Reactions involving hydrogen transfer from triosmium clusters to an activated nitrile

The reactions of H₂Os₃(CO)₁₀, Ia and H₂Os₃(CO)₉PMe₂Ph, Ib with CF₃CN have been investigated. Both la and Ib react with CF₃CN to give the products HOs₃[μ-η₂-(CF₃)CNH](CO)₉Land HOs₃[μ-η¹-NC(H)CF3](CO)₉L, IIa, IIIa, L = CO; IIb and IIIb, L = PMe₂Ph. IIb and IIIb have been characterized crystallographically. In each, one nitrile molecule was added to the cluster and one hydride ligand was transferred to the nitrile ligand, but in IIb the hydride was transferred to the nitrogen atom to form a CF₃CNH ligand which bridges an edge of the cluster while in IIIb the hydride was transferred to the carbon atom to form a CF₃(H)CN ligand which also bridges an edge of the cluster. On the basis of spectroscopic measurements IIa and IIIa are believed to have analogous structures. An isotope scrambling experiment established that the formation of Ilia occurs by an intramolecular process. IIa was decarbonylated to yield the compound HOs₃[μ₃-η₂-(CF₃)CNH](CO)₉, which is believed to contain a triply-bridging iminyl ligand. Ilia reacts with PMe₂Ph to give two mono-substitution products, one of which is IIIb.     

The oxidation of cis- and trans-CHClCHCl

When Cl atoms react with CHClCHCl in the presence of O₂ at 31°C, a long-chain oxidation occurs. The products are the geometrical isomer of the starting olefin and CHClO, HCl, CO, and CCl₂O. The quantum yields of the oxygen-containing products are the same with both isomers and are Φ{CHClO} = 30, Φ{CO} = 11.7, and Φ{CCl₂O} = 1.29. The chlorine atom adds to the olefin and is followed by O₂ addition. The reaction then proceeds with k_6a/k_6b = 19 and k_7a/k₇ ～ 0.5, where k₇ ≡ k_7a + k_7b. The CCl₂H radical oxidizes to regenerate the chain carrier. O(³P) reacts with CHClCHCl at 25°C with a rate coefficient of 6.6 × 10⁸ M^?1 sec^?1 for trans-CHClCHCl and 2.8 × 10⁸ M^?1 sec^?1 for cis-CHClCHCl. The reaction channels are with k_1a/k₁ = 0.23 and 0.28, respectively, for the cis and trans compounds. Reaction (1b) occurs < 4% of the time. Reaction (1c) leads to polymer production and presumably, via redissociation, to the geometrical isomer of the starting olefin. In the presence of O₂ the same long-chain oxidation is observed as in the chlorine-atom initiated oxidation. The chain-initiating step is      

On the mechanism of the Co2(CO)8 catalyzed hydroformylation of olefins in hydrocarbon solvents. A high pressure UV and IR study

High pressure IR and UV spectroscopic experiments confirm the Heck and Breslow mechanism of the hydroformylation of 1-octene and cyclohexene with Co₂(CO)₈ as the starting catalyst. The major repeating unit is HCo(CO)₄, which is formed via the reaction of acylcobalt tetracarbonyl with H₂. The rates are 6.7 × 10^?4 mol l^?1 min^?1 and 8.8 × 10^?5 mol l^?1 min^?1 for 1-octene and cyclohexene, respectively at 80°C and 95 bar CO/H₂ = 1 in methylcyclohexane. The alternative reaction of RCOCo(CO)₄ with HCo(CO)₄ is only a minor pathway, with rates of 1.8 × 10^?5 mol l^?1 min^?1 and 1.1 × 10^?5 mol l^?1 min^?1 for 1-octene and cyclohexene, respectively. It represents an exit from the catalytic cycle. The activation of the catalyst precursor Co₂(CO)₈ is the slowest step of the reaction.     

Hydrido cyclopentadienyliron dicarbonyl and its role in olefin hydroformylation

The compound hydrido cyclopentadienyliron dicarbonyl has been shown by infrared and proton NMR to be present in substantial quantities during hydroformylation of propene and 1-pentene in the presence of [(η⁵-C₅H₅)Fe(CO)₂]₂. This and related observations strongly suggest that the hydride is an important link in the catalytic cycle as is HCo(CO)₄ in Co₂(CO)₈-catalyzed olefin hydroformylation.     

