Formation of anionic carbonylrhodium complexes from Wilkinson's complex under conditions of hydroformylation of formaldehyde

The compositions and the dynamics of transformations of carbonylrhodium complexes formed from Wilkinson's complex, RhCl(PPh₃)₃, dissolved in mesitylene—N,N-dimethylacetamide (DMAA) mixtures in which the DMAA concentration varied from 0 to 100 %, in an atmosphere of synthesis gas = 6 MPa,T=373 K) were investigatedin situ by IR spectroscopy. The anion complexes, [Rh(CO)₂(PPh₃) _x (DMAA) _y ]^– (x=1, 2;y=1, 0) and [Rh(CO)₄]^–, which are the centers of formaldehyde hydroformylation, are produced in noticeable quantities when 100 % DMAA is used as a solvent. Separate steps of the formation of anionic complexes from RhCl(PPh₃)₃ have been identified. Under the conditions of hydroformylation of formaldehyde, CH₂O participates in the formation of the anionic complexes, along with DMAA.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 863–866, May, 1995.     

Transformations of formaldehyde and glycolaldehyde during the hydroformylation of formaldehyde in the presence of rhodium catalysts

Hydroformylation of formaldehyde to give glycolaldehyde (GA) in the presence of RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂, or the RhCl₃ + PPh₃ system inN,N-dimethylacetamide was studied. The hydroformylation is accompanied by the Cannizzaro-Tishchenko reaction, condensation of CH₂O with GA to give C₃-C₁₆ polyoxyaldehydes (POA), and dimerization of GA. The formation of POA, which probably occurs through coordination of GA with a Rh atom, predominates among the side reactions. The optimum conditions for hydroformylation of CH₂O were found to be: RhCl₃ + PPh₃ as the catalyst,T 383 K, 12MPa, [H₂O] 1.8 mol L^–1, [Rh] 2.5 · 10^–3 g-at. L^–1, and [CH₂O] 0.03 g L^–1. At a substrate conversion of 62–67 %, the selectivity of GA formation reaches 96 %, and the yield is 60–65 %.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 1, pp. 75–78, January, 1995.     

Reaction of formaldehyde with the Wilkinson complex in the presence of carboxylic acid amides

N,N-Dimethylacetamide and N, N-dimethyformamide react with RhCl(PPh₃)₃ with displacement of PPh₃ and the formation of a complex with the amide. Formamide and N-propylacetamide do not form similar complexes under similar conditions. In contrast to the reaction of RhCl(PPh₃)₃, which leads to the formation of RhCl(CO)(PPh₃)₂ due to decarbonylation of CH₂O, stabilization of the ₂-CH₂O form of the CH₂O coordinated with rhodium is likely in the reaction of formaldehyde with a rhodium complex containing an N-bonded amide. Under the conditions of hydroformylation of CH₂O in a solution of the Wilkinson complex in an unsubstituted amide the dominating pathway of the transformation of formaldehyde is its reaction with the solvent or the ammonia formed via decarbonylation of the unsubstituted amide.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2670–2673, December, 1989.     

[RhCl(CO)(PPh3)]2. A precursor for the synthesis of cationic rhodium complexes with nitrogen donor ligands

Summary The use of [RhCl(CO)(PPh₃)]₂ as a precursor for the synthesis of complexes of the types [Rh(CO)L₂(PPh₃)]A (A = [ClO₄]^– or [BPh₄]^–; L = pyridine type ligand) and [Rh(CO)(L-L)(PPh₃)]A (A = [ClO₄]^– or [BPh₄]^–; L-L = bidentate nitrogen donor) and the preparation of several complexes of the types [Rh(CO)L(PPh₃){P(p-RC₆H₄)₃}]BPh₄ and [Rh(CO)(phen)(PPh₃){P(p-RC₆H₄)₃}]A (A = [ClO₄]^– or [BPh₄]^–; R = H or Me) is described.Author to whom all correspondence should be directed.     

