details. The ready conversion of [Rh7(CO)16]3- in [HRh14(CO)25]3- upon oxidation has been confirmed by electrochemical techniques. In addition, electrochemical studies point out that the close-packed [H3Rh13(CO)24]2- dianion undergoes a reversible monoelectronic reduction followed by an irreversible reduction. The irreversibility of the second reduction is probably a consequence of H2 elimination from a purported [H3Rh13(CO)24]4- species. Conversely, the body-centered-cubic [HRh14(CO)25]3- and [Rh15(CO)27]3- trianions display several well-defined redox changes with features of electrochemical reversibility, even at low scan rate. The major conclusion of this work is that mild experimental conditions and a tailored oxidizing reagent may enable more selective conversion of [Rh7(CO)16]3- into a higher-nuclearity rhodium carbonyl cluster. It is also shown that isonuclear Rh clusters may display isomeric metal frameworks [i.e., [Rh15(CO)27]3-], as well as almost identical metal frames stabilized by a different number of carbonyl groups [i.e., [Rh15(CO)27]3- and [Rh15(CO)30]3-]. Other isonuclear Rh clusters stabilized by a different number of CO ligands more expectedly exhibit completely different metal geometries [i.e., [Rh17(CO)30]3- and [Rh17(CO)37]3-]. The first pair of isonuclear and isoskeletal clusters is particularly astonishing in that [Rh15(CO)30]3- features six valence electrons more than [Rh15(CO)27]3-. Finally, the electrochemical studies seem to suggest that interstitial Rh atoms are less effective than Ni and Pt interstitial atoms in promoting redox properties and inducing molecular capacitor behavior in carbonyl clusters.

Reactivity of InCp* Towards Transition Metal Carbonyl Clusters: Synthesis and Structural Characterization of the Rh6(CO)16–x(InCp*)x Mixed‐Metal Cluster Compounds, x = 1–2

AbstractWith [Rh6(CO)15(InCp*)], the first example of a transition metal carbonyl cluster with a coordinated InCp* (Cp* = C5Me5) fragment in the ligand environment is reported. This cluster with direct Rh–In bonds forms in the reaction of the hexanuclear carbonyl rhodium cluster Rh6(CO)15(NCMe) with InCp* under mild conditions. This is characterized by means of IR and NMR spectroscopy and crystal structure analysis. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

Spectral Renormalization for Multi-Component Fourier Transform Infrared Absorbance Data: Importance to Multivariate Calibration and Quantitative Exploratory Chemometrics Studies

Although infrared spectroscopy is a very common analytical tool in the chemical sciences, quantitative infrared spectroscopic studies of multi-component solutions (particularly on-line or in-line studies) have been hampered by the lack of a concise and robust numerical approach. Using an inert chemical species as internal standard, the usual absorbance ratio analysis is generalized into a mathematical form that converts typical absorbance measurement A into its renormalized absorbance A(renorm), with the latter directly relating to the absolute moles rather than the concentration of the constituents. The renormalized absorbance has a number of very important properties, including (1) insensitivity to path length changes due to variations in temperature or pressure of the Fourier transform infrared (FT-IR) cell and (2) insensitivity to solution volume changes arising from reaction, chemical transport, or thermodynamic conditions. The methodology is first applied to a simple model test system to demonstrate its utility for multivariate calibration, and then re-applied to a real problem: the calibration of the rhodium carbonyl hydride HRh(CO)4, a long-sought species in organometallic chemistry and homogeneous catalysis (Angewandte Chemie Int. Ed., vol. 41, 3786 (2002)). The utility of the developed methodology for multivariate calibration and exploratory chemometric studies is demonstrated. Emphasis is placed on providing a numerical recipe for the practicing analytical chemist.

Activity of Rhodium-Catalyzed Hydroformylation: Added Insight and Predictions from Theory

We have performed a density functional theory investigation of hydroformylation of ethylene for monosubstituted rhodium-carbonyl catalysts, HRh(CO)3L, where the modifying ligand, L, is a phosphite (L = P(OMe)3, P(OPh)3, or P(OCH2CF3)3), a phosphine (L = PMe3, PEt3, PiPr3, or PPh3), or a N-heterocyclic carbene (NHC) based on the tetrahydropyrimidine, imidazol, or tetrazol ring, respectively. The study follows the Heck and Breslow mechanism. Excellent correspondence between our calculations and existing experimental information is found, and the present results constitute the first example of a realistic quantum chemical description of the catalytic cycle of hydroformylation using ligand-modified rhodium carbonyl catalysts. This description explains the mechanistic and kinetic basis of the contemporary understanding of this class of reaction and offers unprecedented insight into the electronic and steric factors governing catalytic activity. The insight has been turned into structure-activity relationships and used as guidelines when also subjecting to calculation phosphite and NHC complexes that have yet to be reported experimentally. The latter calculations illustrate that it is possible to increase the electron-withdrawing capacity of both phosphite and NHC ligands compared to contemporary ligands through directed substitution. Rhodium complexes of such very electron-withdrawing ligands are predicted to be more active than contemporary catalysts for hydroformylation.

