Reactions of silicon hydrides catalyzed by rhodium(III) sulfoxide complexes

Russian Journal of General Chemistry - Dehydrocondensation reactions of silicon hydrides catalyzed by the rhodium(III) complex [RhCl3(Me2SO)3] in the absence of the second substrate were studied....     

Aqueous rhodium(III) hydrides and mononuclear rhodium(II) complexes

In aqueous solutions, as in organic solvents, rhodium hydrides display the chemistry of one of the three limiting forms, i.e. {Rh(I)+ H+}, {Rh(II)+ H.}, and {Rh(III)+ H-}. A number of intermediates and oxidation states have been generated and explored in kinetic and mechanistic studies. Monomeric macrocyclic rhodium(II) complexes, such as L(H2O)Rh2+ (L = L1 = [14]aneN4, or L2 = meso-Me6[14]aneN4) can be generated from the hydride precursors by photochemical means or in reactions with hydrogen atom abstracting agents. These rhodium(II) complexes are oxidized rapidly with alkyl hydroperoxides to give alkylrhodium(III) complexes. Reactions of Rh(II) with organic and inorganic radicals and with molecular oxygen are fast and produce long-lived intermediates, such as alkyl, superoxo and hydroperoxo complexes, all of which display rich and complex chemistry of their own. In alkaline solutions of rhodium hydrides, the existence of Rh(I) complexes is implied by rapid hydrogen exchange between the hydride and solvent water. The acidity of the hydrides is too low, however, to allow the build-up of observable quantities of Rh(I). Deuterium kinetic isotope effects for hydride transfer to a macrocyclic Cr(v) complex are comparable to those for hydrogen atom transfer to various substrates.     

Asymmetric synthesis at silicon : II. Alcoholysis of prochiral organosilicon compounds catalysed by rhodium complexes

The asymmetric alcoholysis of prochiral organosilanes catalysed by certain rhodium complexes, whether optically active or not, gives rise to alkoxysilanes with an optical purity of up to 57%. The nature of theligands in the rhodium complex has little influence on the optical yields, but the structures of the organosilane and of thealcohol are very important. A mechanism involving rapid and reversible activation of the organosilane, followed by slow reaction with the alcohol, is proposed to account for the results. The small influence of the catalyst ligands is attributed to direct nucleophilic attack of the alcohol on the silicon atom.     

Reactions of some sterically-hindered organosilicon hydrides and iodides with halogens

The reaction of TsiSiMe₂H (I) (Tsi = (Me₃Si)₃C) with I₂ or with a molar equivalent of ICl gives the iodide TsiSiMe₂I (II) in hydroxylic media (MeOH, CH₃CO₂H, CF₃CO₂H) as it does in CCl₄. The reaction with I₂ is very fast in CF₃CO₂H, but in MeOH is only about as fast as in CCl₄. The iodide II reacts with ICl in MeOH to give a mixture of TsiSiMe₂OMe (III) and TsiSiMe₂Cl (IV), but the reaction is markedly slower than that in CCl₄ (in which IV is formed). The hydride I also reacts with INO₃ in MeOH to give II, and the latter reacts with INO₃ to give III. The reactions of TsiSiPh₂H (V) and TsiSiPh₂I (VI) with ICl in MeOH are markedly slower than those of I and II; even with one equivalent of ICl in MeOH, V gives a mixture of VI and the (rearranged) methoxide (Me₃Si)₂C(SiPh₂Me)(SiMe₂OMe) (VII). Reaction of VI with ICl in MeOH gives VII and the rearranged chloride (Me₃Si)₂C(SiPh₂Me)(SiMe₂Cl). The formation of methoxides in the reactions of the iodides II and VI with ICl in MeOH, and the rearrangements observed in the case of VI, are consistent with a mechanism involving an intermediate silicocation. Other mechanistic aspects are discussed.     

Hydrocarbonylation of 2,2-dimethoxypropane catalysed by rhodium and cobalt complexes

The hydrocarbonylation of 2,2-dimethoxypropane (DMP) with synthesis gas catalysed by rhodium and cobalt complexes has been studied. The major product is either diethyl ether or acetaldehyde dimethylacetal (ADMA), arising from the homologation of the methoxy groups of the ketal. The operating conditions and ligand environment of the metal have been optimized to reduce the secondary aldolization reactions.     

The photochemical decomposition of alcohols catalysed by tri(isopropyl) phosphine complexes of rhodium(I)

Photolysis of RhH(PⁱPr₃)₃ or RhH(CO)(PⁱPr₃)₂ in solution in primary alcohols (RCH₂OH) produces H₂, CO and RH, whereas hydrogen and acetone are produced from propan-2-o l; in the presence of hex-1-ene, this last reaction gives acetone and hexane in the absence of illumination.     