Synthesis,stability and reactivity of cationic carbonyl complexes of rhodium(I)

Summary Trans-[RhCl(CO)L₂] (L = PPh₃, AsPh₃ or PCy₃) react with AgBF₄ in CH₂Cl₂ to give the novel species [Rh-(CO)L₂]⁺ [BF₄]^–.nCH₂Cl₂ (n = 1/2 or 1 1/2) (1–3), which we believe to be stabilised by weak solvent interaction. The corresponding stibine compound cannot be isolated by the same process, instead [Rh(CO)₂(SbPh₃)₃]⁺ [BF₄]^– (7) is formed when the reaction is carried out in the presence of CO. When reactions designed to prepare [Rh(CO)L₂]⁺ [BF₄]^– are performed in the presence of CO, or [Rh(CO)L₂]⁺ [BF₄]^– complexes are reacted with CO, [Rh(CO)₂L₂]⁺ [BF₄]^– (L = PPh₃, AsPh₃ or PCy₃) (4–6) are formed. If Me₂CO is used as solvent in the preparation of [Rh(CO)L₂]⁺ [BF₄]^– (L = PPh₃ or AsPh₃), then the products are the four-coordinate [Rh(CO)L₂-(Me₂CO)]⁺ [BF₄]^– (8,9) species. The complexes have been characterised by i.r., ³¹P and ¹H n.m.r. spectroscopy and elemental analyses.     

Reactions of cationic rhodium(I) carbonyl compounds with nucleophiles to form alkoxo,carboalkoxy and carboxylato complexes. Part II

Summary The rhodium(I) carbonyl compounds [Rh(CO)L₂2] [BF₄]. 1/2CH₂Cl_nn2 (L = PPh₂ or AsPh₃) react with the nucleophiles OMe⁻, RCOO⁻ (R = Me, Et) under nitrogen to form [Rh(OR)(CO)L₂] (1)–(2) and [Rh(OOCR)(CO)L₂] (7)–(₁₀), respectively. Addition of [Rh(CO)₂(PPh₃)₂]-[BF ₄] to OMe⁻ under nitrogen produces [Rh(COOMe)-(CO) (PPh₃)₂]-MeOH (3), whilst reactions of [Rh(CO)-(PPh₃)₂] [BF₄]·1/2CH₂Cl₂ and [Rh(CO)₂(PPh₃)₂] [BF₄] with OR_- (R = Me, Et or n-Pr) in the presence of CO produce [Rh(COOR)(CO)₂(PPh₃)₂] (4)–(6). The products have been characterised by i.r., ¹H, ³¹P, ¹³Cn.m.r. spectroscopy and elemental analysis.     

Reactivity of cationic methyl rhodium(III) complexes cis-[Rh(β-diket)(PPh3)2(CH3)(CH3CN)][BPh4] toward ligands of different character: pyridine, carbon monoxide, and triphenylphosphine

Cationic methyl complex of rhodium(III), cis-[Rh(Acac)(PPh₃)₂(CH₃)(Py)][BPh₄] (1) as a single isomer with Py in the trans to PPh₃ position, is formed upon the reaction of cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] with pyridine in methylene chloride solution.Complex 1 was characterized by elemental analysis and by ³¹P{¹H} and ¹H NMR spectra.Cationic pentacoordinate acetyl complexes, trans-[Rh(Acac)(PPh₃)₂(COCH₃)][BPh₄] (2) and trans-[Rh(BA)(PPh₃)₂(COCH₃)][BPh₄] (3), are prepared by action of carbon monoxide on cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄], respectively, in methylene chloride solutions.Complexes 2 and 3 were characterized by elemental analysis and by IR, ³¹P{¹H}, ¹³C{¹H} and ¹H NMR. According to NMR data, 2 and 3 in solution are non-fluxional trigonal bipyramids with β-diketonate and acetyl ligands in the equatorial plane and axial phosphines.In solutions, 2 and 3 gradually isomerize into octahedral methyl carbonyl complexes trans-[Rh(Acac)(PPh₃)₂(CO)(CH₃)][BPh₄] (4) and trans-[Rh(BA)(PPh₃)₂(CO)(CH₃)][BPh₄] (5), respectively.Complexes 4 and 5 were characterized by IR, ³¹P{¹H}, ¹³C{¹H} and ¹H NMR, without isolation.Upon the action of PPh₃ on cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)] [BPh₄], reductive elimination of the methyl ligand as a phosphonium salt, [CH₃PPh₃][BPh₄], occurs to give square planar rhodium(I) complexes [Rh(Acac)(PPh₃)₂] and[Rh(BA)(PPh₃)₂], respectively. The reaction products were identified in the reaction mixtures by ³¹P{¹H} and ¹H NMR.     