The pressure dependence of the rate constant for the reaction: HO + CO → H + CO2

Relative rate measurements of the reactions of the HO-radical with CO [HO + CO → H + CO₂ (1)] and with isobutane [HO + iso-C₄H₁₀ → H₂O + t-(or iso-)C₄H₉ (3)] have been made through the photolysis of dilute mixtures of HONO with CO, iso-C₄H₁₀, NO₂, and NO in simulated air at 700 and 100 torr pressure and 25 ± 2°C. In situ, long path, FT-IR analysis of the reactants and products provided essentially continuous monitoring of the reactions during the course of the experiments. The kinetic analysis of the data coupled with Greiner's estimate of k₃ give new estimates of k₁ = 439 ± 24 ppm^?1 min^?1 in air at 700 torr and k₁ = 203 ± 29 ppm^?1 in air at 100 torr. The results confirm the recent conclusions of Cox and Sie and their co-workers that the rate constant for reaction (1) is pressure dependent. Modeliers of the chemical changes which occur in the troposphere should adopt a new value for the rate constant k₁ which is about a factor of two larger than that in current use by most groups.     

Reactions of 1,1,3,3-tetramethyldisilazane with dicobalt octacarbonyl and iron pentacarbonyl. Thermal decomposition of the cobalt and iron carbonyl silazane complexes

The reaction of (HMe₂Si)₂NH with Co₂(CO)₈ gives the complex [Co₂(CO)₇(SiMe₂)₂NH₂]⁺[Co(CO)₄]⁻. Its thermal decomposition starts with dissociation into the “acid” HCo(CO)₄ and the “base” Co₂(CO)₇(SiMe₂)₂NH. After that, the base and the initial complex decompose further under the action of HCo(CO)₄. The final products of this reaction are CO, NH₃, Co, volatile dimethylcyclosilazane, and a solid residue consisting of cobalt particles encapsulated into a polymethylsiloxane matrix and possessing properties of mixed para- and ferromagnetics with an ultimate specific magnetization of 64–74 G g⁻¹. Tetramethyldisilazane reacts with iron pentacarbonyl under UV irradiation to give relatively stable 1,3-bis(tetracarbonylthydrideiron)-1,1,3,3-tetramethyldisilazane. This product contains Fe−H…N hydrogen bonds, which stabilize it against dehydrogenation and cyclization to diironcyclodisilazane. Thermal decomposition of this product was investigated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 12, pp. 2537–2544, December, 1998.     

The reaction of triphenylcarbinol with HCo(CO)4

The reaction of Ph₃COH with 2 mol of HCo(C0)₄ gives Ph₃CH in quantitative yield. The reaction is cleanly second order (κ₂  2.50 X 10^-4 1 mol^-1 s^-1, in CH₂Cl₂ at 20°C), first order with respect to each reactant. The rate increases markedly with increase in solvent polarity, suggesting Ph₃C⁺ as an intermediate. The rate of the reaction of HCo(C0)₄ with

is more than 10³ as fast as with Ph₃COH. No evidence for the functioning of HCo(C0)₄ as a hydride donor could be secured.     

U¨bergangsmetall—Carbin—Komplexe: LXIV. Von equatorialen,zweikernigen silylcarben-komplexen des rheniumsU¨ber einen neuartigen kationischen silylcarbin-komplex zu axialen carben-komplexen

Decacarbonyldirhenium reacts with LiSi(C₆H₅)₃ to yield, on subsequent alkylation with FCH₃SO₃ or (C₂H₅)₃OBF₄, the equatorial nonacarbonyl[triphenylsily(alkoxy)carbene] dirhenium complexeseq-(CO)₉Re₂C(OR)Si(C₆H₅)₃(Ia, R - CH₃; Ib, R - C₄H₈OCH₃; Ic. R - C₂H₅). Reactions of these compounds with Al₂Cl₆ or Al₂Br₆ produce novel binuclear, cationic silycarbyne complexes, ax-[(CO)₉Re₂CSi(C₆H₅)₃]⁺ AlX₄^- (IIa, X - Cl; IIb, X - Br). Treatment of these complexes with alcohols results in formation of the axial nonacarbonyl(carbene)dirhenium complexesax-(CO)₉Re₂C(OR)Si(C₆H₅)₃ (IIIa, R - CH₃; IIIb, R - C₂H₅). The isomeric carbene complexes Ia and IIIa react with dialkylamine affording the isomeric aminocarbene complexeseq-(CO)₉Re₂C(CH₃)₂]-Si(C₆H₅)₃ (V) andax-(CO)₉Re₂Cl(NR₂)Si(C₆H₅)₃ (IVa, R - CH₃; IVb, R - C₂H₅). Reaction conditions, properties and spectroscopic data of the new compounds are reported.     

Reaction de metathese des olefines induite photochimiquement en presence d'un complexe de metal de transition. IV.- etude cinetique de l'interconversion catalysee cis-trans du butene-2.