Quantum-chemical study of donor-acceptor interactions in rhodium(I) carbonyl carboxylate complexes with phosphine ligands

The DFT B3LYP method was used to optimize the geometries, calculate the IR spectra, and analyze the electronic structures of carbonyl(carboxylato)(phosphine)rhodium(I) complexes, namely, trans-[Rh(Cl)(CO)(PPh3)2], trans-[Rh(OCOR)(CO)(PPh3)2] (R = H, CH3, and CF3), and trans-[Rh(OCOH)(CO)(PX3)2], and free PX3 molecules (X = H, F, CH3, i-Pr, Cy, and Ph). A linear correlation between v(CO) in the IR spectra of trans-[Rh(OCOH)(CO)(PX3)2] and the HOMO energy of the free PX3 molecule was found for phosphines with nonaromatic substituents X. It was concluded that the electronic state of the CO group is mainly determined by the σ-donor properties of phosphines. The distinctive features of the electronic structure of triphenylphosphine are discussed.

On the origin of diastereofacial selectivity in the interaction of β-pinene with rhodium carbonyl: A density functional study

In this work we have performed electronic structure calculations at the density functional theory (DFT) level in order to understand the structural, electronic and energetic factors involved in the diastereofacial selectivity in the interaction of β-pinene with [HRh(CO) 3], used as a model for the unmodified rhodium catalyst of hydroformylation. Analysis of the nature of the metal–ligand interaction of the π-complexes revealed that the catalyst coordination through the more sterically hindered face of β-pinene generates a stronger π-complex, however, being thermodynamically less stable due to the smaller steric hindrance for the catalyst coordination on the other face of the olefin. Our energetic results show that despite the coordination of the olefin to the more sterically hindered face being thermodynamically less favorable, the lower activation energy (8.5 kcal mol −1), the higher stability of the metal–alkyl product (−10.1 kcal mol −1) and the absence of an isomerization pathway for this coordination mode, are responsible for the dramatic preference for this pathway, observed experimentally.

Structure of Adsorbed Organometallic Rhodium: Model Single Atom Catalysts

We have determined the structure of a complex rhodium carbonyl chloride [Rh(CO)2Cl] molecule adsorbed on the TiO2(110) surface by the normal incidence x-ray standing wave technique. The data show that the technique is applicable to reducible oxide systems and that the dominant adsorbed species is undissociated with Rh binding atop bridging oxygen and to the Cl found close to the fivefold coordinated Ti ions in the surface. A minority geminal dicarbonyl species, where Rh-Cl bond scission has occurred, is found bridging the bridging oxygen ions forming a high-symmetry site.

Evaluation of C4 diphosphine ligands in rhodium catalysed methanol carbonylation under a syngas atmosphere: synthesis, structure, stability and reactivity of rhodium(i) carbonyl and rhodium(iii) acetyl intermediates

The carbonylation of methanol to acetic acid is a hugely important catalytic process, and there are considerable cost and environmental advantages if a process could be designed that was tolerant of hydrogen impurities in the CO feed gas, while eliminating by-products such as propionic acid and acetaldehyde altogether. This paper reports on an investigation into the application of rhodium complexes of several C(4) bridged diphosphines, namely BINAP, 1,4-bis(diphenylphosphino)butane (dppb), bis(diphenylphosphino)xylene (dppx) and 1,4-bis(dicyclohexylphosphino)butane (dcpb) as catalysts for hydrogen tolerant methanol carbonylation. An investigation into the structure, reactivity and stability of pre-catalysts and catalyst resting states of these complexes has also been carried out in order to understand the observations in catalysis. Rh(I) carbonyl halide complexes of each of the ligands have been prepared from both [Rh(2)(CO)(4)Cl(2)] and dimeric mu-Cl-[Rh(L)Cl](2) complexes. These Rh(I) carbonyl complexes are either dimeric with bridging phosphine ligands (dppb, dcpb, dppx) or monomeric chelate complexes. The reaction of the complexes with methyl iodide at 140 degrees C has been studied, which has revealed clear differences in the stability of the corresponding Rh(III) complexes. Surprisingly, the dimeric Rh(I) carbonyls react cleanly with MeI with rearrangement of the diphosphine to a chelate co-ordination mode to give stable Rh(III) acetyl complexes. The Rh acetyls for L=dppb and dppx have been fully characterised by X-ray crystallography. During the catalytic studies, the more rigid dppx and BINAP ligands were found to be nearly 5 times more hydrogen tolerant than [Rh(CO)(2)I(2)](-), as revealed by by-product analysis. The origin of this hydrogen tolerance is explained based on the differing reactivities of the Rh acetyls with hydrogen gas, and by considering the structure of the complexes.