The preparation and catalytic hydroformylation activity of some halocarbonylrhodium(I) complexes containing phosphinoalkylorganosilicon ligands

The synthesis and properties of a series of trans-halocarbonylrhodium(I) complexes containing the phosphinoalkylorganosilicon ligands Me₃SiCH₂PPh₂, Me₃Si(CH₂)₃PPh₂, and PPh₂CH₂(Me)$\text{Si(OSiMe}{}_2\text{)}{}_3\text{O}$ have been investigated. The complexes could be prepared by an exchange reaction involving RhCl(CO)(PPh₃)₂ and the organosilicon ligands or in better yields by the reaction of Rh₂Cl₂(CO)₄ with the ligands. Iodorhodium derivatives were obtained as the exclusive products in the latter reaction if a small amount of LiI was present. The catalytic activity of RhCl(CO)(PPh₂CH₂SiMe₃)₂ was similar to that of RhCl(CO)(PPh₃)₂ in the hydroformylation of hex-1-ene at 100°C and 1000 psi pressure of H₂/CO. The catalytic properties of the iodo derivatives RhI(CO)L₂ [L = Me₃SiCH₂PPh₂, Me₃Si(CH₂)₃PPh₂, and PPh₂CH₂(Me)$\text{Si(OSiMe}{}_2\text{)}{}_3\text{O}$] varied considerably, with RhI(CO)(PPh₂CH₂SiMe₃)₂ producing an unexpectedly low linear/branched aldehyde product ratio.     

Carbonyl cationic rhodium(I) and iridium(I) complexes with sulphur donor and triphenylphosphine ligands

Summary The reaction of previously reported Rh^I and Ir^I cationic complexes towards carbon monoxide and triphenylphosphine has been studied. Carbonyl rhodium(I) mixed complexes of the formulae [Rh(CO)L₂(PPh₃)]ClO₄, (L=tetrahydrothiophene(tht), trimethylene sulfide(tms), SMe₂, or SEt₂), [(CO)(PPh₃)Rh{-(L-L)}₂Rh(PPh₃)(CO)](ClO₄)₂ (L-L= 2,2,7,7-tetramethyl-3,6-dithiaoctane (tmdto), (MeS)₂(CH₂)₃ (dth), or 1,4-dithiacyclohexane (dt), [Rh(CO)L(PPh₃)₂]ClO₄ (L= tht, tms, SMe₂, or SEt₂), and carbonyl iridium(I) complexes of the formulae [Ir(CO)₂(COD)(PPh₃)]ClO₄, [Ir(CO)(COD)(PPh₃)₂]ClO₄, [(CO)(COD)(PPh₃) Ir{-(L-L)} Ir(PPh₃)(COD)(CO)](ClO₄)₂ (L-L = tmdto or dt), [(CO)₂ (PPh₃)Ir(-tmdto)Ir(PPh₃)(CO)₂](ClO₄)₂, [(CO)₂(PPh₃) Ir(-dt)₂Ir(PPh₃)(CO)₂](ClO₄)₂, were prepared by different synthetic methods.     