The cis-trans interconversion of olefins in the system W(CO)₆ + CCl₄ + 2-butene is studied, both with initial irradiation of a solution of W(CO)₆ in CCl₄ (photoinduction), and with continuous irradiation of the system, for cis- and trans-butene concentrations between 0.09 and 6.0 M. Analysis of the results of the photoinduction experiments (rate of conversion and kinetic law as a function of the initial concentration of the olefin) allowed us to propose a simple kinetic scheme comprising a cis-trans interconversion of 2-butene and olefin-catalyzed destruction of the catalytic entity (k₂ = (0.62 ± 0.06)x10^?4 M s^?1). In the continuous irradiation experiments the final distribution of the olefin was independent of the initial butene concentration (cis-2-butene/trans-2-butene 3.0) and the reaction kinetics are of first-order (k_obs = (3±1) x10^?4 s^?1. Comparison of the two experiments suggests continuous photochemical regeneration of the catalytically active entity. The first-order reaction kinetics are in agreement with a carbene-metal carbonyl structure of the intermediate     

The stereospecificity at the iron center of the decarbonylation of an ironacetyl complex

The dinuclear complex [(h⁵-1-CH₃-3-C₆H₅C₅H₃)Fe(CO)₂]₂ was synthesized by reaction of Fe₂(CO)9 with 1-methyl-3-phenylcyclopentadiene; it was converted to (h⁵-1-CH₃-3-C₆H₅C₅H₃)Fe(CO)₂CH₃ by reduction with sodium amalgam and addition of CH₃l, and thence to (h⁵-1-CH₃-3-C₆H₅C₅H₃)Fe(CO)[P(C₆H₅)₃] (COCH₃) (I) by reaction with P(C₆H₅)₃. The acetyl I was separated into two diastereomerically related pairs of enantiomers. Ia and Ib, by a combination of column chromatography on alumina and crystallization from benzene/pentane. The photochemical decarbonylation of Ia and Ib in benzene or THF solution was examined by ¹H NMR spectroscopy. This reaction proceeds with high stereospecificity (>84% retention or inversion) at the iron center to yield (h⁵-1-CH₃-3-C₆H₈C₅H₃)Fe(CO)[P(C₆H₅)₃]CH₃(II), enriched in the diastereomerically related pairs of enantiomers, IIa and IIb, respectively. Since IIa and IIb epimerize under the photolytic conditions of decarbonylation, the actual stereospecificity of the conversion of I to II is higher than 84%, and likely 100%. This is supported by the data from kinetic studies of the decarbonylation of I and the epimerization of II, carried out under identical photolytic conditions. The implications of the foregoing results to the mechanism of the decarbonylation are considered. Also described herein is the synthesis of other complexes with two asymmetric centers of the general formula (h⁵-cyclopentadienyl)Fe(CO)(L)(COR) and (h⁵-cyclopentadienyl)Fe(CO)(L)R that contain either an unsymmetrically substituted h⁵-cyclopentadienyl ring or a chiral tertiary phosphine.     

Study of the mechanism of hydroformylation at industrial reaction conditions

With a newly developed analytical technique, i.e. high temperature/pressure IR cell coupled to the reactor, it was possible to study the mechanism of hydroformylation at reaction conditions. It has been conclusively found that the hydrogenolysis of the acyl cobalt complex is performed by HCo(CO)₄ and not by molecular H₂, as proposed byHeck andBreslow.Therefore the formation of HCo(CO)₄ from Co₂(CO)₈ is an intermediate step in the sequence of hydroformylation reaction steps. The rate of hydroformylation of any of the olefins is smaller than the rate of formation of HCo(CO)₄ from Co₂(CO)₈. The IR spectra reveal that always more than 30% of the cobalt is in the form of HCo(CO)₄ under the reaction conditions.It is found that the formation of HCo(CO)₄ from Co₂(CO)₈ is the slowest and most temperature-dependent step of the hydroformylation reaction. Also the reaction between olefin and HCo(CO)₄ is slower than the hydrogenolysis of the acyl complex.The experiments were carried out under industrial oxo conditions. The diffusional effects were eliminated.With 6 FiguresPart of the Ph.D. dissertation 1974. N. H. Alemdarolu, J. M. L. Penninger, andE. Oltay, Mechanism of Hydroformylation, Part II. Mh. Chem.107, 1043 (1976).     