Catalytic activity of homogeneous and silica-anchored rhodium complexes

Using recently synthesized [1] (C₂H₅O)₃Si(CH₂)₃CH(COCH₃)₂ (1) and (CH₃O)₃Si(CH₂)₂–Py (2) (Py=2-pyridyl), a series of homogeneous and silica-anchored rhodium carbonyl complexes were prepared. Their catalytic performance was studied in hydrogenation, hydrosilylation and methanol carbonylation.     

Kinetics and mechanisms of homogeneous catalytic reactions: Part 15. Regio-specific hydroformylation of limonene catalysed by rhodium complexes of phosphine ligands

Limonene hydroformylation was studied in the presence of Rh-based catalytic systems, which were prepared in situ by addition of three equivalents of PPh₃, one of 1,2-bis(diphenylphosphino)ethane (dppe), or one of 1,1,1-tris(diphenylphosphino)ethane (triphos) to Rh(CO)₂(acac) (1). These systems were efficient precatalysts for the target reaction, generating limonenal regio-specifically under mild reaction conditions (80 °C and 20 atm of syngas). The found activity order was: (1)/3 PPh₃?>?(1)/triphos?>?(1)/dppe. The active catalytic species are proposed to be square planar hydrido-carbonyl complexes containing two phosphorus atoms coordinated at the rhodium centre. A kinetic study of this reaction catalysed by (1)/3 PPh₃, the most active catalytic system, allowed us to propose that the mechanism of hydroformylation of limonene is similar to those reported for other olefins using RhH(CO)(PPh₃)₃ or Rh systems containing either dppe or triphos as precatalysts.     

Hydroformylation of cyclic dienes catalysed by acetatocarbonylbis(triphenylphosphine)rhodium(I)

The hydroformylation of cyclic dienes in benzene using Rh(CO₂Me)(CO)(PPh₃)₂ as catalyst was studied. The formation of mono- or di-aldehydes was critically dependent on ring size, the smaller cyclic dienes favouring dihydroformylation. Intermediate alkene-aldehydes could be isolated under appropriate conditions, indicating that initial attack on the diene was by hydroformylation. Under hydroformylation conditions, these intermediates underwent either hydroformylation or hydrogenation, depending on the ring size. Linear dienes gave complex mixtures of products.     

Interaction of rhodium(i) bisphosphine complexes with semicarbazones to give orthometallated rhodium(iii) complexes

Interaction of the cis-[Rh(PR₃)₂(Solv)₂]PF₆ complexes (R = Ar or R₃ = Ph₂Me, Solv — solvent) under Ar with semicarbazones bearing a phenyl group on the imine-C atom gives the rhodium(iii)-hydrido-bis(phosphine)-orthometallated semicarbazone species [RhH(PR₃)₂{(o-C₆H₄(R")C=N—N(H)CONH₂}]PF₆ (R" = Me or Et), which are characterized generally by elemental analysis, ³¹P{¹H} and ¹H NMR spectroscopy, and mass-spectrometry. The PPh₃-containing complex with R" = Me, structurally characterized by X-ray analysis, reveals coordination of the semicarbazone by the ortho-C atom, the imine-N atom, and the amide-carbonyl group. For a semicarbazone containing no Ph group, the rhodium(i) complex [Rh(PR₃)₂(Et(Me)C=N—N(H)CONH₂)]PF₆, containing the ²-semicarbazone bonded via the imine-N and carbonyl, is formed. Attempts to hydrogenate the C=N moiety in the complexes or to catalytically hydrogenate the semicarbazones were unsuccessful.     

Reactions of hydropolysilanes with alcohols catalysed by tris(triphenylphosphine)chlororhodium

[RhCl(PPh₃)₃] is a very effective catalyst for the cleavage of Si-Si bonds by alcohols.     

Carbonyl complexes of rhodium(I) and rhodium(III) with 2,2′-biquinoline

Novel carbonyl complexes of rhodium(I) and rhodium(III) containing the bidenate nitrogen donor ligand 2,2′-biquinoline (biq) have been prepared; they are of the types RhX(CO)₂ biq and RhX(CO)biq (X = Cl, Br, I). Cationic carbonyl and substituted carbonyl complexes of the types [Rh(CO)₂biq]ClO₄ and [Rh(CO)biqL₂]ClO₄, where L is tertiary phosphine or arsine have also been isolated. In spite of considerable steric crowding around the nitrogen atoms, 2,2′-biquinoline behaves much like 2,2′-bipyridine in forming carbonyl complexes of rhodium.     