Trifluoroacetylacetonate rhodium(III) methyl complexes, cis-[Rh(TFA)(PPh3)2(CH3)(L)][BPh4] and cis-[Rh(TFA)(PPh3)2(CH3)(I)] (L = CH3CN, NH3, pyridine), in comparison with their acetylacetonate analogs

The oxidative addition of CH₃I to planar rhodium(I) complex [Rh(TFA)(PPh₃)₂] in acetonitrile (TFA is trifluoroacetylacetonate) leads to the formation of cationic, cis-[Rh(TFA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (1), or neutral, cis-[Rh(TFA)(PPh₃)₂(CH₃)(I)] (4), rhodium(III) methyl complexes depending on the reaction conditions. 1 reacts readily with NH₃ and pyridine to form cationic complexes, cis-[Rh(TFA)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (2) and cis-[Rh(TFA)(PPh₃)₂(CH₃)(Py)][BPh₄] (3), respectively. Acetylacetonate methyl complex of rhodium(III), cis-[Rh(Acac)(PPh₃)₂(CH₃)(I)] (5), was obtained by the action of NaI on cis-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] in acetone at −15 °C. Complexes 1-5 were characterized by elemental analysis, ³¹P{¹H}, ¹H and ¹⁹F NMR. For complexes 2, 3, 4 conductivity data in acetone solutions are reported. The crystal structures of 2 and 3 were determined. NMR parameters of 1-5 and related complexes are discussed from the viewpoint of their isomerism.     

Cationic methyl complexes of rhodium(III): synthesis, structure, and some reactions

Cationic methyl complex of rhodium(III), trans-[Rh(Acac)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (1) is prepared by interaction of trans-[Rh(Acac)(PPh₃)₂(CH₃)I] with AgBPh₄ in acetonitrile. Cationic methyl complexes of rhodium(III), cis-[Rh(Acac)(PPh₃)₂ (CH₃)(CH₃CN)][BPh₄] (2) and cis-[Rh(BA)(PPh₃)₂(CH₃)(CH₃CN)][BPh₄] (3) (Acac, BA are acetylacetonate and benzoylacetonate, respectively), are obtained by CH₃I oxidative addition to rhodium(I) complexes [Rh(Acac)(PPh₃)₂] and [Rh(BA)(PPh₃)₂] in acetonitrile in the presence of NaBPh₄. Complexes 2 and 3 react readily with NH₃ at room temperature to form cis-[Rh(Acac)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (4) and cis-[Rh(BA)(PPh₃)₂(CH₃)(NH₃)][BPh₄] (5), respectively. Complexes 1-5 were characterized by elemental analysis, ¹H and ³¹P{¹H} NMR spectra. Complexes 1, 2, 3 and 4 were characterized by X-ray diffraction analysis. Complexes 2 and 3 in solutions (CH₂Cl₂, CHCl₃) are presented as mixtures of cis-(PPh₃)₂ isomers involved into a fluxional process. Complex 2 on heating in acetonitrile is converted into trans-isomer 1. In parallel with that isomerization, reductive elimination of methyl group with formation of [CH₃PPh₃][BPh₄] takes place. Replacement of CH₃CN in complexes 1 and 2 by anion I⁻ yields in both cases the neutral complex trans-[Rh(Acac)(PPh₃)₂(CH₃)I]. Strong trans influence of CH₃ ligand manifests itself in the elongation (in solid) and labilization (in solution) of rhodium-acetonitrile nitrogen bond.     

Regioselectivity in the rhodium catalysed 1,4-hydrosilylation of isoprene. Aspects on reaction conditions and ligands

The regioselectivity in the Rh catalysed 1,4-hydrosilylation of isoprene was investigated. Variation of solvents and temperature did not significantly affect the isomer distribution between tail-product (I) and head-product (II). The choice of ligands had the greater influence, where Rh^I-based catalysts with the strong electron withdrawing ligand CO favoured production of isomer II, while Rh^I catalysts with strong electron donating ligands (for example triarylphosphines) gave isomer I as the main product. In contrast to the square planar carbonyl complex RhCl(CO)(PPh₃)₂, the square planar thiocarbonyl complex RhCl(CS)(PPh₃)₂, gave I as the major isomer.     