The antioxidant reactivity of sorbitylfurfural towards potential harmful radicals, studied by radiation chemistry techniques

Ionising radiations, employed in a broad range of dose-rate, together with a complex non-linear computation of reaction mechanisms, allow the determination of boundary values of rate constants concerning sorbitylfurfural (SF) reactivity towards a wide series of oxidant and/or virtually harmful radicals. SF reacts with some radicals (H, SO₄ ^-·, CO₃ ^-·, Br₂ ^-·, CH₃ ^·), produced with both pulse and stationary radiolysis in neutral aqueous solution, having electrophilic and/or oxidative behaviour. The rate constants range from diffusional (k = (7–9 ) × 10⁹ M^-1 s^-1) to relatively low values (k = 2 × 10⁵ M^-1 s^-1). The possibility to observe these reactions, by means of radiolytical techniques, is heavily influenced by dose-rate. A relation between the radical E _NHE ⁰ and their reactivity with SF is hinted.     

Synthese und charakterisierung eines stabilen heterobimetallischen TitanCobalt komplexes mit unverbrückter TiCo-bindung

Unusually stable [(^tC₄H₉O)₃Ti-Co(CO)₄] has been prepared by treating the appropriate carbonylmetallate anion with chloro titanium t-butoxide as well as by protolysis of CH₃Ti(O^tC₄H₉)₃ with HCo(CO)₄. Spectroscopic data indicate that the alkoxide and carbonyl ligands are nonbridging, establishing C_3v-symmetry at the cobalt atom.     

Eighteen- and fourteen-electron alumohydride complexes of dicyclopentadienyllutetium. The crystal and molecular structure of monomer (η5-C5H5)2Lu(μ2-H)AlH3·NEt3 with a monodentate alumohydride group

Dicyclopentadienyllutetium monochloride interacts with LiAlH₄in benzene (or toluene) and ether in the presence of a Lewis base to form coordination and electron saturated (18-electron configuration of the Lu atom) dimeric complexes (Cp₂LuAlH₄·L)₂), where L = Et₂O (I), NEt₃ (IIa), C₄H₈O (III). Complexes IIa and III crystallize in monoclinic lattices with parameters: a = 11.35, b = 13.34, c = 14.20 Å, γ = 102°, space group P2₂/b for IIa; a = 8.73, b = 11.06, c = 16.42 Å, γ = 95.6°, space group P2₁/b for III. When a single crystal of IIa is exposed to hard X-rays (Mo-K_α, λ = 0.7106 nm) dissociation of the dimer takes places and a single crystal of monomeric Cp₂Lu(μ₂-H)AlH₃·NEt₃ (IIb) with a monodentate AlH₄ group and 14-electron configuration of the Lu atom is formed. IIb crystallizes in monoclinic lattice with parameters: a = 13.278(4), b = 9.697(3), c = 14.099(4) Å, γ = 94.22°, space group P2₁/a, Z = 4, d_calc = 1.60 g/cm³ (R = 0.046, R_w = 0.047).     

Reactions of conjugated dienes with cobalt carbonyls under hydroformylation conditions. a high pressure i.r. spectroscopic study

Summary The chemistry of cobalt carbonyls in the presence of dienes and high pressure of synthesis gas was studied by online i.r. spectroscopy. Dicobalt octacarbonyl reacts with butadiene under 95 bar CO/H₂ and 80°C to give [³-C₄H₇Co(CO)₃] (1) and [⁴-C₄H₆)₂Co₂(CO)₄] (2). Hydrogenation or hydroformylation are observed only with [HCo(CO)₄] as the starting catalyst, and only at the beginning of the reaction. The results are explained by formation of an alkenyl complex, [-C₄H₇Co(CO)₄], which either reacts with [HCo(CO)₄] to give butene and [Co₂(CO)₈], or loses CO to give (1), depending on the [HCo(CO)₄] concentration. The butene is hydroformylated. At temperatures >100°C (1) is transformed into a CO-free species, which catalyzes the oligomerisation of butadiene. Addition of tributylphosphine (L) leads to the formation of [³-C₄H₇Co(CO)₂L] (5) and [Co₂(CO)₆L₂] (6). In (5) the -allyl moiety is more labile than in (1) and a slow hydrogenation and hydroformylation of the butadiene is observed. In methanol solution the reaction of the cobalt carbonyls to give (1) is incomplete and the remaining H⁺ and [Co(CO)₄]^– catalyze the hydroformylation of butadiene. Isoprene is less reactive than butadiene but otherwise behaves similarly.     

The free radical oxidation of CH2O in the presence of NO2 and NO

NO₂ was photolyzed at 366 nm and 296 K in the presence of CH₂O and O₂ and in some runs with added NO or N₂. The measured products were CO, CO₂ and HCOOH. H₂ and N₂O were not produced. Both the CO and the CO₂ were produced in a linear fashion with irradiation time, but the HCOOH grew after a marked induction period. From the CO₂ quantum yields at high [O₂]/[NO₂] ratios an upper limiting value of 0.16 ± 0.02 was found for k_3b/k₃ where reactions (3a) and (3b) are

This is lower than the value of approximately 0.30 reported for k_3b/k₃ by Chang and Barker. From the CO and CO₂ yields the competition for HCO between O₂ and NO₂ could be measured.