(Acetylacetonato)carbonyl(dicyclohexylphenylphosphine)rhodium(I)

In the title complex, [Rh(acac)(CO)(PCy2Ph)] (acac = acetyl­acetonate, Cy = cyclo­hexyl) or [Rh(C5H7O2)(CO)(C18H27P)], the Rh atom is coordinated by one P [Rh—P = 2.2424 (9) A], two O [Rh—O = 2.0783 (17) and 2.0411 (18) A] and one C [Rh—C = 1.797 (3) A] atoms in a slightly distorted square-planar geometry. The bite angle O—Rh—O is 88.20 (6)° and the calculated effective cone angle (θE) for the dicyclo­hexyl­phenyl phosphine is 163°.

Rhodium catalyzed hydroformylation of 1-octene in microemulsion: comparison with various catalytic systems

In this work, we describe how addition of alkylpolyglycol ether type nonionic surfactant affects the hydroformylation of 1-octene in the presence of phosphine modified rhodium catalyst. Influence of different process parameters such as ligand excess and amount of surfactant on the reaction rate and selectivity were discussed. Direct comparison of microemulsion systems with classic processes was achieved by performing the reactions under comparable homogeneous and biphasic conditions. Thus, the experiments were carried out using catalysts such as unmodified rhodium carbonyl HRh(CO)4 and HRh(CO)(PPh3)3 in homogeneous system, Rh–TPPTS complex in two-phase system and in association with co-solvent.

Rh(I)-catalyzed CO gas-free carbonylative cyclization of organic halides with tethered nucleophiles using aldehydes as a substitute for carbon monoxide

The CO gas-free carbonylative cyclization of organic halides, with tethered nitrogen, oxygen, and carbon nucleophiles, with aldehydes as a substitute for carbon monoxide can be achieved in the presence of a catalytic amount of a rhodium complex. The reaction involves the decarbonylation of the aldehyde by the rhodium catalyst, and the successive carbonylation of an organic halide utilizing the rhodium carbonyl that is formed in situ. Aldehydes having electron-withdrawing groups showed a higher ability to donate the carbonyl moiety.

A theoretical investigation of the activation of propane by a rhodium catalyst

In this work, we report a theoretical study of the activation of propane by cyclopentadienyl carbonyl rhodium, (Cp)Rh(CO), in order to investigate the selectivity of the activation process. Møller–Plesset perturbation theory up to fourth-order (MP4(SDTQ)) and PBE density functional were used along with coupled-cluster single point calculation on the MP2 optimized geometry (CCSD//MP2) for some processes. It was found that the PBE functional was found particular suitable for the calculation of structural parameters and thermal energy correction. The MP3 and PBE results were found in excellent agreement with the CCSD//MP2 results. According to our calculations, there is no kinetic or thermodynamic discrimination, which would lead to a preferable pathway for the C–H bond activation, with the Gibbs free energy differences involved in the two pathways studied, within 1–2 kcal mol −1.

The combination of deconvolution and density functional theory for the mid-infrared vibrational spectra of stable and unstable rhodium carbonyl clusters

Geometrical optimization and frequency calculations on [HRh(CO) 4] were carried out using density functional theory methods with the B3LYP, PBE and B3PW91 functionals in conjunction with the LanL2DZ and DGDZVP basis sets. The accuracy of each calculation was verified by comparing the predicted and the experimentally obtained deconvoluted mid-infrared experimental C O stretching frequencies. The use of the density functional PBE with DGDZVP as the basis set was found to be the most accurate. The same method was then applied to [(C 2H 5)CORh(CO) 4], [Rh 2(CO) 6(μ-CO) 2], [Rh 4(CO) 9(μ-CO) 3] and [Rh 6(CO) 12(μ 3-CO) 4]. Again, vibrational spectral patterns and relative band intensities were in very good agreement with those experimentally observed after BTEM deconvolution. The only inconsistency was a constant shift in the predicted wavenumber assignments of ca. 1.5% for the terminal carbonyl stretching modes. In addition, the optimized geometries were also in good agreement with available X-ray structures of isolatable [Rh 4(CO) 9(μ-CO) 3] and [Rh 6(CO) 12(μ 3-CO) 4]. DFT not only proved to be a valuable tool in validating and confirming the structure of the reactive and unstable species but it also allowed better assignment of the observed spectra especially when vibrational modes were overlapping. The combination of advanced multi-component deconvolution, like band-target entropy minimization (BTEM), with DFT spectral prediction appears to have considerable potential for exploratory in situ studies of reactive rhodium carbonyl systems.

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.