The selective catalytic carbonylation of aromatic azides using homogeneous and polymer bound rhodium(I) complexes

The catalytic activities of rhodium(I) complexes in the carbonylation reaction of aromatic azides, p-RC₆H₄N₃ (R = H, NO₂), at atmospheric pressure and 25 – 80 °C, leading to the corresponding isocyanates have been studied. [Rh(DPE)₂]Cl (DPE = Ph₂PCH₂CH₂PPh₂), [Rh(DPP)₂]Cl (DPP = Ph₂PCH₂CH₂CH₂PPh₂), RhCl(CO)(PPh₃)₂ and [Rh(DPP)(CO)Cl] ₂ are the most active catalysts, and maintain their high activity even in the presence of p-R'C₆H₄NH₂ which gives the corresponding urea, or ethanol which gives the carbamate p-RC₆H₄NHCOOEt. RhCl(CO)(PPh₃)₂ has been heterogenized by reaction with a polymeric phosphine. Its activity in the catalytic carbonylation of aromatic azides was found comparable to that of the homogeneous systems. The heterogenized catalyst can be recycled without any decrease in its catalytic activity.     

Synthesis and characterization of transition metal complexes of a new bidentate ligand {2-(diphenylphosphino)ethyl}benzylamine

A new bidentate ligand {2-(diphenylphosphino)ethyl}benzylamine(DPEBA) was synthesized and characterized based on the IR, mass and ¹H, ¹³C and ³¹P NMR spectra. Various complexes of platinum group metal ions and Ni(II) and Co(II) ions with the ligand were synthesized. Reaction of RuCl₂(PPh₃)₃ or RuCl₂(Me₂SO)₄ with the ligand DPEBA, resulted in formation of a penta-coordinate, Ru(II) species of the composition [RuCl(DPEBA)₂]Cl. Carbonylation of [RuCl(DPEBA)₂]Cl gave an octahedral carbonyl complex of the type [RuCl(CO)(DPEBA)₂]Cl. The reaction of RuCl₃·3H₂O or RuCl₃(AsPh₃)₂MeOH with a twofold excess of the ligand gave an octahedral Ru(III) cationic species [Ru(DPEBA)₂Cl₂]Cl. Carbonylation of the Ru(III) complex gave rise to a carbonyl complex [RuCl(CO)(DPEBA)₂]Cl₂. The ligand DPEBA reacts with cobalt(II) chloride in methanol to give the 1 : 1 complex [Co(DPEBA)Cl₂]. A series of Rh(I) complexes [Rh(DPEBA)₂Cl], [ RhCl(CO)(DPEBA)] and [Rh(DPEBA)₂]Cl were synthesized by the reaction of DPEBA with RhCl(PPh₃)₃, RhCl(CO)(PPh₃)₂ and [Rh(COD)Cl]₂, respectively. Reaction of [Ir(COD)Cl]₂ and IrCl(CO)(PPh₃)₂ with the ligand DPEBA, gave the square-planar complexes [Ir(DPBA)₂]Cl and [Ir(DPEBA)(CO)Cl], respectively. Octahedral cationic complexes of the type [M(DPEBA)₂Cl₂]Cl (M = Rh(III), Ir(III)) were synthesized by the reaction of the ligand DPEBA and rhodium and iridium trichlorides. Reaction of NiCl₂·6H₂O with DPEBA in 1 : 2 molar equivalents, in boiling butanol gave an octahedral neutral complex [Ni(DPEBA)₂Cl₂] which readily rearranges to the square-planar complex [Ni(DPEBA)₂]Cl₂ in methanol. Reaction of Pd(II) and Pt(II) chlorides with DPEBA gave square-planar, cationic complexes of the type [M(DPEBA)₂Cl]Cl (M = Pd, Pt). All the complexes were characterized on the basis of their analytical and spectral data.     