Aqueous phase transfer hydrogenation of aryl ketones catalysed by achiral ruthenium(II) and rhodium(III) complexes and their papain conjugates

Several ruthenium and rhodium complexes including 2,2′‐dipyridylamine ligands substituted at the central N atom by an alkyl chain terminated by a maleimide functional group were tested along with a newly synthesized Rh(III) complex of unsubstituted 2,2′‐dipyridylamine as catalysts in the transfer hydrogenation of aryl ketones in neat water with formate as hydrogen donor. All of them except one led to the secondary alcohol products with conversion rates depending on the metal complex. Site‐specific anchoring of the N‐maleimide complexes to the single free cysteine residue of the cysteine endoproteinase papain endowed this protein with transfer hydrogenase properties towards 2,2,2‐trifluoroacetophenone. Quantitative conversions were reached with the Rh‐based biocatalysts, while modest enantioselectivities were obtained in certain reactional conditions. Copyright © 2012 John Wiley & Sons, Ltd.     

Reactions of 1,4-diaza-3-methylbutadien-2-ylpalladium(II) derivatives with chloro-bridged rhodium(I) complexes

The reactions of the organometallic 1,4-diazabutadienes, RN=C(R′)C(Me)=NR″ [R = R″ = p-C₆H₄OMe, R′ = trans-PdCl(PPh₃)₂ (DAB); R = p-C₆H₄OMe, R″ = Me, R′ = trans-PdCl(PPh₃)₂ (DAB^I; R = R″ = p-C₆H₄OMe, R′ = Pd(dmtc)-(PPh₃), dmtc = dimethyldithiocarbamate (DAB^II); R = R″ = p-C₆H₄OMe, R′ = PdCl(diphos), diphos = 1,2-bis(diphenylphosphino)ethane (DAB^III)] with [RhCl(COD)]₂ (COD = 1,5-cyclooctadiene, Pd/Rh ratio = $\text{1}\text{2}$) depend on the nature of the ancillary ligands at the Pd atom in group R′. In the reactions with DAB and DAB^I transfer of one PPh₃ ligand from Pd to Rh occurs yielding [RhCl(COD)(PPh₃)] and the new binuclear complexes [Rh(COD) {RN=C(R?)-C(Me)=NR″}], in which the diazabutadiene moiety acts as a chelating bidentate ligand. Exchange of ligands between the two different metallic centers also occurs in the reaction with DAB^II. In this case, the migration of the bidentate dmtc anion yields [Rh(COD)Pdmtc] and [Rh(COD) {RN=C(R?)C(Me)=NR″}]. In contrast, the reaction with DAB^III leads to the ionic product [Rh(COD)- (DAB^III)][RhCl₂(COD)], with no transfer of ligands. The cationic complex [Rh(COD)(DAB^III)]⁺ can be isolated as the perchlorate salt from the same reaction (Pd/Rh ratio = 1/1) in the presence of an excess of NaClO₄. In all the binuclear complexes the coordinated 1,5-cyclooctadiene can be readily displaced by carbon monoxide to give the corresponding dicarbonyl derivatives. The reaction of [RhCl(CO)₂]₂ with DAB and/or DAB^I yields trinuclear complexes of the type [RhCl(CO)₂]₂(DAB), in which the diazabutadiene group acts as a bridging bidentate ligand. Some reactions of the organic diazabutadiene RN=C(Me)C(Me)=NR (R = p-C₆H₄OMe) are also reported for comparison.     

Micellar effect in hydroformylation of high olefin catalysed by water-soluble rhodium complexes associated with sulfonated diphosphines

High linear alkenes (1-octene and 1-decene) have been hydroformylated using water-soluble rhodium complexes associated with sulfonated diphosphines in the presence of ionic surfactants or methanol. In all cases, the hydroformylation activities were higher than in experiments without additives. The selectivity in aldehydes was higher when we used cetyltrimethylammonium hydrogensulfate (CTAHSO₄) as the surfactant or methanol as the co-solvent.     

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.     

Hydrosilylation of alkenes catalysed by rhodium complexes immobilized on silica via a pyridine group

2-(2-Trimethoxysilylethyl)pyridine, together with 3-methcryloxypropyltrimethoxysilane, was used to prepare a series of rhodium carbonyl complexes bound to silica via a pyridine group. The rhodium complex Rh₂(CO)₄Cl₂ (Rh₂) was used as the starting compound, and the immobilized complexes were prepared by four different routes which yielded both surface-bonded complexes and complexes bonded within the silicate matrix. These complexes were efficient catalysts of hydrosilylation of octene by triethxysilane. All the immobilized complexes were more than their homogeneous analogues and some could be re-used.     

Asymmetric synthesis of dipeptides by means of homogeneous hydrogenation catalyzed by chiral rhodium complexes

Asymmetric hydrogenation of dehydrodipeptides, α-acylaminocinnamoyl-(S)-amino esters, catalyzed by rhodium complexes with chiral diphosphines gave either (R)-N-acylphenylalanyl-(S)-amino esters or (S)-N-acylphenylalanyl-(S)-amino esters with high diastereomeric purity up to 98–99% on using proper chiral ligands.