The ratio k₉/k_7a was found to be 0.21 ± 0.07 and was independent of pressure. The analysis required knowledge of some other rate coefficients. If those rate coefficients are completely in error, k₉/k_7a could be as high as 0.63. With the literature value of 5.6 × 10⁻¹² cm³ s⁻¹ for k₉, the best value for k_7a is (2.7 ± 0.9) × 10⁻¹¹ cm³ s⁻¹ with a lower limiting value of (8.9 ± 3.0) × 10⁻¹² cm³ s⁻¹.Information was also obtained on the reaction of HO₂ with CH₂O which produces HCOOH. An approximate value of (1.4 – 3.2) × 10⁻¹³ cm³ s⁻¹ was found for the rate coefficient for this reaction which is about 14 – 32 times greater than the estimate of Su et al.     

Kinetics of one-electron oxidation by the ClO radical

Pulse radiolysis studies were carried out to determine the rate constants for reactions of ClO radicals in aqueous solution. These radicals were produced by the reaction of OH with hypochlorite ions in N₂O saturated solutions. The rate constants for their reactions with several compounds were determined by following the build up of the product radical absorption and in several cases by competition kinetics. ClO was found to be a powerful oxidant which reacts very rapidly with phenoxide ions to form phenoxyl radicals and with dimethoxybenzenes to form the cation radicals (k = 7 × 10⁸ −2 × 10⁹ M^-1 s^-1). ClO also oxidizes ClO^-₂ and N^-₃ ions rapidly (9.4 × 10⁸ and 2.5 × 10⁸ M^-1 s^-1, respectively), but its reactions with formate and benzoate ions were too slow to measure. ClO does not oxidize carbonate but the CO^-₃ radical reacts with ClO^- slowly (k = 5.1 × 10⁵ M^-1 s^-1).     

Kinetische untersuchungen zur deprotonierung von Fe3(CO)9(μ2-H)(μ3-S-t-Bu) durch amine

Fe₃(CO)₉(μ₂-H)(μ₃-S-t-Bu) reacts with amines in aprotic solvents to give salts [Fe₃(CO)₉(μ₃-S-t-Bu)]⁻[AminH]⁺ under deprotonation. The association of cluster and amine under formation of a solvated ion pair follows a second order rate law. The isotope effects k_H/k_D as well as the rate constants are strongly correlated with the steric demand of the individual bases used: The largest rate constants and the largest isotope effects (up to k_H/k_D = 13) are observed for bases with the least steric hindrance.     

The reaction of OH with NO2 and the deactivation of O(1D) by CO

NO₂ was photolyzed with 2288 Å radiation at 300° and 423°K in the presence of H₂O, CO, and in some cases excess He. The photolysis produces O(¹D) atoms which react with H₂O to give HO radicals or are deactivated by CO to O(³P) atoms The ratio k₅/k₃ is temperature dependent, being 0.33 at 300°K and 0.60 at 423°K. From these two points, the Arrhenius expression is estimated to be k₅/k₃ = 2.6 exp(?1200/RT) where R is in cal/mole – °K. The OH radical is either removed by NO₂ or reacts with CO The ratio k₂/k^α is 0.019 at 300°K and 0.027 at 423°K, and the ratio k₂/k⁰ is 1.65 × 10^?5M at 300°K and 2.84 × 10^?5M at 423°K, with H₂O as the chaperone gas, where k^α = k₁ in the high-pressure limit and k⁰[M] = k₁ in the low-pressure limit. When combined with the value of k₂ = 4.2 × 10⁸ exp(?1100/RT) M^?1sec^?1, k^α = 6.3 × 10⁹ exp (?340/RT)M^?1sec^?1 and k⁰ = 4.0 × 10¹²M^?2sec^?1, independent of temperature for H₂O as the chaperone gas. He is about 1/8 as efficient as H₂O.     

Comparison of reactivity of Ar(3P0) and Ar(3P2) metastable states. Rate constants for quenching by Kr and CO

A simple method is described for studying the reactions of metastable Ar(³P₀) and Ar(³P₂) atoms separately in a discharge-flow system. CO and Kr quench these states with rate constants in the ratio k₀ (CO)/k₂ (CO) = 8±1 and k₂ (Kr)/k₀(Kr) = 18±2.