Alkyl- und Arylkomplexe des Iridiums und Rhodiums. XIX. Reaktion von Carbonsäuren mit ausgewählten Organoverbindungen von Ir(I) und Rh(I): Bildung von Arylhydrido-, Carboxylatohydrido- und Carboxylato-Derivaten

Alkyl and Aryl Complexes of Iridium and Rhodium. XIX. Reaction of Carboxylic Acids with Selected Organo Compounds of Ir(I) and Rh(I): Formation of Arylhydrido, Carboxylatohydrido, and Carboxylato Derivatives cis-Arylhydridoiridium(III) complexes IrH(Ar)(O₂CR)(CO)(PPh₃)₂ (R = Me: Ar = C₆H₅, 4-MeC₆H₄; R = Et: Ar = 4-MeC₆H₄, 2,4-Me₂C₆H₃) could be prepared by oxidative addition of carboxylic acids to aryliridium(I) compounds Ir(Ar)(CO)(PPh₃)₂. Reaction of aliphatic carboxylic acids with alkyliridium(I) derivatives Ir(Alk)(CO)(PPh₃)₂ and Ir(Alk)[PhP(CH₂CH₂CH₂PPh₂)₂] (Alk = CH₂CMe₃, CH₂SiMe₃) lead to dicarboxylatoiridium(III) hydrides IrH(O₂CR)₂(CO)(PPh₃)₂ (R = Me, Et, i-Pr) and IrH(O₂CR)₂[PhP(CH₂CH₂CH₂PPh₂)₂] (R = Me, Et). Ir(4-MeC₆H₄CO₂)(CO)(PPh₃)₂ was obtained from Ir(CH₂SiMe₃)(CO)(PPh₃)₂ and 4-MeC₆H₄CO₂H. Interaction of organorhodium complexes Rh(R′)(CO)(PPh₃)₂ (R′ = CH₂SiMe₃, 4-MeC₆H₄) and Rh(R′)[PhP(CH₂CH₂CH₂PPh₂)₂] (R′ = CH₂CMe₃, 4-MeC₆H₄) with aliphatic and aromatic carboxylic acids yielded carboxylatorhodium(I) compounds Rh(O₂CR)(CO)(PPh₃)₂ (R = Me, t-Bu, 4-MeC₆H₄) and Rh(O₂CR)[PhP(CH₂CH₂CH₂PPh₂)₂] (R = Me, 4-MeC₆H₄).     

Kinetic Study of the Oxidative Addition Reaction between Methyl Iodide and [Rh(imino-β-diketonato)(CO)(PPh)3] Complexes,Utilizing UV–Vis,IR Spectrophotometry,NMR Spectroscopy and DFT Calculations

The oxidative addition of methyl iodide to [Rh(β-diketonato)(CO)(PPh)₃] complexes, as modal catalysts of the first step during the Monsanto process, are well-studied. The β-diketonato ligand is a bidentate (BID) ligand that bonds, through two O donor atoms (O,O-BID ligand), to rhodium. Imino-β-diketones are similar to β-diketones, though the donor atoms are N and O, referred to as an N,O-BID ligand. In this study, the oxidative addition of methyl iodide to [Rh(imino-β-diketonato)(CO)(PPh)₃] complexes, as observed on UV–Vis spectrophotometry, IR spectrophotometry and NMR spectrometry, are presented. Experimentally, one isomer of [Rh(CH₃COCHCNPhCH₃)(CO)(PPh₃)] and two isomers of [Rh(CH₃COCHCNHCH₃)(CO)(PPh₃)] are observed—in agreement with density functional theory (DFT) calculations. Experimentally the [Rh(CH₃COCHCNPhCH₃)(CO)(PPh₃)] + CH₃I reaction proceeds through one reaction step, with a rhodium(III)-alkyl as the final reaction product. However, the [Rh(CH₃COCHCNHCH₃)(CO)(PPh₃)] + CH₃I reaction proceeds through two reaction steps, with a rhodium(III)-acyl as the final reaction product. DFT calculations of all the possible reaction products and transition states agree with experimental findings. Due to the smaller electronegativity of N, compared to O, the oxidative addition reaction rate of CH₃I to the two [Rh(imino-β-diketonato)(CO)(PPh)₃] complexes of this study was 7–11 times faster than the oxidative addition reaction rate of CH₃I to [Rh(CH₃COCHCOCH₃)(CO)(PPh₃)].     

Iodomethane oxidative addition and CO migratory insertion in monocarbonylphosphine complexes of the type [Rh((C6H5)COCHCO((CH2)nCH3))(CO)(PPh3)]: Steric and electronic effects

The chemical kinetics, studied by UV/Vis, IR and NMR, of the oxidative addition of iodomethane to [Rh((C₆H₅)COCHCOR)(CO)(PPh₃)], with R = (CH₂)_nCH₃, n = 1-3, consists of three consecutive reaction steps that involves isomers of two distinctly different classes of Rh^III-alkyl and two distinctly different classes of Rh^III-acyl species. Kinetic studies on the first oxidative addition step of [Rh((C₆H₅)COCHCOR)(CO)(PPh₃)] + CH₃I to form [Rh((C₆H₅)COCHCOR)(CH₃)(CO)(PPh₃)(I)] revealed a second order oxidative addition rate constant approximately 500-600 times faster than that observed for the Monsanto catalyst [Rh(CO)₂I₂]⁻. The reaction rate of the first oxidative addition step in chloroform was not influenced by the increasing alkyl chain length of the R group on the β-diketonato ligand: k₁ = 0.0333 ([Rh((C₆H₅)COCHCO(CH₂CH₃))(CO)(PPh₃)]), 0.0437 ([Rh((C₆H₅)COCHCO(CH₂CH₂CH₃))(CO)(PPh₃)]) and 0.0354 dm³ mol⁻¹ s⁻¹ ([Rh((C₆H₅)COCHCO(CH₂CH₂CH₂CH₃))(CO)(PPh₃)]). The pK_a^′ and keto-enol equilibrium constant, K_c, of the β-diketones (C₆H₅)COCH₂COR, along with apparent group electronegativities, χ_R of the R group of the β-diketones (C₆H₅)COCH₂COR, give a measurement of the electron donating character of the coordinating β-diketonato ligand: (R, pK_a^′, K_c, χ_R) = (CH₃, 8.70, 12.1, 2.34), (CH₂CH₃, 9.33, 8.2, 2.31), (CH₂CH₂CH₃, 9.23, 11.5, 2.41) and (CH₂CH₂CH₂CH₃, 9.33, 11.6, 2.22).     

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.     

Synthesis,formation constants and reactions of cationic rhodium(I) complexes of nitriles

Reactions of Rh(ClO₄)(CO)(PPh₃)₂ with nitriles produce new cationic rhodium(I) complexes, [RhL(CO)(PPh₃)₂]ClO₄ [L = CH₃CN (1), CH₃CH₂CH₂CN (2) or C₆H₅CN (3)], whose spectral data suggest that the nitriles are coordinated through the nitrogen atom. Formation constants for the reaction Rh(ClO₄)(CO)(PPh₃)₂ + L ⇋ [RhL(CO)(PPh₃)₂]ClO₄, have been measured to be 1.01 × 10⁵ M⁻¹ (CH₃CN), 1.07 × 10⁵ M⁻¹ (CH₃CH₂CH₂CN) and 2.59 × 10⁴ M⁻¹ (C₆H₅CN) at 25°C in monochlorobenzene. The differences in the formation constants for the different nitriles seem to be predominantly due to differences in ΔH (not to differences in ΔS). The nitriles in 1–3 are readily replaced with nitrogen base ligands (unsaturated nitriles and pyridine) and PPh₃.     

Metal catalysed Brooke rearrangement of 3-Halo-1-(trimethylsilyl) propan-2-one (Halo = Cl or Br)

The complexes [IrH(CO)(PPh₃)₃], trans-[IrCI(CO)- (PPh₃)₂], [RhH(PPh₃)₄], [Pd(PPh₃)₄], [Pt(trans-stilbene)(PPh₃)₂] and [Pt(η³-CH₂-COCH₂)-(PPh₃)₂] catalyse the rearrangement of Me₃SiCH₂C(O)CH₂Cl to CH₂?C(OSiMe₃)-CH₂Cl.